Read Cost-Effective Manufacturing: Machining Brass, Copper and its Alloys text version

Copper Development Association

Cost-Effective Manufacturing Machining Brass, Copper and its Alloys

Publication TN44, 1992

Cost-Effective Manufacturing Machining Brass, Copper and its Alloys

Publication TN 44

October 1992 ­ Revised for inclusion on CD-Rom, May 1994

Members as at 1st January 1992

ASARCO Inc Boliden MKM Ltd Thomas Bolton Ltd BP Minerals International Ltd Brandeis Ltd The British Non-Ferrous Metals Federation Chile Copper Ltd CIPEC Falconbridge Ltd Gecamines Commerciale Highland Valley Copper IMI plc Inco Europe Ltd Minpeco (UK) Ltd Noranda Sales Corporation of Canada Ltd Palabora Mining Co Ltd Rtz Limited Southern Peru Copper Corporation Wednesbury Tube

Acknowledgements

The preparation of this publication has been financed by International Copper Association. CDA is also glad to acknowledge useful comments on the draft text, particularly from Dr M Staley (BNFFulmer), Eur Ing Mr J Westlake (Boliden MKM Ltd), the late Mr P Wilkins (Delta Extrusion) and Dr M Wise (University of Birmingham).

Copper Development Association

Copper Development Association is a non-trading organisation sponsored by the copper producers and fabricators to encourage the use of copper and copper alloys and to promote their correct and efficient application. Its services, which include the provision of technical advice and information, are available to those interested in the utilisation of copper in all its aspects. The Association also provides a link between research and user industries and maintains close contact with other copper development associations throughout the world. Website: www.cda.org.uk

Email: [email protected] Copyright: All information in this document is the copyright of Copper Development Association

Disclaimer: Whilst this document has been prepared with care, Copper Development Association can give no warranty regarding the contents and shall not be liable for any direct, indirect or consequential loss arising out of its use

Contents

Contents........................................................................................................................................................1 Figures ...........................................................................................................................................................2 Tables ­ .........................................................................................................................................................2 Introduction .................................................................................................................................................4 Costings ........................................................................................................................................................5 Manufacturing Costs......................................................................................................................................5 Material Costs..............................................................................................................................................10 Starting stock types .................................................................................................................................10 Scrap Recovery............................................................................................................................................11 Illustrations - Cheaper than Steel, Stainless Steel and Aluminium .......................................................12 Illustrations ­ Wrought Preforms for Quick Machining .......................................................................14 Machinability Groups ...............................................................................................................................16 Group 1 - Original Machinability Rating 170 - 150% .................................................................................16 Group 2 - Original Machinability Rating 30 - 60% .....................................................................................16 Group 3 - Original Machinability Rating less than 30%..............................................................................16 Machining Operations...............................................................................................................................29 Tool Materials .............................................................................................................................................29 High speed steels.....................................................................................................................................29 Indexable insert carbide tools..................................................................................................................29 Brazed tip carbide cutting tools...............................................................................................................30 Carbide Tool Materials ...........................................................................................................................30 Diamond Tipped Tools ...........................................................................................................................31 Polycrystalline Diamond (PCD)..............................................................................................................31 Turning ........................................................................................................................................................31 Sand Castings ..........................................................................................................................................31 Wrought Materials ..................................................................................................................................31 Chipbreaker Tools...................................................................................................................................34 Cutoff tools..............................................................................................................................................36 Form tools ...............................................................................................................................................36 Drilling ........................................................................................................................................................37 Tapping........................................................................................................................................................38 Reaming.......................................................................................................................................................39 Milling .........................................................................................................................................................41 Materials Selection ....................................................................................................................................42 High speed machining brass ........................................................................................................................43 Rod for Free-machining purposes................................................................................................................43 Coppers and Copper Alloys.........................................................................................................................44 Coppers........................................................................................................................................................44 Brasses.........................................................................................................................................................44 Nickel-Silvers ..............................................................................................................................................45 Bronzes........................................................................................................................................................45 Copper-nickel alloys and the Aluminium Bronzes ......................................................................................45 Dimensional tolerances and straightness .....................................................................................................46 Dimensions ..................................................................................................................................................46 Machining preforms made by hot stamping or forging................................................................................48 Materials for Castings for Subsequent Machining.......................................................................................51 Material Availability....................................................................................................................................51 Group 1 alloys .........................................................................................................................................51 Group 2 alloys .........................................................................................................................................51 Group 3 alloys .........................................................................................................................................51

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Illustrations - Cast Preforms .................................................................................................................... 53 Illustrations ­ High Precision................................................................................................................... 54 Illustrations ­ Repetition Jobs.................................................................................................................. 56 Illustrations ­ Short Runs......................................................................................................................... 57 Illustrations ­ Machining HC Coppers ................................................................................................... 59 Machinability Testing Methods ............................................................................................................... 60 Cutting Fluids for Copper Alloys............................................................................................................. 64 Functions of cutting fluids........................................................................................................................... 64 Selection and application of cutting fluids .................................................................................................. 64 Type of work material ................................................................................................................................. 65 Effect of Tool Material................................................................................................................................ 65 Type of machining operation....................................................................................................................... 65 Type of cutting fluid.................................................................................................................................... 65 Lubricant Manufacturers' Recommendations.............................................................................................. 67 Addresses of Lubricant Manufacturers........................................................................................................ 78 References .................................................................................................................................................. 79

Figures

Figure 1 ­ Estimation of economic cutting speed (ignoring fixed costs)....................................................... 6 Figure 2 - Universal machinability ratings for a variety of materials (ref. 1), giving a guide to comparative machining costs. ............................................................................................................................................ 6 Figure 3 ­ Chip forming classification (ref 13) ........................................................................................... 28 Figure 4 - Carbide tipped lathe turning tools............................................................................................... 32 Figure 5 ­ Diagram showing land width and chip breaker tool action ........................................................ 34 Figure 6 ­ SIR diagram for determining chip breaker parameters............................................................... 35 Figure 7 ­ Circular and straight cutoff tools................................................................................................ 36 Figure 8 ­ Drill point and clearance angles ................................................................................................. 38 Figure 9 ­ Spiral pointed tap ....................................................................................................................... 39 Figure 10 - Typical stub auto reamer........................................................................................................... 40 Figure 11- Chasers for die heads and collapsible taps................................................................................. 41 Figure 12- Milling cutter rakes and clearances............................................................................................ 42 Figure 13 - Geometry of component and schematic diagram of machining operations in tests conducted by Davies (ref. 4).............................................................................................................................................. 61

Tables ­

Table 1 ­ Comparison of costs of parts made in brass and steel (ref 2)(a) ......................................................... 7 Table 2- Relative Machinability Ratings of Various Metals (after (ref. 22)) ................................................ 9 Table 3 - Wrought coppers and copper alloys ­ availability, properties and machinability........................ 17 Table 4 ­ Cast coppers and copper alloys ­ applications, properties and machinability............................. 24 Table 5 - DKI scheme for classifying machinability of coppers and copper alloys..................................... 28 Table 6 ­ Tool Geometry Recommendations (ref. 14)................................................................................ 33 Table 7 ­ Speeds and feeds for turning ....................................................................................................... 33 Table 8 ­ Speeds and feeds for drilling ....................................................................................................... 37 Table 9 ­ Tapping speeds............................................................................................................................ 39 Table 10 - Reaming speeds and feeds ......................................................................................................... 40 Table 11 ­ Speeds for thread chasing.......................................................................................................... 40 Table 12 ­ Speeds for milling ..................................................................................................................... 42 Table 13 ­ Materials commonly available as rods for free-machining purposes......................................... 46 Table 14 ­ Materials for hot stampings and forgings .................................................................................. 49 Table 15 ­ Lubricant manufacturers' recommendations ............................................................................. 68

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This publication is aimed at: Those wanting a full introduction to the factors affecting machining as a production technique: Start at Introduction and work onwards.

Those requiring guidance on materials selection where good machinability is one of the important properties: See Introduction, Machinability Groups and Materials Selection first

Those who know what material is to be machined and require basic information and guidance: See Introduction, Machinability Groups, Machining Operations and Cutting Fluids for Copper Alloys first

Those requiring an update on relevant recent technical developments:

See the main list of contents for subjects of interest. Common abbreviations for alloying elements

Ag Al As Be Cr Co Cu Fe Mn Silver Aluminium Arsenic Beryllium Chromium Cobalt Copper Iron Manganese Ni P Pb Si Sn Te Zn Zr Nickel Phosphorus Lead Silicon Tin Tellurium Zinc Zirconium

"It is the aim of this publication to promote amongst engineers generally a wider knowledge and appreciation of the machining qualities of copper alloys and also serve as a book of reference as to the methods whereby these qualities may be exploited to the best advantage." W. B. S. From the forward to the book: 'The Machining of Copper and its Alloys', Copper Development Association Publication No 34, 1939.

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Introduction

As one of the most important of manufacturing production processes, machining operations can contribute significantly to profitability. Using the most suitable materials and the best techniques can result in economies in production costs that keep products ahead of competition. Examples in this publication show that components can be made more cheaply in materials such as free-machining brass than from other materials of lower first cost. As part of the process of the manufacture of components, machining is frequently a vital, costeffective step. It has many advantages: Versatility - resetting a machine can be much easier than redesigning complex tooling for mouldings Good Surface Finish Accuracy - machining tolerances are far closer than those obtained by most other production processes Good Screw threads Best materials - choice is not limited since all metals can be machined Low Cost - for many products and production runs, well planned machining operations can be the most cost-effective production method. All coppers and copper alloys can be machined accurately, cheaply and to a good standard of tolerances and surface finish. There are materials that are specially made with excellent machinability as a primary attribute; the best of the free machining brasses set the standard by which all other materials are judged. Other alloys are made with a variety of combinations of properties such as strength, corrosion resistance and cold formability as the primary concerns. These may be less easily machined but techniques are readily available and machining may well be easier and cheaper than for many other types of material. For many years, the International Copper Association (ICA), previously known as International Copper Research Association (INCRA), has sponsored significant programmes in connection with the development of free-machining alloys and improvements in techniques of machining existing coppers. Reference is made to the importance of the results of this work in this publication. As part of the harmonisation processes continuing throughout Europe, there will shortly be published a series of new standards to be adopted by all European national standards organisations without modification. These will supersede all previous European national standards. The materials included are likely to be similar to those already in use but with new designations, a new numbering system and with attributes such as composition and properties that reflect current production requirements. The materials described in this publication are those most likely to be included in the European standards.

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Costings

Correct costing of a product is vitally important. Ignoring overheads, component costs = initial material costs + production costs Component costs should also include the consequential costs of failures before and after despatch, that is, the cost of ensuring fitness for purpose. Consideration needs to be given to the effect of variations in material costs in reducing production costs. It is usually a false economy to aim only at lowest first cost for material. Each organisation will have a costing system suited to requirements; the factors that will be considered include all those contributing to lowest total costs of components that are fit for the end-use purposes. Product costs include not only raw material costs but also the costs of converting the material to the final shape and size, provision of surface protection and/or decoration together with possible service costs throughout the life of the product. Energy costs of the production process and costs of tooling and special equipment that may be needed are other considerations. Copper and its alloys have been recycled effectively for thousands of years. Recycling of both process scrap and the product itself at the end of its working life are therefore also wellestablished relevant factors. This publication is dedicated to aspects of cost-effective machining. Other CDA publications cover the many advantages that coppers and the copper alloys have over alternative materials such as high strength, ductility, toughness and conductivity at ambient, low and elevated temperatures, excellent corrosion resistance and no problems with ageing or degradation by daylight. These benefits can make coppers and copper alloys the most cost-effective choice when all production considerations are evaluated.

Manufacturing Costs

In designing a component, consideration needs to be given to keeping production costs as low as possible, consistent with maintenance of quality. This means keeping machine output high by the use of easily finished feedstock that is both as near final size and as easy to machine as possible. Selection of the best materials and machining techniques is essential. The recommendations of this publication will be found a useful guide. Experience gained during production operations will allow the introduction of relevant improvements. In estimating ways of minimising the cost of manufacturing a component, one of the factors to be considered is the cutting speed. An increase in cutting speed normally has two main effects, the metal removal rate is increased and the tool life is decreased. The first saves money but downtime for tool changing increases costs and a best compromise of least costs has to be evaluated to obtain the most economic cutting speed, see Fig 1.

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Figure 1 ­ Estimation of economic cutting speed (ignoring fixed costs)

Selecting a material stock that is suitable for high-speed machining can allow an increase in machining speeds without increasing tooling costs. This will have a very beneficial effect on productivity.

Figure 2 - Universal machinability ratings for a variety of materials (ref. 1), giving a guide to comparative machining costs.

