Release time：2021-08-23
1. Reasonable selection and dressing of grinding wheel
White corundum grinding wheel is better. Its performance is hard and brittle, and it is easy to produce new cutting edges. Therefore, the cutting force is small and the grinding heat is small. Select medium particle size, such as 46 ~ 60 mesh. The hardness of the grinding wheel is medium soft and medium soft (ZR1, Zr2 and R1, R2), that is, coarse-grained, low hardness grinding wheel, good self excitation can reduce the cutting heat.
It is very important to choose a suitable grinding wheel for fine grinding. GD single crystal corundum grinding wheel is more suitable for high vanadium and high molybdenum conditions of die steel. When machining cemented carbide and materials with high quenching hardness, organic bond diamond is preferred. The self grinding performance of grinding wheel and organic bond grinding wheel is good, and the roughness of grinding workpiece can reach Ra0.2 μ m。 In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheels have shown good machining results. The effect of finish machining on CNC forming grinder, coordinate grinder and CNC Internal and external grinder is better than that of other types of grinding wheels.
In the grinding process, attention should be paid to timely dressing the grinding wheel to keep it sharp. After passivation, the grinding wheel will slip 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 lubricants
Play the three functions of cooling, flushing and lubrication, keep the cooling and lubrication clean, control the grinding heat within the allowable range, and prevent the thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as using oil immersed grinding wheel or internally cooled grinding wheel. When the cutting fluid is introduced into the center of the grinding wheel, the cutting fluid can directly enter the grinding area, which has an effective cooling effect and prevents the workpiece surface from being burned.
3. Try to reduce the quenching stress after heat treatment
Due to the effect of quenching stress and grinding force, the phase transformation of network carbonized structure is easy to cause workpiece cracks. For high-precision dies, in order to eliminate grinding residual stress, low-temperature aging treatment should be carried out after grinding to improve toughness.
4. Eliminate grinding stress
The mold can also be immersed in a salt bath at 260 ~ 315 ℃ for 1.5 minutes, and then cooled in oil at 30 ℃, which can reduce the hardness by 1hrc and the residual stress by 40% - 65%.
5. Constant temperature grinding
For precision grinding of precision dies with dimensional tolerance within 0.01mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. The calculation shows that for a 300mm long steel, when the temperature difference is 3 ℃, the material will have 10.8 μ Change about M (10.8=1.2 × three × 3. The deformation per 100mm is 1.2 μ M/ ℃), and each finishing process needs to consider the influence of this factor.
6. Electrolytic grinding processing
Improve mold manufacturing accuracy and surface quality. During electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding metal, the grinding force is small, the grinding heat is small, and there will be no grinding burrs, cracks, burns, etc. the surface roughness can generally be better than ra0.16 μ m； In addition, the wear of grinding wheel is small, such as the grinding of cemented carbide. The wear amount of silicon carbide grinding wheel is about 400% - 600% of the weight of cemented carbide being ground. When electrolytic grinding is used, the wear of grinding wheel can only remove 50% - 100% of cemented carbide.
7. Reasonable selection of grinding amount
Fine grinding mode is adopted, with small radial feed and uniform fine grinding. If the radial feed rate and the speed of the grinding wheel are properly reduced and the axial feed rate is increased, the contact area between the grinding wheel and the workpiece can be reduced, the heat dissipation conditions can be improved and the temperature of the workpiece can be increased. The surface can be effectively controlled.
