Tool Wear and Machinability

Tool Wear and Machinability

Tool Wear and Machinability - All machining operations on work materials are carried out using cutting tools, made up of High Speed Steel (HSS), carbides etc. With the use, all cutting tools are subject to wear and tear, they become blunt and therefore cannot work to the specifications of size and surface finish required on the workpiece. This is the stage of tool failure.

Tool failure implies that the tool has reached a point beyond which it will not function satisfactorily until it is reground. Correspondingly, the term tool life refers to the machining time between regrinding and not to that (time) which elapses before the tool is consigned to scrap. Tool failure may occur as a result of

(a) Gradual microscopic wear (on either the rake or clearance faces), or

(b) Some more suddenly occurring phenomenon as overheating, chipping of the cutting edge, plastic deformation of the tool tip or thermal cracking.

Tool wears out due to the characteristic crater which appears on the rake face. Cratering has been most serious in the case of machining steel with the so called straight tungsten carbide tools i.e., tools in which hard particles of tungsten carbide are held in a matrix or bond of cobalt. In Clearance face or Flank wear, there is the appearance of a land on the clearance face or flank of the tool.

The wear which has taken place at any given time may be specified by either the width of the wear land or the volume of worn metal. Machinability signifies the ease/difficulty with which a workpiece material can be machined. It expresses the following cutting properties of a material.

1. Length of tool life,

2. Power required making a cut,

3. Surface finish, and

4. Cost of removing a given amount of metal.

Standard cutting tests are not infallible, since machinability is influenced by the

Coolant,

Cutting speed,

Feed, and

Tool angles.