Friction stir incremental forming of polyoxymethylene: process outputs, force and temperature

Abstract

Despite good creep and fatigue durability, high resistance against chemicals and good surface finish, Polyoxymethylene (POM) has been sidelined in incremental sheet forming (ISF) literature due to its low formability at room temperature. This paper addresses the issue by deploying a cost-effective friction-induced heat at the tool-sheet interface. This work demonstrates a combined experimental, analytical, and numerical approach to investigate the effects of elevated temperature in ISF of POM. For this purpose, the formability of POM was first experimentally investigated under the interactive effects of the process parameters. Employing the membrane analysis approach, the stress state in the FSISF process was defined. The tool-sheet contact area was calculated as a function of toolpath and the relevant process parameters. The Johnson-Cook plasticity model was calibrated based on several universal mechanical tests at various temperatures and rates. Embedding the stress state, contact area, and the material model inside an algorithm developed by adopting the Finite Difference Method, force, friction-induced heat, and temperature at the tool-sheet interface were evaluated. Simulation results were validated by experimental outcomes. A threshold boundary for the maximum allowable tooltip temperature was established to avoid heat-induced defects while ensuring the sheet formability.