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How to solve the problems in plastic mold processing?

Update:23-06-2020
Summary:

In the processing of plastic injection mould, what we a […]

In the processing of plastic injection mould, what we are most troubled by are some common shortcomings, which will directly lead to the use of the workpiece, and even the workpiece cannot be used here. Therefore, we must try to avoid showing some Disadvantages, 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 function is hard and brittle, and new cutting edges are prone to occur. Therefore, the cutting force is small, the grinding heat is small, and the medium particle size is used for the particle size, such as 46~60 mesh is better. Choose medium-soft soft (ZR1, ZR2 and R1, R2) in 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 select GD single crystal corundum grinding wheel. When processing hard alloys and materials with high quenching hardness, diamond with organic binder is preferred The grinding wheel and the organic binder grinding wheel have good self-grinding, and the roughness of the workpiece can reach Ra0.2μm. In recent years, with the use of new data, 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 varieties of grinding wheel. In the grinding process, we must pay attention to dressing the grinding wheel in time and insist on the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slip and knead on the surface of the workpiece, resulting in burns on the surface of the workpiece and reduced strength.

 


   2. The mold processing reasonably uses cooling and smoothing fluid to exert the three major effects of cooling, washing and smoothing, insisting on cooling and smooth cleaning, and then controlling the grinding heat within the allowable range to avoid 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. The cutting fluid is introduced into the center of the grinding wheel, and the cutting fluid can directly enter the grinding area, exerting an effective cooling effect and avoiding burns on the surface of the workpiece.
   3. The quenching stress after heat treatment is reduced to the lowest limit. Due to the quenching stress and network carbonization arranged under the effect of grinding force, the arrangement of the phase change is very easy to crack the workpiece. Regarding precision molds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be performed after grinding to improve resistance.
   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 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 the temperature difference of 300mm steel is 3℃, the data has a change of about 10.8μm (10.8=1.2×3×3, the amount of deformation per 100mm is 1.2μm/℃), and each finishing process needs to be fully considered The influence of this factor.
   6. Electrolytic grinding is used to improve the precision of mold making and appearance quality. During electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding the metal, the grinding force is small and the grinding heat is also small. Grinding burrs, cracks, burns and other phenomena will not occur. The general appearance roughness can be better than Ra0 .16μm; otherwise, 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 grinding wheel The amount of wear is only 50% to 100% of the amount of carbide removal.
   7. Choose the amount of grinding reasonably, choose the precision grinding method with even smaller radial feed and even precision grinding. If the radial feed rate and grinding wheel speed are appropriately reduced, the axial feed rate is increased, so that the contact area between the grinding wheel and the workpiece is reduced, the heat dissipation conditions are improved, and then the progress of the surface temperature is effectively controlled.

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