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Machinability Ratings

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There are many different metals commercially available. Some are easier to machine than others. Many years ago, a system was developed to rate the relative ease or difficulty of machining various metals. These ratings are called "Machinability Ratings." Machinists and manufacturing engineers use machinability ratings when they select tool material, feed rates, and machine speeds for metal cutting and grinding operations. We use machinability ratings along with the other factors included in our Machining and Grinding System Survey when we recommend coolants and cutting oils for these operations. This Skill Builder explains how machinability ratings are established. It also lists the ratings for common metals. difficult to machine. For example, Inconel is an alloy that is very difficult to machine and it has a rating of 0.09! The machinability ratings (MR) in the tables were established for materials with Brinell hardness numbers (BHN) as listed. When a material listed is to be machined and is found to have a BHN different from that shown in the table, a ratio is applied. The ratio of the BHN in the table to the actual BHN of the workpiece is multiplied by the listed machinability rating (MR) to provide the MR of the actual workpiece. For example, a 3140 at a BHN of 197 is shown on the table to have an MR of 0.55. The 3140 to be machined has an actual BHN of 220. Therefore 197 divided by 220 times 0.55 equals 0.49. This means the machinability of the 3140 at a BHN of 220 has an MR of 0.49.

About Machinability Ratings

"Machinability" is not an exact term. It means "the ease with which a given material may be worked with a cutting tool." The cutting process is impacted by variables like cutting speed, dimensions of the cut, tool form, tool material, the cutting fluid, rigidity of tool holding device, and the level of tool/part impact relative to constant or intermittent contact. However, the machinability rating provides a starting point for understanding the severity of a metalworking operation. Machinability ratings are "relative" ratings. They compare the ease of machining an alloy to a standard. That standard is 160 Brinel hardness B1112 cold drawn steel machined at 180 surface feet per minute. B1112 was assigned a score of 1.00. The machinability of all other alloys is compared to the standard score of 1.00. The American Iron and Steel Institute (AISI) tested many alloys and compared the normal cutting speed, tool life and surface finish to that obtained when machining B1112. Materials with scores above 1.00 are easier to machine than B1112. Likewise, materials with scores of less than 1.00 are more

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Machinability Ratings Cont.

Skill Builder Tables

The attached tables contain machinability ratings for many alloys. The tables used in this Skill Builder were obtained from Tool and Manufacturing Engineers Handbook, Volume 1, Fourth Edition from the Society of Manufacturing Engineers.

Machinability Table - Part 1

Material

12% (chrome stainless steel) 80B40 81B45 86B45 98B40 1020 (Castings) 1040 (Castings) 1330 3140 3250 3312 3340 3450 4130 (Castings) 4130 4140 4140 (Leaded) 4145 4340 (100% pearlitic) 4340 (Spheroidized) 4340 (Castings) 4620 4640 4815 5120 6130 6135 6180 8030 (Castings) 8430 (Castings)

BHN

165 195 179 212 185 134 190 223 197 220 191 220 197 175 183 190 187 200 221 206 300 170 187 183 191 183 190 207 175 180

MR

0.70 0.35 0.60 0.35 0.40 0.60 0.45 0.60 0.55 0.45 0.50 0.45 0.45 0.35 0.65 0.55 0.70 0.55 0.45 0.65 0.25 0.65 0.55 0.55 0.65 0.55 0.55 0.40 0.45 0.40

Material

A-8640 A-8645 A-8650 A-8740 A-8745 A-8750 AM 350 AM 355 AMS 6407 AMS 6418 AMS 6427 B-1112 B-1113 C-1008 C-1010 C-1015 X-1020 C-1025 C-1030 C-1040 C-1045 C-1050 C-1095 C-1117 C-1118 C-1120 C-1137 C-1141 Cast Iron (soft) Cast Iron (med)

BHN

170 210 212 200 219 212 420 360 180 195 180 160 170 155 150 131 148 143 190 205 217 205 210 170 160 160 197 240 160 195

MR

0.55 0.50 0.45 0.55 0.45 0.40 0.14 0.10 0.50 0.50 0.50 1.00 1.35 0.55 0.55 0.60 0.65 0.65 0.65 0.60 0.50 0.50 0.45 0.90 0.80 0.80 0.75 0.50 0.60 0.40

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Material

8620 8630 8630 (Castings) 8720 9255 9260 9262H A-286 A-3115 A-3120 A-4023 A-4027 A-4032 A-4037 A-4042 A-4047 A-4150 A-4320 A-4340 A-4820 A-5140 A-5150 A-6120 A-6140 A-6145 A-6152

BHN

194 190 240 190 218 221 255 300 160 150 183 189 190 200 200 209 208 200 210 205 202 207 187 205 207 195

MR

0.60 0.60 0.30 0.60 0.45 0.45 0.25 0.10 0.65 0.65 0.70 0.70 0.70 0.65 0.60 0.55 0.50 0.55 0.50 0.45 0.60 0.50 0.50 0.50 0.50 0.50

Material

Cast Iron (hard) Cast Iron (Chilled White) Cast Iron (Grey Pearlitic) Chromaoloy Discaloy E-3310 E-4137 E-52100 E-6150 E-9310 E-9315 H-11 Hastelloy B (cast) Hastelloy C Hastelloy X Haynes Stellite #21 (cast) Haynes Stellite #25 Haynes Stellite #31 (cast) High Speed Steel 18-4-1 High Speed Steel 8-2-1 Inconel Inconel X Inconel 700 Inconel 702 Inconel 901 Inconel 901

