The Wear Form Of The Blade

1) Front blade surface damage

When cutting plastic materials at a high speed, the area near the cutting force on the rake face will wear into a crescent concave shape under the action of chips, thus also known as crescent concave wear. 

In the early stage of wear, the rake angle of the tool increases, which improves the cutting conditions and facilitates the curling and breaking of chips. However, when the crescent depression further increases, the strength of the cutting edge is greatly weakened, which may ultimately lead to the breakage and damage of the cutting edge. When cutting brittle materials or plastic materials with lower cutting speeds and thinner cutting thicknesses, there is generally no crescent pit wear.

2) Blade wear

The wear of the tool tip refers to the wear on the back face of the arc of the tool tip and the adjacent secondary back face, which is a continuation of the wear on the back face of the tool. Due to the poor heat dissipation conditions and stress concentration here, the wear speed is faster than that of the rear cutting surface. Sometimes, a series of small grooves with a spacing equal to the feed rate are formed on the auxiliary rear cutting surface, which is called groove wear. 

They are mainly caused by the hardened layer and cutting patterns on the machined surface. When cutting hard to cut materials with high work hardening tendency, groove wear is most likely to be caused. The wear of the tool tip has the greatest impact on the surface roughness and machining accuracy of the workpiece.

3) Rear blade wear

When cutting plastic materials with a large cutting thickness, the back face of the tool may not come into contact with the workpiece due to the presence of chip buildup. In addition, the rear cutting surface usually comes into contact with the workpiece, forming a wear band with a back angle of 0 on the rear cutting surface. 

Generally, in the middle of the working length of the cutting edge, the wear on the back face is relatively uniform, so the degree of wear on the back face can be measured by the width VB of the wear band on the back face of the cutting edge.

Due to the fact that various types of tools almost always experience back face wear under different cutting conditions, especially when cutting brittle materials or plastic materials with smaller cutting thicknesses, the wear of the tool is mainly the back face wear. 

Moreover, the measurement of the width of the wear band VB is relatively simple, so VB is usually used to represent the degree of tool wear. The larger the VB, not only will it increase the cutting force and cause cutting vibration, but it will also affect the wear at the tool tip arc, thereby affecting the machining accuracy and surface quality.