The reason why PCD cutter has the advantages of high cutting speed, long tool life and low cost of mass-processing workpieces is that it has the following performance characteristics that other tool materials cannot match.
1. Extremely high hardness and wear resistance
The hardness of polycrystalline diamond is 3 to 4 times higher than that of cemented carbide, close to that of natural diamond, and its wear resistance is more than 100 times higher. The abrasiveness is consistent, and it is difficult for cracks to pass from one grain to another, and its crack resistance is better than that of single crystal diamond.
2. Low fiction coefficient and high elastic modulus
The friction coefficient between the PCD cutter and the workpiece material is lower than that of other tool materials except single crystal diamond, usually between 011 and 013. A small friction coefficient can reduce the cutting force and reduce the cutting temperature.
The elastic modulus of PCD is much larger than that of cemented carbide, so the cutting edge is not easily deformed during the cutting process, and the original geometric parameters of the cutting edge can be maintained to a large extent, and the cutting edge can be kept sharp for a long time.
3. Good thermal conductivity and low thermal expansion coefficient
The high thermal conductivity and thermal diffusivity make the polycrystalline diamond cutters easy to dissipate the cutting heat during cutting, so that the temperature in the cutting area will be lower and the tool service life will be long. The low thermal expansion coefficient makes the tool less likely to deform greatly during the cutting process.
4. The edge is sharp and the roughness of the edge is small
The cutting edge of the PCD cutter is very sharp. Generally, the peak serration of the cutting edge is less than 5 μm, and the blunt radius of the cutting edge is less than 4 μm. In most cases, the rake face of the PCD cutter is a mirror surface, and the surface roughness can reach 0101 μm, which can make the chips flow out easily along the rake face and reduce the generation of built-up edge.
In order to improve engine performance, the engine piston material is changed from low-silicon aluminum alloy to medium-silicon aluminum alloy, and even high-silicon aluminum alloy is used.
The excellent characteristics of PCD blanks make PCD cutters widely used in processing aluminum alloys, especially high-silicon aluminum alloys. The hardness and wear resistance of high silicon aluminum alloy are higher than other aluminum alloys. When cutting, the tool alternately cuts soft aluminum base and hard silicon particles, and ordinary tools are easy to wear. At the same time, the tool is also easy to produce built-up edge, which will deteriorate the machining accuracy and surface roughness.
In order to avoid built-up edge and work hardening, the cutting edge must be sharp and the cutting face must be smooth, and PCD cutters meet these requirements.
1. Although the PCD cutter has extremely high hardness, its toughness is not as good as that of cemented carbide, and it is much lower than that of high-speed steel. Therefore, the main failure form of PCD cutter is chipping. Chipping is usually caused by vibration during machining. Reducing tool overhang and improving the rigidity of the machine tool can help reduce vibration. A high-rigidity machining machine is a prerequisite for using PCD cutters, and most machining workshops process the finishing process of high-silicon aluminum pistons on more advanced CNC machine tools.
2. Higher cutting speed can also protect the cutting edge of PCD cutter. When turning with PCD cutters, the cutting speed used should be 2 to 3 times higher than that with carbide tools, otherwise it is difficult to obtain satisfactory processing results.
3. PCD cutters can be divided into surface processing tools, hole processing tools, and ring groove processing tools. When surface machining or boring aluminum pistons with PCD cutters, coolant is usually not required, while semi-closed ring groove machining requires smooth chip evacuation and cooling and lubrication of the cutting edge.