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Table 1 ­ Comparison of costs of parts made in brass and steel (ref 2)(a)

Component

Fitting body

Manifold adaptor

Air brake Hose fitting

Actuating sleeve

Pneumatic hose fitting

Knob insert (knurled)

Application

Underwater pump assembly

Automotive

Automotive

Pneumatic power

Aircraft

Garden equipment

Special Features

Teflon coated

Better quality cheaper

Safety-related

Deep hole

Deep hole

Productivity savings

Part weight (g) Brass (b) premium (%) Cycle time ­ Brass (sec) Cycle time ­ Steel (sec) Productivity gain using brass (%) Cost saving using brass (£1/1,000)

49 23 4.5 8.0 102

33 30 3.2 5.9 110

41 36 5.6 9.1 86

36 17 4.75 8.4 102

26 42 3.7 8.3 157

5.4 32 3.75 5.5 68

3.92

0.58

33.98 (c)

40.60 (d)

25.08 (e)

2.62

Notes: (a) Comparisons are between CuZn36Pb3 (CZ124) free-machining brass and leaded free-machining steel 12L14. Comparisons are based on multi-spindle auto production. (b) Brass material cost premium includes scrap allowance. (c) Brass v plated steel. For bare steel the saving is £26.26 per 1,000 parts (d) Brass v plated steel. For bare steel the saving is £33.58 per 1,000 parts (e) Brass v plated steel. For bare steel the saving is £20.09 per 1,000 parts

(Courtesy CDA Inc, USA)

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Fig 2 shows machinability ratings for a selection of materials such as high-speed machining brass, a leaded ductile brass, naval brass, a wrought aluminium alloy and a leaded freemachining steel. These results are comparable since they were obtained under identical testing conditions to ASTM E 618 and are derived from the conditions needed to attain an eight hour tool life using form tools and drills in an automatic lathe using 19mm feedstock to produce a total of 80,000 components (ref. 1). As Table 1 shows, the economic benefit to be obtained (ref. 2) by specifying free-machining brass can mean that its use can frequently be justified on production costs alone, before consideration of other properties such as strength, conductivity and corrosion resistance. Table 2 gives some comparisons with other materials showing the better machinability of brass and other copper alloys, when compared with other materials that might be considered for component manufacture. Particularly noticeable is the comparatively good machinability of the aluminium bronzes when compared with materials used in similar corrosive environments such as stainless steel and Monel.

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Table 2- Relative Machinability Ratings of Various Metals (after (ref. 22))

Machinability ratings according to Carboloy Systems Div. where steel En1a = 1.00. The higher the rating, the better the machinability.

Material Description

Free-cutting mild steel Plain low carbon steel Plain medium carbon steel High strength low alloy steel 1.5% NiCrMo High strength low alloy stee l2.5% NiCrMo 1% carbon, 1% Cr ballbearing steel

BS Designation

Old

En1a En3 En8 En24

New

220M07 070M26 080A40 817M40

US Designation

B1112 C1025 C1040 A4340

Hardness HB

160 143 205 210

Machinability Rating (steel)

1.00 0.65 0.60 0.50

En25

826M31

6407

180

0.50

En31

535A99

E52100

206

0.30

Low carbon case hardening steel 18/8 stainless steel K-Monel Titanium alloy Titanium alloy Aluminium alloy Free-cutting aluminium alloy Aluminium bronze Aluminium silicon bronze Copper-chromium Copper-nickel Copper Free-machining copper Forging brass Free-cutting brass

En32

080M15

C1015

131

0.60

En58j

316

316 K500 A-70 C-130

195 240 188 255 95 95

0.35 0.35 0.27 0.18 1.40 2.00

AA2017 AA2011

2017-T 2011

CA104 CA107 CC101 CN102 C101 C109

CuAl10Ni5Fe4 CuAl6Si2Fe CuCr1 CuNi10FeMn Cu-ETP CuS

C63000 C64400 C18200 C70600 C11000 C14700

200 180 140 90 50 50

0.60 1.80 0.60 0.60 0.60 2.40

CZ122 CZ121

CuZn40Pb2 CuZn39Pb3

C35300 C36000

70 70

2.70 3.0

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Material Costs

The initial cost of material is only part of its contribution to total product cost. Careful optimization of feedstock can reduce significantly the subsequent production costs by minimising the amount of finish machining that is required. The machinability of the material should be as good as possible, while still being compatible with other property requirements, in order to maximise production rates. Selection of optimum materials is discussed in the following sections. The size and shape of the feedstock can also be tailored to suit; the closer it is to final size, the lower the costs of finish machining. Having considered the size of the production run and many other economic and technical considerations, the most economic starting stock for finish machining can be selected from many types of wrought and cast forms. Dependent on component design and the amount of metal to be removed, many of these can be classified as 'near net shape' costing little to finish.

Starting stock types

Stock supplied in long lengths - easily fed in to a machine; may be dimensionally correct as supplied in two dimensions only: · · · · Extruded round rod, supplied in straight lengths with or without chamfered ends that facilitate entry in to machine tools. Extruded rectangle, hexagon or other profile nearer to net shape. The extra cost over round rod offset by product cost savings over a long run. Extruded hollow round, hexagon or other profile. Extruded and drawn stock round or shaped rod or section supplied in straight lengths or wire supplied in coil for semi-continuous feedstock. Drawing improves properties and gives closer dimensional tolerances. Continuously cast round or profile supplied in straight lengths solid or hollow.

·

Three-dimensional Preforms · · · · Simple hot stampings made in low-cost dies - a wrought material of good strength and relatively low cost. More complex hot stampings made nearer to final shape requirements. Secondary dies allow the inclusion of hollows. Sandcastings - for relatively short runs of complex shapes, ideal for valves and other pipe fittings, pumps and heavy electrical components. Diecastings, gravity or pressure type - for longer runs of complex components made to close tolerances and needing machining only for close-tolerance faces or holes.

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Flat Stock · · Rolled plate, sheet or strip - for components made flat or bent, pressed or deep drawn to shape in short or long runs. Further details of these production methods and the considerations that apply are given in a CDA Datadisk (ref. 21).

Scrap Recovery

Where significant quantities of scrap are generated the effect of resale value in reducing product costings can be significant. Copper and copper alloys have been recycled as part of production economics for many centuries; however, techniques are still being improved. It is well worth the effort to ensure that scrap is kept segregated by alloy and free from contamination. It is also frequently worth recovering lubricant for re-use, clean swarf commands a better price since contaminants have an adverse effect on the remelting environment. When significant economic quantity orders are being negotiated with manufacturers, the value of agreed returns such as swarf, offcuts and rod ends can make a useful contribution to profit. Smaller users can also gain by careful segregation and disposal of scrap, especially if benefits are built in to employee incentive schemes.

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Illustrations - Cheaper than Steel, Stainless Steel and Aluminium

Screw Manufacture (Delta EMS Ltd) Bar feed automatic capstan lathes are used to produce millions of screws. Continuous feed from coiled rod ensures maximum production rates. It is important to ensure quality control on the coil material so that the machining parameters are kept constant. The real cost of producing a component is the sum of the cost of the material and the cost of work performed on it. It is obviously false economy to use material of the cheapest first cost if subsequent extra production costs outweigh the savings.

Machinability Demonstration The dramatic differences in machinability of brass and steel were underlined by this demonstration. "Kebabs" made up of alternate sections of brass and steel were turned using a carbide tipped finishing tool. The picture shows the marked differences in the swarf types.

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Valve Chest (Meco International) This component is a good example of the cost savings which can be achieved by radical re-assessment of the design. The part is machined from shaped extruded brass bar using programmed robotically controlled tooling. The use of the extruded preform minimises waste material.

Cable glands and fire extinguisher heads in aluminium and brass (Hawke Components Ltd) This picture shows two examples of components which can be manufactured in either aluminium or brass. The cable glands are cheaper in brass because it is easier to machine and less labour intensive. Free machining aluminium cannot be used because it does not have adequate corrosion resistance. The fire extinguisher head is made out of brass because aluminium tends to gall when screwed into a steel cylinder.

Part of a motor casing (Hayward Tyler Fluid Dynamics Ltd) This is part of a motor for a fire pump to operate undersea for fire protection of North Sea oil rigs. The casting is in aluminium bronze to BS1400 AB2. This material is used in preference to stainless steel because of the 50% saving in machining costs. With a machining operation of this complexity this saving represents considerable sums of money. The accurate external work is completed first, and then the internal grooves to locate the stator and end plates are machined. The set-up time can be as long as 16 hours and the machining takes 4 days with a further 5 days taken up with milling and tapping.

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Illustrations ­ Wrought Preforms for Quick Machining

Chamfered brass rod ready for despatch (Boliden MKM Ltd) Chamfered ends facilitate easy entry of bars into automatic lathes.

Extruded Hexagonal Bar (Delta Extruded Metals Co Ltd) Components made from this high speed machining rod are shown along side the bar stock emphasising the efficient use of material.

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Tube plate For small batches, this tube plate is machined from brass plate 8mm thick. For larger batch production, savings can be made by starting with a diecast preform which eliminates all but a final finish machine.

T Piece and Bushing (Delta EMS Ltd) Near-net-shape hot stampings provide cost-effective preforms for these parts. Machining is then only required on mating faces and for threading.

A selection of extruded profiles Complex profiles can be extruded to order. In many cases the die costs are quickly repaid by savings in machining time and the reduction in material wastage.

Fittings for the pneumatics industry (Norgren Martonair Ltd) This push-in tube is shown at various stages of its manufacture. Hot stamping as it comes out of the die; after cropping and acid dipping; machined; and finally, bright nickel plated. The maching takes place in one operation on automatic CNC machines.

Union Nut (Delta EMS Ltd) These fittings could easily be produced from solid rod, hollow rod or from hot stampings. For reasonably long production runs hot stampings are the most cost-effective choice. Machining is only required to thread the finished nuts.

Shaped Hollows Standard shapes of hollow bar are available from stock and, though slightly more expensive than solid bar, will often prove to be a more cost-effective choice for the manufacture of hollow components. Complex shaped hollows can be produced to special order.

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Machinability Groups

For centuries, copper and copper alloys have been used to make a very wide variety of products that depend for their usefulness on combinations of such properties as strength, ductility, hardness, conductivity and corrosion resistance. They have an appearance that is functional, decorative and an accepted indication of good quality and fitness for purpose. Compositions and available forms have been developed to meet nearly every need of the engineering designer and this has resulted in a very wide range of materials being available. The needs of production engineers have also been met by modifications that enable many of the materials to be fabricated easily and cheaply. Some are less easy to machine than others because to make them so would prejudice other properties. In the new European standards there are likely to be about 40 compositions standardised for cast coppers and copper alloys and about 140 for wrought materials. These standards will shortly be adopted without modification by all European countries, replacing existing national standards such as the present BS 2870 to 2875 series for wrought semi-manufactured coppers and copper alloys and BS1400 for cast coppers and copper alloys. Broadly, they include most of the first preference materials from all existing European national standards. Other similar materials are included in ASTM specifications. Most of these are available in differing forms and tempers that also affect machinability. In machining, the cutting action involves initially shearing the cut metal (as swarf or chips) from the machining stock and then removing the swarf from the cutting tool in a way that allows further swarf to follow freely. Both of these actions are controlled by a wide variety of factors, of which the metal composition and structure is one. Others include, for example, tool geometry and cutting speeds and feeds. Because of the numbers and interaction of these variables, machinability ratings are, therefore, for initial guidance only, and should be developed further in the light of experience. For machining purposes, coppers and copper alloys can be roughly divided in to three categories:

Group 1 - Original Machinability Rating 170 - 150%

Materials specifically made to be freely machinable. These have alloying additions that encourage the formation of short-chipping swarf that clears easily from the toolface. They enable components to be produced very quickly, accurately and cheaply. The group includes the free-machining brasses, coppers and bronzes.

Group 2 - Original Machinability Rating 30 - 60%

Materials with good machinability but with first priority given to other properties. Typical materials in this group are the unleaded brasses.

Group 3 - Original Machinability Rating less than 30%

Materials that are not as easy to machine as the alloys in groups 1 and 2 because they are longer chipping. They may generate higher temperatures and stresses on cutting tools because of their mechanical properties. They can be successfully handled using techniques that may be similar in some respects to those needed for many ferrous materials and usually at lower speeds than those used for groups 1 and 2.

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Table 3 - Wrought coppers and copper alloys ­ availability, properties and machinability

17

18

19

20

21

22

23

Table 4 ­ Cast coppers and copper alloys ­ applications, properties and machinability

24

25

26

A summary of the coppers and copper alloys commonly available in Europe is included in Table 3 and Table 4 together with the range of properties, remarks regarding usage and guidance on machining techniques. The 'Machinability Group' is the broad classification previously described giving a good general idea of machining characteristics. The 'Percentage Machinability Rating' figures were originally derived after a consideration of a number of the factors involved in machining, namely: chip size, surface finish and power requirement. The original free machining brass (CZ121) containing a nominal 3 per cent lead was given a rating of 100 and other alloys divided into the three groups shown above. The machining (turning) parameters of feed, speed and depth of cut as well as tool rake and clearance angles were linked to these groupings for tools made of carbon- and high speed steels and with carbide tips. The ratings are arbitrary, applying mainly to simple turning processes but having some significance for other operations such as form turning, drilling, thread turning and milling. In view of the difficulties in applying the original machinability ratings to all types of operations, the use of the Groups is a better general guide, together with remarks pertinent to each material. Materials, tool geometry, cutting rates, lubricants and other factors all affect machinability and are discussed in other sections. The indicated speeds and feeds, together with the rake and clearance angles may be taken as starting points which can be modified subsequently to suit such variables as machine tool characteristics, material composition, grain structure and temper together with depth of cut, cutting fluid and the requirements of the ultimate application. The use of special techniques can make machining of some materials not normally rated as 'freemachining' comparatively easy. An example of this is the use of chipbreaker tool geometry for machining high conductivity copper. As described later, this results in the swarf being readily cleared from the toolface, giving better surface finish and much higher production rates. Also included in the tables are data extracted from a DKI publication (ref 14). This includes consideration of the effect of material condition, characterised by tensile strength and hardness, on machining characteristics. For the wrought alloys, this causes some modification of their machinability groups, as defined in Table 3, according to structure, swarf type, typical tool wear and formability. In addition to these criteria the chip characteristics have others such as modulus of elasticity, specific heat, thermal conductivity, material texture and others so that within a given chip grouping other specific characteristics can be included. Main group I Comprises lead, tellurium or sulphur, alloyed copper base materials with homogeneous or heterogeneous structure which are easily machinable. Main group II Contains moderately or well machinable (mostly lead free) copper base materials of higher mechanical strength and better cold working characteristics than the materials comprising group 1 metals with heterogeneous structure which, because of their better plasticity, produce longer swarf.

