How to reduce the defects in plastic mold processing?
The quenching stress after heat treatment is reduced to the minimum, because the quenching stress and reticulated carbonized tissue under the action of grinding force, the microstructure produces phase change and easily cracks the workpiece.Use the cooling lubricating fluid rationally, give play to the three functions of cooling, washing and lubrication, keep the cooling and lubrication clean, so as to control the heat of grinding within the allowable range, so as to prevent the thermal deformation of workpiece.The specific operations are as follows:
1. Improve the cooling conditions during grinding, such as using oil sand soaking wheel or internal cooling wheel.The cutting fluid is introduced into the center of the grinding wheel. The cutting fluid can enter directly into the grinding area to play an effective cooling role and prevent the surface of the workpiece from being burned.Use the cooling lubricating fluid rationally, give play to the three functions of cooling, washing and lubrication, keep the cooling and lubrication clean, so as to control the heat of grinding within the allowable range, so as to prevent the thermal deformation of workpiece.
2. Reduce the quenching stress after heat treatment to the minimum, because the quenching stress and reticulated carbonized tissue under the action of grinding force, the microstructure will produce phase change and easily cause the workpiece to crack.In order to eliminate the residual stress of grinding, the high precision mould should be treated with low temperature aging after grinding to improve the toughness.
3, eliminate grinding stress can also will die in 260 ~ 315 ℃ of salt bath at 1.5 min, and then in 30 ℃ oil cooling, so can drop 1 HRC hardness, residual stress reduced by 40% ~ 65%.
4. For precision grinding of precision molds whose dimensional tolerance is less than 0.01mm, attention should be paid to the influence of ambient temperature. Constant temperature grinding is required.By calculating, the 300 mm long steel, temperature 3 ℃, the change of the material there are about 10.8 microns, (10.8 = 1.2 * 3 * 3, 1.2 mu per 100 mm deformation m / ℃), various finishing processes are required to fully consider the influence of this factor.
5. Adopt electrolytic grinding to improve mold manufacturing precision and surface quality.During electrolytic grinding, the grinding wheel scrapes the oxide film: instead of grinding metal, so the grinding force is small and the grinding heat is small. There will be no burr, crack or burn.In addition, the abrasion of grinding wheel is small, for example, when grinding hard alloy, the abrasion of silicon carbide grinding wheel is about 400% ~ 600% of the weight of polished hard alloy. When using electrolytic grinding, the abrasion of grinding wheel is only 50% ~ 100% of the abrasion of hard alloy.