Adjusting the Residual Stress State in Wire Drawing Products via In-Process Modification of Tool Geometries

Abstract

After conventional forming processes, the residual stress distribution in wires is frequently unfavorable for subsequent processes, such as bending operations. High tensile residual stresses typically occur near the wire surface and normally limit further processability of the material. Additional heat treatment operations or shot peening are often used to influence the residual stress distribution in the material after conventional manufacturing, which is time- and energy-consuming. This paper presents an approach for influencing the residual stress distribution by modifying the forming process, especially regarding die geometry. The aim is to reduce the resulting tensile stress levels near the surface. Specific forming elements are integrated into the dies to achieve this residual stress reduction. These modifications in the forming zone have a significant influence on process properties, such as plastic strain and deformation direction, but typically do not influence product geometry. This paper describes the theoretical approach and model setup, the FE simulation, and the results of the experimental tests. The characterization of the residual stress states in the specimen was carried out through X-ray diffraction using the sin²Ψ method.

Keywords: FE simulation; residual stress measurements by X-ray diffraction; residual stress modification; wire-drawing.

Figure 1

(a) Wire-drawing tool, (b) residual stress distribution to ref. [8], and (c) critical areas on a torsion bar spring.

Figure 2

Tool principle—interchangeable dies for different geometry variants.

Figure 3

XRD analysis—basic system and measurement setup for wire workpiece.

Figure 4

Flow curve S355 k_f (φ) for the FE simulations.

Figure 5

FE model setup and residual stresses after wire drawing (example conventional geometry).

Figure 6

Geometry variants with special geometric elements.

Figure 7

FE simulation of wire drawing—plastic strain over the specimen cross-section.

Figure 8

FE simulation of wire-drawing—axial and tangential residual stresses over the specimen cross-section as a function of the geometric elements.

Figure 9

Experimental drawing forces of the die geometry variants, conventional, convex and concave (three specimens per variant).

Figure 10

XRD-Measurements: Average residual stresses of the specimens drawn with conventional, convex, and concave die geometry variants (four measuring points on the circumference 0°, 90°, 180°, and 270°; three specimens per variant).