27

Main group III This includes two types of copper-based materials that are not so easy to machine. Type 'a', with their homogeneous structure and excellent cold working characteristics produce strong swarf and long, tough swarf ribbons. Type 'b' contains heterogeneous materials such as high strength copper-aluminium alloys (aluminium bronzes) and the low alloyed copper-based materials in the hardened condition.

Table 5 - DKI scheme for classifying machinability of coppers and copper alloys

Main Group I Characteristic Structure Homo/heterogeneous with chip breaking particles (Pb, S, Te) Short (brittle chip) Low Generally poor Generally good Main Group II Heterogeneous (coarse dispersed phases) without Pb particles Medium (helical chip) Medium Generally good Moderate Main Group III a. Homogeneous b. Heterogeneous (fine dispersed phase) Long and tough (strip, tangle and helix) High a. Very good b. Inferior a. Moderate b. Good

Swarf type Tool wear (relative) Cold forming of wrought material Hot forming of wrought material

The types of swarf categorised are subdivided in to other categories as shown in Fig 3.

Figure 3 ­ Chip forming classification (ref 13)

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Machining Operations

Tool Materials

The most economic tool material can be chosen after consideration of factors such as run size, tolerance requirements, downtime and toolsetting costs in addition to the actual cost of the cutting tool. There are five main types of cutting tools in common usage for copper based materials: · · · · · High Speed Steel (HSS) Indexable Carbide Inserts Carbide Brazed Tips Diamond (single crystal) Polycrystalline Diamond (PCD)

Ceramic and cermet tools are not commonly used for machining copper-based materials.

High speed steels

High speed steels are still used for many operations, especially for short runs where special shapes and forms are necessary. They are relatively cheap and easy to regrind. Cutting speeds are moderate but tool life is generally good with most brasses, coppers and copper alloys due to the comparatively low temperatures generated during machining. High speed steels differ from other steels by having a high content of stable carbides (about 27%), giving a good wear resistance and hot hardness. They are normally made by conventional melting and working techniques; the various grades have different contents of alloying elements such as cobalt and vanadium, and carbide structures that are dependent on the manufacturing process. Sintered or hot isostatically pressed materials can show improved wear properties due to the addition of higher contents of vanadium and other alloying elements not possible with conventional manufacturing techniques.

Indexable insert carbide tools

Indexable insert carbide tools are now the most popular tool materials, a wide variety of grades and geometries being available. Tool setting is very quick and production runs of over 120,000 cuts per edge are common. Tools are more frequently changed after accidental damage than because of wear. The inserts are available in standard packages for operations such as turning, boring and milling and are easily used on CNC machine tools. The inserts are made by sintering a mixture of tungsten carbide and cobalt powders pressed to the required shape. High cutting speeds and substantial metal removal rates are normal and a copious supply of coolant should be directed at the component. The cutting speed should be high enough to raise the temperature at the tool cutting edge sufficiently to prevent a built-up edge forming since carbide tools are more sensitive to stress fluctuations and impact damage than HSS tools. The upper cutting speed limit may be limited by any of several factors: · · · Component clamping and rigidity Power available at the spindle Heat generation, particularly with alloys of group 3. 29

· · ·

Type of swarf and efficiency of its removal Noise limitations Safety considerations

If the speed is too low build-up occurs which can result in rapid attrition and hence wear of the cutting edge. Coated tips using wear resistant coatings such as titanium nitride should not be used except when turning aluminium bronzes and do not offer much advantage in the machining of other copper-based alloys compared with uncoated tools (ref 15). Since copper alloys are not chemically aggressive to normal tool materials, the advantage is not so great as when some other materials are machined.

Brazed tip carbide cutting tools

Brazed tip carbide cutting tools continue to retain their role in tooling programmes because of the ease with which they can be adapted to particular requirements that may mean modified radii, rake angle or special chipbreaker geometries. This type of cutter is often used when brass or gunmetal is to be cut using combination multi-cutter gangs on a common spindle. This necessitates the manufacture of fairly complex toolholders but the extra cost is offset by long life, high machining rates and the advantage to productivity of multiple machining in one pass. The speeds and feeds used are similar to those for indexable carbide tipped tools. For special materials such as sintered copper-based components, carbide tips are useful for reamers.

Carbide Tool Materials

Carbide Tool Materials are classified according to ISO 513 in terms of their suitability for three main categories of application: · · · P for use with long-chipping materials K for short chipping materials M for intermediate grades

Group K materials are typically plain tungsten carbide and cobalt grades but some contain small additions of tantalum carbide and titanium carbide. Groups M and P contain more titanium carbide and tantalum to impart more wear resistance for the machining of steels, which is of little significant benefit for the machining of most coppers and copper alloys. Materials with a larger carbide grain size and higher cobalt content have a good toughness but lower hardness, while smaller grain sizes and cobalt contents give better wear resistance but lower toughness. Each group is therefore available in a number of grades with increasing numerical values giving greater toughness but lower wear resistance. This means that increasing the grade number (e.g. K40) permits an increased feed rate, decreasing it (e.g. K10) permits a faster cutting rate. For most free-machining brasses, coppers and copper alloys, K10 is generally recommended with K20 used for interrupted cuts or milling. For more difficult jobs, K40 or M40 are sometimes recommended while P01 or P05 can be used for high-speed finishing cuts.

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Diamond Tipped Tools

Diamond tipped tools are not needed for most machining operations on coppers, but they have been used for many years for special purposes, especially where fine finishes are required. Typically, good quality commutators are finished with diamond tipped tools in order to minimise brush wear in service. Copper components for special electronic purposes also benefit from this type of finish. Naturally, care must be taken not to shatter the diamond. High machining speeds and small cuts are normal, and frequently no lubricant is used.

Polycrystalline Diamond (PCD)

Polycrystalline Diamond (PCD) tipped tools can give extremely good tool life, possibly up to five hundred times that of carbide. Machine down-time can therefore be reduced to an absolute minimum. The very low wear rate can be used with advantage when extremely tight tolerances on dimensions and surface finish have to be maintained over long production runs. Great care must of course be taken not to crash the machine tools or the extra life advantage is lost.

Turning

The variables of speed, feed and depth of cut present almost unlimited combinations for attaining economic machining rates. This is just as true for copper and the copper alloys as it is for other engineering materials. For brasses and most other copper alloys, it is generally good practice to use the highest practical cutting speed, a relatively light feed, and a moderate depth of cut.

Sand Castings

Sand castings provide a particular exception to this rule. Most sand castings retain an extremely hard and abrasive surface scale even after sand blasting, pickling, or tumbling. This hard surface needs to be removed with one cut if possible, by using a low turning speed and a relatively coarse feed in order to keep a reasonable tool life. After the scale has been removed, higher speeds and lighter feeds can be used to advantage. If carbide tools are used for machining sand castings there is less need for speed to be reduced for the initial heavy cut.

Wrought Materials

Wrought materials and cleaned castings can be machined using, as a guide, the basic recommendations in Figure 4, table 6 and table 7. The indicated speeds, feeds, rakes and clearances for cutting tools can be taken as starting points which can be modified to suit such variables as composition, grain structure, temper, depth of cut, cutting fluid and the ultimate application. Speeds are quoted in surface metres per minute (sm/m) from which revolutions per minute (rpm) can be calculated using the radius or diameter of the job.

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Figure 4 - Carbide tipped lathe turning tools

Note: Rake angles are based on the tool shank being set parallel with the centre line of the work and with the tool point on centre. Placing the tool point above or below centre will change the effective rake angles appreciable, particularly on work of small diameter. On a set-up where the tool holder is not parallel with the centre line, the rake angles should be ground so that when the tool is mounted, they are in correct relation.

The less ductile copper materials need little or no rake, while the more ductile alloys usually benefit from a comparatively steep rake to prevent the formation of a collar by deformation ahead of the cutting edge, but high rake angles result in the formation of continuous chips. The moderate rake angles suggested for use on the alloys in Group 1 reduce the tendency of the tool to hog into the work. More pronounced rakes are used for alloys in Group 2 and 3 to provide a free chip flow. In fact, the side rake angles used for machining the alloys in Group 3 (the least machinable) somewhat exceed those generally used for machining steel. The rakes and clearances given in Figure 4 do not take into consideration tool shape, nose radius, or front cutting edge angles for roughing or finishing cuts, which vary considerably and depend on the particular job. In all cases the tool shank is assumed to be set parallel with the centre line of the work and the tool point on the centre. Clearances should be only sufficient to provide a free cutting action. On roughing cuts with carbon steel or high speed steel turning tools, a nose radius of 0.8mm with up to 5° end cutting edge angle should prove satisfactory. Too large a nose radius or too small an end cutting edge angle is often the cause of chatter. For light finishing cuts, using a moderate speed and coarse feed, end cutting edge angles may be smaller. Table 6 shows more detailed recommendations from the DKI work (ref. 14) for the types of tool geometry referred to in table 3 and table 4.

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Table 6 ­ Tool Geometry Recommendations (ref. 14) Carbide-tipped Number (Tables 3& 4)

0 1 2

High Speed Steel clearance angle (°)

5 10 10

clearance angle (°)

0 8 8

tool normal rake (°)

6 6 6

tool normal rake (°)

8 8 8

Chipbreaker angle (°)

50

4 5 6 7 8

8 12 20 20 20

6 6 6 6 6

10 14 25 25 25

8 8 8 8 8 20 70 50

Table 7 ­ Speeds and feeds for turning

High Speed Steel Material Group 1 Roughing Speed, sm/m Feed mm/rev Cut mm Finishing Speed sm/m Feed mm/rev Cut mm 90-200 0.07-0.4 0.4-0.75 45-90 0.015-0.4 0.4-0.75 22-45 0.15-0.5 0.4-0.75 150-450 0.15-0.4 0.4-0.75 150-300 0.15-0.4 0.4-0.75 90-240 0.2-0.4 0.4-0.75 300-800 0.05-0.15 0.1-0.3 90-200 0.15-0.5 1-3 45-90 0.4-0.9 1-3 22-45 0.4-1.0 1-3 120-300 0.4-0.65 1.1-3 120-180 0.4-0.75 1.1-3 75-180 0.4-0.75 1.1-3 2 3 1 Carbide Tipped Tools Material Group 2 3 Compax Diamond

For copper alloys, compax diamond tools are usually used with a back rake of +10° to +20° and a side rake of +5° to +20°. On small-diameter lathe work the alloys in Group 1 are usually machined at the highest practical spindle speed, the feed being adjusted to suit such conditions as depth of cut, available power, coolants, and finish requirements. For larger work on lathes, heavy boring mills, etc. where high cutting speeds are not practicable, speeds should be near to the lower end of the suggested limits. High efficiency with carbide tipped tools is attained by using a light feed, a moderately heavy depth of cut, and the highest cutting speed consistent with satisfactory tool life. The speeds and 33

feeds given in Table 7 are typical for copper and copper alloys and are based on a depth of cut of about 1.0 to 3mm per cut for roughing and 0.4 to 0.75mm for finishing. A starting point may be taken as half-way between the limits given and the speed can be adjusted upwards or downwards until the best results are obtained.

Chipbreaker Tools

Many of the Group 3, non-free-machining materials such as high-conductivity copper normally give long ribbons of unbroken swarf when turned. Where this causes problems with swarf clearance it is possible to vary tool geometry by adding a chipbreaking ridge behind the cutting edge in order to give the short, broken swarf characteristic of free-machining materials when the following conditions are met: · · An exit angle (between the chip and the bar axis) of 20 to 60°. A suitable chip curler is on the tool with a geometry that prevents the chip from reverting to a flat, continuous strip.

If the correct land width can be selected according to the methods reported by Staley et al (ref. 3), even oxygen-free copper can be machined without difficulty. The tool geometry for this type of work is critical and is best determined using the SIR Diagram shown in Figure 6. It is evident that there is a direct relationship between the chip thickness or rigidity and the land width. As chip thickness is directly related to the feed, it follows that the feed is directly related to the land width. From basic cutting considerations, both tool geometry and cutting conditions can alter chip thickness so that, in order to maintain a constant chip thickness, the feed would have to be altered accordingly.

