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What are the characteristics of the structure of hard alloy wire drawing molds
The structure of hard alloy wire drawing molds is basically the same as that of steel. It can be made into single process molds, as well as composite and continuous molds. However, due to its inherent brittleness, it is not recommended to use it during punching, as the cutting edge is subjected to force on one side. The mold structures used in mass production are mostly continuous mold structures.
Regardless of the construction method used, compared with ordinary steel, hard alloy wire drawing molds have the following structural characteristics:
1. Most hard alloy wire drawing molds adopt a floating die handle structure to prevent the influence of press accuracy on the stamping process during stamping.
2. The mold frame has sufficient rigidity. The template should be 5-10mm thicker than ordinary steel mold templates, and 45 grade steel is often used.
3. The movement of the guiding mechanism mold should be smooth and reliable, with high precision requirements. Generally, a mold frame with ball guide columns is used, and a four guide column guide structure is often used.
4. To avoid cracking of the hard alloy during stamping, hardened pads should be installed on both concave and convex surfaces.
5. The discharge top out device should adopt a fixed discharge plate structure as much as possible to avoid impact on the mold during stamping. When using an elastic unloading plate, a small guide post needs to be installed to guide the unloading plate. To prevent impact force, the height h of the unloading plate pressing step should be one material thickness smaller than the thickness H of the guide plate, h=H-t-0.05.
6. The clearance between convex and concave molds is larger than that of steel molds, usually 0.15 times the thickness of the material or 1.5 times the clearance of ordinary molds.
7. The guide plate, positioning pin, and guide pin should undergo heat treatment and hardening treatment.
8. The structure should be relatively stable after the combination of mold inserts and fixed plates.
Hard alloy wire drawing molds will experience shrinkage during the sintering process, and the amount of shrinkage varies greatly among different batch numbers due to differences in composition, pressing, and sintering processes; Due to varying degrees of shrinkage in different parts of the mold blank, it often forms a "saddle" or "horn mouth" shape. The fluctuation of the external dimensions of the mold blank, although in line with the mold blank standard, far exceeds the interference fit requirement during installation, resulting in severe uneven pre stress during installation and significantly reduced service life. Therefore, the mold blank needs to be subjected to external cylindrical grinding, and special fixtures need to be used on the grinding machine to grind with diamond grinding wheels.
