Influence fl uence of Bend Holding on Springback and Time-Dependent Springback in Sheet Metal Bending

Springback of sheet metals consists of two components: springback caused by elastic recovery during unloading and time-dependent springback caused by viscoplastic phenomena over time after unloading. While springback can be reduced by punch holding (or bend holding), the influences fl uences of bend holding on each of these two springback components are unclear. This study aims to elucidate the effects ff ects of bend holding on these two springback components and total springback by conducting L-bending tests on an advanced high-strength steel (SPCN118Y) sheet and an aluminum (A1050-O) sheet. The total springback two days after unloading decreased when bending was held because the springback during unloading decreased due to stress relaxation while holding. The time-dependent springback also tended to decrease with bend holding in most cases, but its amount and reduction were considerably smaller than those in the springback during unloading. The percentage of time- dependent springback to total springback was larger for A1050-O than for SPCN118Y. The percentage of SPCN118Y was not much affected ff ected by bend holding, while that of A1050-O became larger when bending was held. [doi:10.2320/matertrans.MT-P2024003] / matertrans.MT-P2024003]