Numerical analysis of plastic die deformation during high temperature copper extrusion

Abstract

In copper extrusion, billet temperatures of 600°C or more are very common and the dies are therefore exposed to high thermo-mechanical stress. This causes deflection and wear of the dies and thus reduced quality of the extruded profile. In the present study, die deflection and residual deformation after several extrusion cycles was investigated by means of extrusion trials and numerical analyses. Material models of four tool materials (hot-work tool steels 1.2367 and CS1, nickel-based alloy 718, cobalt-based alloy Stellite 1) and the copper alloy CW024A were provided by hot compression tests. Extrusion trials were carried out applying four different dies, each made of another tool material. Using the FEM based software DEFORM 2D, the extrusion trials were modeled and decoupled die stress analyses were performed, which simulated three consecutive load cycles. The focus of the data interpretation was in die deflection in proximity of the die land due to the thermo-mechanical load and residual plastic deformation after relief of the mechanical load. Larger values of deflection close to the die land were observed for the hot-work tool steels, while the deflection of nickel- and cobalt-based alloys was negligibly small. Also, remarkable plastic deformation was only determined for the hot-work tool steels, with increasing values for every simulated load cycle. This analysis characterizes the performance limits of hot-work tool steels and the benefits of nickel- and cobalt-based alloys regarding contour accuracy during high temperature copper extrusion.

Progression of plastic die deformation during copper extrusion

“…Subsequently, a total of twelve extrusion trials with consecutive 3D scans was carried out using the four dies made of different tool materials and performing three repetitions per die. On average, the maximum die force was 3.4MN and the highest temperature measured in the bearing channel was approximately 800 °C [6]. The results of surface comparisons of the die made of hot-work tool steel 1.2367 are presented in Fig.…”

“…At this point, the excellent high-temperature properties of the nickel-base alloy become apparent [7]. Due to almost invariant high-temperature strength up to temperatures of 700°C [6] and the work hardening occurring in the area of the inlet radius and bearing channel, the unchanged process conditions of the three extrusion cycles do not lead to any significant change in die geometry. The surface comparisons for the die made of cobalt-based alloy 2.4775 are shown in Fig.…”

“…In the subsequently performed decoupled die stress analysis, elasto-plastic models were implemented to describe the material behavior of the different die materials. The identification of the required flow behavior of the tool and billet materials as well as model design and verification are described in detail in [6]. Since only very small deformations in the range of a few microns are predicted for the two tools made of 2.4668 and 2.4775, solely the two hot-work tool steels investigated will be discussed below.…”

“…To estimate the strain of the surface modifications during service, knowledge of the deformation behavior of the dies is required. For this purpose, tool deformation was investigated in a previous study by means of FEM-based numerical analyses [6]. In the present study, the extrusion dies were 3D scanned to determine the actual die deformation and to compare it with the results of the simulations.…”