How to Solve the Defects of Plastic Mold Processing
Release date:2019-09-30 10:24
In the process of plastics melting and plasticizing, plastic products die is prone to defects. The solution is to reduce the quenching stress after heat treatment to the minimum, because quenching stress and reticulated carbide structure under the action of grinding force, the transformation of the structure is very easy to cause cracks in the workpiece. Reasonable use of cooling lubricant, play the three major roles of cooling, washing and lubrication, keep cooling, lubrication clean, so as to control grinding heat within the allowable range to prevent thermal deformation of the workpiece.
1. Improve the cooling conditions during grinding, such as using oil-immersed grinding wheel or internal cooling grinding wheel. By introducing cutting fluid into the center of the grinding wheel, the cutting fluid can directly enter the grinding zone to play an effective cooling role and prevent the surface burns of the workpiece. Reasonable use of cooling lubricant, play the three major roles of cooling, washing and lubrication, keep cooling, lubrication clean, so as to control grinding heat within the allowable range to prevent thermal deformation of the workpiece.
2. Reduce the quenching stress to the minimum after heat treatment, because quenching stress and reticulated carbide structure under the action of grinding force can easily cause cracks in the workpiece due to phase transformation of the structure. In order to eliminate residual stress in grinding of high precision die, low temperature aging treatment should be carried out after grinding to improve toughness.
3. Elimination of grinding stress can also immerse the die in a salt bath at 260-315 C for 1.5 minutes and then cool it in oil at 30 C, so that the hardness can be reduced by 1 HRC and the residual stress can be reduced by 40%-65%.
4. For precision grinding of precise dies with dimension tolerance less than 0.01 mm, attention should be paid to the influence of ambient temperature and constant temperature grinding. From the calculation, it can be seen that when the temperature difference of 300mm steel is 3 C, the material changes about 10.8um (10.8=1.2*3*3, 1.2um/ C for every 100mm), and the influence of this factor should be fully taken into account in every finishing process.
5. Electrolytic grinding is used to improve the precision and surface quality of the die. In 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. It will not produce grinding burrs, cracks, burns and other phenomena. Generally, the surface roughness can be better than Ra 0.16 um. In addition, the wear of the grinding wheel is small, such as grinding carbide, the wear of silicon carbide grinding wheel is about grinding away. The weight of cemented carbide is 400%-600%. When electrolytic grinding is used, the wear of grinding wheel is only 50%-100% of that of cemented carbide.