Mechanical property determination for combined sheet and bulk metal forming process by plane strain compression test

Abstract

A new forming technique has been developed and improved to reduce the forming load, eliminate forming defects and minimize material waste. The Combined sheet and bulk metal forming process (SBMF) is developed by combining the advantages of both sheet and bulk forming processes. The workpiece is started by using a thick sheet. It will form the material by a common stamping process to preform a skeleton shape and later on the local feature is forged to get the precise dimension. To design this process, Finite Element Modeling (FEM) was applied for the process analysis to determine the flow behavior during the deformation. The flow stress is normally obtained from the conventional tests, namely, upsetting or tensile test, in which the flow behavior would be much different from the real behavior of the SBMF process. To make the simulation result more accurate, plane strain compression test (PSCT) was proposed to determine the flow stress of the material. To achieve the plane strain condition is not realistic and would be rather difficult. The spread exponent was proposed in the equation to determine the accurate effective stress which would compensate the effect of the nonplane strain condition. In this experiment, the material was SS316L with the thickness of 4.5 mm. Teflon and oils were used as lubricants to reduce friction. FEM of PSCT was conducted by using the flow stress obtained from PSCT with different friction coefficients. It was found that the load-stroke curve obtained from the Teflon lubrication condition could provide the friction coefficient closed to zero. This should be suitably used in the test for determining the flow stress in PSCT.