Machinability Tool Factors

Manufacturing & Design

The term machinability refers to the ease with which a metal can be machined to an acceptable surface finish. Materials with good machinability require little power to cut, can be cut quickly, easily obtain a good finish, and do not wear the tooling much; such materials are said to be free machining. The factors that typically improve a material's performance often degrade its machinability. Therefore, to manufacture components economically, engineers are challenged to find ways to improve machinability without harming performance.

Machinability can be difficult to predict because machining has so many variables. Two sets of factors are the condition of work materials and the physical properties of work materials.

The Machinability Factors, C

Common Workpiece

Cm at w / D ratios:

Materials w/D < = 0.5 0.5 < w / D < 0.7 w/D = (0.7-1.0)
Carbon and alloy steels 1.0 1.3 1.5
Stainless and tool steels 1.6 1.8 2.2
Gray cast iron 2.1 2.6 3.1
Ductile and malleable cast irons 1.0 1.3 1.5
Titanium alloys 1.0 1.5 1.7
Heat-resistant alloys 1.6 1.8 2.2
Aluminum alloys, s < = 70,000 psi* 0.7 0.8 0.9
Aluminum alloys, s > 70,000 psi 0.8 0.9 1.0
Copper alloys, s < = 70,000 psi 0.8 0.9 1.0
Copper alloys, s > 70,000 psi 1.0 1.3 1.5
Notice: w = Radial width of cut, inches
D = Cutting diameter, inches
w/D = Ratio of the radial width of cut to cutting diameter
* Ultimate tensile strength
 
Tool Wear Factors, Cw
Milling Depth of cut Feed per tooth   Cw
Category (min-max), in. (min-max), in. A * , in2  
Light 0.020-0.100 0.003-0.006 <= 0.0006 1.1
Medium 0.100-0.200 0.006-0.010 <= 0.002 1.2
Heavy-duty 0.200-0.400 0.010-0.020 > 0.002 1.3
 
* A = cross-sectional area of the chip

Machine Efficiency Factors, E

Type of Drive E, %
Direct Drive 95
Direct Belt Drive 90
Back Gear Drive 75
Geared Head Drive 70-80
Oil - Hydraulic Drive 60-90
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