For the preparation of PCD cutting tools, especially various high-precision (dimensional tolerances up to 2μm) and non-standard composite PCD cutting tools, the most critical processes include welding, cutting and grinding of PCD cutting tools.
The welding process not only determines the welding strength of PCD blades, but also affects the cutting performance of PCD cutting edges. For PCD cutting tools with complex cutting edge shapes that cannot be ground, the required cutting edge can be obtained through rough and finish cutting on a five-axis CNC slow wire cutting machine.
For cutting edges that require precision machining, a small margin can be left during high-precision cutting and the size requirements can be achieved through another precision machining.
For the preparation of PCD cutting tools, the welding between PCD composite plates and hard alloy or steel base materials is very important. The welding methods for PCD mainly include laser welding, vacuum diffusion welding, vacuum brazing, high-frequency induction brazing, etc. The brazing process of PCD composite sheets is one of the key technologies that restrict the promotion and application of PCD cutting tools.
It is well known that the brazing of hard alloys mostly uses high-temperature brazing technology (brazing temperature is about 1000℃), while PCD composite plates must use low-temperature brazing technology, otherwise thermal damage will be caused to the PCD composite plate, affecting its cutting performance.
However, the joint strength of low-temperature brazing is often lower and easy to open during tool processing. At present, many domestic tool manufacturers are troubled by the thermal damage and difficult brazing of PCD cutting tools.
Currently, most domestic and foreign PCD cutting tool manufacturers use high-frequency welding technology. The most important technical parameters of this technology include welding temperature, welding time, insulation environment, and insulation time. The welding temperature will directly affect the internal structure of PCD cutting edges. If the welding temperature is too high, it will cause carbonization of PCD cutting edges and affect its cutting performance; if the welding temperature is too low, it will cause poor welding and affect the joint strength.
Welding time refers to the time to maintain the welding temperature. If the insulation time is not enough, the brazing agent is difficult to melt fully and evenly, which will also cause poor welding. If the insulation time is too long, the PCD cutting edge will be affected its cutting performance because it is under high temperature for a long time.
If the PCD cutting tool after welding is cooled in the air, the welding shall not be strong due to the large thermal stress between PCD and the tool body. In severe cases, cracks will even occur on the PCD cutting tool. Therefore, it is best to quickly place the welded tool into a vacuum or inert gas medium with a certain temperature for insulation for a certain time to allow it to cool down slowly.
PCD cutting tools need to be cut on a CNC five-axis linkage slow wire cutting machine.
The principle of electro-erosion grinding is to form positive and negative electrodes between PCD cutting tools and electric aluminum wire, and achieve the effect of eroding PCD through discharge between positive and negative electrodes.
The grinding of PCD cutting tools is divided into grinding of outer circle and grinding of chamfer. The machines used are outer circle grinder and multi-axis manual tool grinder. When grinding PCD cutting tools, ceramic bonded diamond grinding wheel has the advantages of high grinding efficiency, high durability, and low processing cost compared with the resin-bonded or metal-bonded diamond grinding wheel. The particle size, concentration, and bonding agent of diamond grinding wheels have a great influence on the grinding quality and efficiency of PCD cutting tools, and using a grinding wheel with smaller particle size can result in lower surface roughness of the grinding surface per minute.
The law of the influence of the speed of the grinding wheel on the surface roughness is: when the speed is high or low, the surface roughness value is relatively large, while when the speed is at a certain intermediate level, the surface quality is better.
The law of the influence of grinding pressure on surface roughness is exactly the opposite: when the grinding pressure is at a certain intermediate level, the surface roughness value is the largest, while when the grinding pressure is high (such as 5.5Pa) or low (such as 2.5Pa), the corresponding The surface roughness has almost no difference, which is different from the traditional grinding law.
Generally speaking, when the machining quality requirements are met, a grinding wheel with a larger particle size should be selected as much as possible (the particle size of the coarse-grained grinding wheel can be selected as 22μm, the semi-fine grinding wheel particle size can be selected as 15μm, and the fine grinding wheel particle size can be selected as 9μm).
At present, TY-ROUT is a good diamond grinding wheel because its diamond grains are orderly arranged and the removal rate (the volume of PCD removed per minute) is 20-30 times that of a grinding wheel with disordered diamond grains, but its grinding cost is relatively higher. The grinding of PCD cutting tools also has strict requirements on grinding pressure, cooling liquid, etc. The best speed for grinding PCD cutting tools should be 2500r/min (when the grinding wheel diameter is 150mm). The concentration of the cooling liquid is 4%, and the grinding pressure is 150N. The surface roughness of the PCD cutting tool ground can reach Ra0.012μm.
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