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Seven skills of reducing defects in mold processing

Release time:2021-11-26

In order to improve the performance of molds, many manufacturers will properly process their own molds. Mold processing refers to the processing of forming and blank making tools, including shear molds and die-cutting molds. However, in many cases, processing defects will be reflected after mold processing, resulting in the decline of mold performance. How to construct mold processing defects, the following seven measures can be taken to build mold processing defects.

1. For the 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, the grinding heat is small, and the use of medium grain size, such as 46~60 mesh, is better. The hardness of the grinding wheel adopts medium soft and soft (ZR1, Zr2 and R1, R2), that is, the low hardness, coarse grain grinding wheel, which has good self excitation and can reduce the cutting heat.

It is very important to choose a suitable grinding wheel for fine grinding. In view of the high vanadium and molybdenum content of die steel, Gd single crystal corundum grinding wheel is more suitable. When machining cemented carbide and materials with high quenching hardness, organic bonded diamond grinding wheel is preferred. Organic bonded 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 wheel has shown good processing effect. When it is processed on CNC forming grinder, coordinate grinder, CNC CNC Internal and external grinder, its processing effect is better than other kinds of grinding wheels.

During grinding, the grinding wheel should be trimmed in time to keep it sharp. When the grinding wheel is passivated, it will rub and squeeze on the surface of the workpiece, resulting in surface burns and strength reduction.

2. Use cooling lubricant reasonably, give play to the three functions of cooling, washing 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 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, which plays an effective cooling role and prevents the workpiece surface from being burned.

3. After heat treatment, the quenching stress shall be minimized, because the quenching stress and network carbonization structure are under the action of grinding force, and the workpiece is easy to crack due to the phase transformation of the structure. For high-precision dies, in order to remove the residual stress of grinding, low-temperature aging treatment should be carried out after grinding to improve the toughness.

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

5. For the 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. According to the calculation, when the temperature difference of 300mm long steel parts is 3 ℃, the material change is about 10.8 μ m (10.8=1.2 × three × 3. The deformation per 100mm is 1.2 μ M/ ℃), all finishing processes should fully consider the influence of this factor.

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 the metal, so the grinding force is small, the grinding heat is small, and there will be no grinding burrs, cracks, burns and other phenomena. Generally, the surface roughness can be better than ra0.16 microns; In addition, the wear of grinding wheel is set to be small. For example, when grinding cemented carbide, the wear of silicon carbide grinding wheel is about 400% - 600% of the weight of cemented carbide, while in electrolytic grinding, the wear of grinding wheel is only 50% - 100% of cemented carbide.

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

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