The i̇nvestigation of post warm-formed mechanical properties and sprinback behaviour of high-strength DP800 steel

Springback is known for being one of the most undesired outcomes of a bending process since it disrupts the assembly of formed products, wasting time and energy. Heating the sheet metal before the bending process is a broad application used in the industry to alleviate the undesired effects of spring-back. However, in many cases, the consequences of a warm or hot bending process on the mechanical properties of bent products are not thoroughly considered. In this study, the effects of the warm bending process combined with the process parameters such as blank-holder force and lubrication on the spring-back behaviour of DP800 steel have been examined. Additionally, the post-mechanical properties of the bent specimens have been investigated. For this, sheets of DP800 steels have been bent to a hat-shaped product at four different temperatures (25 ℃ , 200 ℃ , 300 ℃ , 400 ℃), by using three different blank-holder force (25bar, 75bar, 125 bar), and two different lubricants (graphite and teflon). According to the results, it has been shown that reducing the blank-holder force and applying a better lubricant (teflon) has had a considerable effect in attaining a lower spring-back. Additionally, while increasing the temperature has positively impacted the spring-back, it has been found that the post-mechanical strength of bent sheets at warm temperatures has not shown a significant reduction.