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Session B2: Modeling II: Predicting Microstructure

and Performance

ADVANCES IN ALUMINUM WELD SIMULATIONS APPLYING WELDSIM

H. G. Fjær(*), O. R. Myhr(**), S. Klokkehaug(**), E. J. Holm(*)

ABSTRACT

This paper describes recent developments and applications of the advanced simulation model WELDSIM. This model is applicable for welding of age hardening aluminum alloys, and computes the evolution of temperatures, microstructure, residual stresses and distortions. The model is today extensively applied in seeking adequate welding procedures in the fabrication of welded automotive parts in aluminum, and it has become an attractive alternative to the traditional procedure of trial and error based optimization of the welding parameters. In the present work, results from weld simulations have been compared to corresponding measurements during welding, and a very good agreement has been obtained. The model has also been applied investigating the possibilities of minimizing the distortions in the welding of automotive parts. The simulations have shown how the fixture design, the weld sequence as well as the welding parameters, significantly affects the resulting weld distortions.

INTRODUCTION

Extruded aluminum profiles are to an increasing extent applied in automotive components like space frames, engine cradles and windshield frames where weight saving is essential. Welding is a key operation in the manufacturing of such parts, and robotic GMA welding is by far the most commonly applied process for high volume production. A major problem associated with welding is the thermally induced deformations caused by the intense non-homogeneous heating and cooling of the material. These deformations are unavoidable in welding, but can usually be minimized to an adequate level by proper selection of the welding parameters and the fixture design. In order to obtain weld deformations within the geometrical tolerance limits, two principally different approaches can be applied, as schematically outlined in Figure 1. The loop on the left hand side of the diagram (i.e. the "physical welding" loop) illustrates the traditional trial and error based procedure applying welding experiments and a robotic welding unit. The welding is followed by measurements of the resulting distortions and the corresponding deviations from the nominal geometry. If the distortions are outside the tolerance limits, some adjustments are done for the welding conditions, the fixture- or the geometric design as indicated in the rectangular window of the figure before another component is welded. The welding is followed by measurements of the resulting geometry, and this loop is repeated until a certain combination yields weld distortions that are acceptable.

The loop on the right hand side (i.e. the "virtual welding" loop) utilizes a computer instead of a welding cell, where the simulation results provide direct information on the positions the distortions are outside the tolerance limits. It is easy to change the input data systematically in order to analyze their individual effect on the resulting local and global distortions. A post

Institute for Energy Technology, Box 40, N-2027 Kjeller, Norway (**) Hydro Automotive Structures Raufoss, Box 15, 2831 Raufoss, Norway

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