How to control the grinding accuracy and reduce defects of the key parts of the mold and die?

Grinding process is an important process to control the matching accuracy of mold assembly and the machining accuracy of key parts. According to our production experience, the following methods can be used to control the grinding accuracy of key parts of mold and die and reduce defects:

 

1. Rational use of cooling lubricant, give full play to its cooling, washing, lubrication role, keep the cooling lubricant clean, control grinding heat within the allowable range, to prevent workpiece thermal deformation. It is recommended that oil-immersed grinding wheel or internal cooling grinding wheel should be used to improve the cooling conditions during grinding. Cooling lubricant should be introduced into the center of the grinding wheel so that it can enter the grinding zone directly and play an effective cooling role to prevent surface burn of the workpiece.

 

2. A suitable process should be adopted to minimize the quenching stress after heat treatment. Because the quenching stress and reticulated carbide structure under the grinding force, phase transformation in metal structure, easy to cause cracks in the key parts of mold. In order to eliminate the residual stress in grinding, the high precision mold should be aged at low temperature to improve its toughness after grinding.

 

3. Grinding stress can also be eliminated by using this process: the mold is immersed in a salt bath at 260-315 C for 1.5 minutes and then cooled in oil at 30 C, thus reducing hardness by about 1 HRC and residual stress by 40% - 65%.

 

4. For large size precision mold parts with dimension tolerance less than 0.01 mm, attention should be paid to the influence of ambient temperature in precision grinding. Constant temperature grinding is required. According to the calculation, the length of 300mm steel piece will change about 10.8μm when the temperature difference is 3℃. (according to the deformation of 1.2μm/℃ per 100mm), and the influence of this factor should be fully considered in every fine machining process.

 

5. Electrolytic grinding is used to improve the manufacturing accuracy and surface quality of mold and die. In electrolytic grinding, the grinding wheel scrapes oxide film instead of grinding metal, so the grinding force is small, the grinding heat is low, and the burr, crack, burns and other phenomena will not occur. The general surface roughness can be better than Ra 0.16μm. At the same time, the wear of the grinding wheel is small, for example, when grinding on cemented carbide, the wear of silicon carbide wheel is about 400% - 600% of the cemented carbide grinding, but the wear of the grinding wheel by electrolytic grinding is only 50% - 100% of the cemented carbide grinding.

 

Hope these methods are useful for you. Thank you for visiting our website www.yea-lin.com.