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Measures to prevent defects in mould processing

Update:30-08-2020
Summary:

Most of our commonly used workpieces are manufactured b […]

Most of our commonly used workpieces are manufactured by moulds. Therefore, when manufacturers are manufacturing, if they are developed in batches, some defects will inevitably occur. In order to maximize the performance utilization rate of the workpieces, we can adopt Preventive measures to avoid defects.

1. Reasonably select and dress the grinding wheel. The grinding wheel of white corundum is better. Its performance is hard and brittle, and it is easy to produce new cutting edges. Therefore, 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. In the hardness of the grinding wheel, medium soft and soft (ZR1, ZR2 and R1, R2) are used, that is, coarse-grained, low-hardness grinding wheels. Good self-excitation can reduce cutting heat. It is very important to choose an appropriate grinding wheel during fine grinding. For the high vanadium and high molybdenum condition of the mould steel, it is more suitable to use GD single crystal corundum grinding wheel. When processing cemented carbide and materials with high quenching hardness, the organic binder diamond is preferred. The grinding wheel and the organic binder grinding wheel have good self-grinding properties, and the roughness of the ground workpiece can reach Ra0.2μm. In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheels have shown very good processing effects. It is better than other types of grinding wheels for finishing on CNC forming grinders, coordinate grinders, and CNC internal and external cylindrical grinders. In the grinding process, attention should be paid to dressing the grinding wheel in time to keep the grinding wheel sharp. When the grinding wheel is passivated, it will rub and squeeze on the surface of the workpiece, causing burns on the surface of the workpiece and reducing its strength.

2. Reasonably use cooling lubricating fluid, play the three roles of cooling, washing and lubrication, keep cooling and lubrication clean, so as to control the grinding heat within the allowable range 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 effective cooling and prevent burns on the surface of the workpiece.

 

 

3. Reduce the quenching stress after heat treatment to the maximum, because the quenching stress and the net-like carbonized structure under the action of the grinding force, the structure of the phase change will easily cause the workpiece to crack. For high-precision moulds, in order to eliminate the residual stress of grinding, low temperature aging treatment should be carried out after grinding to improve toughness.

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

5. For precision grinding of precision moulds with dimensional tolerances within 0.01mm, attention should be paid to the influence of ambient temperature and constant temperature grinding is required. From the calculation, it can be seen that when the temperature difference of 300mm long steel parts is 3℃, the material has a change of about 10.8μm, (10.8=1.2×3×3, the deformation amount per 100mm is 1.2μm/℃), and each finishing process needs to be fully considered The influence of this factor.

6. Electrolytic grinding is used to improve mould manufacturing accuracy and surface quality. During electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding the metal, 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 of the silicon carbide grinding wheel is about 400% to 600% of the weight of the cemented carbide that is ground. When electrolytic grinding is used, the wear of the grinding wheel The amount is only 50% of the cemented carbide grinding amount.

7. Reasonably choose the amount of grinding, and use a fine grinding method with a small radial feed or even fine grinding. If the radial feed rate and the grinding wheel speed are appropriately 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, thereby effectively controlling the increase in surface temperature.

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