Figure 5 ­ Diagram showing land width and chip breaker tool action

These factors are put together in the 'SIR-diagram' to act as a rough guide or starting point for machinists to allow them to manufacture tools for cutting high conductivity coppers with controlled or broken swarf. 34

The first box shows the actual feed on the left. Increasing the side cutting edge (approach) reduces the chip thickness, causing the same effect as a decrease in the feed. The values examined were the extremes of 0° and 35°, values for intermediate angles can be interpolated. As cutting speed is increased, the chip thickness decreases, giving the same effect as decreasing the feed. Depth of cut will limit the choice of feed due to it having a large influence on the exit angle; thus as the depth of cut increases, the feed will also have to increase to maintain an exit angle in the range 20-60°. Further to this, a large nose radius will be required when cutting with large depths of cut to achieve the exit angle requirement. The 'nose radius box' is therefore incorporated to show the minimum nose radius for a given depth of cut; i.e. where the 'feed' line crosses the wavy curve, read off the nose radius. Box 5 shows that increasing the combined rake will reduce the chip thickness, thus giving the same effect as decreasing the feed. When machining high-conductivity coppers, the use of low rake angles within ranges 2-6 and 4-8° would promote thick chips and deformation (collar) ahead of the tool. Therefore tools with a combined angles >50° are recommended. The final box shows the direct relationship between the feed top scale and the land width. Note that, due to the various factors across the diagram, the diagram, the actual feed is not the same as the feed in the final box; i.e. the final box is a 'modified feed'. The diagram only gives a rough estimate of the cutting parameters and tool geometry required for chip curling in copper cutting and must be used in conjunction with the exit angle requirement of 20-60°. The diagram is likely to be different for other materials. The example shows that a feed of 0.125mm/rev, a cutting speed of 400 sfpm (130sm/m, a depth of cut of 1.7mm, a nose radius of 0.5mm and a combined side and back rake of 40° are best served by a land width of 3.75mm. Cutting parameters need to be carefully maintained as the tool geometry takes in to account the expected amount of build-up of metal on the tool. The advantage of easier swarf clearance may be slightly offset by an increase in tool wear because of the greater compression of the swarf by the chipbreaker. Further consideration of the effects of chipbreaker geometry is included in the DKI publication (ref 14)

Figure 6 ­ SIR diagram for determining chip breaker parameters

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Cutoff tools

For most cutoff tools, high speed steel is satisfactory for use with most of these materials. Straight tools normally have sufficient taper for side clearance and need to be ground only for top rake where required, and on the front end for the necessary clearance in the cut. Circular cutoff tools are normally used in automatic screw machines since the work is usually of small diameter and because the tool frequently cuts off into drilled or tapped holes. The design of the cutting edge shown in the diagram has several advantages. Top rake on circular tools is the same as for straight-blade tools; a side clearance of 0.5 to 1° is sometimes used for deep parting operations or if, with some materials, there is a tendency towards binding. Speeds used are about the same as for HSS form tool operations, best results being obtained with a relatively high cutting speed and a feed of from 0.015 to 0.04mm/rev. A suitable lubricant should always be used.

Figure 7 ­ Circular and straight cutoff tools

Form tools

For HSS form tools the speeds and feeds are controlled by the width of the tool in relation to the work diameter, the amount of overhang and the shape of the contour. Feeds of 0.025 to 0.075 mm/rev should be used for roughing and 0.012 to 0.05 mm/rev for finishing, the speed being adjusted to suit. Ample lubricant is needed. The cutting angles and clearances suggested in the drawings are based on the use of high speed steel or carbon steel form tools. The front clearance of a circular form tool depends principally on the diameter of the tool. It is usually 7 to 12°, but it can be accentuated by grinding the cutting edge of the tool below centre, then raising the toolholder so that the cutting edge is on the centre line of the work. It is important to bear in mind that the contour of a machined part will be the exact reverse of the form tool only when all cutting edges are parallel with the centre line of the work and of the form tool.

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Drilling

Where the volume of work does not call for use of special drills, standard carbon-steel or highspeed steel drills (with clearance and point angles as supplied by the manufacturer) can be used for drilling alloys in Groups 1 or 2. When ground as suggested in Figure 8, they can also be used for the alloys and coppers in Group 3. The helix angle of a standard twist drill is usually between 26 and 30°, but varies, according to the manufacturer and the diameter of the drill. Flattening the cutting edges as suggested will overcome any tendency of the drill to pull into the metal. High-speed steel drills of special design are frequently used in regular production work. Flat and straight-flute drills, having a natural zero-degree rake angle, are widely used for drilling alloys in Groups 1 and 2, particularly in automatic lathe work. The slow-spiral or 'brass' drill, with a decreased helix angle ranging from 10° to 22° and with wide, polished flutes and a thin web, provides large chip clearance with a decreased rake angle. It is often used for deep-hole drilling, for auto turning work, and other high-speed drilling operations on Groups 1 and 2 alloys. The point angle and lip clearance shown in Figure 8 can be used on all types of drills. All copper alloys are occasionally drilled dry, but better results are obtained when a suitable lubricant is used. As the alloys in Group 1 are produced principally in rod form for use in automatic screw machines, a lubricant is ordinarily used. A lubricant is desirable when drilling Group 2 alloys, particularly for deep holes and where accuracy is necessary. A lubricant should always be used when drilling Group 3 alloys and coppers.

Hand feeding is frequently used for shop drilling and feeds exceed those normally used for mild steel. For alloys that work-harden easily, such as annealed aluminium bronze, keep the drill cutting continuously to prevent glazing. The drill should be kept cutting, without interruption, as long as chips are being ejected. In holes that are deep in relation to drill diameter, back off occasionally for chip relief, especially if no lubricant is being used. Many factors control the speed in drilling operations, e.g. diameter of drill, wall thickness, depth of hole, but general recommendations are given below.

Table 8 ­ Speeds and feeds for drilling

Speed sm/min Group 1 Group 2 Group 3 60-150 25-75 15-40 Feed mm/rev 0.005-0.075 0.075-0.5 0.075-0.5

For groups 2 and 3, the feed range suggested, 0.075 to 0.5 mm/rev is for drills from 3 to 20 mm diameter. The lighter feeds are used with the smaller drills, for deep holes, and where it is necessary to maintain accuracy. Larger drills can take proportionately heavier feeds, especially the oil-tube type, where lubrication is supplied under pressure. If carbon steel drills are used speeds should be halved.

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Figure 8 ­ Drill point and clearance angles

Tapping

Possibly the principal reason for torn threads or broken taps is the selection of a tap drill which is either too small or too close to the size of the root diameter. In the majority of cases where a specified thread fit is not needed, and where the depth of hole is at least equal to the diameter of the tap, a 75 per cent to 80 per cent depth of thread is sufficient. A 100 per cent thread is only 5 per cent stronger than a 75 per cent thread, yet it needs more than twice the power to tap and presents problems of chip ejection and makes it necessary for the tap to be specially designed for the particular alloy. For hand tapping the alloys in Groups 1 and 2, and where the quantity of work or nature of the part does not permit use of a tapping machine, regular commercial two and three flute highspeed steel taps should prove satisfactory. The rake should be correct for the metal being cut and the chamfer should be relatively short so that work-hardening or excess stresses do not result from too many threads being cut at the same time. High speed steel taps with ground threads are used in machine tapping. In instances where the threads tend to tear as the tap is being backed out, a rake angle should be ground on both sides of the flute. For machine tapping of alloys in Groups 1 and 2, regular two, three, or four flute taps with narrow lands, deep, polished flutes, and a two or three thread chamfer are usually satisfactory. For the metals in Group 3, particularly copper, the nickel silvers and copper-nickel, which produce tough, stringy chips, spiral pointed taps with two or three flutes are preferred for tapping through holes or blind holes drilled sufficiently deep for chip clearance. These taps produce long, curling chips, which are forced ahead of the tap. Spiral fluted bottoming taps can be used for machine (and hand) tapping of blind holes in copper and all types of copper alloys, and wherever adequate chip relief is a problem. The suggested rake angles and tapping speeds should serve as a starting point and they can then be modified for the particular conditions of the job. The speeds indicated are based on the use of taps to produce fine to moderate pitch threads. Appreciably lower speeds should be used for coarse pitch threads, and speeds should be reduced by about 50 per cent if carbon steel taps are used.

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Table 9 ­ Tapping speeds

Speed sm/min Group 1 Group 2 Group 3 45-75 20-45 10-20

On automatic lathes that are working upon Group 1 alloys, maximum spindle speed is frequently used when tapped holes are of relatively small size, or where the thread has a fine pitch.

Figure 9 ­ Spiral pointed tap

Reaming

Practically all standard types of hand and machine reamers can be used successfully on copper materials. Straight-flute reamers with narrow lands and polished flutes are commonly used, but on some types of work they have a tendency to chatter. Standard spiral-flute reamers with a helix angle of between 7 and 12° will overcome chatter and produce a smoother finish. Left-hand spiral and right-hand cut reamers give excellent results either for straight or tapered holes in all three groups of alloys. Depending on the diameter, length of hole, and wall thickness, high-speed steel reamers can be used at the following speeds and feeds:

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Table 10 - Reaming speeds and feeds

Speed sm/min Group 1 Group 2 Group 3 up to 60 22-45 20-30

Feed mm/rev 0.2-1.0 0.2-1.0 0.2-1.0

Figure 10 - Typical stub auto reamer

Circular, radial, and tangential thread chasers for self opening die heads and tap chasers on collapsible taps can be used for internal and external threading of copper, brass, and bronze on all types of automatic turning machines and a variety of horizontal and vertical threading machines. Cutting fluid should be used for all thread chasing operations. The rake angles and clearances indicated in Figure 11 should be modified by the relation of the pitch to the diameter of the thread, the thread form, the thread fit needed, and other special considerations. The cutting speeds suggested are for threads of moderate pitch.

Table 11 ­ Speeds for thread chasing

Speed sm/min Group 1 Group 2 Group 3 30-45 15-27 3-9

40

On automatic lathes that are working upon Group 1 alloys, maximum spindle speed is frequently used when threading small diameter work or fine pitch threads.

Figure 11- Chasers for die heads and collapsible taps

Milling

Practically all commercial types of milling cutters can be used to machine copper, brass, or bronze. Because of the wide variety of cutters available and the diverse nature of milling operations, the cutting angles and clearances suggested in Figure 12 are fundamental and should be modified to meet job conditions. For copper alloys, as a general rule, the clearance behind the cutting edge should be sufficient to prevent a rubbing or burnishing action. Excessive vibrations and digging in are usually indications of too much rake or clearance, and sometimes of too high a speed. Coarse tooth spiral cutters with a helix angle of 20 to 30° and helical cutters with a helix angle of up to 53° have a shearing action that tends to resist digging in, even on the free cutting alloys of Group 1. With adequate rake and clearance, and with land width held to a minimum, these cutters produce fine finishes on all three groups of alloys, even at coarse feed and high speeds. Staggered tooth, side milling cutters with alternate spiral teeth are used for deep slotting operations, particularly on Group 3 alloys. Spiral fluted end mills are fast cutting and produce a better finish than end mills with straight flutes. Double angles on the back of the teeth, as shown in Figure 12, are normally used for regrinding and give the cutting edges adequate clearance and strength. The clearance angle should be 41

greater for small cutters than for large ones and the maximum clearance angles given are for cutters about 75 to 100mm diameter. Only the face of the tooth is ground when resharpening form and gear cutters. This is done radially, or in line with the centre, to preserve the cutting form of the tooth. On this type of cutter the clearance remains constant without grinding. The surface speeds recommended are based on the use of high-speed steel cutters with a suitable cutting fluid. (For carbon steel cutters, reduce the speed by about 50 per cent). In many instances these speeds may be increased several hundred per cent, depending upon such variables as depth of cut, width of cutter, machine rigidity, desired finish, and rate of feed, which may vary from 0.15 to 6.0 or more metres per minute.

Table 12 ­ Speeds for milling

Speed sm/min Group 1 Group 2 Group 3 60-75 45-60 15-45

When milling alloys in Group 3, some experimentation with clearance angles may be profitable.

Figure 12- Milling cutter rakes and clearances

Materials Selection

If there are no alternatives to the material to be machined, this section may be ignored. It lists and discusses the various coppers and copper alloys commonly available. More details of compositions, properties and applications are given in other CDA publications (ref. 19, 20)

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High speed machining brass

High speed machining brass will be first choice material if machinability is a paramount consideration. It can be machined consistently at rates that keep production costs very low and make components costs very competitive. As has been shown in the earlier section on costings, components made of brass can be made at lower total production cost than similar items made of other materials of lower first cost. Besides being cost-effective, free-machining brass comes with good strength, excellent high temperature ductility and reasonable cold ductility, good conductivity, excellent corrosion resistance, good bearing properties and low magnetic permeability. It has an attractive yellow colour but can be plated if required. The material contains about 58% copper and 38% zinc, with an addition of 3 or 4% of lead to give the high-speed, free-machining quality that produces swarf that clears easily from the tool and with minimal energy requirements. It is readily available from all good stockists in small quantities and also from manufacturers in economically larger quantities tailored if necessary to meet special requirements. The British Standard designations are CZ121Pb4 and CZ121Pb3. In European national and CEN standards there will be new, computer friendly, material numbers applicable or alternatively the compositional designations CuZn38Pb4 and CuZn39Pb3 will be used. The 4% lead alloy was developed some years ago and shows better machinability than the 3% material, especially when being drilled. In the original work (ref. 4), it was clearly established that it is necessary to use properly controlled production methods in order to make a good product. These apply to any good free-machining brass and include a continuous casting technique including rapid cooling in order to keep the insoluble lead globules finely dispersed. Rapid solidification also has the advantage of retaining in solution any iron and silicon impurities that might otherwise precipitate out to form hard particles in the brass that would accentuate tool wear. Preheating for extrusion should also be for as short a time as possible. These reasons emphasise why material should be obtained from reputable sources. Such manufacturers can also, if required, carry out non-destructive eddy-current and/or ultrasonic testing to verify that every length of material is internally sound.

