1. Definition of composite squeeze casting
Direct squeeze casting technology pressure directly acts on the surface of liquid metal, the pressure transmission distance is short, but the melt must be accurately and quantitatively filled. At the same time, direct squeeze casting is to carry out closed die extrusion after filling. There is a secondary filling process for complex shaped parts, which is easy to form defects such as cold separation. Therefore, it is only suitable for the production of castings with simple shape and symmetrical structure. Indirect squeeze casting is a process in which the pressure is transmitted to the molten metal in the die cavity through the runner, so the pressure is transmitted for a long distance, and it is easy to produce shrinkage porosity and other defects. However, indirect squeeze casting is flexible, easy to control the casting size, and does not need to configure accurate quantitative filling system, so it is suitable to produce castings with complex shape, uneven wall thickness, dimensional accuracy and high surface roughness. However, this kind of pressing method will not form plastic deformation structure inside the casting, and the mechanical properties of the casting is slightly lower than that of the direct squeeze casting. At the same time, because the indirect squeeze casting process adopts the filling system, it is difficult to maintain high pressure during the solidification process of the casting, which is not conducive to the production of alloy castings with large solidification range The internal quality of die casting is low, and the material utilization rate of indirect squeeze casting is relatively low.
In order to solve the problem of forming large and complex parts, it is necessary to combine the advantages of direct squeeze casting with that of indirect squeeze casting, which can produce plastic deformation structure inside the casting and is suitable for forming complex parts. Based on the analysis and comparison of squeeze casting technology, a new squeeze casting method, compound squeeze casting, is put forward in this paper. In this method, an independent filling device is used to fill the mold in the pre closed mold state, and then the molten metal is pressurized by the upper mold of the mold until the casting solidifies, and the molten metal is in a closed state during the whole process.
2. According to the definition of composite squeeze casting, the process flow of the composite squeeze casting forming method is as follows:
(1) The molten metal is transferred to the holding furnace in advance, as shown in Fig. 2-1 a);
(2) The upper mold and the lower mold are pre assembled, as shown in Fig. 2-1 b);
(3) The molten metal is led into the filling cavity through the closed pipe, as shown in Fig. 2-1 C);
(4) The molten metal is fed into the mold cavity by the filling head to complete the filling, as shown in Fig. 2-1 d);
（5） The metal melt is extruded from the upper die down and solidified under pressure, as shown in Fig. 2-1 E);
(6) Open the mold and take out the casting, and the filling head goes down to the initial position, as shown in Fig. 2-1 f).
In this forming process, pre closing refers to the formation of a closed mold filling space, which is closed relative to the extruded alloy body in the mold cavity, while the gas, a small amount of slag collection and exhaust spillage are throttled and communicated with the outside.
In this method, the closed pipe is used to transport molten metal, which reduces the unfavorable factors such as molten metal oxidation and suction. At the same time, the die pressure fully acts on the molten metal, which has the advantages of short extrusion pressure transfer distance, fast pressure build-up speed, less pressure loss and high utilization efficiency, and is conducive to the extrusion casting of large and complex parts.