Built-up edge and spurs
(1) When the built-up edge cuts the plastic metal material, because the workpiece material is squeezed, the chip generates a lot of pressure on the rake face of the tool, and friction generates a large amount of cutting heat. At this high temperature and pressure, the part of the chip that is in contact with the rake face of the tool is relatively slowed down due to the influence of friction, forming a "retention". When the friction force is greater than the binding force between the internal qualities of the material, some of the materials in the remaining layer will adhere to the cutting edge to form a wedge-shaped metal block with high hardness (usually 2~3.5 times the hardness of the machined material), which surrounds the cutting edge and covers part of the rake face, this wedge-shaped metal block is called built-up edge, as shown in Figure 2-6-9.
1) Advantages: The hardness of built-up edge is higher than that of raw materials, which can replace the cutting edge for cutting, and improve the resistance of the cutting edge; At the same time, the presence of built-up edge makes the actual rake angle of the tool larger, and the tool becomes sharper.
2) Disadvantages: The existence of built-up edge is actually a process of forming, falling off, forming and falling off again: the partially detached built-up edge will adhere to the surface of the workpiece: and the actual position of the tool tip will also change with the change of built-up edge: at the same time, because it is difficult for built-up edge to form a sharper cutting edge, it will produce a certain vibration in machining. Therefore, the surface quality and dimensional accuracy of the workpiece obtained after processing will be affected.
3) There are many causes of built-up edge. These factors mainly include cutting conditions such as workpiece material, cutting speed, cutting fluid, tool surface quality, tool rake angle, and tool material. When the workpiece material has high plasticity and low strength, the friction between the chip and the rake face is large, the chip deformation is large, and it is easy to stick to the knife and produce built-up edge, and the size of built-up edge is also large. When cutting brittle metal materials, the chips are crushed, the contact length between the knife and the chips is short, the friction force is small, the cutting temperature is low, and it is generally not easy to produce built-up edge.
4) Inhibition measures for built-up edge tumors.
A ：The chip velocity should be appropriate. The cutting speed is affected by the influence of the cutting temperature on the maximum friction coefficient of the rake face and the material properties of the workpiece, and the generation of built-up edge can be reduced by controlling the cutting speed to control the cutting temperature below 300 °C or above 500 °C.
B : Increase the rake angle appropriately. The larger the rake angle, the sharper the tool relative and the less chip deformation, the cutting force is reduced and the friction of the surface is reduced, thus reducing the conditions for the formation of built-up edge. It has been shown that enlargement of the anterior angle to 35° generally does not produce built-up edge.
C : When the feed increases, the cutting depth increases, and the contact length between the tool and the chip increases, which is easy to form built-up edge. If the feed rate is appropriately reduced, the possibility of built-up edge can be reduced.
D : The use of cutting fluid with good lubricating performance can also reduce or prevent the occurrence of built-up edge.
(2) Scale spine refers to the scale of the processed surface, as shown in Figure 2-6-10, it is a phenomenon that often occurs when cutting plastic metals at a lower cutting speed, which deteriorates the quality of the machined surface and increases the surface roughness value. When machining workpieces in machining centers, the generation of scaling can be reduced by changing the tool geometry, increasing the rake angle and keeping the cutting edge sharp, and using coated inserts.
