The development of squeeze casting theory

1.Basic theory of squeeze casting

Pressure is one of the most important process parameters in squeeze casting. In squeeze casting, pressure has an important influence on thermophysical parameters, alloy state diagram, nucleation and growth, and microstructure refinement. In the book squeeze casting, the author has carried out effective theoretical deduction. The calculated results are in good agreement with the experimental results. The conclusions and viewpoints are of guiding significance to the researchers engaged in squeeze casting. Luo Shoujing analyzed four plastic flow patterns of metal in direct squeeze casting, namely, the initial metal plastic flow pattern, the basic plastic flow pattern, the final plastic flow pattern and the dense metal flow at the final solidification. The correctness of the theoretical analysis is proved by the observation of the microstructure of the metal plastic flow in the squeeze casting of carbon steel.

Under the condition of different materials and process parameters (specific pressure and holding time), the test curves measured have similarity or the same regularity. Through the comprehensive analysis of the curve, the physical meaning of the force displacement curve is given, which can be used to judge the effectiveness of the squeeze casting process and the internal quality of the extrusion parts. Different quality grades of castings can be obtained by squeeze casting

① At last, the solidification zone consists of crystallization and plastic dense structure under pressure;

② The final solidification zone is only the solidification structure of crystallization under pressure;

③ The final solidification zone is free solidification structure.

The force stroke curve is very important to guide production and obtain high quality castings. In the mechanical analysis of direct squeeze casting process, the theoretical curve of pressure stroke in squeeze casting process gives the analytical formula of specific pressure value, which is meaningful. For indirect squeeze casting, especially for indirect forward squeeze casting, the pressure applied to the liquid metal is from bottom to top, which is opposite to the direction of liquid metal shrinkage. If there is no shrinkage cavity, shrinkage porosity and other defects in the casting, The actual specific pressure applied should be larger than the theoretical value given, that is to say, the self gravity of the liquid metal when it shrinks should be overcome. Therefore, the analytical formula of the specific pressure should be modified.

Based on the analysis of the relationship among solidification, shrinkage, plastic deformation and feeding in the process of squeeze casting, three factors, i.e. mechanical factor F, time factor θ and velocity factor V, are defined, and their specific expressions are obtained. Furthermore, the criterion of no shrinkage cavity in squeeze casting is put forward: F, θ, V are greater than or equal to 1. It is verified that the criterion can be used to guide process design and prevent shrinkage defects.

2.Application of computer in Squeeze Casting

In the study of liquid forging die CAD, the finite difference method is used to simulate the temperature change and solidification process in the process of squeeze casting [8], the computer simulation in the forming process of axisymmetric parts in hydrostatic liquid forging [9], the computer simulation and verification in the solidification process of liquid forging show the process of squeeze casting from different aspects and deepen people’s understanding of the process itself. In the coding design of Squeeze Casting Die CAD, the author provides two coding design methods:

① If the designer is not satisfied with the sketch, he can re-enter the code until the designer is satisfied.

② In the way of man-machine dialogue coding, through computer interaction dialogue, the computer displays the structural sketch of the squeeze casting die until the modification is satisfied; after the coding design is completed, input specific parameters to the simulated squeeze casting drawing to determine the specific dimensions of each part of the squeeze casting die and automatically draw the general assembly drawing and the part drawing of the die.

3.Research on Squeeze Casting Die Technology

Combined with the teaching of die-casting mold, plastic mold, stamping mold and other mold courses, the author has carried out a systematic study on the squeeze casting mold, The following articles were published: “design features and research of indirect squeeze casting die”, “design and research of squeeze casting die for shaker base”, “structural design of liquid forging die for shaker shell”, “design of indirect positive squeeze liquid forging die for rudder surface”, “design of squeeze casting die for crane motor shell” and “design of liquid forging die for upper cover of airport runway center line light”. The book “design of liquid die forging die” compiled by Professor Chen Bingguang is of great reference value to researchers engaged in Squeeze Casting Research and application. Through the continuous measurement of the surface temperature of the squeeze casting, the general model to determine the surface temperature of the casting is obtained by using the lumped parameter and the dimensionless analysis method, which provides the basis for the design and control of the squeeze casting process.

4.Effect of squeeze casting on metal properties

With the increase of extrusion pressure, the number of non-equilibrium eutectic phase decreased, the number of primary phase α increased and refined. Extrusion casting of ZA-27 alloy can greatly reduce the shrinkage defects, increase the density of the alloy, refine and improve the structure, reduce the dendrite segregation, and significantly improve the plasticity and strength.