In order to improve the performance of the mold, many manufacturers will properly process their molds. Mold processing refers to the processing of forming and billet tools, and also includes shearing dies and die-cutting dies. It will also reflect processing defects, resulting in a decline in mold performance, so how to build mold processing defects? The following seven measures can solve the defects of mold processing.
1. Reasonable selection and dressing of grinding wheels
The grinding wheel using white corundum is better, its performance is hard and brittle, and it is easy to produce new cutting edges, so the cutting force is small, the grinding heat is small, and the medium particle size is used in the particle size, such as 46-60 mesh is better. The hardness of the grinding wheel is medium-soft and soft (ZR1, ZR2 and R1, R2), that is, coarse-grained, low-hardness grinding wheels, which have good self-excitation and can reduce cutting heat. It is very important to choose the appropriate grinding wheel for fine grinding. For the high vanadium and high molybdenum conditions of the mold steel, it is more suitable to choose GD single crystal corundum grinding wheel. When processing cemented carbide and materials with high quenching hardness, diamond with organic binder is preferred. Grinding wheel, organic binder grinding wheel has good self-grinding property, and the roughness of the workpiece can reach Ra0.2μm. In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheel has shown a very good processing effect. Finishing on CNC forming grinders, coordinate grinders, and CNC internal and external cylindrical grinders, the effect is better than other types of grinding wheels. During the grinding process, it is necessary to pay attention to dressing the grinding wheel in time to keep the grinding wheel sharp. 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 its strength.
2. Rational use of cooling lubricant
Play the three major functions of cooling, washing and lubrication, keep the cooling and lubrication clean, so as to control the grinding heat within the allowable range, so as to prevent thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as using oil-immersed 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 area to exert an effective cooling effect and prevent the surface of the workpiece from being burned.
3. Reduce the quenching stress after heat treatment to a minimum
Because of the quenching stress and the network carbonized structure under the action of the grinding force, the phase transformation of the structure can easily cause cracks in the workpiece. For high-precision molds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be carried out after grinding to improve toughness.
4. Eliminate grinding stress
It is also possible to immerse the mold 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 1HRC, and the residual stress can be reduced by 40%-65%.
5. Constant temperature grinding
For precision grinding of precision molds with dimensional tolerances within 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 300mm, when the temperature difference is 3°C, the material will change by about 10.8μm, (10.8=1.2×3×3, the deformation per 100mm is 1.2μm/°C), and all finishing processes must be fully considered. influence of this factor.
6. Using electrolytic grinding
Improve mold manufacturing accuracy and surface quality. During electrolytic grinding, the grinding wheel scrapes off the oxide film instead of grinding metal, so the grinding force is small, the grinding heat is also small, and there will be no grinding burrs, cracks, burns, etc., and the general surface roughness can be better than Ra0 .16μm; In addition, the wear of the grinding wheel is small, such as grinding cemented carbide, the wear amount of the silicon carbide grinding wheel is about 400% to 600% of the weight of the ground carbide. Only 50% to 100% of the removal amount of cemented carbide.
7. Reasonably choose the amount of grinding
Fine grinding with a small radial feed or even fine grinding. If the radial feed and the speed of the grinding wheel are appropriately reduced, and the axial feed is increased, the contact area between the grinding wheel and the workpiece will be reduced, and the heat dissipation conditions will be improved, thereby effectively controlling the increase in surface temperature.
