1.Analysis of temperature field in filling process
The actual production requires that the minimum temperature distribution is at the overflow groove, and the shell of the casting is the low temperature zone of the casting. In order to observe the temperature field distribution under different experimental parameters, the numerical simulation of the automobile steering wheel formed by side casting method is carried out, as shown in Fig. 1. According to the simulation results, the temperature of the rim and spoke is in the solid-liquid range of aluminum alloy liquid (850-883k) after the filling of some test schemes. This is because in the filling process of die casting, early solidification may occur. During solidification, more liquid metal is needed to fill in the shrinkage caused by solidification. If not filled in time, shrinkage porosity and shrinkage cavity will occur. If the temperature difference is large, the difference of solidification rate will be increased with the increase of solidification time. The smaller the temperature difference and solid rate at the end of mold filling, the closer the solidification rate of liquid metal in the cavity during solidification.
In this way, the shrinkage porosity and other defects caused by the large difference of solidification rate of liquid metal can be reduced. Therefore, it can be seen that the temperature distribution under the conditions of group (c), (E), (g), (I) in Fig. 1 is uniform and reasonable, and is not in the range of solid-liquid.
2.Analysis of surface defects in mold filling process
Figure 2 shows the distribution of surface defects under nine different test conditions. It can be seen that most of the oxides generated are concentrated in the overflow tank, which plays the role of slag accumulation, so the design of overflow tank is more reasonable. Moreover, a small amount of oxide is also generated at the rim and hub of the steering wheel, which is mainly due to the drop of liquid metal temperature and uneven temperature distribution, resulting in cold shut and porosity. Careful observation of the color distribution of the nine groups of simulation images shows that the number of defects in Fig. 2 (E) and (f) is less.
3.Comprehensive analysis of orthogonal test
The temperature and oxide formation on the surface during the filling process of the above 9 groups of tests were synthesized. The influence factors of casting quality are quantified. The reasonable temperature distribution is taken as 1, the unreasonable temperature distribution is taken as 0; the less serious defects are taken as 1; the serious defects are taken as 0. After sorting out the data, the comprehensive values of groups 1-9 were 0, 0, 1, 0, 2, 1, 1, 0, 1. The combined values of three groups of data of the same factor are added to get the comprehensive values of the factor A1:1; a2:3; a3:2; b1:1; b2:2; b3:3; c1:1; c2:1; c3:4.
According to the measurement standard of the test, the rationality of the process parameters is determined by the comprehensive value of the factors. According to the calculation results, a2b3c3 is the best horizontal combination: punch speed 3M · s – 1, pouring temperature 920k, mold temperature 600k