The effect of the blank holding force on formability in hot deep drawing of boron steel considering heat transfer phenomena and friction coefficient by simulation and experimental investigation

Abstract

The blank temperature and blank holding force (Bf) are important parameters affecting the formability in the hot deep drawing process. Also, the interfacial heat transfer coefficient has a great influence on the temperature distribution in the drawing process. This study examined the effect of the blank holding force (Bf) on the formability of boron sheets. The evaluation was carried out by considering the interfacial heat transfer coefficient and friction coefficient (µ) between blank and punch. A J-stamp relative computer simulation was employed to model the experimental process and examine the interfacial heat transfer coefficient and µ values. Moreover, experiments by applying different Bf were carried out to verify the simulation result. By matching the simulation data with experimental results, the appropriate friction coefficient according to Bf for hot deep drawing was evaluated. The results showed that the µ values between blank and punch decreased with increasing Bf. Based on the evaluated values of interfacial heat transfer coefficient and µ, the forming depth, maximum punch load, thickness, thinning rate and equivalent strain according to Bf were examined, respectively. The result shows that a larger Bf has a more significant effect on the variation of the thickness, thinning rate and equivalent strain of the samples during the drawing process. Furthermore, the thinning rate and equivalent strain variations for samples in fracture and without fracture state were also examined, respectively. The thinning rate did not show a larger difference according to Bf. However, the equivalent strain, both in fracture and without fracture state, decreased sharply when increasing the Bf.