Abrasives wear hard spots such as carbides, oxides, nitrides and debris in the workpiece material, which draw grooves on the tool surface, resulting in tool wear. Its wear strength (i.e. wear speed) depends on the hardness difference between the hard point and the tool. The measures to reduce wear can be heat treatment to reduce and soften the hard points contained in the workpiece material, or select the tool material with high hardness and fine grain. Abrasive wear is often the main reason for the wear of low-speed cutting tools.

Bonding wear due to the bonding (cold welding) phenomenon at the knife chip interface, when the bonding part flows and separates along the front with the chip, if the bonding strength is low, it will shear and separate along the bonding surface; If the bond strength is high, the shear occurs outside the joint surface. Generally, most of the shear occurs in the chip bottom layer. However, due to the microstructure defects of the tool material, or due to high-temperature softening, fatigue and other reasons, the shear may also occur in the surface layer of the tool material, resulting in the particles on the surface layer of the tool being torn away. When the particle size is small, it is called bonding wear, and when the particle size is large, it is called spalling. The appearance feature of bonded wear surface is rough surface. The influencing factors of bond wear are complex. The strength ratio of the contact area between tool material and workpiece material affects the bonding wear strength to a great extent, and their hardness ratio sometimes has a decisive influence. The tear strength of hundreds of small particles is quite related to the tear strength of more particles. The higher the hardness of the tool, the finer the grains and the smaller the size of the falling particles. Increasing the stiffness of the system and reducing the vibration will help to avoid the falling off of large particles.

3-diffusion wear two metals in contact with each other. Due to the concentration difference of chemical components, the atoms at the interface will diffuse each other,

However, the diffusion is very slow at room temperature and can be increased thousands of times at high temperature. In high-speed cutting, the contact area between the tool and the chip and the machining surface has high temperature, high pressure, strong adhesion and large plastic deformation. Some elements (iron, carbon, cobalt and tungsten) diffuse faster, which changes the chemical composition and microstructure of the metal on the surface of the tool, reduces the strength and increases the brittleness, thus aggravating the wear of the tool. The tool surface quotient of diffusion wear is almost as smooth as polishing. For cemented carbide tools, Co, C and W in the tool surface diffuse to the workpiece material, II; Fe in the part material diffuses to the tool, decarburizes and depleted tungsten on the surface of the tool, and generates intermediate compounds with low strength and high brittleness, which aggravates the wear of the tool. Because the bonding of tic is stronger than that of WC, YT cemented carbide has strong diffusion wear resistance. Diffusion wear is a phenomenon occurring at high temperature. Its main influencing factors are the chemical properties, relative moving speed and temperature of tool materials. The chemical properties of the combination of tool materials and workpiece materials have a greater impact than the mechanical properties, but the temperature plays a decisive role. YG alloy diffuses obviously at about 800 ° C and YT alloy at about 1000 ° C. after that, the diffusion rate increases by one time for every 20 ° C increase in temperature. The measure to reduce tool wear is to reasonably select the tool material to make it have good chemical stability combined with the workpiece material; Reasonably select cutting parameters and reduce cutting temperature. It should also be mentioned that when the temperature increases from low to high, the bonding wear does not always increase. Each combination of tool material and workpiece material has an optimal cutting temperature.

4. Chemical wear at a certain cutting temperature, the tool material reacts with some elements in the surrounding medium or cutting fluid to form compounds to accelerate tool wear, which is called chemical wear. For example, oxygen in the air and chlorine and sulfur in extreme pressure cutting fluid react with tool materials to accelerate tool wear.

In addition to the above four causes of tool wear, there are also fatigue damage and thermoelectric wear. The above four reasons can be divided into two categories. Abrasive wear and bonding wear belong to mechanical wear. They exist under various cutting conditions and are the basic cause of tool wear, but they are often the main cause of tool wear in low speed cutting.

Diffusion wear and chemical wear belong to thermal wear, which is the reason for tool accelerated wear, that is, the main reason for tool wear in high-speed cutting. However, there is no strict boundary between them, and they affect each other. Under certain cutting conditions, some wear may play a leading role. The measures to reduce wear and tear also need to find out the main causes according to the specific situation in order to suit the remedy to the case. However, cutting temperature or cutting speed closely related to it has a decisive effect on wear. Figure 3-27 shows the relationship between various wear strength ratios and cutting speed.