According to the specific parameters of semi-solid vertical squeeze casting machine, combined with the laboratory test data, the process parameters of rheo squeeze casting were preliminarily determined. The filling process simulation of wheel shaped squeeze casting parts is shown in Figure 1.
The filling process has a great influence on the microstructure and mechanical properties of squeeze casting parts. Many defects such as entrainment, inclusion and oxide scale are related to the whole filling process. Indirect squeeze casting was used in the test equipment. During injection filling, the alloy melt was gradually filled into the whole cavity by the injection hammer from bottom to top.
It can be seen from Figure 1 that after the injection hammer starts to move upward, the semi-solid alloy melt begins to fill the mold cavity. When t = 0.36s, it can be found that due to the larger gate diameter (80mm), the filling speed is faster, and the speed of the central part of the alloy melt and the wall around the cavity with larger diameter is slower; when t = 0.60s, the filling speed is faster When t = 0.84s, the flow velocity of the alloy melt begins to flow into the narrow annular part of the mold cavity, and the flow velocity decreases gradually until the center of the alloy melt When t = 1.08s, the flow characteristics of the previous step are maintained, and the flow at the bottom of the periphery is more obvious, resulting in the uneven flow of this part; t = 1.33s At the same time, the flow velocity in the center and the bottom of the gate becomes slow; t = 1.81s When the narrow annular channel is filled, defects such as entrainment, shrinkage cavity and porosity are easy to occur at the top of the center, and melt intersection occurs at the junction of the narrow annular channel and the outside of the annular channel, where inclusions, pores and cold traps are easy to occur; t = 2.29s Because the gap of overflow slot is small, the reflux will not affect the quality of squeeze casting parts. Therefore, the opening of overflow slot and exhaust slot greatly improves the quality of squeeze casting parts.
As shown in Figure 2, under the process parameters, by simulating the squeeze casting forming process, the filling defects with and without overflow groove are compared. From Figure 2 (a) and (c), it can be found that the probability defects and porosity without overflow groove are higher than those with overflow groove 2 (b) and (d) are more, so it is beneficial to eliminate gas and inclusion and improve product quality by setting overflow tank with reasonable distribution and structure.