Investigation into the effects of weld zone and geometric discontinuity on the formability reduction of tailor welded blanks Mahmoud Abbasi a,⇑ , M. Ketabchi a , A. Ramazani b , Mohammad Abbasi c , U. Prahl b a Department of Mining and Metallurgy, Amirkabir University of Technology, Tehran, Iran b Institute of Ferrous Metallurgy, RWTH Aachen, Aachen, Germany c Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran article info Article history: Received 16 January 2012 Received in revised form 23 February 2012 Accepted 25 February 2012 Available online 30 March 2012 Keywords: Tailor welded blank Formability Weld zone Simulation abstract Numerous advantages of application of tailor welded blanks (TWBs) in automobile industry, namely reduction of weight, fuel consumption and air pollution, have made the manufacturers eager to investi- gate in this field. On the other hand, while experiments generally provide valuable information in regard with mechanical behaviors, but utilization of simulation methods has extended vastly due to time and cost saving issues. One challenging issue in numerically analyzing the forming behavior of transversely welded TWBs, welded by laser welding methods, has been the presence of weld zone. While some researchers believe that during simulation, the weld zone can be neglected due to its minority and con- sequently the simulation time will be less, the others confess that the consideration of weld zone increases the accuracy of the results although the time of simulation enhances. In this research, the effect of weld zone presence on the formability of transversely CO 2 laser welded TWBs was studied experimen- tally and numerically (FE-method). The studied TWBs were consisted of IF-steels with different thicknesses (0.8 and 1.2 mm), and limiting dome height as well as forming limit diagram were used for formability assessment. Experiments in regard with limiting dome height test showed that the deci- sive factor in decreasing the dome height is geometric discontinuity and the effect of weld zone is about 6%. Moreover, simulation results indicated that the consideration of weld zone did not have any obser- vable effect on limiting strains, although tearing occurred at lower punch stroke. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction To meet restricting fuel economy standards while remaining economically competitive, the automotive companies are con- stantly looking for innovative means of reducing vehicle weight and manufacturing costs, respectively. The use of tailor welded blanks (TWBs) is an opportunity to meet these seemingly conflict- ing requirements. A TWB consists of two or more base metal sheets with different materials and/or thicknesses and/or coatings welded together in a single plane prior to forming [1]. However, due to great advantages of application of TWBs, it is important to understand and predict the formability of TWBs in the automotive industry during deep drawing process. While different experimental methods have been presented to evaluate the forming characteristics of sheet metals generally [2], but due to the cost and time issues, numerical methods based on FE-analyses have been the points of focus of researchers. Gaied et al. [3], presented a numerical model to predict the forming height dome and a specific forming curve of TWBs. They also presented a new method based on the analysis of the major strain rate using the discrete Gaussian convolution to measure the critical strain at necking. Tang et al. [4], could forecast the weld line move- ment by application of a one-step finite element method coupled with optimization algorithms. The whole tendencies of the calcu- lated ones were coherent with the measured ones except for some discrepancies which were respected to simplification of boundary conditions and assumption of deformation history. One common challenging issue in dealing with forming charac- teristics of TWBs welded by laser machine, during simulation pro- cesses, is the weld region. While Gaied et al. [3] and He et al. [5], due to minority size, have neglected this region to compensate cost and time, Heu and Siegert [6] and Abdullah et al. [7] believe that consideration of weld region improves the results. In this research, the effect of two parameters, namely geometric discontinuity and presence of weld region, on formability decrease was investigated individually. Geometric discontinuity is common characteristic of TWBs with thickness ratio (TR) greater than 1. Thickness ratio is defined as the ratio of thick monolithic sheet to thin monolithic sheet and it is property of TWBs consisted of blanks with different thicknesses [8]. The studied TWB was a blank 0927-0256/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.commatsci.2012.02.039 ⇑ Corresponding author. Address: 424 Hafez Ave., Tehran, Iran. Tel.: +98 21 64542949; fax: +98 21 66405846. E-mail address: Mahmoud.abbasi@iehk.rwth-aachen.de (M. Abbasi). Computational Materials Science 59 (2012) 158–164 Contents lists available at SciVerse ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci