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The effect of die geometry and workpiece diameter on the mechanics of Micro Form-Rolling

Form-rolling is a rotary forming process, in which the workpiece is rotated between a pair of flat dies. It can be used to form complex shapes on axisymmetric metal parts. Microparts are those with at least two submillimetre dimensions and the parts form-rolled during this research project fall within this category. The research project report presented here aims to establish a better understanding of the effects that workpiece diameter, material, area reduction and die geometry have on the microform-rolling process and the quality of the formed parts. Particular emphasis was placed on the factors leading to internal failures, such as the area reduction experienced by the part during the forming process. Microform-rolling trials using a variety of die/workpiece combinations were carried out on an EWM AF3 Form-rolling machine. Ti-6Al-4V Titanium alloy and AISI 316 stainless steel workpieces were rolled during this research and after rolling, they were mounted, sectioned and then examined under a microscope to determine the presence, location and magnitude of any defects. The elasto-plastic FE packages DEFORM 2D and 3D were used to model the microform-rolling process. The stress distributions present in the workpiece during rolling were examined to determine a better understanding of the mechanics of the process. Signs of failure were also monitored, high damage values were apparent in some simulations indicating where and when, internal failure was likely to ensue.