machinability ratings

MACHINABILITY RATINGS
OVERVIEW
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.
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 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.
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MACHINABILITY RATINGS
TABLES
The tables on the below pages contain
machinability ratings for many alloys. The
tables in this Skill Builder were obtained from
Tool and Manufacturing Engineers Handbook,
Volume 1, Fourth Edition from the Society of
Manufacturing Engineers.
CONCLUSION
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-orminus leeway to applying the values. Again,
use this as a guideline to understand the
difficulty of machining.
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12.13-V002
MACHINABILITY RATINGS
MACHINABILITY TABLE - PART 1
MATERIAL
BHN
MR
MATERIAL
BHN
MR
12% (chrome stainless steel)
165
0.70
A-8640
170
0.55
80B40
195
0.35
A-8645
210
0.50
81B45
179
0.60
A-8650
212
0.45
86B45
212
0.35
A-8740
200
0.55
98B40
185
0.40
A-8745
219
0.45
1020 (Castings)
134
0.60
A-8750
212
0.40
1040 (Castings)
190
0.45
AM 350
420
0.14
1330
223
0.60
AM 355
360
0.10
3140
197
0.55
AMS 6407
180
0.50
3250
220
0.45
AMS 6418
195
0.50
3312
191
0.50
AMS 6427
180
0.50
3340
220
0.45
B-1112
160
1.00
3450
197
0.45
B-1113
170
1.35
4130 (Castings)
175
0.35
C-1008
155
0.55
4130
183
0.65
C-1010
150
0.55
4140
190
0.55
C-1015
131
0.60
4140 (Leaded)
187
0.70
X-1020
148
0.65
4145
200
0.55
C-1025
143
0.65
4340 (100% pearlitic)
221
0.45
C-1030
190
0.65
4340 (Spheroidized)
206
0.65
C-1040
205
0.60
4340 (Castings)
300
0.25
C-1045
217
0.50
4620
170
0.65
C-1050
205
0.50
4640
187
0.55
C-1095
210
0.45
4815
183
0.55
C-1117
170
0.90
5120
191
0.65
C-1118
160
0.80
6130
183
0.55
C-1120
160
0.80
6135
190
0.55
C-1137
197
0.75
6180
207
0.40
C-1141
240
0.50
8030 (Castings)
175
0.45
Cast Iron (soft)
160
0.60
8430 (Castings)
180
0.40
Cast Iron (med)
195
0.40
8620
194
0.60
Cast Iron (hard)
262
0.20
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MACHINABILITY RATINGS
MACHINABILITY TABLE - PART 1
MATERIAL
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
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
0.30
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 (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
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BHN
500
190
293
135
196
200
206
197
223
204
190
200
170
197
220
210
240
360
290
225
200
300
MR
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
0.35
0.40
0.30
0.15
0.09
0.11
0.20
MACHINABILITY RATINGS
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
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
MACHINABILITY TABLE (STAINLESS STEEL) - PART 3
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
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MACHINABILITY RATINGS
MACHINABILITY TABLE (TITANIUM ALLOYS) - PART 4
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
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
MACHINABILITY TABLE (ALUMINUM ALLOYS WROUGHT & CAST) - PART 5
MATERIAL
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
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)
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MACHINABILITY RATINGS
MACHINABILITY TABLE (OTHER MATERIALS) - PART 6
MATERIAL
BHN
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
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
Leaded commercial bronze
2.40
Leaded copper
Leaded naval brass
2.40
2.10
MATERIAL
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
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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