Plastic mold processing seven skills to reduce defects!

1. Reasonably select and trim the grinding wheel. The 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. It is better to use the medium particle size on the particle size, such as 46 ~ 60 mesh. It is better to use the medium soft and soft (ZR1, Zr2 and R1, R2) on the hardness of the grinding wheel, that is, the coarse-grained and low hardness grinding wheel. Good self excitation can reduce the cutting heat.

It is very important to choose an appropriate grinding wheel during fine grinding. In view of the high vanadium and high molybdenum condition of die steel, Gd single crystal corundum grinding wheel is more suitable. When machining cemented carbide and materials with high quenching hardness, diamond grinding wheel with organic binder is preferred. The organic binder grinding wheel has good self grinding performance, and the workpiece roughness can reach Ra0.2 μ m. In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheels have shown very good machining effects, which are superior to other types of grinding wheels in precision machining on CNC molding grinding machines, coordinate grinding machines, CNC Internal and external cylindrical grinding machines.

In the grinding process, it is necessary to pay attention to the timely dressing of the grinding wheel to maintain the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slide and squeeze on the surface of the workpiece, causing the surface burn of the workpiece and the strength reduction.

2. Use the cooling and lubricating fluid reasonably, give play to the three functions of cooling, washing and lubrication, and keep the cooling and lubrication clean, so as to control the grinding heat within the allowable range, so as to prevent the thermal deformation of the workpiece. Improve the cooling conditions during grinding, such as using oil impregnated 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 to play an effective cooling role and prevent workpiece surface burns.

3. The quenching stress after heat treatment is reduced to the minimum, because the quenching stress and network carbonization structure produce phase transformation under the action of grinding force, which is very easy to cause cracks in the workpiece. For high-precision dies, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be carried out after grinding to improve the toughness.

4. To eliminate grinding stress, the mold can also be immersed in a salt bath at 260 ~ 315 ℃ for 1.5 min, and then cooled in oil at 30 ℃, so that the hardness can be reduced by 1hrc and the residual stress can be reduced by 40%~65%.

5. For the precision grinding of precision dies with dimensional tolerance within 0.01 mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. According to the calculation, when the temperature difference of 300mm long steel is 3 ℃, the material is 10.8 μ About M, (10.8=1.2 × three × 3. 1.2 deformation per 100mm μ M/ ℃), and the influence of this factor should be fully considered in all finishing processes.

6. Electrolytic grinding is adopted 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, so the grinding force is small and the grinding heat is small. Grinding burrs, cracks, burns and other phenomena will not occur. Generally, the surface roughness can be better than ra0.16 μ m； In addition, the wear of the grinding wheel is set to be small. For example, when grinding cemented carbide, the wear amount of the silicon carbide grinding wheel is about 400% - 600% of the weight of the cemented carbide removed. When electrolytic grinding is used, the wear amount of the grinding wheel is only 50% - 100% of that of the cemented carbide removed.

7. Select the grinding amount reasonably, and adopt the fine grinding method with small radial feed, or even 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 is reduced, and the heat dissipation conditions are improved, so as to effectively control the increase of the surface temperature.