Rod for Free-machining purposes

A new European standard is being published covering materials intended primarily for economic machining operations. It has been prepared following consultations between manufacturers, who well know their customers' main requirements, and leading users. It includes the main materials already standardised in European countries with some modifications made in the light of recent experience. Tolerances are included for all dimensions and for twist and end chamfer. As with all standards, these represent normal commercial practice and manufacturers are normally able to meet special requirements by arrangement. The types of materials included are shown in Table 13 and cover a wide range of requirements from those where machinability is of paramount importance to others where a combination of properties is needed. Following the principles included in ISO 197, the CEN/ISO designation gives a good general idea of the composition using the usual chemical abbreviations, a list of which is included in Appendix 1. The main alloying additions are listed, generally in descending order, and the remainder of the alloy is copper. More details on properties, available forms and remarks regarding usage of these and other materials are in Table 3 and Table 4 for wrought and cast materials. The new numbering system for CEN materials will, when published, facilitate computer recognition of the materials. 43

Materials with an existing BS designation listed are likely to be more easily available in the UK than others. The others may be available from specialist stockists or, in economic quantities, from manufacturers.

Coppers and Copper Alloys

As mentioned previously, there are many different coppers and copper alloys available to meet the need for a very wide variety of types and combinations of mechanical and physical properties. In order to achieve the right balance of properties that suit particular applications, it has often been necessary to tailor materials specially for the purpose. Machinability is just one of the factors to be considered when choosing the right material for a particular product. All attributes have to be considered and balanced when choosing the most cost-effective way of producing a component to suit a purpose and lifetime.

Coppers

Coppers of commercial purity, such as are used for electrical purposes are mainly specified for the manufacture of components when there is a need for their high conductivity, corrosion resistance and ductility. Because of their softness, they are not the easiest to machine though not difficult using recommended procedures. However, additions of other elements such as sulphur, tellurium or lead may be made to produce 'free machining coppers' with only a slight effect on conductivity. Similar considerations apply to the deoxidised pure copper used for water service tubing, water cylinders, pressure vessels and other applications requiring excellent welding or brazing properties. Small additions of chromium, zirconium, beryllium and other elements are used to produce high-strength high-conductivity alloys, many of which can have their properties further improved by heat treatment. For the production of electrodes for resistance welding a common material is copper-chromium which can have an addition of sulphur to improve machinability. All these alloyed coppers can be machined satisfactorily with experience. When machining copper-beryllium alloys, care should be taken that the material does not overheat and give off toxic fume. Normal turning, drilling and similar operations are considered safe provided that adequate lubricant is used. Operations such as grinding without lubricant or welding should be avoided unless approved fume extraction equipment is used. Appropriate advice is available from suppliers. Many of the alloyed coppers, such as those containing chromium, zirconium and beryllium, achieve their high strengths and relatively high electrical conductivities from precipitationhardening after a solution heat treatment. These alloys retain their strengths at temperatures where other high conductivity copper alloys tend to soften. Advice should be sought from the manufacturer concerning the changes in machinability and dimensional tolerances brought about as a result of the heat treatments.

Brasses

Brasses are the most commonly used copper alloys. The addition of zinc strengthens the material and incidentally changes the colour to a yellow or gold effect. The ratio of copper and zinc can be varied for advantages and the addition of other elements gives still more variety of combinations of properties such as machinability, strength, hardness, ductility (hot or cold), conductivity and corrosion resistance as well as many others.

44

Lead additions are used to improve machinability. The lead is insoluble in the solid brass and segregates as small globules that help the swarf to break up in to small pieces and may also help to lubricate the cutting tool action. The addition of lead does, however, affect cold ductility which may control both the way in which material is produced and the extent to which it can be post-formed after machining. Additions of manganese, iron, aluminium, silicon and other elements are used to increase strength and hardness while tin, aluminium and arsenic are used to further improve the good corrosion resistance of brasses, making them suitable for use in more aggressive environments. The additions of lead for improved machinability have been made for many years. Such brasses are standard for the manufacture of water fittings and give years of satisfactory service in all closed-circuits such as central heating systems and in the majority of fresh water supplies. Generally such fittings give no cause for concern when used for fresh water for drinking purposes but in certain well-known areas the supply water can be aggressive to brass and the use of a material that is immune to dezincification (such as cast gunmetal) or dezincification resistant (such as CZ132, CuZn36Pb2As) is recommended for service above ground and mandatory for underground fittings.

Nickel-Silvers

Nickel-Silvers are copper-nickel-zinc alloys similar in many respects to the brasses but with even better corrosion resistance. They have a silvery colour that is dependent on the nickel content and are well known because of their usage for electro-plated nickel silver (EPNS) decorative tableware. They also have significant usage as wire or strip in hard tempers used for springs and relay contacts. Leaded versions are available where free-machining rods are required and for hot stampings.

Bronzes

Bronzes are alloys of copper and tin. In the UK they are generally deoxidised with phosphorus which improves strength and hardness and the alloys are then known as phosphor bronzes. They are used for bearings and gears. In wire and strip form they have good elastic properties and are used for contacts. Lead is often added to improve machinability and to improve bearing properties. Gunmetals are alloys of copper, tin and zinc. They are readily cast and have good machinability and good corrosion resistance. They are used for pumps, bearings, valves and "bronze" statuary.

Copper-nickel alloys and the Aluminium Bronzes

Copper-nickel alloys and the Aluminium Bronzes were both developed for service in severe marine environments. The copper-nickel alloys are very ductile and suitable for the manufacture of plate, sheet and tube that combines the resistance to biofouling of copper with a corrosion resistance in fast-flowing seawater that is significantly better. Additives to improve machinability would have a disastrous effect on properties such as weldability and are therefore very uncommon. With experience, copper-nickel alloys can be machined with greater ease than alternative materials such as stainless steels. There are a wide range of available aluminium bronzes, mostly as casting alloys but some are suitable for hot working by rolling, forging or extrusion. Only those with a low alloy content can be cold worked to a significant extent. The strength and corrosion resistance of these alloys is excellent, being even better than most other common copper alloys in marine environments. Lead can be added to improve machinability but this is not included in most standard specifications because of its adverse effect on other properties. 45

When rough machining aluminium bronze castings it is important that the initial cut is heavy enough to get through the cast surface in one operation and that carbide tipped tooling is used. This is because the surface oxide contains alumina which is extremely abrasive. The machinability of this type of alloy is generally not so good as the free-machining brasses but still much better than other materials, especially most stainless steels. For general and finish machining, fine grain plain carbide tools are recommended. Steel-cutting grade carbides (e.g. P types) and titanium nitride coated tools are not recommended.

Notes

Hardness The hardness (or temper) of all wrought materials can have a marked effect on machinability. As a general rule, soft materials are not so easy to machine as harder ones of similar composition but this does not necessarily apply to free machining grades. It must also be remembered that any heat treatment subsequent to machining may affect dimensional tolerances.

Dimensional tolerances and straightness

Dimensional tolerances and straightness of machining rods will normally be in accordance with appropriate standards unless otherwise agreed. Small diameter material is naturally sensitive to handling techniques; care is needed to avoid distortion in transit or storage. Ends of rods may be chamfered at one or both ends by arrangement to facilitate entry in to automatic machines.

Dimensions

Dimensions may be affected if a material is in a highly stressed state before machining, or even when machining induces such stresses. Relief of internal stress can lead to distortion of components otherwise machined within tolerance. Retained internal stresses in cold worked starting stock can be removed before machining by an appropriate stress-relief anneal. For details of suitable treatments, please see CDA publications relevant to the materials being machined.

Table 13 ­ Materials commonly available as rods for free-machining purposes

Alloy Designation ISO/CEN Nearest BS Equivalent CEN Material Number Remarks

Free-machining coppers (see text for notes regarding improved machining techniques for the usual high-conductivity coppers using chipbreaking tools.) CuSP C111 CW114C Free-machining copper-sulphur is the preferred highconductivity copper for turning. Containing no tellurium or lead,it is also more amenable to recycling.

CuTeP

C109

CW118C

Copper-tellurium is often preferred to copper-sulphur for deep-hole drilling work. Leaded free-machining copper.

CuPb1P

CW113C

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Table 13 (continued)

Alloy Designation ISO/CEN Nearest BS Equivalent CEN Material umber Remarks

Brasses - Copper-zinc alloys, generally with a lead addition These brasses have excellent machinability but very limited cold workability. They are used where subsequent bending or riveting is not important. CuZn38Pb4 CuZn39Pb3 CuZn36Pb3 CZ121Pb4 CZ121Pb3 CZ124 CW609N CW614N CW603N British high-speed machining brass Standard European free-machining brass for which the100% machinability rating was established Higher copper content gives better ductility which means thebrass can be cold drawn to higher tensile strengths. Equivalentto ASTM C36000, the standard US free-machining brass Most popular alloy for hot stamping and high-speed machining

CuZn40Pb2

CZ122

CW617N

These brasses contain 2% lead and have good machinability and some cold workability. Workability increases with increasing copper content (and corresponding decrease in zinc content): CuZn39Pb2 CuZn37Pb2 CuZn38Pb2 CZ120 CZ131 CZ128 CW612N CW606N CW608N Good machinability but ductility lower than CZ131

These brasses contain about 1% of lead and are machinable and have good to very good workability: CuZn39Pb1 CuZn38Pb1 CuZn35Pb2 CuZn35Pb1 CuZn39Pb0.5 CZ137 CZ129 CZ129 CW611N CW607N CW601N CW600N CW610N

This brass was specially developed for the manufacture of water fittings for use with supply waters. It is resistant to dezincification, has good machinability and some cold workability: CuZn36Pb2As CZ132 CW602N

Special brasses, including the free-machining versions of some brasses with improved corrosion resistance and others of higher strength. CuZn36Sn1Pb CuZn36Pb2Sn1 CuZn40Mn1Pb1 CuZn37Mn3Al2PbSi CuZn40Mn1Pb1AlFeSn CuZn40Mn1Pb1FeSn CZ112 CZ134 CZ136 CZ135 CZ114 CZ115 CW712R CW711R CW720R CW713R CW721R CW722R Leaded Naval brass Brass for architectural sections High tensile brass with silicon High tensile brass (free-machining type) High tensile brass (free-machining type, low aluminium)

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Table 13 (continued)

Alloy Designation ISO/CEN Nearest BS Equivalent CEN Material umber Remarks

Leaded Nickel Silvers (Copper-nickel-zinc alloys) These are the free-machining versions of the alloys that are notable for their silvery colour, good resistance to corrosion and good strength. The alloys become whiter in colour with increasing nickel content: CuNi18Zn19Pb1 CuNi12Zn30Pb1 CuNi10Zn42Pb2 CuNi7Zn39Pb3Mn2 CuSn4TeP CuSn4Pb2P CuSn5Pb1 CuSn4Pb4Zn4 NS101 NS113 CW408J CW406J CW402J CW400J CW457K CW455K CW458K CW456K Free-machining phosphor bronze Free-machining phosphor bronze Free-machining bronze

Free-machining wrought bronzes (Copper-tin alloys):

Machining preforms made by hot stamping or forging

Both of these processes involve hot working of material cut to a suitable size; forging is generally between flat, open hammer faces while hot stamping involves the use of shaped dies. Forging gives a good fine-grained non-directional structure and is suitable for short runs. The expense of shaped dies is justified by a reduction in product costs because of reduced machining and faster production rates. Dies may be two-part or include extra cores that reduce still further the amount of machining required. Hot stamped components have a good surface finish that usually needs machining only where holes, threads or mating faces are required. Table 14 shows all the materials likely to be included in the European standard, classified according to general availability throughout Europe and hot working characteristics. Those with a pre-existing BS designation are likely to be the easiest to obtain within the UK. Most of the leaded duplex brasses and high-tensile brasses are readily hot stamped at moderate temperatures to close tolerances, causing little die wear. Choice will depend on the properties required by the end use and material availability. Tough pitch copper is fairly easy to hot work but needs to be at a higher temperature. The free-machining coppers are too brittle at elevated temperatures to be easy to hot work, though open forging is possible with care. Similar remarks apply to the high-conductivity alloyed coppers and copper alloys. Duplex aluminium bronzes can be hot worked, again they need to be pre-heated to a higher temperature than the brasses. With care, the copper-nickel alloys shown can be readily hot worked provided that impurities do not cause hot shortness. The leaded nickel brasses shown are the preferred choice when nickel silvers are required.

