In the NC machining process, when the tool is chipped, edged, deformed, or damaged due to wear, it loses the machining function and cannot guarantee the machining quality of the part. This phenomenon is called tool failure. The main forms of tool damage and its causes include the following:
Back face wear
Abrasive wear appears on the flank face of the tool, which is caused by mechanical alternating stress. If the tool material is soft, the back angle is small, the cutting speed is too high in the machining process, and the feed is too small, these will cause excessive wear of the back face of the cutting tool, and thus reduce the dimensional accuracy of the machining surface, and increase Friction resistance in large cutting. Therefore, the tool material with higher wear resistance should be selected as much as possible, and at the same time, the cutting speed should be reduced, the feed amount should be increased, and the tool back angle should be increased so as to avoid or reduce the possibility of tool surface wear after the tool is generated.
Boundary wear
This is the wear that occurs at the contact surface of the main cutting edge with the workpiece. The main cause is the surface hardening of the workpiece and the friction caused by the zigzag cuttings. The solution is to reduce the cutting speed and feed rate, while selecting the wear-resistant tool material, and increase the tool's rake angle to make the cutting edge sharper.
Front rake wear
This occurs on the rake face of the tool and wears due to friction and diffusion. The main reasons for this are the contact of the chips with the workpiece material and the diffusion of the heat-generating area. In addition, the tool material is too soft, the cutting speed is too high in the machining process, and the feed amount is too large, which also causes the wear of the rake face. The wear of the rake face will cause the tool to deform, interfere with chip evacuation and reduce the strength of the cutting edge. It is possible to reduce the cutting speed and feed rate, and at the same time choose a coated cemented carbide tool to solve this problem.
Plastic deformation
This is the deformation of the tool cutting edge under high temperature or high stress. This is due to the fact that the cutting speed and feed rate are too fast, there are hard spots in the workpiece material, the tool material is too soft and the cutting edge temperature is too high. Plastic deformation can affect the quality of chip formation and cause the tool to chip. It is possible to reduce the occurrence of plasticity by reducing the cutting speed and feed rate, and selecting tool materials with high wear resistance and good thermal conductivity.
Bubbler
This is an adherent substance formed by the workpiece material sticking to the tool. The build-up of BUE significantly reduces the machining quality of the workpiece surface. It also changes the shape of the cutting edge and ultimately leads to chipping of the cutting edge. By increasing the cutting speed, it is possible to solve this problem by selecting coated carbide or cermet cutting materials and using appropriate cooling liquids during processing.
Edge peeling
This is a small gap in the cutting edge, non-uniform wear. The reason for this is due to factors such as interrupted cutting and poor chip evacuation. The method of reducing the flaking of the cutting edge is to reduce the feed speed during machining, select a tough tool material, and a blade with high cutting edge strength.
Crack
The chipping is the collapse of the tool edge, which not only damages the tool but also damages the workpiece. The causes of chipping include excessive wear of the tool edges and high machining stress, as well as excessive tool material, insufficient cutting edge strength, and excessive feed. In order to avoid chipping, it is better to choose alloy materials with better toughness, minimize the feed rate and cutting depth during processing, and also select high strength blades with larger tip radius.
Hot crack
This is due to temperature changes caused by interrupted cutting, a crack perpendicular to the cutting edge. Hot cracks will reduce the quality of the workpiece surface, resulting in edge spalling. When selecting a tough alloy tool and minimizing the feed and depth of cut during machining, dry cutting or sufficient cooling liquid during wet cutting is not likely to cause hot cracks. .
