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Title: Numerical and Experimental Studies on Strain Distribution and Weld Line Movement in Stretch Forming of Tailor Welded Blanks

Abstract

Use of laser welded blanks of multiple sheets of material which are referred to as Tailor Welded Blanks (TWB) is one of the current interests for automotive industries as it reduces manufacturing cost, weight of the vehicle and also improves the quality of the component. As the varieties of TWB applications are increasing, the effects of the difference in material properties, surface properties, weld and its orientation on blank formability have become important both in deep-drawing and stretch forming. In this work, formability of two types of TWBs has been studied experimentally by performing out-of-plane stretch forming tests using a 101.6 mm diameter hemispherical punch. The materials used in this study were Interstitial-Free (IF) steel sheet samples of different thickness (1.0mm and 1.5 mm) and samples of same thickness (1.5 mm) but with different surface characteristics (galvanized and ungalvanized). In the stretch forming experiments, the limiting dome height (LDH) and strain distribution were measured. The influence of weld orientation with respect to major surface strain on formability was studied by conducting experiments in or close to plane strain condition. It has been found that thickness ratio and difference in properties have significant influence on major and minor strain distributions andmore » weld line movement, but the difference in surface characteristics has a minor effect. The simulations results agreed well with the observations from the experimental work conducted on stretch forming of TWBs.« less

Authors:
;  [1]
  1. Department of Mechanical Engineering, Indian Institute of Technology, Delhi New Delhi-110016 (India)
Publication Date:
OSTI Identifier:
21057369
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 908; Journal Issue: 1; Conference: NUMIFORM '07: 9. international conference on numerical methods in industrial forming processes, Porto (Portugal), 17-21 Jun 2007; Other Information: DOI: 10.1063/1.2741013; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPUTERIZED SIMULATION; DISTRIBUTION; DRAWING; INTERSTITIALS; LASER WELDING; MANUFACTURING; SHEETS; STEELS; STRAINS; SURFACE PROPERTIES; SURFACES; THICKNESS; WELDED JOINTS

