Finite-element prediction of distortion during gas metal arc welding usingthe shrinkage volume approach

Distortion is a potential problem with all welded fabrications. To a large extent, industrial control of weld induced distortion is achieved by relian ce on past experience, simple empirical formulae or rectification procedure s. Rectification can be costly whilst in large complex structures, empirica l formulae are rarely applicable. Classical approaches to the modelling of welding distortion and residual stress, whilst accurate, have not been read ily useable within industry. The time and cost associated with running such models appear to be the main reasons contributing to this situation. Never theless, the use of computer simulative techniques has the potential to sig nificantly reduce the cost of welded fabrications by allowing for predictio ns to be made long before a single weld bead is put down on the workshop fl oor. Therefore, computer models that are aimed at predicting welding phenom ena not only need to be accurate, but must also be affordable and capable o f making predictions within industrial time frames if they are to be used b y fabricators. This paper presents one such strategy. The Shrinkage Volume Method is a linear elastic finite-element modelling technique that has been developed to predict post-weld distortion. By assuming that the linear the rmal contraction of a nominal shrinkage volume is the main driving force fo r distortion, the need to determine the transient temperature field and mic rostructural changes is eliminated. In so doing, the model solution times a re reduced significantly and the use of linear elastic finite-element metho ds permits large, highly complex welded structures to be modelled within a reasonable time frame. Verification of the modelled results was carried out by an experimental program that investigated the distortion of plain carbo n steel plates having differing vee-butt preparations. The initial models, which had assumed the edge preparation to be representative of the overall shrinkage volume, were in reasonable agreement with the experimentally dete rmined distortion values. Further improvements to these results were made b y using a thermal model to define better the effective weld shrinkage volum e. (C) 1999 Elsevier Science S.A. All rights reserved.