Face wear (Crater wear):
On the face of the tool there is a direct contact of tool with the chip. Wear takes the form of cavity crater, which has its origin above the cutting edge. With time, cavity goes on widening. This is prominent in ductile materials. The crater occurs on the rake face of the tool at the point of impingement of the chip with tool and does not actually reach the cutting edge but ends near the nose and on the periphery which serves as the focal points of development of crack and extends to the cutting edge causing a rapid rupture. It leads to weakening of tool, increase in cutting temperature, friction and cutting forces. The tool life due to crater wear can be determined by fixing the ratio of width of crater to its depth.
Flank wear (Edge wear):
This wear is also called “wearland”. Work and tool are in contact at cutting edge only. Usually wear first appears on the clearance face of the tool in the form of a wear land, and is mainly the result of friction and abrasion. • Adhesion is also a factor because welding of the tool to the work material causes a built-up edge which is torn away, taking particles of the tool material with it. Thermal cracking, due to thermal shock, is also a cause of breakdown of small particles, leading to flank or edge wear. • Flank wear starts at cutting edge and then starts widening along the clearance face. It is independent of cutting conditions and tool/work materials Crater wear is prominent in ductile metals, but the flank wear becomes predominant in materials having brittle and flaky chip and discontinuous chip. It is important even in ductile materials if surface finish is the main criteria.
While all other modes of tool failure can be effectively reduced by changing speed, feed or depth of cut, the flank wear is a progressive form of deterioration which will ultimately result in failure inspire of best precautions.