Abstract
In order to obtain input data for numerical simulations of tube forming, the material properties of tubes need to be determined. A tube tensile test can only be used to measure yield stress and ultimate tensile stress. For tubes with a large diameter/thickness ratio (D/t), tensile specimens are cut out and processed in a similar way as with sheet metal. However, for thin tubes with a diameter/thickness ratio below 10, the tensile specimens could not be cut out. The flow curve of the analyzed tube with a small diameter and D/t ratio of 7 was determined with a ring-shaped specimen. The experimental force-travel diagram was acquired. A reverse-engineering method was used to determine flow curves by numerical simulations. Using an L25 orthogonal array of the Taguchi method different flow curve parameters and friction coefficient combinations were selected. Tube upsetting with determined parameter combinations was performed with the finite element method. With analysis of variance influential equations among selected input parameters were determined for the force levels at six upsetting states. With the evaluation of known friction coefficients and flow curve parameters, K, n, and ε0 according to the Swift approximation were determined and proved by the final shape of the workpiece.
Highlights
Thin-walled tubular materials are used in several industrial fields, ranging from the automotive industry [1], piping systems, bent tubular holders, and chassis [2,3] to small products in shoe industries where toroidal products are required [4]
This paper presents a determination of a flow curve of a tubular material with an increased strength of E420 + CR2 quality for the diameter/thickness ratio (D/t) ratios of 7
Since the D/t ratio is too small for a tensile specimen to be cut out, a reverse engineering approach was selected aimed at determining the flow curve parameters
Summary
Thin-walled tubular materials are used in several industrial fields, ranging from the automotive industry [1], piping systems, bent tubular holders, and chassis [2,3] to small products in shoe industries where toroidal products are required [4]. Metals 2016, 6, 257 tensile stress, flow curve, material’s anisotropy, etc.) for a majority of forming processes In some cases, such basic testing procedures insufficiently determine the yield loci of the material used. Numerical analyses of a bending process by using the finite element method (FEM) call for the data of a flow curve, which could not be obtained with a tensile test of the tube itself. The real cross-section of the tube could not be determined, and the procedure can be used only for the determination of yield stress Rp and ultimate tensile stress Rm. This paper presents a determination of a flow curve of a tubular material with an increased strength of E420 + CR2 quality for the D/t ratios of 7. Since the D/t ratio is too small for a tensile specimen to be cut out, a reverse engineering approach was selected aimed at determining the flow curve parameters
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