The main drawback of spring floating is that its floating force is difficult to control. However, due to its simple structure, low cost and convenient maintenance, the spring floating formwork is generally welcomed by small and medium-sized powder metallurgy manufacturers. However, compacts formed by spring-floating negative molds, especially those of book-type parts, tend to produce lateral cracks of varying lengths or even entire circumferences. Some of these cracks may cause the product to break and be scrapped in the subsequent processing of the blank, and the assembly of the defective part to the host may also pose a greater hidden danger.
Problem Analysis The reason why the spring floating mold is generated by the lateral crack of the green compact can be analyzed. It can be seen that in the powder pressing process, after the upper punch 1 forces the female mold 2 to descend into position, the powder is formed, the upper punch 1 starts to be reset, the spring 5 supporting the female mold 2 is naturally reset upward, and the female mold 2 is forced up. shift. Since the contact area between the female mold 2 and the green compact is larger than the contact area between the core rod 9 and the green compact, that is, the friction between the female mold 2 and the green compact is greater than the friction between the core rod 9 and the green compact, so on the female mold 2 As the shift occurs, the blank also moves up. At this time, the lower punch 10 and the core rod 9 are both fixed. At this time, a negative pressure zone is formed between the lower end surface of the compact and the upper end surface of the lower punch 1. The larger the floating amount of the female mold, the more negative pressure is in this area. Large, under the action of atmospheric pressure, when the compact is moved up with the negative mold, the lower part is subjected to the reverse pulling force. Since the formation of the powder compact is mainly based on the connection between the powder particles, the strength is low, and when it is subjected to the reverse force, the mechanical joint between the powders is pulled apart, and cracks are generated on the surface of the compact. In the case of a low mold cleanness and poor powder formability, the lateral cracking of the green compact is more pronounced.
Spring floating negative mold negative pressure zone formation 1 upper punch; 2 yin transverse; 3 die sleeve; 4 upper template; 5 spring; 6 lower template; 7 wall panel; 8, 13 pressure plate; 9 core rod; ; 11 guide column; 12 under the punch; 14 under the seat cover; 15 ejector solution to understand the cause of the lateral crack of the spring floating female mold blank, you can know that the key to eliminate it is to eliminate the blank A negative pressure zone formed in the cavity before the mold. In this paper, the method for solving this problem is called / synchronous demoulding method 0, that is, after the powder is formed, the upper punch is unloaded and the lower punch is synchronized with the upper punch, and the compact is pushed out of the cavity. When the upper punch 1 and the female die 2 are lowered into position, the pull rod 21 drives the movable card board 19 just under the step of the top post 18. When the upper punch 1 is reset, the pull rod 21 is driven again, the movable card board 19 and the top post 18 are ascended together, and the top post 18 is pushed out of the cavity by the 34 powder metallurgy industry, the 10th page Page 3 ejector 16 and the lower die punch 10 . At this time, under the action of the separating rod 22, the movable chuck 19 is separated, and the top post 18 pulls down the lower punch 10 by the jack 16 under the action of gravity. There is no negative pressure zone in the cavity during the whole process, thus avoiding the formation of transverse cracks in the compact.
Spring floating pressing and synchronous demolding structure 1 punch; 2 female mold; 3 mold sleeve; 4 upper template; 5 spring; 6 lower template; 7 wall plate; 8, 13 plate; 9 core; 10 lower punch; 11 guide columns; 12 lower punches; 14 booms; 15 core rod seats; 16 top rods; 17 bearing plates; 18 top columns; 19 movable card plates; 20 under punching seat covers; 21 pull rods; 22 separating rods; Small spring.
Conclusion The reason for the lateral crack of the spring floating female mold blank is that there is a negative pressure zone in the cavity. The synchronous demoulding method can eliminate the negative pressure zone in the cavity and avoid the generation of transverse cracks in the compact. The mold frame release stroke can be adjusted arbitrarily, and the punching machine and the hydraulic machine can be applied.
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