Tool Wear, Tool Life & Machinability

 HELLO FRIEND 

 i am back with anther post in this post i am talking about what is the Tool Wear, Tool Life & Machinability. 

in this post i am gonna to show what is life and how the wear is occur and how to improve machine ability so let’s start with out wasting time.

first of all talking about what are the failure of tool.

Tool Failure

Tool failure is two types

1. Slow‐death: The gradual or progressive wearing away of rake face (crater wear) or flank (flank wear) of the cutting tool or both.

2. Sudden‐death: Failures leading to premature end of the tool.

The sudden‐death type of tool failure is difficult to predict. Tool failure mechanisms include plastic deformation, brittle fracture, fatigue fracture or edge chipping. However it is difficult to predict which of these processes will dominate and when tool failure will occur.

Tool Wear

(a) Flank Wear

(b) Crater Wear

(c) Chipping off of the cutting edge

Fig.1 Tool Wear

Flank Wear: (Wear land)

Reason

Abrasion by hard particles and inclusions in the work piece.

Shearing off the micro welds between tool and work material.

Abrasion by fragments of built‐up‐edge ploughing against the clearance face of the tool.

At low speed flank wear predominates.

If MRR increased flank wear increased.

Flank Wear: (Wear land)

Effect

Flank wear directly affect the component dimensions produced.

Flank wear is usually the most common determinant of tool life.

Flank Wear: (Wear land) GARPH

Fig.2 Flank Wear

here is the graph of time vs flank wear graph

Primary wear

The region where the sharp cutting edge is quickly

broken down and a finite wear land is established.

Secondary wear

The region where the wear progresses at a uniform rate.

Tertiary wear

The region where wear progresses at a gradually increasing rate.

In the tertiary region the wear of the cutting tool has become sensitive to increased tool temperature due to high wear land.

Re‐grinding is recommended before they enter this region.

Tool life criteria ISO

(A certain width of flank wear (VB) is the most common

criterion)

Uniform wear: 0.3 mm averaged over all past

Localized wear: 0.5 mm on any individual past

Crater wear

More common in ductile materials which produce

continuous chip.

Crater wear occurs on the rake face.

At very high speed crater wear predominates.

For crater wear temperature is main culprit and tool

defuse into the chip material & tool temperature is

maximum at some distance from the tool tip.

Crater depth exhibits linear increase with time.

It increases with MRR.

Fig 3. crater wear vs time

Crater wear has little or no influence on cutting forces,  work piece tolerance or surface finish.