What Is Machinability Index? Criteria Considered In Evaluating Machinability?

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🔗What Is Machinability? Factors affecting and advantages of machinability

What is machinability index of metal?

Machinability index is used to compare the machinability of different materials in the various cutting process. It is an attempt to quantify the relative machinability of different material. The rated machinability may vary for different cutting operation such as turning, milling, forming etc. In order to find the machinability index, factors like tool material, tool geometry, tool life and other cutting conditions are fixed except the speed. Then find the speed at which tool cut the material for a pre-determined tool life. Then it is compared with a standard material. Here machinability of standard steel is arbitrarily fixed as 100%. The slower speed indicates, low metal removal rate and hence poor machinability.

Machinability index, I (%)=  V_i/V_s ×100

Vi = Cutting speed of metal investigated for 20 minute tool life
Vs = Cutting speed of standard steel for 20 minute tool life

What are the criteria considered in evaluating machinability?

Following are parameters needs to considered for machinability measurement

  • Tool life, and types of wear tool subjected to. Crater wear, flank wear etc.
  • Cutting forces Power consumption.
  • Shape, size, type of chips. Tendency to burr. Cutting ratio of chip.
  • Efficiency and rate of chip removal.
  • Quality and properties of workpiece material.
  • Quality of surface finish and dimensional accuracy.
  • Temperature at cutting zone.


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