How to reduce defects in mold processing?

In many cases, even after the mold is processed, defects will still be present, leading to a decline in the mold’s performance.

1. Select and adjust the grinding wheel reasonably, and use a white corundum grinding wheel as it has good performance, being hard and brittle, and is prone to generating new cutting edges. Therefore, the cutting force is small, and the grinding heat is low. The medium grit size (such as 46-60 mesh) is preferable. The hardness of the grinding wheel should be moderately soft and soft (ZR1, ZR2 and R1, R2), that is, coarse grit and low hardness grinding wheels. The self-energizing property is good, which can reduce cutting heat. It is very important to select the appropriate grinding wheel during fine grinding. For the high vanadium and high molybdenum situation of the mold steel, a GD single crystal corundum grinding wheel is more suitable. When processing hard alloys and materials with high quenched hardness, organic binder diamond grinding wheels should be preferred. Organic binder grinding wheels have good self-milling property and can achieve a roughness of Ra0.2 μm. In recent years, with the application of new materials, CBN (cubic nitrogenized boron) grinding wheels have shown very good processing effects. They perform better than other types of grinding wheels in precision processing on CNC forming grinders, coordinate grinders, and CNC internal and external circle grinders. In grinding processing, it is necessary to promptly adjust the grinding wheel to maintain its sharpness. When the grinding wheel becomes dull, it will slide and squeeze on the workpiece surface, causing burn damage to the workpiece surface and reducing its strength.
2. Reasonably use the cooling lubricant to achieve the three functions of cooling, cleaning and lubrication, maintaining a clean and cool environment, thereby controlling the grinding heat within the allowable range and preventing the workpiece from thermal deformation. Improve the cooling conditions during grinding, such as adopting oil-coated grinding wheels or internal cooling grinding wheels, etc. Introduce the cutting fluid into the center of the grinding wheel, and the cutting fluid can directly enter the grinding area to exert an effective cooling effect, preventing the workpiece surface from being burned.
3. Reduce the quenching stress after heat treatment to an extremely low level. Because the quenching stress and the reticular carbide structure, under the action of the grinding force, undergo phase transformation, which is very likely to cause cracks in the workpiece. For high-precision molds, in order to eliminate the residual stress from grinding, a low-temperature aging treatment should be carried out after grinding to enhance the toughness. Shanghai Mold Processing
4. To eliminate the grinding stress, the mold can be immersed in a 260~315℃ salt bath for 1.5 minutes, and then cooled in 30℃ oil. In this way, the hardness can be reduced by 1 HRC, and the residual stress can be decreased by 40% to 65%.
5. For the precision grinding of precision molds with a dimensional tolerance of less than 0.01mm, it is necessary to pay attention to the influence of environmental temperature and require constant temperature grinding. Through calculation, it can be known that for a steel piece 300mm in length, when the temperature difference is 3℃, the material changes by approximately 10.8μm (10.8 = 1.2 × 3 × 3, with a deformation of 1.2μm/℃ for every 100mm). All the precision processing procedures need to fully consider the impact of this factor.
6. Electrolytic grinding processing is adopted to improve the manufacturing accuracy and surface quality of the molds. During electrolytic grinding, the grinding wheel removes the oxide film instead of grinding the metal, resulting in low grinding force and low grinding heat. No phenomena such as grinding burrs, cracks, or burns occur. Generally, the surface roughness can be better than Ra0.16μm. In addition, the wear of the grinding wheel is small. For example, when grinding hard alloys, the wear of silicon carbide grinding wheels is approximately 400% to 600% of the weight of the ground hard alloys. With electrolytic grinding, the wear of the grinding wheel is only 50% to 100% of the weight of the ground hard alloys.
7. Select the grinding parameters reasonably, and adopt the fine grinding method with a smaller radial feed rate, or even perform precision grinding. For example, appropriately reduce the radial feed rate and the grinding wheel speed, increase the axial feed rate, so that the contact area between the grinding wheel and the workpiece is reduced, and the heat dissipation conditions are improved, thereby effectively controlling the increase in surface temperature.