Passive granular medium-based tube press hardening

点击翻译按钮获取中文摘要

The aim of the project is the investigation of the passive granular medium-based tube press hardening to facilitate the manufacturing of profile components with an unlimited length. The common process for hot forming of profile components is based on gaseous media. A problem is the compressibility of the gas, so that high forming pressures are associated with a high-risk potential and limit in the stroke rate due to the pressure build-up time.An alternative are granular media, which allow the press hardening process of steel pipes by high pressure resistance and temperature stability. In the case of active granular medium-based tube press hardening, the forming force is generated by an axial punch insertion into the pipe end and transferred to the component via the granules. However, due to the internal friction, the granule column does not behave hydrostatically. This feature leads to the limitation of the producible pipe length, the achievable expansion and formability of small radii. In order to remove these significant restrictions and to achieve the ease of application, the passive granular medium-based tube press hardening has to be researched. In this process principle, the forming force is generated by closing the forming die. By the lateral pressure build-up not only the limitation of the tube length is removed, but also the attainable strain paths and profile shapes are extended by the compression of the tube cross-section.To achieve the project objective, the influence of the parameters such as e.g. the geometric conditions, the kinematics, the granular filling and the temperature control will be taken into account. Based on this, the pressure and temperature distribution will be analyzed, which influence the strains and mechanical properties. Accordingly, process limits and a working area have to be determined.The project starts with the characterization of the ceramic beads and the quartz sand as forming media, the 22MnB5 as a pipe material and their interactions. With this knowledge, the project contains furthermore the process design and the resulting product properties. In addition to the numerical simulation, an analytical model is necessary to determine the pressure and temperature distribution in the granular medium and the pipe component. The theoretical investigation also includes the evolution of the microstructure, so that depending on the process conditions components of different strength can be obtained. For validation, different variants are studied in an experiment, such as the two-dimensional forming without granular flow in the axial direction or the forming with induced axial flow for producing profiles with graded cross-sectional area. In addition, the new tool technology will be developed in terms of the heat supply of the pipe component by shunt heating, so that the in-situ heating process takes place directly after the granular filling and insertion into the tool for a maximum effective cooling rate.