A novel method for the spring-back analysis of a hot stamping steel

Spring-back of sheet metal affects the dimensional accuracy of the components after stamping and has to be eliminated or corrected. Advanced high strength steels (AHSS) are prone to spring-back while forming at ambient temperatures. Hot stamping process is an effective technique to reduce the spring-back upon forming. The forming temperatures and the phase transformations associated with quenching are known to influence the spring-back. However, the detailed experimental analysis on spring-back behaviour is limited due to the difficulty in physically simulating the thermal-mechanical conditions prevailing in a typical hot forming process. In the present work, a novel V-bending tech-nique is presented for effectively measuring the spring-back using a thermal-mechanical simulator, GleebleTM. V-bending is carried out by applying a compressive force along the longitudinal plane of AHSS steel strips at forming temperatures. Upon V-bending, samples were cooled at different cooling rates while maintaining the forming loads to simulate die quenching. Results indicate that the spring-back decreases and becomes close to zero (at a cooling rate of 20 K s(-1)) with an increase in cooling rate for a hot stamping steel. Further, an increase in cooling rate results in spring-forward owing to the formation of an increased volume fraction of martensite. (C) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the spring-back behavior of advanced high strength steel using a thermal-mechanical simulator GleebleTM. Results show that increasing the cooling rate reduces spring-back and leads to spring-forward, due to the increased volume fraction of martensite.