How to reduce defects in Molding Process
In order to improve the mold performance, many manufacturers will properly process their molds. Mold processing refers to the processing of forming and blanking tools. In addition, it also includes shearing molds and die-cutting molds. However, in many cases, the molds are processed. It will also reflect processing defects, resulting in a decline in mold performance. How to build mold processing defects? The following seven measures can reduce mold processing defects.
Reasonable select and dress thegrinding wheels
The white corundum grinding wheel is hard and brittle, and easy to produce new cutting edges. Therefore, the cutting force and grinding heat is small, and the medium grain size is used, such as 46 to 60 mesh. The hardness of the grinding wheel is medium soft and soft (ZR1, ZR2 and R1, R2), that is, coarse-grained, low-hardness grinding wheels, and 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 mold 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-grind ability, and the roughness of the ground work piece can reach Ra0.2μm. In recent years, with the application of new materials, CBN (cubic boron nit ride) 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 work piece, causing burns on the surface of the work piece and reducing its strength.
Use cooling lubricants rationally
Play the three roles of cooling, washing, and lubrication to keep cooling and lubrication clean, so as to control the grinding heat within the allowable range to prevent thermal deformation of the work piece. 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 work piece.
Reduce the quenching stress after heat treatment to a minimum
Because of the quenching stress and the net-like carbonized structure under the action of the grinding force, the phase change of the structure can easily cause cracks in the work piece. 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.
Eliminate grinding stress
You can also immerse the mold in a salt bath at 260-315°C for 1.5 minutes, and then cool it in oil at 30°C, so that the hardness can be reduced by 1HRC and the residual stress can be reduced by 40%-65%.
Constant temperature grinding
For precision grinding of precision molds with dimensional tolerances within 0.01 mm, 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.
Use electrolytic grinding
Improve mold 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 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 only 50% to 100% of the removal of cemented carbide.
Reasonably choose the amount of grinding
Use the fine grinding method with 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 work piece is reduced, and the heat dissipation conditions are improved, thereby effectively controlling the increase in surface temperature.
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