Heat Assisted Local Forming and Joining Processes: Simulation and Experimentation

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The increasing demand in the automotive and aerospace industries for higher properties in their manufactured parts is closely connected to the lower thickness of the sheet metal that could be involved in the forming processes and consequently the lighter weights of these parts at the end. The main concern is the poor formability of high grade materials, especially at room temperature. For this reason, many efforts are actually made towards warm to high temperature sheet metal manufacturing processes but there is still an important gap between the prediction of the numerical models and the actual processes because of the complex evolution of the microstructure during forming at elevated temperature. One aspect following a heat assisted forming process is the transformation induced plasticity effect (TRIP) in the microstructure that can occur in phase changing materials. Higher hardening capability are exhibited following this transformation and one can take an advantage of the enhanced properties of the manufactured parts to decrease furthermore their thicknesses for weight reduction and then improved fuel efficiency in transportation. A typical example of a dynamic heat assisted forming process involving hard-to-shape high strength materials is the sheet-metal spinning for aerospace applications. The process progressively transform flat metal blank into hollow shapes, mainly with axisymmetric profiles. The method uses a tool i.e. a roller which forces a metal blank onto a revolving mandrel. The roller is pressed against the blank and is moved axially into complex trajectories to achieve finally a hollow-shaped product. With the great number of parameters (speed, temperature dependent properties, strain rate, tool trajectories, induced anisotropy.) involved in the procedure a comprehensive design of experiments would be too demanding in terms of costs and dedicated time. Finite element models are of great help to reproduce complex processes and can offer very in deep details on the ongoing forming process and the final properties of the parts. The key is the accurate information input in the numerical model and its ability to reproduce precisely the heat transfer, the strain hardening, the anisotropy and eventually the TRIP phenomena. In this project, the focus will be on the simulation model and its ability to represent these phenomena evolving with time in the material. A crystal plasticity model will be implemented in the finite element analysis to follow these complex evolutions. Eventually, phase transformation could be monitored with the appropriate amount of locally heat input at the forming tool contact zone to enhance the sheet metal formability. The goal is to bring conventional forming processes to new technological levels by adding high tech heating sources (like laser heating) in the forming steps of hard to shape high strength materials, enhancing material properties and maintaining heat assisted operation at lowest cost as possible.