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Description
Both advanced high strength steels and aluminum alloys gained increasing popularity because of the constant effort to meet the social pressure of reducing the vehicle weight while keeping their safety. The ratio between material strength and weight is much higher when compared to other materials, while the ductility is similar. Thus, the high springback after forming is one of the disadvantages of these materials, particularly when exhibiting twisting and side wall curl, which are the two most difficult types of springback to control and compensate in die engineering.
This study analysis the influence of several material and numerical parameters on the prediction of the twist springback. The benchmark selected is the one proposed by the Numisheet 2022 Benchmark #1: Springback Prediction of Twist Die Panel [1], which considers a tool used by the A/SP (Auto/Steel Partnership) for springback analysis for several years. Two processing conditions were considered: (i) blank holder force that constrains the metal flow and (ii) draw bead-like feature known as a stake bead, which changes the forming conditions from draw to stretch forming, at the end of the process. The modeling of the elasto-plastic behavior of the sheet materials uses a wide range of experimental data, provided by the benchmark committee for a DP980 steel and a 6xxx aluminum alloy. In addition to the effect of the sheet material on the springback, the effect of the following parameters is also analyzed numerically: (i) friction coefficient; (ii) beads; (iii) modulus of elasticity; (iv) work hardening law and (v) yield criterion. All numerical simulations were performed with the finite element in-house code DD3IMP.
The twist springback is larger in the steel in comparison with the aluminum alloy, which is in good agreement with the experimental measurements [1]. The process parameter that most affects the twist springback is the presence of the stake bead, reducing significantly the springback . In addition, the reduction of the friction coefficient and of the Young modulus also leads to an increase in springback. On the other hand, the yield criterion has little influence on springback.
Reference
[1] Z.G Qin, T. Stoughton, D. Anderson, D.J. Zhou, E. McCarty, E. Smith, J. Park. SpringBack Prediction of a Twist Die Panel, https://www.tms.org/portal/MEETINGSEVENTS/TMSMeetings_Events/Upcoming_TMS_Meetings/NUMISHEET2022/benchmarkTests/BM1__Springback_Prediction_of_a_Twist_Die_Panel/portal/Meetings___Events/2021/NUMISHEET2021/bm1.aspx?hkey=cd02072e-ef7d-4c4a-8765-49b187db31f7