Parameter-formability relationship in ISF of tri-layered Cu-Steel-Cu composite sheet metal: Response surface and microscopic analyses

This study analyzes the parameters effects on the formability in Incremental-Sheet-Forming (ISF) of a tri-layered Cu-Steel-Cu composite sheet. The effects are found to be very complex, highly interactive, and somehow different from those reported in the literature for the monolithic sheet metals. High rotational speed and feed rate pose positive effect, regardless of tool size and step size, when the composite sheet is annealed to low temperature (e.g., 400°C). These high settings have adverse effects, contrarily, specifically when the tool diameter is large and the sheet is annealed to high temperature (e.g., 700°C). This, as per microscopic observation, is attributed to delamination of high-annealed laminates (characterized by low bond strength). The delamination as dictated by hole drill tests possibly occurs due to a reason that the laminates experience low compressive residual stress when processed with the aforesaid parameters. The XRD analysis reveals that the formation of any new element does not occur during ISF, thus ruling out the potential effect of material processing on microstructural change on the sheet fracture. Finally, a correlation is formulated using which one without doing experiments can choose the optimum parameters for the ISF of composite sheet with objective to maximize the formability.