ASSESSMENT OF PROCESS MODELING TOOLS FOR TUBE HYDROFORMING USING ABAQUS SOFTWARE: FINITE ELEMENT MODELING AND FAILURE MODES ANALYSIS. Mihaita Matei, *Augustin Gakwaya, Julie Lévesque, Michel Guillot Department of mechanical engineering, Université Laval, Québec, Canada (*corresponding author: agakwaya@gmc.ulaval.ca ) ABSTRACT A modeling and simulation methodology based on ABAQUS software is presented for a multistage tube hydroforming (THF) process. Using adequate loading paths and appropriate numerical parameters, it is possible to avoid potential failures that are prone to occur under uncontrolled process. Two examples are considered. First, the failure mechanisms during the initial bulge forming are analysed and useful wrinkles in main deformation areas are used to obtain a good part. Then the simulation of a multistage THF process integrating both a rotary draw bending and a hydroforming stages is performed for assessing the process parameters and numerical difficulties encountered in modeling of a real component. KEY WORDS: Bending process, Tube hydroforming process, deformation, failure mechanisms, aluminum tubes, wrinkles. 1. INTRODUCTION Tube hydroforming (in short THF) describes a metal forming process whereby tubular blanks are deformed into complex shapes within a die cavity using simultaneously hydraulic internal pressure and axial compressive forces. Compared to the conventional stamping, or deep drawing processes, the tube hydroforming process is still a relatively new forming method in terms of large scale production and thus with a limited knowledge base about the process and associated tool design. The process still struggles with long cycle times and expensive equipments, [3]. These drawbacks have made its acceptance in the forming industry lag behind. However, tube hydroforming is a unique forming method since during deformation due to inner pressure; it is possible to feed material axially by cylinders at the tube ends. If necessary, counter punches can even be used to control the tube expansion [2]. Research is thus being performed continuously on the subject and improvements in process control, tooling and lubrication together with advances in simulations, contribute to a more general acceptance and utilisation in industrial production, see Hartl [2]. The main advantages of THF over the conventional stamping processes are weight and cost reduction, better structural integrity, increased strength and reduction in part numbers [2,3]. It is even possible to tailor the properties of the hydroformed tube by varying its initial cross section and wall thickness. Tubes with variable cross-sections can be hydroformed in two ways: closed die tube expansion, or tube crushing [5,12, 13]. In closed die expansion, the tube is formed between two die halves through the use of internal fluid pressure. In tube crushing, die closure is utilized to assist deformation like in corner filling. During the deformation, part of the section is in contact with the die. If the material/die interface were frictionless, the strain would be uniformly distributed all over the section and a section with a constant thickness would be formed. However, friction at the material/die interface restricts the flow of material in contact with the die and causes non-uniform distribution of strain. It causes a variation in the thickness of the formed tube along the cross-section with the smallest thickness at the corners. Thus the frictional behavior at the material–die interface is crucial in tube hydroforming. However, one of the major tasks in setting up a THF process is to avoid failure by finding an appropriate balance between material feeding and internal pressure, so as a part is successfully formed without any defects and with a minimum waste of materials. An inappropriate combination of internal pressure and axial feeding can lead to occurrence of defects such as buckling, bursting and wrinkling during the tube hydroforming process. Dohmann et al. [12] pointed out that wrinkles are unavoidable in the intake region of the expansion tool, but can be eliminated by increasing the internal pressure in the calibration stage.