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Table 14 ­ Materials for hot stampings and forgings

Generally Available Alloy Designation ISO/CEN Nearest BSEquivalent CEN Material Number CW509L CW608N CW612N CW614N CW617N CW613N CW616N CW619N CW602N CW713R CW714R CW718R CW721R CW722R Machinability Group Alloy Designation ISO/CEN

Available to Special Order

Nearest BS Equivalent

CEN Material Number

Machinability Group

These materials are very readily hot worked: CuZn40 CuZn38Pb2 CuZn39Pb2 CuZn39Pb3 CuZn40Pb2 CuZn39Pb2Sn CuZn40Pb1Al CuZn40Pb2Sn CuZn36Pb2As CuZn37Mn3Al2PbSi CuZn37Pb1Sn1 CuZn39Mn1AlPbSi CuZn40Mn1Pb1AlFeSn CuZn40Mn1Pb1FeSn CZ109 CZ128 CZ128 CZ121-Pb3 CZ122 CZ132 CZ135 CZ134 CZ114 CZ115 2 1 1 1 1 1 2 2 1 2 2 2 2 1 CuZn37 CuZn38Pb1Sn1 CuSn39Sn1 CuZn39Pb0.5 CuZn39Pb1 CuZn23Al6Mn4Fe3Pb CuZn35Mn2Ni2Al1Pb CuZn40Mn1Pb1 CuZn40Mn2Fe1 CZ108 CZ133 CZ137 CZ129 CZ136 CW508L CW712R CW719R CW610N CW611N CW704R CW710R CW720R CW723R 2 2 2 2 1 2 2 2 2

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Table 14 (continued) Generally Available Alloy Designation ISO/CEN Nearest BS Equivalent CEN Material Number Machinability Group Alloy Designation ISO/CEN Nearest BS Equivalen t C106 CA107 CB101 CC101 C112 NS101 CEN Material Number Machinability Group Available to Special Order

These materials are less easy to hot work: Cu-ETP Cu-OF CuAl8Fe3 CuAl10Fe3Mn2 CuAl10Ni5Fe4 CuAl11Fe6Ni6 CuCr1Zr CuNi2Be CuNi2Si CuNi10Fe1Mn CuNi30Mn1Fe C101 C103 CA106 CA105 CA104 CC102 CN102 CN107 CW003A CW008A CW303G CW306G CW307G CW308G CW106C CW110C CW111C CW352H CW354H 3 3 3 3 3 3 3 3 3 3 3 Cu-HCP Cu-DHP CuAl6Si2Fe CuAl7Si2 CuAl9Ni3Fe2 CuAl10Fe1 CuBe2 CuCr1 CuCo1Ni1Be CuCo2Be CuZr CuNi1Si CuNi3Si CuNi7Zn39Pb3Mn2 CuNi10Zn42Pb2 CW021A CW024A CW301G CW302G CW304G CW305G CW101C CW105C CW103C CW104C CW120C CW109C CW112C CW400J CW402J 3 3 3 3 3 3 3 3 3 3 3 3 3 1 1

These materials are also hot workable:

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Materials for Castings for Subsequent Machining

Gunmetals are the most common cast copper alloys. They are a range of copper-tin-zinc-lead alloys with good castability and machinability. Compositions are again varied to suit end-use requirements. Other common cast materials include the leaded bronzes, phosphor bronzes, leaded phosphor bronze and aluminium bronzes. These are detailed in Table 4.

Material Availability

All the standardised coppers and copper alloys are listed in Tables 3 and Table 4, which gives common designations, commonly available forms and some guidance on properties, applications and machinability considerations. The materials listed include most of those generally available in Europe and believed to be made by at least two manufacturers. Highlighted are those most easily available in the United Kingdom. The tables include machinability ratings for each material.

Group 1 alloys

In Group 1 will be found mainly the brasses and coppers with additions made specifically for use where machining will be one of the most important manufacturing operations.

Group 2 alloys

In Group 2 are the coppers and alloys produced to meet combinations of property requirements including some such as cold formability that are not prominent in Group 1 materials. This improvement is effected by the change in structure from homogenous to duplex which occurs when the zinc content exceeds 37 per cent. Since lead also increases machinability it is added to alloys in this group in quantities up to 1 per cent. Post-machining operations such as flaring, bending, thread-rolling, and severe knurling often require additional ductility to prevent fracturing. Hence the lead addition is limited to effect a compromise. Some of the alloys in this Group are, by their composition and structure, intended to satisfy certain corrosive service or strength requirements. Although they do not contain lead the duplex structure gives good machinability.

Group 3 alloys

Group 3 alloys have machinability ratings of less than those of Group 2. They are either coppers or alloys in which corrosion resistance, strength, or colour properties are more important than machinability. The low zinc alloys - 90/10 brass (CZ101), 85/15 brass (CZ102) and 80/20 brass (CZ103) - are often referred to as gilding metals. They are attractive in colour and are used for many ornamental objects. The hardware industries make many articles from these alloys. The other alloys in this group have a wide variety of uses. Copper-cadmium is a high-strength alloy which is used for such electrical applications as terminals and connectors. The phosphor bronzes, which contain copper, tin and small amounts of phosphorus, are strong and tough as a group.

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More information on the original British material specifications can be found summarised in CDA Technical Notes(ref, 19, 20), and fully described in the relevant British Standards. These are BS2870-2875, covering copper and copper alloys in wrought, semi- manufactured forms, and BS 1400 'Specification for copper alloy ingots and copper and copper alloy castings'. As previously mentioned, these are due to be superseded by relevant common European specifications, given BS numbers.

Spreader for an expanding mandrel for a coiler for a rolling mill or wire rod mill

(Westley Brothers plc) This large casting in aluminium bronze to BS 1400 AB2 is being machined to precise dimensions.

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Illustrations - Cast Preforms

Water Meter Casing (Delta EMS Ltd) This is produced from a complex, thin walled, pressure die casting to close tolerances. Minimal machining is then required.

Valve - sectioned to show internal structure (Saunders Valve Co Ltd) An elaborately cored shell moulding is used to make this valve. Machining is then only required on mating faces and for threading.

Sprue of precision cast brass keys for a musical instrument (Boosey & Hawkes Ltd) Precision casting allows components to be produced to very intricate shapes. Minimal finish machining is then required.

A selection of continuously cast shapes (Delta Encon Ltd) Continuous casting using the ENCON process produces bars of material with particularly good, uniform mechanical properties. Complex cross sectional shapes can be made to high precision. Where surfaces have to be machined, an allowance of less than 1mm can be used because of the exceptionally sound surface characteristics of the con-cast material.

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Illustrations ­ High Precision

Fire Extinguisher Valve (Hawke Components Ltd) This fire extinguisher valve is designed so that it can easily be removed from the pressure cylinder when refilling takes place. It is produced from 35mm diameter bar using a series of drilling, tapping, boring and milling operations. The use of brass is cost-effective because of the dramatic savings in machining costs over those for steel.

Motor Commutator (Parvalux Electric Motors Ltd) This small motor commutator is diamond turned to very close tolerances ensuring minimal brush wear in service.

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Bearing Cages (RHP Industrial Bearings Ltd) These bearing cages are machinined to high precision tolerances from extruded brass hollow bar giving the reliability required for heavy duty bearings in high speed applications.

Aluminium Bronze Screw Connectors (Balcombe Engineering Ltd) High precision components in phosphor bronze and aluminium bronze for naval applications.

Connectors for Digital Exchanges (Greenpar Jubilee Ltd) The central part of the connectors are machined from beryllium copper originally supplied as solid hexagonal rod, the rest being brass. The whole connector is finally gold plated to ensure complete contact and correct conductivity.

Copper-Tellurium Electrodes (Graphite Technologies plc and Incast Precision Engineers for Finecast (Maidenhead ) Ltd) A selection of EDM electrodes produced in Tellurium-Copper. The use of Cu-Te saves up to 30% machining time compared with hard-drawn high conductivity copper, and also has the advantage of a completely burr-free finish.

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Illustrations ­ Repetition Jobs

Terminals (Greenpar Jubilee Ltd)

These miniature electronic terminals are made to a high standard of precision and reliability by the million.

Live and neutral pins for 13 amp plug (Tenable Screw and Delta Extruded Metals Ltd) Production is simplified and material is saved by the use of a shaped, extruded bar for the pins. The extruded bar is sliced, the pin tip is finished and the top is drilled and tapped for the connector screw. Plastic insulation is then added.

Riveted electrical components (Crabtree Electrical Industries Ltd) These components are made from CZ131 brass and are shown at production stages after extrusion, after machining and after riveting. The components are very reliable in service and ecomomical to manufacture in high volumes

Water and gas pipeline fittings (Currie and Warner Ltd)

This picture shows the variety of components which can be manufactured by fast repetition machining. One component is sectioned to reveal the internal detail.

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Illustrations ­ Short Runs

Spring Case and Primary Gear for a Carriage Clock (Biddle & Mumford Gears Ltd)

This component is quickly and economically machined from solid brass bar. Efficient swarf recovery ensures costeffective manufacture.

'A' Frame for a Skeleton Clock (Biddle & Mumford Gears Ltd)

These components are CNC milled to close tolerances. Short runs are economically possible because of the short time needed to reset a CNC machine.

Copper Electrodes for EDM

(University of Birmingham School of Manufacturing and Mechanical Engineering and the IRC in Materials for High Performance Applications) The picture shows two solid copper electrodes (centre) which were used to make the two halves of the forging die (top) by electro discharge machining. The finished forging made using the dies is shown at the bottom. The electrodes are made from C101 high conductivity copper because of its high conductivity and ease of machining. They are produced using CNC machinery to ensure repeatability and an accuracy of about +0.013 mm. Using a high precision copper electrode allows the manufacture of a forging die by EDM to an accuracy of +0.025mm which in turn can be used to produce high accuracy components requiring minimal finishing.

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Machining a contractor piece from CZ 121 brass on a Worth Graffat rotary transfer machine at Swissmatic Ltd (Swissmatic Ltd and Kuwait Petroleum Lubricants Ltd) The operations involved include sawing, drilling, tapping and broaching. The lubricant is Q8 Neat Oil Bach NQ.

Pneumatic Assemblies These components are made by silver soldering together two separately formed and machined parts and then bending the assembly to shape.

Model Railway Components Short runs of special purpose items for model kits are easily and economically made from brass.

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Illustrations ­ Machining HC Coppers

End rings for an electric motor (Thomas Bolton Ltd)

These rotor rings and end rings are precision machined from copper-chromium which has good creep strength and conductivity at the operating temperature.

Components for Power Industry (Thomas Bolton Ltd)

The cost of these large, complex items is minimisComponents for ed by making near-to-net shape preforms by forging or casting in free machining copper. Complex machining operations are then easily performed to a high standard of accuracy.

Chip breaker tool (Dr. M Staley, BNF-Fulmer) Overhead view of a high-conductivity copper bar being machined at 150m/min, showing the chip curler tool promoting chip breaking.

A selection of components machined from high conductivity copper, electronic grade

(Dawson Shanahan Ltd) Specially developed high-precision machining techniques are used to produce these components cost-effectively in oxygen-free copper, Cu-OFE. The items in the foreground are semiconductor heat sinks for use in diodes and thyristors for large current applications. The items with the narrow slots are interruptors for emergency power switching. The carefully machined slots control the electric arc which forms as the contact is broken.

Welding Nozzles

(Flame-Equipment Ltd) These welding nozzles are drilled with very fine, deep holes. The preferred material for such components is copper-tellurium because of its excellent thermal conductivity and the ease with which it can be drilled.

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Machinability Testing Methods

There is no method of assessing machinability that is equally applicable to all machining operations since materials behave differently. It is accepted, for instance, that of the two popular free-machining high conductivity coppers, copper-sulphur is better for turning operations while copper-tellurium is preferred for deep hole drilling. There are however, two main methods of classifying material machinability properties. One is an assessment of the type of swarf generated, an important property since the reliable operation of automatic equipment is dependent on swarf clearing easily and not obstructing the tooling or clogging lubricant filters. The other involves assessing the rate at which tooling wears and needs to be replaced, a factor that affects productivity significantly. Other criteria of interest include power requirements and surface finish. Fundamental work on quantifying machinability is mainly based on the work initially reported by Taylor (ref. 5) in 1906 and subsequent work such as those by Ernst and Marchant (ref. 6) . These are discussed in standard textbooks such as that by Trent (ref. 7) and Smith (ref. 18) and in many other papers. Many absolute and ranking tests have been summarised by Mills and Redford (ref. 8). A previous CDA publication (ref. 9) issued in 1939 is recognised as the first really useful guide to machining copper and its alloys. An article published in 1943 (ref. 10) first classified coppers and copper alloys according to a combination of chip shape, surface finish and power requirements. The standard free-machining brass at that time was given an arbitrary standard rating of 100% and all other coppers and alloys related to that. Since then there has been considerable work on other, non copper-based, materials which has resulted in a profusion of 100% base ratings. There has also been the development of the improved high-speed machining brass containing more lead that was given a 150% rating. The figures are a meaningful guide to performance but must be used with discretion in the light of the many variables that affect machinability. A subsequent CDA publication (ref. 11) classified the materials in to just three broad groups but recent work (ref. 3) has shown that the use of chipbreaker tools can make the machining of some of the group 3 materials relatively easier.

In discussing machinability, the large number of variables must be borne in mind. Some of these are:

· Material variables - Composition (more than 140 wrought and 40 cast materials) and internal structure as affected by casting technique, fabrication methods, thermal history and product form. Machining operation - Single point turning, form tool turning, drilling, milling, tapping, broaching, etc. Machining variables

· ·

Tool material, tool geometry (several variables), speed, feed rate, available power, lubrication techniques and machine variables (such as rigidity).

Multiplication of all these as a preliminary to assessing all their inter-variable effects results in a sum that is at least financially indigestible. However much work has already been done by a number of workers and it is hoped that soon there will be available a knowledge base summarising what has been published (ref. 12). The work at BNFMRA (subsequently BNF-Fulmer that introduced the 4% lead high-speed machining brass was reported by Davies (ref. 4). It included a study of the existing brasses commonly used world-wide. Testing, see Figure 13, was by means of large scale machining

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trials involving five operations including single-point turning, form tool turning, centring, drilling and parting off. The results gave a better understanding of the compositions, impurity effects and material production factors affecting machinability that has been widely adopted by leading manufacturers.

