Effects of Punch Geometry on Formability and Forming Load —Forming of Tube with Differential Wall Thickness by Ironing of Inner Surface—

Abstract

With the focus on the forming of a tube with differential wall thickness by the ironing of the inner surface, the interaction of the effects of punch geometry (length of parallel part L_P, semiangle α_P and clearance C_P) on the formability and forming load is investigated by experimentally consistent finite element analysis. Results of the analysis show that L_P and α_P significantly affect the forming load, while C_P has little effect on the load. The punch with larger L_P, or the punch with smaller α_P or smaller C_P, realizes a higher formability because the slipping of steel tube, which is a result of shape defects, does not occur even if Δμ is small. Furthermore, it is theoretically clarified, through discussions on the forces that suppress/induce the slipping of the tube, that slipping does not occur if a large surface pressure is generated on the parallel part of the punch. Since the surface pressure generated on the parallel part of the punch during tube forming varies depending on α_P and the area of the parallel part of the punch varies depending on L_P, L_P and α_P should both be taken into account in designing the punch. On the other hand, C_P does not affect the other design factors and can be designed independently.

 

This Paper was Originally Published in Japanese in J. Japan Soc. Technol. Plasticity 62 (2021) 87–94.

Fig. 19 Relationship between punch shape and formability (Δμ = 0.10). Lines showing the forming limit for each α_P.