Tool Wear

Tool failure and remedies

Tool Wear		Remedy
Thermal cracks	Small cracks running across the cutting edge, caused by thermal shock loads in interrupted cutting operations, particularly in milling, Danger of breakage !	use grade with greater resistance to thermal shock check use of cutting fluid; Cutting fluid should not generally be used for interrupted cuts if cutting fluid essential, use copius flow of the same
Chip control	Effective chip control is essential for trouble-free operation. Key factors are work material, feed and depth of cut. Too short chips result in vibrations and cutting edge overloading. Danger of breakage! Too long chips tends to coil around the workpiece and also the tool.	avoid too small depths of cut below 1 x radius, except in finishing if chips are too long; select chipbreaker geometry for smaller chip sections or increase feed if chips are too short; select chipbreaker geometry for larger chip section or reduce feed when form turning shoulders check sequence of operations
Surface finish	Surface roughness is a tool-life citerion often applied in finishing operations. It is affected by the configuration and condition of the cutting point, the cutting conditions and the rigidity of the machining setup Chatter marks or surface damage due to unfavourable chip flow call for special measures.	increase cutting speed increase radius use cermets where possible when cutting steel avoid vibrations use cutting fluid vary feed slightly change approach angle select different chipbreaker geometry check rigidty of tool and holding system
Shape and dimensional accuracy	Shape and dimensional accuracy are affected by the condition of the overall machine-part-tool setup	select grade with adequate wear resistance check cutting parameters, including machining allowance check rigidity of tool and work holding systems keep cutting forces low
Vibrations, instability	Vibrations in the workpiece usually occur with thin-walled parts and non-rigid setups. Unbalance and excessive cutting forces also cause problems	select larger approach angle for the tool use positive geometries use smaller radii change turning frequency reduce chip cross sections
Burring	Burring cannot always be avoided when machining steel workpieces. Chamfering operations should therefore be planned wherever possible	select inserts with positive geometry use insert with sharp cutting edges, eg. cermets reduce approach angle check sequence of operations