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An important emerging technical area is computer-based modeling of the various manufacturing processes that are used in many diverse industries. These models are used to optimize manufacturing techniques to reduce fabrication costs and improve the service performance. One manufacturing process important in steel fabrication is welding. It can be a useful tool to aid in reducing fabrication costs and service durability by optimizing the weld process and is the subject of this paper.

Welding remains to be one of major manufacturing processes in the automotive industry. In addition to resistance welding, arc welding processes have recently received an increasing attention as some of the advanced designs of automotive structures are being introduced, such as hydro-formed frame structures. As such, it has become increasingly important that math-based design and manufacturing tools be developed to achieve concurrent design and welding process development in today's competitive environment. In this paper, some of the state of the art computational modeling techniques are first summarized. These modeling techniques can be used to establish welding procedure effects on weld quality, residual stresses, distortions, and more importantly, on structural integrity of the welded structures. The applications of some of the advanced analysis techniques are demonstrated by using a number of detailed case studies.

Recent rapid advances in mesh-insensitive structural stress procedures are summarized in this report. In addition to their effectiveness in reliably calculating structural stresses for both simple weld details and complex structures, the mesh-insensitive structural stress procedure provides an effective mean for drastically simplifying stress intensity factor solutions for welded joints, by extending the structural stress definition for characterizing notch effects at welds. The results achieved so far and significant implications are summarized below: (1) The mesh-insensitive structural stresses can be consistently related to fatigue behavior in welded joints and the calculation methods can be readily implemented as processing procedures (2) As a stress based transformation process, the mesh-insensitive structural stress methods map complex 3D geometry and loading mode to a simple strip geometry subjected to a simple structural stress state.

In this paper, an advanced computational framework is presented for integrated simulation of hydroforming effects and welding assembly operations. The finite element procedures take advantages of existing commercial finite element codes such as ABAQUS by employing a series of user-developed interface modules and a unified material constitutive model formulated with internal state variables that are used to track stress/strain histories induced during forming and welding operations. Its applications in design and welding assembly of hydrofomed components are demonstrated with a series of selected case studies. Based on the detailed finite element simulations described in the above, the following important observations can be made: Weld placements are extremely important in order to mitigate the significant cold work effects in hydroforming.