Stability of steel thixoforming process J. C. PIERRET, A. RASSILI, G. VANEETVELD, J. LECOMTE-BECKERS ThixoUnit ULg, Material Sciences Unit, Department of Aerospace and Mechanical Engineering, University of Liège, Liège 4000, Belgium Received 13 May 2010; accepted 25 June 2010 Abstract: To improve the industrialization of the process, the study of a thixoforming line stability was proposed. The thixoforming line is fully automated to optimize the repeatability of the experiments. Parameters of the heating cycle, the slug temperature, the tool temperature and the forming speed were studied. For each of them, a range of the expected variations in a steady-state process as well as the effects of these variations on the process itself (forming load and parts quality) were given. These variations are shown to be acceptable. Three different tools were used in the experiments. Some mathematical simulations were realized on the finite elements code Forge2008© with a semi-solid constitutive law. The capacity of the model to represent the process stability was discussed. The simulation results are in agreement with the experiment results. Key words: thixoforming; steel; high melting point; stability; robustness; process 1 Introduction Recent studies[1−4] have shown that thixoforming can be applied to steel with good results. Nevertheless, these researches mainly focused on the possibility to shape parts and the quality of these parts. The goal of this work is to bring some new elements about robustness and stability of the steel thixofoming process. In this way, the study focuses on the process sensitivity to a variation of its main parameters and its repeatability for a given set of optimized parameters. The influence of the parameters on the process was determined thanking to the quantification of the forming load and the qualitative observations of the parts quality. 2 Experimental This research was realized on the pilot thixoforming production line[4] located at the University of Liège (Fig.1). This line is composed of: 1) a feeding treadmill that transports slugs, 2) an inductive heating (150 kW, 2−10 kHz), 3) a high-speed feeding robot, 4) a cleaner- lubricating robot that also takes parts out of the press, 5) a hydraulic 5 000 kN high-speed press and 6) a cooling/thermal treatment area. 2.1 Direct extrusion tool During this work, we have used three different tools. The first one (Fig.2), developed in collaboration with the AscoMetal CREAS research center, is a direct extrusion tool that basically consists of a reduction of the slug diameter. The deformation rate is linked to the ratio of slug diameter to channel diameter. For this tool, the inductive heating is done directly inside the hydraulic press and the die passes through the inductor when the heating is over. There is no transfer for the heated slug to the tool. At the beginning of the cycle, the slug stands on an inconel 718 punch covered by a Nefacier© (thermal insulator) patch. The punch stands on a load sensor. When heating cycle is finished, the tool will be pushed down through the inductor and forming step occurs. Deformation ends as soon as the two cylinders enter into contact. At this time, the whole tool moves down, digging the damping platform. The consequence is that the load sensor does not measure anything. The lower cylinder height can be adjusted by annular wedges. This setting was done because, classically, using a hydraulic press, the forming speed is variable as there is a decreasing of the punch speed at the end of forming[5−7]. The tool was heated by resistive elements and its temperature was measured by thermocouples. Foundation item: Project (415814) supported by the FIRST Europe, THIXOFROR. Corresponding author: PIERRET Jean-Christophe; Tel: +32-4-3615946; E-mail: jc.pierret@ulg.ac.be Trans. Nonferrous Met. Soc. China 20(2010) s937-s942