1. Machinability & Physics of Metal Cutting

2. Objectives Be able explain machinability
Understand how material is removed from and the effects it has on the surface finish of a work-piece
Analyze and troubleshoot chip formation

3. What is machinability?
Machinability is the ease with which a material can be machined, the wear created to the cutting edge, surface finish obtained and power consumption.

4. What factors play a role in machinability?
Mechanical properties of material (Hardness, Yield, Shear, etc.)
Geometry of tool tip (Rake angle, relief angle)
Tool Type (HSS, Carbide, CBD, PCD)

5. Stainless Steel / Super alloy
Machinability Chart
Carbon Steel
1015
72%
1018
78%
1020
1022
1030
70%
1040
64%
1042
1050
54%
1095
42%
1117
91%
1137
1141
1141 annealed
81%
1144
76%
1144 annealed
85%
1144 stressproof
83%
1212
100%
1213
136%
12L14
170%
1215
Alloy Steel
2355 annealed
70%
4130 annealed
72%
4140 annealed
66%
4142 annealed
41L42 annealed
77%
4150 annealed
60%
4340 annealed
57%
4620
4820 annealed
49%
52100 annealed
40%
6150 annealed
8620
86L20
9310 annealed
51%
Stainless Steel / Super alloy
302 annealed
45%
303 annealed
78%
304 annealed
316 annealed
321 annealed
36%
347 annealed
410 annealed
54%
416 annealed
110%
420 annealed
430 annealed
431 annealed
440A
15-5PH condition A
48%
17-4PH condition A
A286 aged
33%
Hastelloy X
19%
Tool Steels
A-2
42%
A-6
33%
D-2
27%
D-3
M-2
39%
O-1
O-2
Cast Iron
ASTM class 25
55%
ASTM class 30
48%
ASTM class 35
ASTM class 40
ASTM class 45
36%
ASTM class 50
Aluminum
aluminum, cold drawn
360%
aluminum, cast
450%
aluminum, die cast
76%

6. Traditional Metal Cutting
To machine, the tool or work-piece must rotate or move in a linear direction.
In order to remove material, the cutting tool must engage the work-piece. The rate of speed at which this engagement occurs is called Feed-Rate. Feed-Rate controls the thickness of the chip and is a major factor in the type of chip that is formed.
Depth of cut, also known as in-feed is the depth of material set to be removed by the cutting tool.

7. Chip Removal in Traditional Machining Operations

8. Physics of Chip Removal
Metal chips are sheared not “cut” from the work piece

9. Physics of Chip Removal
Deformation Zone / Plastic Deformation

10. Physics of Chip Removal
Elongation of the crystalline structure occur in the direction of the cut.

11. Physics of Chip Removal
Plastic Flow

12. Physics of Chip Removal
Rupture
Chip

13. Physics of Chip Removal
Affect of rake angle on chip thickness

14. Chip Formation Three basic types of chips in machining
Discontinuous chip
Continuous chip
Continuous chip with Built up edge

15. Chip Formation Discontinuous chip
Brittle work materials (e.g. Cast Irons)
Low Cutting Speed
Large feed and depth of cut
High tool chip friction (small rake angle)

16. Chip Formation Continuous chip
Ductile work materials (e.g. Low carbon steel)
High cutting speeds
Small feeds and depths of cut
Sharp cutting edge on tool
Low tool-chip Friction

17. Chip Formation Continuous chip with BUE (Built up edge)
Ductile materials
Too low rake angle
Lack of cutting fluid
Feed rate
Tool life affected

18. Chip Formation
BUE breaking off tool face onto new work surface

19. Questions?