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5.5 TEMPERATURES IN CUTTING

•There are three main sources of heat when cutting,

1.Heat is produced as the tool deforms (works) the metal

2.Friction on the cutting face

3.Friction on the tool flank

chip

friction

2 tool

				1
				shear
	work piece has relative
motion towards tool

3

•Heat is mostly dissipated by,

1.The discarded chip carries away heat

2.Coolant will help draw away heat

3.The workpiece acts as a heat sink

4.The cutting tool will also draw away heat.

** factors 1 & 2 dissipate 75 to 80%, factors 3 and 4 dissipate 10% each [Krar, ]

5.6 TOOL WEAR

•Tool wear is still a significant problem in cutting.

•Typical types of tool wear include,

-Flank wear

-Crater wear

•Flank wear - the point of the tool degrades

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Iw

This wear controls tool life, and will change work dimensions

• Crater wear also decreases tool life

possible fracture line

dc

where,

dc = crater depth

•Tool failure can typically grouped under one of the following categories,

-Complete Failure - the tool is unusable

-Flank Failure - this can be estimated with maximum lw values,

• Roughing Cuts

0.03” for carbide tools 0.06” for high speed steel

• Finishing Cuts

0.010” for carbides 0.015” for high speed steel

-Work surface finish is inadequate

-Work dimension outside tolerance

•Flank wear can be discussed as a function of time,