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These seven tricks can effectively solve the common defects in mold processing

date：2023/08/10

During the processing of the mold, the most annoying thing is some common defects. These defects will directly lead to the performance of the workpiece, and even the workpiece cannot be used here. Therefore, we must try to avoid some defects when processing the mold. , The following provides seven magic weapons for this problem.

1. Choose and dress the grinding wheel reasonably. The white corundum grinding wheel is better. Its performance is hard and brittle, and it is easy to produce new cutting edges. Therefore, the cutting force is small, the grinding heat is small, and the medium particle size is used for the particle size, such as 46 to 60 mesh is better. Medium and soft (ZR1, ZR2 and R1, R2) are used for the hardness of the grinding wheel, that is, coarse-grained, low-hardness grinding wheel, good self-excitation can reduce cutting heat. It is very important to select the appropriate grinding wheel for fine grinding. In view of the high vanadium and high molybdenum conditions of the mold steel, it is more suitable to use GD single crystal corundum grinding wheel. When processing hard alloys and materials with high quenching hardness, organic binder diamond is preferred Grinding wheels, organic binder grinding wheels have good self-grinding, and the roughness of the workpieces can reach Ra0.2μm. In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheels have shown very good processing results. Finishing on CNC forming grinding machine, coordinate grinding machine, CNC internal and external cylindrical grinding machine, the effect is better than other types of grinding wheels. In the grinding process, it is necessary to repair the grinding wheel in time to maintain the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slip and squeeze on the workpiece surface, causing burns on the workpiece surface and reduced strength.
2. Cooling lubricant is used reasonably in mold processing, which plays the three major roles of cooling, washing and lubrication, keeping cooling and lubrication clean, so as to control grinding heat within the allowable range to prevent thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as the use of oil-immersed grinding wheels or internal cooling grinding wheels. Introduce the cutting fluid into the center of the grinding wheel, the cutting fluid can directly enter the grinding area, and play an effective cooling role to prevent burns on the surface of the workpiece.
3. The quenching stress after heat treatment is reduced to the minimum, because the quenching stress and the mesh carbonized structure are subject to the grinding force, and the phase change of the structure is very easy to crack the workpiece. For precision molds, in order to eliminate the residual stress of grinding, low temperature aging treatment should be carried out after grinding to improve toughness.
4. To eliminate grinding stress, the mold can also be immersed in a salt bath at 260~315℃ for 1.5min, and then cooled in oil at 30℃, so that the hardness can be reduced by 1HRC and the residual stress can be reduced by 40%~65%.
5. For precision grinding of precision molds with dimensional tolerances within 0.01mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. It can be seen from the calculation that when a 300mm long steel part has a temperature difference of 3℃, the material has a change of about 10.8μm, (10.8=1.2×3×3, the amount of deformation per 100mm is 1.2μm/℃), each finishing process needs to be fully considered The influence of this factor.
6. Adopt electrolytic grinding process to improve mold manufacturing accuracy and surface quality. During electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding metal, the grinding force is small and the grinding heat is also small, and there will be no grinding burrs, cracks, burns and other phenomena. The general surface roughness can be better than Ra0 .16μm; In addition, the wear of the grinding wheel is small, such as grinding cemented carbide, the wear amount of the silicon carbide grinding wheel is about 400% to 600% of the weight of the cemented carbide. When using electrolytic grinding, the wear of the grinding wheel The amount is only 50% to 100% of the amount of carbide removal.
7. Choose the amount of grinding reasonably, and use the fine grinding method with even smaller radial feed or even fine grinding. If the radial feed rate and the grinding wheel speed are appropriately reduced, the axial feed rate is increased to reduce the contact area between the grinding wheel and the workpiece, and the heat dissipation conditions are improved, thereby effectively controlling the increase in the surface temperature.