Microstructure and Modelling of Shear Forming

The advent of multiaxial CNC machines has generated renewed interest in flexible incremental forming manufacturing methodologies, such as shear forming. These processes use rotating tools in constant local contact with the workpiece, which is often also rotating, to generate shape. As a consequence, much lower loads than conventional forming are needed to produce components with no need for expensive special tooling. Potential has already been established by demonstrating manufacture of high-value products, e.g. turbine and satellite parts, with high dimensional accuracy from difficult to manufacture materials. Thus, huge opportunities exist for these processes to replace the current method of manufacture for a range of high value components, e.g. eliminating lengthy machining, reducing material waste and process times; or the manufacture of a complicated shape without the development of expensive tooling. However, little is known about the exact deformation conditions during processing and why certain materials are better than others for shear forming, leading to significant trial and error before production.
Three alloys were used for this project: Timetal 54M, Jethete M154 and Inconel 718. General microscopy and Electron Backscatter Diffraction were used to measure strains and orientation maps during shear forming and compared with finite element simulations of the process. It was found that in all cases simple shear deformation was dominate but its extent varied through the thickness, with greater levels of deformation at the roller side. A Design of Experiments analysis was also conducted in order to understand the impact of process parameters in the properties of the final workpieces. Such information was the key to develop a reliable Finite Element Model (FEM) that closely resembles the deformation paths of this process. Three methods of damage calculations were embedded in the finite element model and it was found that the forming limit diagram approach had most potential to identify ultimate failure in shear forming, however its use was still not entirely adequate for this process and a different approach was suggested based on previous works found in the literature. Finally, a methodology to test the potential of materials to be shear spun is proposed based on the finite element model developed and these findings.