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The bottom is in contact with the center of the bottom surface of the inner hole of the die sleeve. The structure of double convex surface is adopted, which is conducive to the close pressing of the center part with large force. When the gap left around is available for interference matching, the surplus metal extruded from the hole wall can be stored.

Die hardness, domestic manufacturers choose YG20C, Cr12MoV, Cr12, Japanese manufacturers choose YG15, DC53, the former strength is slightly higher, the hardness is slightly lower, and the latter is on the contrary, because of the hardness is high, wear resistance is better, the outer hexagon die this is another reason for the Japanese die life is high.The hardness of high carbon alloy steel is 60 ~ 62HRC, while the hardness of die sleeve is similar, neither of which exceeds 42HRC.

For the bulk, under other conditions the same cold upsetting die, small (large) interference coefficient of the preload is small (large).The failure of mould core out of mould sleeve may be caused by small interference coefficient or unguaranteed machining size.Japanese manufacturers adopt conical surface cold pressure fit for hexagon die, and the interference coefficient is 0.85%, which is lower than that of Russia, which is 1.3% ~ 1.5%.