Design and analysis of hollow section extrusion of the underframe part of a railroad vehicle using mismatching refinement with domain decomposition

In order to reduce the weight of a high-speed railroad vehicle, the main body has been manufactured by hollow section extrusion using aluminium alloys. A porthole die has been utilized for the hollow section extrusion process, which involves complicated die geometry and flow characteristics. The design of the porthole die is very difficult because of this complexity. Three-dimensional finite element analysis for a complicated hollow section is also an arduous task from the viewpoint of appropriate mesh construction and computational time. In the present work, mismatching refinement, an efficient domain decomposition method with a different mesh density for each subdomain, is implemented for the analysis of the hollow section extrusion process. In addition, a modified grid-based approach with the surface element layer is utilized for three-dimensional mesh generation of a complicated shape with hexahedral elements. The effects of porthole design are discussed through simulation of the extrusion of an underframe part of a railroad vehicle. An experiment has also been carried out for comparison. Comparing the velocity distribution at the outlet with the thickness variation of the extruded part, it is concluded that the analysed results can provide reliable measures for deciding on whether the die design is acceptable to obtain uniform wall thickness. The analysis results are then successfully extended to industrial porthole die design.