How to reduce mould processing defects

Update:15-09-2020
Summary:

In order to improve the performance of the mould, many […]

In order to improve the performance of the mould, many manufacturers will properly process their moulds. mould processing refers to the processing of forming and blanking tools. In addition, it also includes shearing moulds and die-cutting moulds. However, in many cases, the moulds are processed. It will also reflect processing defects, resulting in a decline in mould performance. How to build mould processing defects? The following seven measures can build mould processing defects.

1. Reasonable selection and dressing of 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, the grinding heat is small, and the medium grain size is used, 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 for fine grinding. For the high vanadium and high molybdenum condition of the mould steel, GD single crystal corundum grinding wheel is more suitable. When processing hard alloys and materials with high quenching hardness, organic binder diamond is preferred. The grinding wheel, organic binder grinding wheel has good self-grindability, 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. Finishing on CNC forming grinder, coordinate grinder, CNC internal and external cylindrical grinder, the effect is better than other types of grinding wheels. 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 slip 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. Introduce the cutting fluid into the center of the grinding wheel, the cutting fluid can directly enter the grinding area, play an effective cooling role, 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 can easily cause the workpiece to crack due to the phase transformation of the structure. 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. To eliminate the grinding stress, the mould can also be immersed in a salt bath at 260~315℃ for 1.5min, and then cooled in 30℃ 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 for a 300mm long steel, when the temperature difference is 3℃, the material will have a change of about 10.8μm (10.8=1.2×3×3, the deformation 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. 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. 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, adopt 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 of ​​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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