Figure 13 - Geometry of component and schematic diagram of machining operations in tests conducted by Davies (ref. 4)

Following the establishment of an ASTM universal machinability test (ref. 13), Thiele et al have reported (ref. 1) on the comparative machinability of three brasses, two steels and a freemachining aluminium alloy and established a universal machinability index. This is used on an automatic lathe and involves the production of a part using rough and finish form tool work together with drilling two different diameters and parting off. The test is neither simple nor inexpensive, see Figure 14, but does yield a commercially relevant rating suitable for both materials selection decisions and machine shop costings. The results gave the rankings shown in Figure 2 and resulted in the development of a nomograph to help estimate production rates. 61

As a further extension of this work it was possible to obtain comparative costings of many industrial components made in both free-machining steel and free-machining brass (ref. 2). Despite the extra initial cost of the brass, the overall cost savings, shown in Table 1 were significant and resulted in production being switched to brass. This was even without consideration of the further saving to be made by the lack of need for a further plating operation that is normally required to protect steel parts from corrosion in storage and service. The work published by the Deutsches Kupfer Institut (DKI) (ref. 14) , referred to earlier and in the main tables, includes a comprehensive review of the main factors affecting the machinability of coppers and copper alloys. Swarf types are characterised and illustrated and detailed guidance recommendations given for the machining characteristics of many materials. There is a useful summary of the common formulae used in evaluating and costing machining operations. It is available from the DKI in German or in English translation from CDA Information Department. The machining of conventional tough pitch and oxygen-free high conductivity coppers is of great interest because the free-machining grades of high conductivity copper are not so readily available or inexpensive as the free-machining brasses. Copper is traditionally cut with a higher rake angle and the use of more lubricant than brass in order to produce a cleaner chip and thus a better finish by preventing deformation ahead of the tool. Conventional tools tend to give swarf that is generated in long spirals and may obstruct the machine. Samandi and Wise (ref. 15) and Staley et al (ref. 3) described work that investigated the use of chipbreakers of various types. The SNMG-61 geometry shown in Figure 15 was amongst the most useful of commercial tips available. A relationship was established that gave the best chipbreaker geometry to suit the material and cutting conditions.

Figure 15 SNMG-61 style sintered-in chip breaker tool investigated by Samandi and Wise (ref. 15), gave the best chip breaking performance with unleaded 60/40 brass (CZ109).

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A recent report on the machinability of copper based alloys by Samandi and Wise (ref. 15) covered the characteristics of a range of alloys using single point turning to investigate tool force, chip thickness, tool temperature, tool wear and chip form. The materials investigated included: CuZn30 (CZ106 70/30 or cartridge brass), CuZn40 (CZ109 60/40 unleaded duplex brass), CuZn40Pb2 (CZ122 leaded brass) CuZn36Pb2As (CZ132 dezincification resistant brass) CuZn14Si4 (silicon brass to UNS C87500)

Three leaded gunmetals, including CuSn5Pb5Zn5 (85/5/5/5 gunmetal) CuNi10Fe1Mn (CN102 90/10 copper-nickel), CuNi30Mn1Fe (CN107 70/30 copper-nickel) CuAl10Ni5Fe4 (CA104 duplex aluminium bronze) and CuAl6Si2Fe (CA107 aluminium-silicon bronze). As expected the unleaded brasses formed continuous chips throughout the 25-600m/min cutting speeds investigated although self chipbreaking can be achieved except at very low feed rates. A chipbreaker tool can be used with advantages when self chipbreaking is unstable. For these materials, there was no advantage in using titanium nitride coatings on HSS tools. The leaded brasses formed discontinuous chips; there was also a significant reduction in tool forces due to the lubricity of the lead. The possibility of lead smearing across the machined surfaces was thoroughly investigated. At cutting speeds up to 700 m/min it could occur but was easily removed with acetic acid or an ultrasonic clean. An interesting observation was that the amount of surface lead was reduced by using tools with a large nose radius or by using worn tools, whereas rake angle had little effect. Leaded gunmetals with more than 1% of lead also gave free-machining discontinuous chips and could be machined at speeds of up to 360m/min.

The duplex aluminium bronze gave segmented chips when cut at speeds over 25m/min but these could give high force fluctuation causing the need for a tough tool. Aluminium-silicon bronze showed a lower cutting force, allowing higher metal removal rates. For the aluminium bronzes it was also shown that tool materials should not contain or be coated with titanium compounds since a reaction causes quick failure of the tool. Carbide tipped tools containing 10% cobalt and 0.8µm size tungsten carbide particles are preferred. The copper-nickel alloys produced continuous chips under all cutting conditions. For these alloys the use of a coating of titanium nitride reduced tool force and almost doubled tool life. Some work has been carried out on the development of suitable lead-free brasses (ref. 16) for possible use in countries where environmental considerations are onerous but as yet there is no satisfactory substitute. Most free-machining brass is made from recycled scrap containing lead and alternatives would therefore be significantly more expensive if excluding the use of this material supply. It is generally agreed that further work is needed to develop a cheap and effective universal test for machinability ratings. 63

Cutting Fluids for Copper Alloys

As previously described, the machinability of copper and its alloys varies from Group 1 (free cutting alloys) through Group 2 (readily machined alloys) to Group 3 (difficult-to-machine alloys and coppers). The effect of machinability on tooling, feeds, speeds and the depth of cut have already been discussed. These machinability ratings and the machining operations have also to be considered in order to select the most cost-effective cutting fluid.

Functions of cutting fluids

It is generally accepted that the primary functions of a cutting fluid are to cool and lubricate the tool and therefore: · · · · · lengthen tool life and/or permit high metal removal rates produce a good surface finish reduce cutting force cooling the chip and workpiece and hence assisting in maintaining dimensional accuracy carrying swarf away from the cutting zone

In addition, the cutting fluid performs a number of important secondary functions such as:

Care is taken when formulating a cutting fluid to ensure no undesirable side effects are encountered and in particular that the cutting fluid is: · · · · · non corrosive to workpiece and machine tool components - while copper alloys do not rust, some can be easily stained. stable during its service life easily drained or washed from the components. non toxic and non irritant readily disposable when exhausted

For some applications cutting fluids may be required to have particular characteristics such as transparency and compatibility with machine lubricants. The influence of cooling on tool life can be vital. Water is an excellent cooling medium and is therefore an obvious constituent where cooling is a prime requirement. For many operations, mineral oils properly directed and applied in ample quantity do provide sufficient cooling. The most effective form of lubrication is where two sliding surfaces are completely separated by an oil film. However, in the cutting zone, due to the high pressures necessary to shear metals and resultant high temperatures involved in the majority of cutting operations, this situation is not encountered, therefore load carrying and friction reducing additives have to be incorporated. Laboratory tests and field experience have proved additives incorporated in cutting fluids are effective in prolonging tool life and maintaining a good surface finish.

Selection and application of cutting fluids

The relative importance of the functional requirements of cutting fluids depends upon the machining characteristics of the workpiece, the type of cutting tool material and the nature of the machining operation. These various effects are outlined in the following sections.

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Type of work material

With free machining alloys of Group 1, which produce short chips, cooling of the tool is seldom necessary although cooling of the work may be necessary in certain applications. In addition, lubrication between the flank of the tool and the workpiece may increase tool life. The hard brasses and bronzes of Group 2 require a balance between cooling and lubrication whilst with the ductile materials of Group 3 which produce long continuous chips, lubrication will be the main consideration.

Effect of Tool Material

In machining operations with single-point tools, such as turning, boring, shaping and planing, the choice of cutting fluids is to some extent influenced by the cutting tool material employed. When using carbide tipped tools at moderate speeds, the cutting may be performed dry but lubricant such as water-soluble fluid can be used rather than neat oil to prevent fuming or haze generation at the higher operating speeds. Invariably the use of a cutting fluid will permit increases in speed, feed and productivity, improve surface finish, improve tolerances and lengthen tool life. High speed steel tools require efficient cooling unless very low speeds are employed. Best results will be achieved at high speed by using a cutting fluid which combines both cooling and lubricating properties.

Type of machining operation

Lubricants should be selected carefully with respect to the machining characteristics of the operations. Regular quality checks should be carried out with a simple hand-held refractometer to ensure that the cutting fluid is within specification. In drilling, the chief functions of a cutting fluid are cooling and the removal of swarf, whereas for precision finishing operations, particularly those with expensive tools such as reamers, taps, discs, broaches, milling cutters and hobs, lubrication is more important. For milling and hobbing, however, a cutting fluid with excessive lubricity should be avoided since it may cause the cutting edges to slide over the work surface during the initial part of the cut. For reaming, the cutting fluid should be of low viscosity to effectively flush away the chips, since any accumulation will cause the reamer to bind and may produce scored and oversize holes.

Type of cutting fluid

Of the variety of cutting fluids that are available, many are recommended by their manufacturers for use in the machining of copper alloys. Watermix cutting fluids. Watermix cutting fluids fall into two main groups, soluble oils and synthetic cutting fluids. Soluble oils These are mixed with water to form emulsions of oil in water. They consist of blends of mineral oils, emulsifying agents and other additives which stabilise the emulsion and prevent corrosion. The oil droplet size determines whether the emulsion is of the milky or translucent type.

65

Emulsions provide maximum cooling with limited lubricating properties as they are used at high dilutions. Typically 3 to 10% of fluid is used, giving oil to water ratios from 30 to 10 : 1 for general machining operations. To enhance their lubricating properties, soluble oils may also incorporate fatty oils or extreme pressure additives. Care should be taken in preparation of these emulsions, in particular when mixing, the oil should always be added to the water. Synthetic and semi-synthetic cutting fluids. These form true or colloidal solutions when added to water, they consist of water soluble corrosion inhibitors and surface active load carrying materials. Fully synthetic products contain no mineral oil, however, there are some that do contain a small percentage of mineral oil, these are known as semi-synthetic cutting fluids. During use some watermix cutting fluids may be depleted of oil or additives whilst others may be more concentrated by the evaporation of water. It is desirable to check the dilution's strength frequently and to make adjustments in accordance with the manufacturer's recommendations. The dilution strength can usually be readily checked by refractometer. All watermix cutting fluids tend to become contaminated with fine swarf, tramp oil and other extraneous matter and regular supervision and monitoring of their condition is advisable. They should also be checked for bacterial degradation although copper and copper alloys do provide some protection. Neat cutting oils. Neat cutting oils are used without addition of water. They consist of refined mineral oils containing proportions of extreme pressure additives and in many cases, selected fatty oils. The extreme pressure activity of neat cutting oils should be controlled according to the type of metal to be worked and the nature of the machining operation. All extreme pressure lubricants must balance lubrication performance against staining characteristics particularly in the case of copper based alloys. The design of automatic and semi-automatic machine tools is frequently such that it is difficult to exclude cutting fluids completely from enclosed gear systems and therefore neat oils are usually favoured for such machines. Careful choice of the neat cutting oil shows that no ill effects result from the intermixing of machine lubricants and the cutting lubricants. In many cases a common grade will satisfy both needs. Neat cutting oils may or may not contain special-purpose additives. Generally mineral oils have now completely replaced animal and vegetable oils as the latter are less stable in use. Compounded oils. The main reason for the inclusion of additives in neat cutting oils is that in some machining operations the load carrying properties of a straight mineral oil are inadequate for the severe conditions experienced in the cutting zone. Small additions of fatty oils such as animal or vegetable oils improve lubricity and the cutting oils reinforced in this way are known as compounded oils. These compounded oils are particularly useful in the machining of difficult copper alloys and give excellent tool life and good surface finish without staining. EP Oils. For the more difficult machining operations even the compounded oils cannot give the lubrication performance required and neat oils containing EP (extreme pressure) additives have to be used. EP cutting oils usually contain additives based on sulphur or chlorine or a combination of both and are recognised as necessary where the highest degree of lubricating efficiency is required. Sulphur can be present in two forms, active or inactive. In the mild or inactive type of fluid it is chemically combined with a fatty oil additive which is blended with 66

mineral oil to produce a sulphurised fatty oil. The active version contains sulphur in elemental form dissolved in mineral oil and is generally referred to as a sulphurised mineral oil. In general the presence of free or elemental sulphur is undesirable when copper and its alloys are to be machined as it tends to blacken the surface. Chlorine is usually present as a chlorinated paraffin which is blended sometimes singly with mineral oils and sometimes in combination with fatty oils and sulphurised additives. Where staining is to be avoided inactive neat oils containing sulphur, chlorine or fat can be used. However care should be taken to clean the finished component as soon as possible after machining and to ensure that the swarf is free from such contaminants before resale. An inactive oil is defined as one which will not darken a copper strip immersed in it for 3 hours at 100° C. Excess lubricant in swarf can be removed in a centrifuge to recover the lubricant and obtain a better return on the scrap. When metal swarf is being recycled it is normal practice to remove residual lubricants with heat before remelting is possible. This results, of course, in the evolution of gases from any lubricant residues. Chlorine-free lubricants When scrap is being recycled, the presence of any residual undesirable chemicals such as chlorine can cause environmental hazard. Where required, many manufacturers are now able to supply chlorine-free lubricants that prevent this problem.

Lubricant Manufacturers' Recommendations

Table 15 should be used as a guide to grades of cutting fluids recommended by some of the leading companies in the industrial oil field. More information can be obtained from individual companies, who can also advise on any health precautions that may be required in use.

