Machinability

The ease with which the machining can be done is called machinability of work material.

The machinability of work material is influenced by the following parameters:

1. The properties of work material.
2. The cutting forces induced during machining.
3. Uses of cutting fluids.
4. process parameters during machining.

The following criteria will be used for defining the machinability of work material:

1. Tool life: Under similar conditions of machining higher the tool life indicates the better machinability.
2. Surface finish: Under similar conditions of machining better the surface finish indicates the better machinability.
3. Material Removal Rate (MRR): Under similar conditions of machining higher the MRR indicates the better machinability.
4. Specific cutting energy:  Under similar conditions of machining lower the specific cutting energy indicate the better machinability.
5. Forces and Power: Under similar conditions of machining lower the forces and power indicate the better machinability.
6. Shear angle: Under similar conditions of machining higher the angle indicate the better machinability.

The above criteria will be used only when more than one workpiece is given. If only one workpiece is given the machinability can be indicated by using machinability index (M.I),

M.I = V_t / V_s,

V_t = the cutting velocity for 60 min tool life on test workpiece.
V_s = the cutting velocity for 60 min tool life on standard workpiece.

The standard workpiece can be taken as the free machining steel or free cutting steel because at the time of definition of machinability index the free cutting steel is the one which has highest machinability.