Study on the forming system of compound squeeze casting for large parts

With the rapid development of economy, the domestic demand for large and complex parts is increasing in the fields of automobile, aviation, architecture and military engineering, and the trend of lightweight development of large parts is becoming more and more obvious, such as large aluminum alloy car seat frame, car gearbox box, car gearbox box, etc. Usually, the large-scale parts of this kind of non-ferrous metals are formed by low-pressure casting. Because there are many defects such as porosity, shrinkage cavity and inclusion in the castings, the performance indexes of the formed parts are often difficult to meet the use requirements. Although forging can form parts with high performance, it has large deformation resistance, high requirements for equipment, poor flow filling performance of metal. For parts with complex structure, it often needs multiple processes to complete, high production cost, not suitable for producing parts with complex shape, not suitable for producing parts with complex shape, especially large-scale parts with complex structure Spare parts.

Squeeze casting is a kind of technology which combines the characteristics of casting and forging. It has the advantages of high utilization rate of liquid metal, simple process and stable quality. It is a kind of energy-saving liquid forming technology and so on. It is a kind of energy-saving liquid forming technology. Research at home and abroad shows that squeeze casting is suitable for manufacturing wheel hub, valve body, piston and sheet metal castings. It is an alternative forming technology for low-cost manufacturing of large complex parts.

According to the process characteristics, squeeze casting can be divided into direct squeeze casting and indirect squeeze casting. The method of direct squeeze casting is that the pressure is directly applied to the whole liquid surface of the molten metal, and the mold is not equipped with a filling system, so the solidification speed of the molten metal is fast, and the obtained casting structure is dense. Theoretically, it can produce nearly 100% dense castings to produce close to This method is suitable for producing castings with simple shape and symmetrical structure, such as piston, caliper, cylinder, etc. The main disadvantage of this method is that the molten metal poured into the cavity must be accurately quantified, otherwise the dimensional accuracy of the casting will be unstable due to the change of the molten liquid quantity; the casting is required to solidify in one direction to the punch to ensure the effective transmission of pressure, which limits the shape of the product, and there are some difficulties in forming the castings with complex shape. The indirect squeeze casting method is to close the die and form a closed die cavity.

The indirect squeeze casting method has the advantages of short runner length, large section, low filling speed and long holding time. It is easy to control the casting size and does not need to configure accurate quantitative filling system. This method can make full use of the heat capacity of the liquid metal in the filling device, make the casting easy to form and supplement the parts under pressure, so it is suitable to produce castings with complex shape, uneven wall thickness, high dimensional accuracy and surface roughness. However, this way of pressing will not form plastic deformation structure in the casting, and the mechanical properties of the casting are lower than that of the direct casting. At the same time, because the indirect squeeze casting process uses the filling system, it is difficult to maintain a higher pressure in the solidification process of the casting, which is not conducive to the production of castings with large solidification interval, and the internal quality of the casting is also poor.

For large and complex parts formed by squeeze casting, if the direct squeeze casting method is adopted, the molten metal will be directly filled into the mold cavity. When the amount of molten metal filled is large, the molten metal will wait for extrusion in the mold cavity for a long time, and the casting is easy to produce cold separation, and it is also difficult to ensure the precise amount of molten metal. If the indirect squeeze casting method is adopted, because the volume of the casting is large, the squeeze pressure is difficult to transmit The defects are easy to appear at the far end of the sprue. It can be seen from the above analysis that if the direct squeeze casting method or the indirect squeeze casting method are used alone, there are shortcomings in forming large parts. In this paper, a new composite squeeze casting method is proposed according to the squeeze casting characteristics of large parts, and the large parts composite squeeze casting forming equipment is systematically developed to solve the problem of metal melt conveying device and large parts composite in the forming equipment The key technical problems such as the design and manufacture of the die of the combined extrusion casting, and the forming of large-scale and complex parts are realized through the experiments, so as to establish the technical foundation for the research and development of the larger extrusion casting equipment and the forming of various large-scale parts.