Divided by wear performance
The material being processed often has some very hard particles, which can make grooves on the tool surface, this is abrasive wear. Abrasive wear exists on all surfaces, the rake face is the most obvious. Moreover, abrasive wear can occur at various cutting speeds, but for low-speed cutting, due to the lower cutting temperature, the wear caused by other reasons is not obvious, so abrasive wear is the main reason.
2.Cold welding wear
During cutting, there is a lot of pressure and strong friction between the workpiece, the cutting and the front and rear faces, so cold welding will occur. Due to the relative movement between the friction pairs, the cold welding will produce cracks and be taken away by one side, resulting in cold welding wear. Cold welding wear is generally more serious at moderate cutting speeds. According to experiments, brittle metals are more resistant to cold welding than plastic metals; Multiphase metals are smaller than unidirectional metals; Metal compounds have a lower tendency than simple cold welding; Group B elements in the periodic table of chemical elements have a low tendency to cold weld with iron. Cold welding of high-speed steel and cemented carbide is more serious during low-speed cutting.
In the process of cutting at high temperature and the contact between the workpiece and the tool, the chemical elements of both parties diffuse each other in the solid state, changing the composition and structure of the tool, making the surface of the tool fragile, and intensifying the wear of the tool. The diffusion phenomenon always maintains the continuous diffusion of objects with high depth gradients to objects with low depth gradients. Because the workpiece, chips and tool materials are different, thermoelectric potential will be generated in the contact area during cutting. This thermoelectric potential has the effect of promoting diffusion and accelerating tool wear. This kind of diffusion wear under the action of thermoelectric potential is called "thermoelectric wear".
When the temperature rises, the surface of the tool is oxidized to produce softer oxides and the wear formed by the friction of the chips is called oxidative wear.
Divided according to the form of wear
1.Rake face damage
When cutting plastic materials at a higher speed, the part on the rake face close to the cutting force will wear into a crescent concave shape under the action of chips, so it is also called crater wear. In the early stage of wear, the tool rake angle is increased, which improves the cutting conditions and facilitates the curling and breaking of the chips. However, when the crescent cavity is further increased, the cutting edge strength is greatly weakened, which may eventually cause the cutting edge to collapse and damage Case. When cutting brittle materials, or cutting plastic materials with a lower cutting speed and a thinner cutting thickness, crater wear will generally not occur.
2.Tool tip wear
Tool nose wear is the wear on the flank surface of the tip arc and the adjacent secondary flank surface. It is the continuation of the wear on the flank surface of the tool. Due to the poor heat dissipation conditions and the concentration of stress, the wear speed is faster than the flank. Sometimes a series of small grooves with a distance equal to the feed are formed on the secondary flank, which is called groove wear. They are mainly caused by the hardened layer and cutting lines on the machined surface. When cutting hard-to-cut materials with a high tendency to work hardening, it is most likely to cause groove wear. Tool tip wear has the greatest impact on the surface roughness and machining accuracy of the workpiece.
When cutting plastic materials with a large cutting thickness, the flank face of the tool may not contact the workpiece due to the existence of built-up edge. In addition, usually the flank face will come into contact with the workpiece, and a wear zone with a clearance angle of 0 is formed on the flank face. Generally, in the middle of the working length of the cutting edge, the flank wear is relatively uniform, so the degree of wear of the flank can be measured by the width VB of the flank wear zone of the cutting edge. Since various types of tools almost all have flank wear under different cutting conditions, especially when cutting brittle materials or cutting plastic materials with a smaller cutting thickness, the tool wear is mainly flank wear, and the wear zone The measurement of the width VB is relatively simple, so VB is usually used to indicate the degree of tool wear. The larger the VB, not only will increase the cutting force and cause cutting vibration, but also affect the wear of the arc of the tool tip, thereby affecting the machining accuracy and the quality of the machined surface.
Methods to prevent tool damage
1.According to the characteristics of the processed materials and parts, the various types and grades of tool materials should be selected reasonably. Under the premise of certain hardness and wear resistance, the tool material must be guaranteed to have the necessary toughness;
2.Reasonably choose the tool geometry parameters. By adjusting the front and rear angles, main and auxiliary deflection angles, and blade inclination angles; Ensure that the cutting edge and tip have good strength. Grinding a negative chamfer on the cutting edge is an effective measure to prevent tool collapse;
3.Ensure the quality of welding and sharpening, and avoid various defects caused by poor welding and sharpening. For the cutting tools used in key processes, the cutting tools should be ground to improve the surface quality and check for cracks;
4.Choose the cutting amount reasonably to avoid excessive cutting force and high cutting temperature to prevent tool damage;
5.Try to ensure that the process system has better rigidity and reduce vibration;
6.Take the correct operation method, try to make the tool not bear or bear less sudden load.
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The silicon carbide substrate preparation process mainly includes raw material synthesis, silicon carbide crystal growth, ingot processing, ingot cutting, cutting piece grinding, grinding piece polishing, polishing piece cleaning, etc.Among them, the key and difficult points of preparation are mainly the crystal growth, cutting, grinding and polishing links, which are the key points and difficulties in the entire substrate production process, and become the bottleneck that limits the yield rate and production capacity of silicon carbide.
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