During the processing of the mold, the most troublesome thing for everyone is the common defects. These defects will directly lead to the use performance of the workpiece, and even the workpiece cannot be used here. Therefore, we must try to avoid some defects when processing the mold. Here are seven magic weapons for this issue.
1. Reasonably select and trim the grinding wheel. The grinding wheel with white corundum is better. Its performance is hard and brittle, and it is easy to produce new cutting edge. Therefore, the cutting force is small, the grinding heat is small, and the medium grain size is used in the particle size. 46~60 mesh is better. The hardness of the grinding wheel is medium soft and soft (ZR1, ZR2 and R1, R2), that is, the grinding wheel with coarse grain size and low hardness. The self-excitation is good to reduce the cutting heat. It is very important to choose the appropriate grinding wheel for fine grinding. For the high vanadium and high molybdenum condition of the mold steel, it is more suitable to use GD single crystal corundum grinding wheel. When processing hard alloy and quenching hard material, the organic binder diamond is preferred. The grinding wheel and the organic binder grinding wheel have good self-grinding ability, and the roughness of the ground workpiece can reach Ra0.2μm. In recent years, with the application of new materials, the CBN (cubic boron nitride) grinding wheel shows a very good processing effect. Finished in CNC forming grinding machines, coordinate grinding machines, CNC internal and external cylindrical grinding machines, the effect is better than other types of grinding wheels. In the grinding process, it is necessary to pay attention to dressing the grinding wheel in time to keep the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slide and squeeze on the surface of the workpiece, causing burns on the surface of the workpiece and reducing the strength.
2, mold processing rational use of cooling lubricants, play the three major functions of cooling, washing, lubrication, keep cooling and lubrication clean, thus controlling the grinding heat within the allowable range to prevent thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as the use of oil-impregnated grinding 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 zone to exert an effective cooling effect to prevent the surface of the workpiece from being burned.
3. The quenching stress after heat treatment is reduced to a minimum, 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 precision molds, in order to eliminate the residual stress of grinding, low temperature aging treatment should be carried out after grinding to improve the toughness.
4, 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%.
5. 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 for a steel piece with a length of 300 mm, the material has a change of about 10.8 μm at a temperature difference of 3 ° C (10.8 = 1.2 × 3 × 3, and the deformation amount per 100 mm is 1.2 μm / ° C), and each finishing process needs to be fully considered. The impact of this factor.
6, 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%~600% of the weight of the hardened carbide. When grinding with electrolytic grinding, the wear of the grinding wheel The amount is only 50%~100% of the amount of cemented carbide.
7. Reasonable choice of grinding amount, fine grinding method with even radial feed rate and even fine grinding. If the radial feed amount and the grinding wheel speed are appropriately reduced, the axial feed amount is increased, the contact area between the grinding wheel and the workpiece is reduced, and the heat dissipation condition is improved, thereby effectively controlling the surface temperature increase.