Citation Formats

Panda, Sushanta Kumar, and Kumar, D. Ravi. Numerical and Experimental Studies on Strain Distribution and Weld Line Movement in Stretch Forming of Tailor Welded Blanks. United States: N. p., 2007. Web. doi:10.1063/1.2741013.
Panda, Sushanta Kumar, & Kumar, D. Ravi. Numerical and Experimental Studies on Strain Distribution and Weld Line Movement in Stretch Forming of Tailor Welded Blanks. United States. doi:10.1063/1.2741013.
Panda, Sushanta Kumar, and Kumar, D. Ravi. Thu . "Numerical and Experimental Studies on Strain Distribution and Weld Line Movement in Stretch Forming of Tailor Welded Blanks". United States. doi:10.1063/1.2741013.
@article{osti_21057369,
title = {Numerical and Experimental Studies on Strain Distribution and Weld Line Movement in Stretch Forming of Tailor Welded Blanks},
author = {Panda, Sushanta Kumar and Kumar, D. Ravi},
abstractNote = {Use of laser welded blanks of multiple sheets of material which are referred to as Tailor Welded Blanks (TWB) is one of the current interests for automotive industries as it reduces manufacturing cost, weight of the vehicle and also improves the quality of the component. As the varieties of TWB applications are increasing, the effects of the difference in material properties, surface properties, weld and its orientation on blank formability have become important both in deep-drawing and stretch forming. In this work, formability of two types of TWBs has been studied experimentally by performing out-of-plane stretch forming tests using a 101.6 mm diameter hemispherical punch. The materials used in this study were Interstitial-Free (IF) steel sheet samples of different thickness (1.0mm and 1.5 mm) and samples of same thickness (1.5 mm) but with different surface characteristics (galvanized and ungalvanized). In the stretch forming experiments, the limiting dome height (LDH) and strain distribution were measured. The influence of weld orientation with respect to major surface strain on formability was studied by conducting experiments in or close to plane strain condition. It has been found that thickness ratio and difference in properties have significant influence on major and minor strain distributions and weld line movement, but the difference in surface characteristics has a minor effect. The simulations results agreed well with the observations from the experimental work conducted on stretch forming of TWBs.},
doi = {10.1063/1.2741013},
journal = {AIP Conference Proceedings},
number = 1,
volume = 908,
place = {United States},
year = {Thu May 17 00:00:00 EDT 2007},
month = {Thu May 17 00:00:00 EDT 2007}
}
  • A Tailor welded blank (TWB) consists of sheet materials of different thicknesses or different alloy compositions that are welded together prior to forming. The weaker of the two sheets deforms more causing weld line movement. This paper proposes methods to predict optimum position of the weld line in a flat tailor welded blank so as to reduce weld line movement in formed tailor welded blanks. Two simulation based methods - back propagation and contour of minimum strain are studied to reduce weld line movement. These methods are based on blank shape modification.
  • The simulation of the forming process of Ti-TWBs at elevated temperatures using finite element analysis to determine the optimum forming conditions of Ti-TWBs is presented in this paper. For verification of the simulation results, titanium alloy (Ti-6Al-4V) was selected for the first instance to prepare the specimen of Ti-TWBs. The thickness combinations of 0.7mm/1.0mm and in widths of 20mm, 90mm and 110mm were used. A specific tooling system with temperature control device was developed to the forming of Ti-TWBs at 550 deg. C. A cylindrical punch of 50mm diameter was designed and manufactured. Different forming parameters (i.e. traveling distance ofmore » the punch and the stroke as well as the time of each forming process) and material characteristics under various temperatures were measured. In addition, the true stress and strain values by tensile test as well as the major and minor strain distributions of forming Ti-TWBs at elevated temperatures by Swift Forming test were carried out and applied as input into the finite element program. The simulation results indentify failure locations and Limit Dome Height (LDH) of Ti-TWBs at elevated temperatures and were compared with the measured ones. Finally, the optimum forming conditions of Ti-TWBs were determined based on the experimentally verified simulation results.« less
  • Beginning in 1992, tailor-welded blanks (TWBs) were used in the US automotive industry to consolidate parts, reduce tolerances, save weight, and increase stiffness. This business is expanding rapidly; more than $500 million of annual TWB sales are expected by 1997. Welds in steel are generally stronger than the base material, such that weld failure by preferential localization is not a critical issue. However, the forming characteristics of TWBs must be understood in order to design and produce high-quality parts with reasonable production and tooling costs. Three formability issues were addressed in this study: the intrinsic ductility and relative formability ofmore » three weld types (CO{sub 2} and Nd:YAG laser welds and mash-seam welds with and without mechanical postweld processing); the value and correspondence of mechanical tests to each other and to press performance; and the prediction of the forming behavior using the finite element method (FEM). Two failure modes for TWBs were identified. While the local ductility of welds can differ greatly, little difference in press formability was measured among the weld types. More important than weld ductility are the changed deformation patterns which depend on the differential strength but depend little on local weld properties. Finite element method (FEM) simulations of dome tests and scale fender-forming operations show good agreement with measurements, as long as boundary conditions are known accurately. The importance of weld-line displacement is discussed and several simulations are compared with experiments.« less
  • Tailor Welded Blanks (TWB) technology is one of the several approaches that have been used to reduce the weight of the automobile body. TWBs are made up of two or more blanks having different/same properties (geometry, material etc.) prior to forming. The formability of these blanks depends on material and geometric parameters like strength ratio and thickness ratio. The study of these blanks can be classified on the basis of the weld orientation chosen viz. transverse weld or longitudinal weld with respect to the major straining direction.This paper studies the formability issues related to transverse TWB by FE simulation. Themore » formability is assessed by analyzing tensile and Limit Dome Height (LDH) tests. The weld region is assumed to be a line in all the simulations. While modeling the tensile test, ultimate tensile strength (UTS) and elongation are monitored, and in LDH testing, pole height and maximum load (in near plane strain condition) are monitored. LDH testing shows that as thickness ratio increases, the load bearing capacity and the pole height decreases. There is a contribution from both the thicker and the thinner blank to the overall deforming volume. Failure location analysis shows that there is an abrupt change in the location of the failure from punch nose region to weld line region as the thickness ratio reaches a critical magnitude (1.08).The study of material properties shows that as the yield strength ratio (S ratio) and strain hardening exponent ratio (N ratio) between the blanks increases, the maximum load which the blank can sustain without failure (UTS) increases. This becomes constant and comparable to that of single sheet at higher N and S ratios.« less
  • A comparison of welding techniques was performed to determine the most effective method for producing aluminum tailor-welded blanks for high volume automotive applications. Aluminum sheet was joined with an emphasis on post weld formability, surface quality and weld speed. Comparative results from several laser based welding techniques along with friction stir welding are presented. The results of this study demonstrate a quantitative comparison of weld methodologies in preparing tailor-welded aluminum stampings for high volume production in the automotive industry. Evaluation of nearly a dozen welding variations ultimately led to down selecting a single process based on post-weld quality and performance.