67

Table 15 ­ Lubricant manufacturers' recommendations For neat oils and water-miscible lubricants suitable for materials in machinability groups 1, 2 and 3 (or all ( ) materials) Note: If swarf is to be sold for recycling, please see text regarding the need for lubricant to be free from chlorinated additives. (These are sample recommendations only, consult manufacturers' literature for full details) Form Tool Turning

Autos CNC BP OILS UK LTD Neat Oils Bezora 120 1

Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES

1

1

1

1

1

1

1

1

Low viscosity, additive free, recommended for free-cutting materials General purpose emulsion, 3-5%. Long life micro-emulsion, 35%.

Dilutable BP Oil 7395 BP Oil 7332 Syncut 32 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 1&2 1&2 3 3 1&2

Oil-free high performance heavy duty fluid. 4-10%.

CASTROL (UK) LTD Neat Oils Ilocut 462 Highly fatted, mineral oil blend specific for coppersand copper alloys, low in active sulphur.

68

Autos CNC Ilocut 482

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES Fatty/mineral oil blend, with chlorinated additive, recommended for copper alloys. Fatty mineral oil blend with chlorinated additiverecommended for coppers and copper alloys. Specifically formulated for coppers and copper alloys. 2.5 - 10% concentration 2-4% concentration, see manufacturers recommendations.

Ilocut 486

Dilutable Cooledge CB

Hysol G

CENTURY OILS LTD Neat Oils Coppacent 1 Coppacent 2 Kloricent 2 Walcut B2 Walcut 36 Walcut 927 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 1&2 Mineral oils with non-staining sulphurised additives Mineral oil with non-staining chlorinated additives. Chlorinated EP mineral oils

69

Autos CNC Dilutable Epicent B Supercent C Clearcent N DE LA PENA LTD Neat Oils 560 570

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES

Non-phenolic EP. 3-10% Nitrite & phenol free, 3-7%

Low viscosity chlorinated. Medium viscosity sulphochlorinated with inactive sulphur. Very low viscosity for honing and super-finishing. Nitrite & phenol-free EP soluble oils, 2-4%

585 Dilutable 750 750 ITW DEVCON Dilutable Safetap Safemist

Synthetic, 7%

70

Autos CNC Safesystem 1000 Safesystem 2000 ELF OILS LTD Neat Oils Elfcut BB22 Etirelf CB26

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding 5% 5%

NOTES

Medium viscosity with fatty additives, non-staining. Medium viscosity, high proportion of fatty additives for heavy duty machining. Chlorinated oil. Non-phenolic mineral oil. 4% recommended.

Aleda ED22 Dilutable Sarelf ABS ESSO PETROLEUM CO LTD Neat Oils Dortan N12 Dortan N13

Suitable for cam-operated high speed automatics Low viscosity EP oil for medium to heavy automatics.

71

Autos CNC Dortan N14

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES Chlorinated, sulphur additives. Heavy machining, low staining. Low viscosity with synthetic fatty additive.

Dortan N55 Dilutable Aquarius Aquarius EP Aquarius EP Plus Aquarius EPT 1 1&2 1 1&2 1 1&2 1 1&2 3 1 1&2 3 1 1&2 1 1&2 3 1 1&2 3

General purpose, 3-5% Chlorinated, 5-10% Suitable for more ductile materials. 3-10% Recommended for more arduous machining operations. 10%

GULF OIL Neat Oils Gulfcut BN Gulfcut EN Gulfcut FN Gulfcut ENX Dilutable Gulfcut Cascade 200 1 1 1 1 1 1 1 Biostable semi-synthetic, 26% anti-misting grade

72

Autos CNC Gulfcut Cascade 300

Gulfcut Cascade 350

Turning 1&2

Form Tool Turning 1&2

Drilling 1&2

Boring 1&2

Broaching 1&2

Tappping 1&2

Milling 1&2

Sawing 1&2

Grinding

NOTES Biostable semi-synthetic 310%

Biostable semi-synthetic EP, 310%

1&2

HOUGHTON VAUGHAN PLC Neat Oils Cindolube 3100 Cindolube 3101 Dilutable Solcut CB Hocut B60 CB Q8 - Kuwait Petroleum Lubricants Ltd Neat Oils Q8 Bach NK Q8 Bach NC Q8 Bach NP Dilutable Q8 Beethoven T Q8 Beethoven SC Conventional oil based Conventional oil based, EP 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 1 2&3 Mineral oil blend with additives, 3-5% Non-staining biostable EP, 5% 1 1 1 1 1 1 1 1 1 1 1 1 Neat cutting oil Neat cutting oil

73

Autos CNC

Q8 Beethoven VNF Q8 Beethoven XUA MOBIL OIL Co Neat Oils Mobilmet 424 Mobilmet 427 Dilutable Mobilmet 120 Mobilmet 151 Solvac Double Solvac 57 Neat Oils Ovomet GP Ovomet HP Ovomet LV 2&3 1&2 1&2 3 1 3 1&2 2&3

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES

Semi-synthetic biostable semi-synthetic biostable

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

1&2 2&3

Anti-mist chlorine-free grades

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

1&2 3 1&2 3

Non-phenolic, chlorine & nitrite-free grades. 3-10% 5% 3%

OVOLINE LUBRICANTS

1&2 2&3

1&2 2&3

1 2&3

1 2&3

1 2&3

1 2&3

1 2&3

1 2&3

1 2&3

All chlorine free

74

Autos CNC

Dilutable Novamet S Estramet

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES

Semi-synthetic ester based for light/medium machining, chlorineand nitrite free

SHELL OILS Neat Oils Macron B Macron C Macron F Dilutable Dromus B SRO SRO EP 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 Non-phenolic, nitrite free. Non-phenolic, nitrite-free With EP additives 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 1&2 3 Non-staining medium viscosity Higher additives than Macron B EP oil

SMALLMAN LUBRICANTS LTD Neat Oils Crowncut 822 Dilutable 2&3 2&3 2&3 2&3 2&3 2&3 2&3 2&3 2&3 Medium viscosity fatty chlorinated oil.

75

Autos CNC

Crownsol S170B Crown Novasol 265 TEXACO LTD Neat Oils Cleartex Plus 32

Turning

1&2 3

Form Tool Turning

1&2 3

Drilling

1&2 3

Boring

1&2 3

Broaching

1&2 3

Tappping

1&2 3

Milling

1&2 3

Sawing

1&2 3

Grinding

1&2 3

NOTES

Conventional soluble oil. 4-5% Semi-synthetic cutting fluid. 45%

Non-chlorinated EP specially developed for machining copper and its alloys Chlorinated EP. Fatty with inactive sulphur. For use where good surface finish is required. General purpose biostable. 2.55% EP version of Aquatex HB for improved surface finish. 2.5-5%

Metalworking oil 32 Dilutable Aquatex HB Aquatex H3 TOTAL OIL GREAT BRITAIN LTD Neat Oils Scilia L Scilia B

Non-additive cutting oil Non-staining EP oil

76

Autos CNC

Dilutable Lactua HP2

Turning

Form Tool Turning

Drilling

Boring

Broaching

Tappping

Milling

Sawing

Grinding

NOTES

EP cutting oil. 2-10% Coppers and copper alloys should be cleaned after machining

WYNN OIL (UK) LTD Neat Oils Titalub 13 Perfolub 40 Dilutable Special lubricant for difficult work

Microcool 387 Microcool 440 WF 370 Contocool 805

Semi-synthetic recommended for copper & copper alloys.

Synthetic

77

Addresses of Lubricant Manufacturers

BP Oil UK Ltd, Kensington House, 136 Suffolk Street, Queensway, Birmingham B1 1LW Castrol (UK) Ltd., Burmah Castrol House, Pipers Way, Swindon, Wilts. SN3 1RE Century Oils Ltd, PO Box 2, New Century Street, Hanley, Stoke-on-Trent ST1 5HU De la Pena Ltd, Racecourse Road, Pershore, Worcs WR10 2DD. ITW Devcon, Brunel Close, Park Farm, Wellingborough, Northants., NN8 6QX Elf Oil Ltd., Olympic Office Centre, 8, Fulton Road, Wembley, Middx HA9 0ND ESSO Petroleum Co Ltd., Ermyn Way, Leatherhead, Surrey, KT22 8UX Gulf Oil, The Quadrangle, Imperial Square, Cheltenham. GL50 1TF Houghton Vaughan plc., Legge Street, Birmingham B4 7EU Kuwait Petroleum Lubricants Ltd, Knowsthorpe Gate, Cross Green Industrial Estate, Leeds LS9 0NP. Mobil Oil Company, Mobil House, 54-60 Victoria Street, London SW1E 6QB Ovoline Lubricants, Pipewellgate, Gateshead, Tyne & Wear. NE8 2BN Shell Oils, Industrial Sales Centre, Cobden House, Station Road, Cheadle Hume, Cheshire, SK8 5AD Smallman Lubricants Ltd, Great Bridge Street, West Bromwich, West Midlands B70 0DE Texaco Ltd., 1, Knightsbridge Green, London SW1X 7QJ Total Oil Great Britain Ltd., Commercial Marketing Dept., Charles House, 17-23 Vaughan Road, Harpenden, Herts. AL5 4DY Wynn Oil (UK) Ltd. Unit 3, Headly Park 9, Headly Park East, Woodley, Reading RG5 4SG

78

References

(1) E W Thiele et al, "Comparative Machinability of Brasses, Steels and Aluminium alloys: CDA's Universal Machinability Index", SAE Technical Paper 900365, February 1990, Copper Development Association Inc, New York. "Free-cutting brass for lower screw machine product cost", six product information sheets, 1991, Copper Development Association Inc, New York, USA. See CDA Publication No 100 Brass Beats Steel. M A Staley, E F Smart and M L H Wise, "The Machining of High Conductivity Coppers", INCRA Project 343A Final Report, Nov 1984, International Copper Association. D W Davies "Improved free-machining leaded brass: Part 1 Summary Report" British Non-Ferrous Metals Research Association (Now BNF-Fulmer) Research Report RRA 1778, April 1971. BNF-Fulmer, Wantage. F W Taylor "On the art of cutting metals", Trans ASME 28, 31, 1906. H Ernst and M E Merchant, "Chip formation, friction and high quality machined surfaces", Surface Treatment of Metals, ASM 29, 299, 1941. E M Trent, "Metal Cutting", 3rd Edition, Butterworth, London, 1991. B Mills and A H Radford, "Machinability of Engineering Materials". Applied Science Publishers, London & New York, 1987. "Machining Copper and its alloys", CDA Publication No 34, 1939, Copper Development Association (Out of Print).

(2)

(3)

(4)

(5) (6) (7) (8) (9)

(10) "Machining copper and its alloys", Met Ind 65, 1944, p373. (11) "Machining Copper and its alloys", CDA Technical Note TN3, 1970, Copper Development Association (Out of Print). (12) R Francis and D W Davies "Proposal for the preparation of a knowledge base on the machining of copper and its alloys". Private communication. (13) "Standard test method of evaluating machining performance of ferrous metals using an automatic screw/bar machine", ASTM E618, American Society for Testing and Materials, Philadelphia, USA. (14) "Richtwerte fuer die spanende Bearbeitung von Kupfer und Kupfer legierungen". ("Factors Affecting the Machining of Copper and Copper alloys") DKI i 18, 1983, Deutsches Kupfer Institut, Berlin. (Available in English translation from CDA) (15) M Samandi and M L H Wise, "Machinability of Copper Based alloys", INCRA Project 384 Final Report, March 1989, International Copper Association. (16) J T Plewes and D N Loiacono, "Free-cutting copper alloys contain no lead", Adv Mat & Proc., 1991, Oct, pp23-27. (17) "Machining of Copper and Copper alloys". ASM Handbook Vol 16, 9th Edition, 1989. (18) G. T. Smith, 'Advanced Machining: The Handbook of Cutting Technology', 1989. 281pp., IFS Publications, UK

79

(19) 'Copper and Copper alloys: Compositions and Properties', CDA Technical Note TN10, 1986, 28pp. (See also CDA Datadisc D1) (20) 'Copper and Copper alloy Castings: Properties and Applications' CDA Technical Note TN 42, 40pp, 1991. (See also CDA Datadisc D3) (21) 'Cost-Effective Manufacturing - Process Selection', CDA Datadisc D4, 1992. (22) R Bakerjian, Tool and Manufacturing Engineers Handbook, Vol 4, Design for Manufacturability, pp11.3-11.5 (source: Carboloy Systems Div), Society of Manufacturing Engineers, Dearborn, Michigan.

Copies of INCRA Reports (now ICA) can be obtained from International Copper Association, 260 Madison Avenue, New York, NY 10016, USA, Additional data on specific machining operations, tools and techniques may be obtained from the following: Production Engineering Research Association (PERA), Melton Mowbray Leicestershire LE13 OPB. Machine Tool Industry Research Association (MTIRA), Hulley Road, Macclesfield, Cheshire SK10 2NE. also individual machine tool manufacturers for recommendations for specific copper alloys. Lists of copper alloy manufacturers and stockists obtainable from: Association of Bronze and Brass Founders, Heathcote & Coleman, 136 Hagley Road, Edgbaston, Birmingham B16 9PN. (cast product manufacturers) British Non-Ferrous Metals Federation, 10, Greenfield Crescent, Birmingham B15 3AU. (wrought product manufacturers)

80

Copper Development Association 5 Grovelands Business Centre Boundary Way Hemel Hempstead HP2 7TE Website: www.cda.org.uk Email: [email protected]

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