In the process of plastic melting and plasticizing, the mold of plastic products is prone to defects. The solution is to reduce the quenching stress after heat treatment to a very low level, because the quenching stress and the reticulated carbonized structure are under the action of grinding force. Extremely easy to crack the workpiece. Reasonable use of cooling lubricants, play the three major functions of cooling, washing, lubrication, keep cooling and lubrication clean, and thus control the grinding heat within the allowable range to prevent thermal deformation of the workpiece.
1. Improve the cooling conditions during grinding, such as the use of oil-impregnated 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 zone to exert an effective cooling effect to prevent the surface of the workpiece from being burned. Reasonable use of cooling lubricants, play the three major functions of cooling, washing, lubrication, keep cooling and lubrication clean, and thus control the grinding heat within the allowable range to prevent thermal deformation of the workpiece.
2. The quenching stress of the plastic product after heat treatment is reduced to a very low level, because the quenching stress and the reticulated carbonized structure under the action of the grinding force, the phase change of the structure is extremely easy to cause cracks in the workpiece. For high-precision molds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be performed after grinding to improve the toughness.
3, eliminate the grinding stress can also be immersed in the 260 ~ 315 ° C salt bath for 1.5min, and then cooled in 30 ° C oil, so the hardness can be reduced by 1HRC, residual stress reduced by 40% ~ 65%.
4. For precision grinding of precision molds with a dimensional tolerance of less than 0.01 mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. It can be seen from the calculation that the steel piece with a length of 300 mm has a change of about 10.8 μm when the temperature difference is 3 ° C. The influence of this factor must be fully considered in each finishing process.
5, using electrolytic grinding processing to improve mold manufacturing accuracy and surface quality. In electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding the metal, the grinding force is small, the grinding heat is small, and no grinding burrs, cracks, burns, etc. occur, and the surface roughness is generally better than Ra0. .16μm; In addition, the wear of the grinding wheel is small, such as grinding cemented carbide, the wear of the silicon carbide grinding wheel is about 400% to 600% of the weight of the hardened carbide. When grinding with electrolytic grinding, the wear of the grinding wheel The amount is only 50% to 100% of the amount of cemented carbide.