BHN

262 500 190 293 135 196 200 206 197 223 204 190 200 170 197

MR

0.20 0.70 0.70 0.50 0.40 0.40 0.60 0.30 0.50 0.40 0.40 0.45 0.12 0.20 0.09 0.06 0.12 0.06

220 210 240 360 290 225 200 300

0.35 0.40 0.30 0.15 0.09 0.11 0.20

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Machinability Table - Part 2

Material

M-252 M-308 Malleable (pearlitic) Malleable (standard) Molybdenum (cast) Monel (K Monel) Monel (K-R Monel) Monel (R Monel) Monel (S Monel cast) NE-9261 Ni-Hard Ni-Resist Nimonic 75 Nimonic 80 Nimonic 90 Nitrolloy (135)

BHN

220 352 185 120 190 240 240 208 300 198 550 145 220 270 300 200

MR

0.05 0.05 0.90 1.10 0.30 0.35 0.45 0.45 0.25 0.50 0.03 0.45 0.17 0.12 0.10 0.45

Material

Nodular Iron #1 Nodular Iron #2 Nodular Iron #3 Potomac M Rene 41 Rycut 40 Stressproof Super Triscent Turbaloy Udimet 500 V-57 Vasco X4 Vascojet 1000 Waspalloy Tungsten Estimated

BHN

183 200 230 200 215 187 203 180 135 290 375 150 190 270

MR

0.60 0.50 0.40 0.45 0.15 0.65 0.50 0.40 0.40 0.09 0.08 0.50 0.45 0.12 0.05

Machinability Table - Part 3 (Stainless Steel)

Material

PH 15-7 Mo 17-4 PH 17-7 PH 301 302 303 304 310 316 317

BHN

270 388 200 183 178 180 160 160 195 195

MR

0.20 0.28 0.20 0.55 0.50 0.65 0.40 0.30 0.35 0.35

Material

403 405 410 416 418 420 430F 440C 440

BHN

200 145 160 200 160 207 147 240 160

MR

0.55 0.60 0.55 0.90 0.40 0.45 0.65 0.35 0.50

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Machinability Table - Part 4 (Titanium Alloys)

Material

A-55 A-70 A-110 C-120

BHN

160 188 220 240

MR

0.30 0.27 0.23 0.20

Material

C-130 C-140 MST

BHN

255 285 380

MR

0.18 0.15 0.09

Machinability Table - Part 5 (Aluminum Alloys Wrought & Cast)

Material - Cast

A-132-T A-214 A-356-T B-113 D-132-T 108 112 122-T 195-T 212 218-T 220-T 319-T 333-T 355-T 750-T

BHN

MR

1.10 2.00 1.40 1.80 1.30 1.40 1.80 1.40 1.90 1.60 2.40 2.30 1.60 1.30 1.60 1.80

Material - Wrought

2011 2014-T 2017-T 2024-T 3003 3004 5052 5056 4032-T 6051-T 6061-T 6063-T 7075-T Aluminum-bronze (5% Al)

BHN

MR

2.00 1.40 1.40 1.50 1.80 1.80 1.90 1.90 1.10 1.40 1.90 1.90 1.20 0.60

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Machinability Table - Part 6 (Other Materials)

Material - Cast

Aluminum-bronze (8% Al) Aluminum-bronze (9.25% Al) Aluminum-bronze (9.5% Al) Aluminum silicon-bronze Architectural Bronze Beryllium-copper (no heat treat) Chromium-copper Commercial bronze (90% Cu) Cupro-nickel Deoxidized Copper Electrolytic tough-pitch copper Extruded leaded nickel-silver (10%Ni) Forging brass Free-cutting brass High-leaded brass High-leaded brass (tube) High silicon-bronze Leaded commercial bronze Leaded copper Leaded naval brass

BHN

MR

0.60 0.60 0.60 1.80 2.70 0.60 0.60 0.60 0.60 0.60 0.60 2.40 2.40 3.00 2.70 2.40 0.90 2.40 2.40 2.10

Material - Wrought

Leaded nickel-silver (12% Ni) Leaded nickel-silver (18% Ni) Leaded phosphor-bronze (5% Tin) Leaded silicon-bronze Low brass (80% Cu) Low leaded brass Low-leaded (tube) Manganese bronze Medium leaded brass Muntz metal Naval brass Nickel Nickel-silver (18% Ni) Nickel-silver (20% Ni) Phosphor-bronze (5% Tin) Phosphor-bronze (8% Tin) Phosphor-bronze (10% Tin) Red brass (35% Cu) selenium or tellurium copper Special free-cutting phosphor bronze Zinc

BHN

MR

1.30 1.50 1.50 1.80 0.90 1.80 1.80 0.90 2.10 1.20 0.90 2.00 0.60 0.60 0.60 0.60 0.60 2.70 2.70 2.00

Summary

The use of the machinability rating is a method to assist you in recognizing how easy or how hard a given alloy is to machine in comparison to others. Like any specific appliction method, there is always a plus-or-minus leeway to applying the values. Again, use this as a guideline to understand the difficulty of machining.

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