Upsetting Analysis of High-Strength Tubular Specimens with the Taguchi Method

Abstract

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 L 25 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 ε 0 according to the Swift approximation were determined and proved by the final shape of the workpiece.

Investigation of the Geometry of Metal Tube Walls after Necking in Uniaxial Tension

“…Another assumption is that metal tubes share the same mechanical property as metal bars [9]. Apparently, these approximations are not accurate when analyzing the forming process of metal tubes [10]. Only the mechanical properties obtained from direct measurement from the tube specimens can characterize the forming mechanics of tube metals with a higher accuracy [11][12][13][14][15].…”