During the melting and plasticizing process of plastic toys, plastic toys are prone to defects. The solution is to reduce the quenching stress after heat treatment to an ultra-low limit, because the quenching stress and the reticulated carbonized structure are under the action of the grinding force. The occurrence of phase transitions can easily cause cracks in the workpiece. Toy manufacturers stated that they need to use cooling lubricants reasonably, and play the three major functions of cooling, washing, and lubrication to keep the cooling and lubrication clean, so as to control the grinding heat within the allowable range to prevent thermal deformation of the workpiece.
Specific operation methods:
1. 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 prevent the surface of the workpiece from being burned. Reasonable use of cooling and lubricating fluid, play the three major functions of cooling, washing and lubrication, keep cooling and lubrication clean, so as to control the grinding heat within the allowable range to prevent thermal deformation of the workpiece.
2. Reduce the quenching stress after heat treatment to an ultra-low limit, because the quenching stress and the reticulated carbonized structure under the action of the grinding force, the phase transformation of the structure is extremely likely to cause the workpiece to crack. For high-precision molds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be performed after grinding to improve toughness.
3. To eliminate the grinding stress, the mold can also be immersed in a salt bath at 260 ～ 315 ℃ for 1.5min, and then cooled in 30 ℃ oil, so that the hardness can be reduced by 1HRC and the residual stress can be reduced by 40% ～ 65%.
4. For precision grinding of precision molds with dimensional tolerance within 0.01mm, pay attention to the influence of environmental temperature. Plastic toy manufacturers require constant temperature grinding. From the calculation, it can be known that for a 300mm long steel part, the material has a change of about 10.8μm when the temperature difference is 3 ° C (10.8 = 1.2 × 3 × 3, 1.2μm / ° C deformation per 100mm), and all finishing processes need to be fully considered The impact of this factor.
5. Adopt electrolytic grinding to improve the precision and surface quality of mold manufacturing. 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 grinding burrs, cracks, burns, etc. will occur. Generally, the surface roughness can be better than Ra0. .16μm; In addition, the wear of the grinding wheel is small, such as grinding carbide, the wear of silicon carbide grinding wheel is about 400% to 600% of the weight of the cemented carbide. The amount is only 50% to 100% of the amount of carbide removal.