During the processing of plastic molds, the most troublesome ones are the common shortcomings. These shortcomings will directly lead to the function of the workpiece, and even the workpiece cannot be used here. Therefore, we must try to avoid showing some Disadvantages, here are seven magic weapons for this problem.
1. Reasonable selection and dressing of grinding wheels. It is better to use white corundum grinding wheels. Its function is hard and brittle, and it is easy to generate new cutting edges. Therefore, the cutting force is small, the grinding heat is small, and the medium particle size is used. 46 ~ 60 mesh is better, medium and soft (ZR1, ZR2 and R1, R2) are selected for the hardness of the grinding wheel, that is, the coarse-grained, low-hardness grinding wheel has good self-excitation and can reduce cutting heat. It is very important to choose the appropriate grinding wheel for precision grinding. According to the high vanadium and high molybdenum conditions of the mold steel, the use of GD single crystal corundum grinding wheels is more suitable. When processing hard alloy and hardened hard materials, diamond with organic binder is preferred. Grinding wheels, organic binder grinding wheels have good self-grinding properties, and the roughness of the ground 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 grinders, coordinate grinders, CNC internal and external cylindrical grinders, the effect is better than other types of grinding wheels. In the grinding process, pay attention to trimming the grinding wheel in time and stick to the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slip and knead on the surface of the workpiece, causing the surface of the workpiece to burn and reduce the strength.
2. Mold processing uses the cooling and smoothing fluid reasonably, exerts the three major effects of cooling, washing and smoothing, insists on cooling, smoothing and cleaning, and then controls the grinding heat within the allowable range to avoid thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as using oil-immersed wheels or internal cooling wheels. The cutting fluid is introduced into the center of the grinding wheel, and the cutting fluid can directly enter the grinding area to exert an effective cooling effect and avoid burns on the surface of the workpiece.
3. The quenching stress after heat treatment is reduced to the lowest limit. Due to the effect of the grinding force, the quenching stress and the reticulated carbonization are arranged to cause a phase change to easily cause the workpiece to crack. Regarding precision molds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be performed after grinding to improve the resistance.
4. To eliminate the grinding stress, the mold can be immersed in a salt bath at 260 ~ 315 ℃ for 1.5min, and then cooled in oil at 30 ℃, so the hardness can be reduced by 1HRC, and the residual stress can be reduced by 40% ~ 65%.
5. Regarding the precision grinding of precision molds with a dimensional tolerance within 0.01mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. It can be known from the calculation that when the temperature difference of 300mm long steel pieces is 3 ° C, the data will change by about 10.8μm (10.8 = 1.2 × 3 × 3, 1.2μm / ℃ deformation per 100mm), and all finishing processes need to be fully considered The impact 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 metal, the grinding force is small and the grinding heat is small, and no burrs, cracks, burns, etc. will occur. Generally, the surface roughness can be better than Ra0. .16μm; otherwise, the wear of the grinding wheel is small, such as grinding hard alloy, the wear of silicon carbide grinding wheel is about 400% ~ 600% of the weight of the hardened carbide. When electrolytic grinding is used, the The amount of wear is only 50% to 100% of the amount of carbide removal.
7. Reasonably choose the amount of grinding, choose the precision grinding method with small radial feed and even precision grinding. For example, the radial feed and the wheel speed are appropriately reduced, and the axial feed is increased, so that the contact area between the wheel and the workpiece is reduced, the heat dissipation conditions are improved, and then the progress of the surface temperature is effectively controlled.