Compared with T10 steel dies, the service life of tungsten carbide dies used in standard parts production is increased ten times to tens of times. Therefore, it is widely used in the cold piers of small size screws. Compared with the foreign tungsten carbide dies, there are obvious gaps in the domestic small tungsten carbide dies.

 

As for tungsten carbide die for a cold pier with a half round head, which is a slot screw or a sunk cross screw, its life can reach 900~1 000 million times in Japan. However, the life of the mold in China is only 200~400 million times, while the quality is not stable. We have carried on the thorough analysis and research to this.

 

 

Size and Structural Shape of Die Structure

Main reason for the low service life of the domestic mould is not the size proportion. The inner hole and the outer ring of the mould core designed by the domestic manufacturers are cylindrical. The bottom of the mold core and the bottom of the inner hole of the mould sleeve are both flat. This structure is simple, and the processing is easy. When the cold setting is used, because of the undirected angle, the surface of the hole in the die sleeve is easily pressed and twisted, and even the mold core will produce micro crack and crack, which makes the pressing quality difficult to be stable.

 

In Japanese manufacturers, the contact part between the inner hole and the mold core adopts a double taper and a double convex matching structure, thus the shape is complex, and the processing difficulty is difficult. However, the guiding angle is conducive to ensuring the quality of the insert. The bottom of mould core of Japanese mold and the bottom of the inner hole of die sleeve are double convex and structure, which is beneficial to the central part of the maximum force to close tightly, and the gap left in the surrounding can be supplied for interference fit, and the excess metal squeezed from the wall of the hole is stored. This is the reason why the die life is long, and the quality is stable in Japan.

 

Hardness and Density of Tungsten Carbide Die

Manufacturers in China tend to choose YG20C; Japanese manufacturers choose YG15, the former has slightly higher strength and slightly lower hardness, while the latter is the opposite. Because of the high hardness and good wear resistance. It is another reason why the die life is high in Japan. The hardness of the die sets at home and abroad is similar, neither of them exceeds HRC40.

 

Processing Quality of Outer Surface

The die core quality of the manufacturers in China is poor, while the mold core table quality of the Japanese manufacturers is better. And its whole surface roughness is in the range of 0. 32~0. 25um. The surface and roughness of the mold core have an effect on the life of the die, and the surface roughness is poor, especially in the form of a depression, hole or crack, which will be the source of stress concentration and fracture, causing premature cracking and failure of the mold core. Roughness of the inner hole worksheet of the die core has a greater impact on life expectancy.

 

Insert Mode and Condition After Setting

Cold setting technology is adopted in venders at home and abroad. Insert quality has an effect on the service life of the die. After the die setting, the hole wall in the mold sleeve is damaged by the metal plastic flow and the hole wall table inside the mold sleeve. The mould damage of the domestic manufacturers is serious, indicating the poor quality of the set.

 

Both the mold core and the mold sleeve are not completely pressed, and the middle force is in the suspended state. When the mold works, this part is not subjected to the compression stress but the bending stress or shear stress. Therefore, the core is prone to crack in the working process, causing early failure.