Study of non-linear strain path in sheet metal forming

Abstract: At present, Sheet Metal Forming (SMF) is not just limited to increasing demand from automobile industries but also to various other manufacturing industries that utilize sheet metal forming processes. The surplus demands for optimised manufacturing products warrant the need for an extended decisive study on SMF.  One such area of study in SMF is formability. Traditionally, formability is predicted using the conventional Forming Limit Curve (FLC). But when it comes to complex SMF processes, FLC failure model can sometimes overestimate (for low uniaxial straining) or underestimate (for bi-axial straining) failure. This thesis focuses on suitable test procedures to generate non-linear strain paths and prediction of formability using the concept of Generalized Forming Limit Curve (GFLC). Initially, through systematic literature review, two-step process is chosen as the test procedure in this thesis. The test procedure was simulated in LS-Dyna to obtain results which are then used by GFLC concept to predict formability for a bi-linear deformation history. The predicted formability using the concept of GFLC is then compared with the predicted formability using FE-simulation and using experimentation.  The found percent error for GFLC prediction compared to that of FE-simulation prediction is 11% and the percent error for GFLC prediction and experimentation prediction is 14%. However, these two predictions can not be used to validate the GFLC prediction. This is because in this thesis GFLC procedure uses data obtained from FE-simulation with GISSMO failure model. Through literature, it is identified that the GFLC concept can be applied for multi-linear deformation histories to predict formability and the method to do so is explained in detail in this thesis. Finally, it is concluded that the use of the GFLC concept in conjunction with the two-step drawing process to predict formability for bi-linear deformation history is acceptable.