Notes on Machinability

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

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

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

M.I = V_t / V_s,

V_t = the cutting velocity for 60 min tool life on the 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 the machinability index, the free cutting steel is the one that has the highest machinability.