Forming defects prediction in cup drawing and embossing of a thick steel sheet

Diogo M Neto,José L Alves,Luis F Menezes,Marta Cristina Oliveira,Pedro D Barros

doi:10.25518/esaform21.1525

Abstract

The accurate prediction of forming defects is fundamental for the virtual try-out of metallic sheet components. However, the constitutive model can have a strong impact on the numerical predictions, namely the cup earing, the occurrence of wrinkles and the tearing failure. The process conditions considered in this work are the ones established for the “Benchmark 2 – Cup Drawing of Anisotropic Thick Steel Sheet”, proposed under the Numisheet 2018 international conference. The axisymmetric cups are obtained from a steel sheet with 2.8 mm of thickness, resorting to different process conditions to induce different defects. The advanced yield criterion proposed by Cazacu and Barlat is used to define the anisotropic behavior of the blank. The calibration of the material parameters is carried out by fitting the following experimental data from: (i) uniaxial tensile tests performed in every 15º to the rolling direction; (ii) biaxial tension tests to evaluate the directions of the plastic strain rates in the first quadrant of the yield loci. The numerical predictions are compared with the experimental measurements, allowing to assess the accuracy of the finite element model to predict each type of forming defect. The cup earing and the strain localization are accurately predicted, while the wrinkles amplitude is clearly underestimated.

Highlights

The deep drawing of cylindrical cups is commonly used to evaluate the performance of constitutive models, namely the recently developed advanced yield criteria [1]
The numerical predictions are in very good agreement with the experimental measurements since the springback is very low in this axisymmetric component
The influence of the orthotropic plastic behavior modelling on the numerical prediction of forming defects is studied, adopting the advanced yield function proposed by Cazacu and Barlat [10] to describe the material anisotropy of the thick steel sheet

Summary

Introduction

The deep drawing of cylindrical cups is commonly used to evaluate the performance of constitutive models, namely the recently developed advanced yield criteria [1]. The flange wrinkling can occur in deep drawing of cylindrical cups, for low values of blank holder force. The fracture can occur either with or without severe strain localization, requiring the development of alternative models capable of predicting the formability limits. These models take into account the constitutive model that best describes the material mechanical behavior. The geometry of the forming tools used in Tasks 2 and 3 is presented in Fig. 1 (b), where the lifter disappears, and the punch shape is modified to include a center boss. In order to reduce the friction forces, lubricant was applied to both surfaces of the blank, stripper, punch, die and lifter contacting surfaces

Finite element model

Results and Discussion

Conclusions