1、1 Welding Simulation of Cast Aluminium A356 X-T. Pham*, P. Gougeon and F-O. Gagnon Aluminium Technology Centre, National Research Council Canada Chicoutimi, Quebec, Canada Abstract Welding of cast aluminium hollow parts is a new promising technical trend for structural assemblies. However, big gap b
2、etween components, weld porosity, large distortion and risk for hot cracking need to be dealt with. In this paper, the MIG welding of aluminium A356 cast square tubes is studied. The distortion of the welded tubes was predicted by numerical simulations. A good agreement between experimental and nume
3、rical results was obtained. Introduction Aluminium structures become more and more popular in industries thanks to their light weights, especially in the automotive manufacturing industry. Moreover, welding of cast aluminium hollow parts is a new promising technical trend for structural assemblies 1
4、-3. However, it may be very challenging due to many problems such as big gap between components, weld porosity, large distortion and risk for hot cracking 4,5. Due to local heating, complex thermal stresses occur during welding； residual stress and distortion result after welding. In this paper, the
5、 aluminium A356 cast tube MIG welding is studied. The software Sysweld 6 was used for welding simulations. The objective is to validate the capability of this software in predicting the distortion of the welded tubes in the presence of large gaps. In this work, the porosity of welds was checked afte
6、r welding using the X-ray technique. The heat source parameters were identified based on the weld cross-sections and welding parameters. Full 3D thermal metallurgical mechanical simulations were performed. The distortions predicted by the numerical simulations were compared to experimental results m
7、easured after welding by a CMM machine. Experiments Experimental setup Two square tubes are made of A356 by sand casting and then machined. They are assembled by four MIG welds, named W1 to W4. Their dimensions and the welding configuration are depicted in Figure 1. Both small (inner) and large (out
8、er) tubes are well positioned on a fixture using v-blocks as shown in Figure 2. The dimensions of the tubes make a peripheral gap of 1 mm between them. This fixture is fixed on a positioner that allows the welding process to be carried out always in the horizontal 2 position. The length of each weld
9、 is of 35 mm. The Fronius welding head, which is mounted on a Motoman robot, was used for the MIG welding process. Table 1 indicates the parameters of the welding process for this welding configuration. Table 1: MIG welding parameters. Voltage Amperage Speed Thick1 Thick2 Gap (V) (A) (m/min.) (mm) (
10、mm) (mm) 23 260 1.25 4 4 1 a) b) Figure 1: Tube welding configuration: a) cross-section view, b) tube dimensions 3 Figure 2: Experimental setup for tube welding Testing The porosity of welds was observed before and after welding using the X-ray technique to check the quality of these welds according
11、 to the standard ASTM E155. The whole welded tubes were then tested by traction on a MTS testing machine. The final dimensions of the welded tubes are measured on a CMM machine at many points on the tubes. The distortion of the welded tubes is determined by comparing the final positions with the ini
12、tial positions of the tubes. Numerical analysis In Sysweld, a welding analysis is performed based on a weak-coupling formulation between the heat transfer and mechanical problems. Only the thermal history will affect on the mechanical properties, but not in reverse direction. Therefore, a thermal me
13、tallurgical mechanical analysis is divided into two steps. The first step is a thermal metallurgical analysis, in which the heat transferred from the welding source makes phase changes during the welding process. The results of temperature and phase changes from the first step are then used as input
14、 for the second analysis. It is a pure thermo-elasto-plastic simulation 6. Heat source model identification Before running a welding simulation, it is necessary to determine the parameters of the heat source model. This is called heat source fitting. Actually, it is a thermal simulation using this heat source model in the steady state, which iscombined with an
