How to solve common defects in mold processing?
In the process of mold processing, what bothers everyone are some common defects, which will directly affect the working performance of the workpiece, and even make the workpiece unusable here. So when processing molds, we must try to avoid some defects.
Reasonable selection and dressing of grinding wheels, white corundum grinding wheels are better, their performance is hard and brittle, and it is easy to produce new cutting edges, so the cutting force is small and the grinding heat is small. It is best to use medium grain size, such as 46~60 mesh, medium soft and hard (ZR1, ZR2, R1, R2) grinding wheel hardness, that is, coarse grain size, low hardness grinding wheel. Good self-excitation can reduce cutting heat. It is very important to choose a suitable grinding wheel for precision grinding. In view of the high molybdenum content of mold steel, Gd single crystal corundum grinding wheel is more suitable. When processing cemented carbide and high hardness materials, choose organic bond diamond grinding wheel. Organic bond grinding wheel has good self-grinding performance, and the workpiece roughness can reach Ra0.2M m. In recent years, with the application of new materials, CBN grinding wheel has been widely used, showing good processing effect. The finishing effect of CNC forming grinders, three-coordinate grinders, and CNC internal and external cylindrical grinders is better than other types of grinding wheels. During the grinding process, attention should be paid to timely dressing of the grinding wheel to maintain the sharpness of the grinding wheel. After the grinding wheel is passivated, friction and extrusion will occur on the surface of the workpiece, causing the surface of the workpiece to burn and reduce its strength.
In mold processing, cooling lubricants should be used reasonably to play the three major roles of cooling, cleaning, and lubrication, and keep the cooling and lubrication clean, so as to control the grinding heat within the allowable range and prevent thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as using oil-immersed grinding wheels or internally cooled grinding wheels. When the cutting fluid is introduced into the center of the grinding wheel, it can directly enter the grinding area, play an effective cooling role, and prevent the surface of the workpiece from burning.
Due to the phase change of quenching stress and network carbide structure under the action of grinding force, it is easy to cause the workpiece to crack, and the quenching stress after heat treatment is minimized. In order to eliminate the residual stress of grinding, low-temperature aging treatment should be carried out after grinding to improve the toughness of precision molds.
To eliminate grinding stress, the mold can be immersed in a salt bath of 260~315 for 1.5 minutes, and then cooled in oil at 30 to reduce the hardness by 1HRC and the residual stress by 40%~65%.
For precision grinding of precision molds with dimensional tolerance within 0.01mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. According to calculations, when the temperature difference of a 300mm long steel piece is 3, the material change is about 10.8m (10.8=1.233, and the deformation per 100mm is 1.2m/), and the influence of this factor should be fully considered in each finishing process.
Electrolytic grinding is used to improve the manufacturing accuracy and surface quality of the mold. During electrolytic grinding, the grinding wheel scrapes off the oxide film instead of grinding the metal, so the grinding force is small, the grinding heat is small, and there will be no grinding burrs, cracks, burns, etc. The general surface roughness can be better than Ra 0.16 m, and the grinding wheel wear is small. For example, when grinding cemented carbide, the wear of silicon carbide grinding wheel is about 400% to 600% of the weight of cemented carbide, and the wear rate of grinding wheel is only 50% to 100% of cemented carbide. Choose reasonable grinding parameters, adopt radial feed small precision grinding method or even fine grinding. Appropriately reduce the radial feed speed and grinding wheel speed, increase the axial feed speed, can reduce the contact area between the grinding wheel and the workpiece, improve the heat dissipation conditions, and effectively control the surface temperature.