The main function of squeeze casting die in the forming process is to complete the liquid metal forming and ensure the forming accuracy and part performance index. Due to the technical details involved, there are few relevant foreign materials. In China, the design of squeeze casting die has been improved continuously. The references that have reference value for the design of squeeze casting die for large castings are mainly reflected in the floating structure of the die, the improvement of quantitative filling accuracy through the die, and the improvement of parts performance by using the die structure to increase the extrusion effect.
The floating die structure can realize the simultaneous pressure up and down or radial pressure to increase the extrusion effect. Yandesheng et al. Used the floating structure (as shown in Figure 1) to realize the simultaneous pressure up and down of the bearing cover casting to improve the product performance; Hanzhiqiang et al. Used the floating lower die (as shown in Figure 2) to generate radial pressure on the inner ring of the cylinder liner through the mandrel with conical surface. The characteristics of these two patents are that two or more springs are used to support the floating structure. However, in actual production, due to the stiffness error of the spring itself and the change of the elastic coefficient at different temperatures, the elastic support force is uneven, resulting in higher requirements for the guiding accuracy of the floating structure. When the casting is large, it is difficult to ensure a smooth movement. Therefore, when designing the squeeze casting die for large parts, the floating structure can be used for reference to improve the elastic support.
The hydraulic floating die adopts the form of lower hydraulic cylinder to support the floating structure, as shown in Figure 3. The demoulding process of the structure and the oil circuit design of the lower hydraulic cylinder are complex. In the extrusion process, it is necessary to accurately ensure the action coordination of the upper die, the floating structure and the lower hydraulic cylinder.
In terms of improving the accuracy of quantitative filling, gaomingdeng and others invented an extrusion die structure with overflow channel and overflow cavity (as shown in Figure 4). The die is provided with overflow channel and overflow cavity at the position corresponding to the highest position of the part. Because the overflow scheme is adopted, by determining the distance between the overflow channel and the highest point of the part, the excess liquid metal can flow into the overflow chamber to realize the quantitative filling and forming of the part liquid metal, so as to achieve the near net shape of the part. The mold can relax the operator’s control over the filling amount of molten metal, and has the effects of reducing human factors, saving equipment investment, improving production efficiency, reducing physical labor and reducing manufacturing costs. It is suitable for small batch production and trial production.
Feiliangjun et al. Invented a squeeze casting die structure that can be partially pressurized (as shown in Figure 5). A pressurization system consisting of a pressurization channel, a pressurization punch and a pressurization cylinder is set at the thick wall hot joint of the casting on one side of the casting cavity. The pressurization system and the extrusion piston realize real-time control through the circuit system. By controlling the sectional area of the pressurization punch, the pressurization distance and the pressurization start time, The molten metal in the pressurization channel is filled into the hot spot of the thick wall of the casting to avoid the casting problem of loose shrinkage cavity at the thick wall and improve the density of the internal structure of the whole casting, so as to improve the quality of the casting and reduce the scrap rate.
Zhangsangen et al. Invented a die structure that can realize multiple extrusion (as shown in Figure 6), which is formed between each extrusion punch and the moving die or fixed die δ Sliding fit of clearance, and the extrusion punch is connected with a die locking mechanism. In the die locking state, each extrusion punch has a forging amount of H distance, which can realize multiple extrusion in multiple directions and double extrusion up and down at the same time. Because the molten metal solidifies rapidly in the mold cavity, the second extrusion process is equivalent to forging, so it requires a large pressure.
The design and manufacture of die for composite squeeze casting of large parts is also a very important research content of this paper. Selecting a large wheel hub with a single weight of about 60kg as the forming specimen, and designing and manufacturing a mold that meets the forming requirements is an important prerequisite to achieve the research goal.