Development Status and Prospect of Die Casting Technology (Part Two)

Develop new die casting equipment and its control systems.
Die casting is a process of making molten metal fill the cavity of the mold at the high speed under high pressure, and it is a complicated process of dynamic thermodynamics. On the one hand, die casting can produce castings with the complex thin wall, beautiful appearance and high precision. On the other hand, the general die casting process is hard to reach the requirements of the laminar filling and then will get gases and inclusions into the cavity. The workpiece which can have the compact structure and the heat treatment can not be produced, and the mechanical property of the workpiece will also be affected. If we reduce the speed of filling to improve the filling state of molten metals, those advantages brought by die casting production must be sacrificed, and the method of reducing the speed may not work for workpieces with thin walls. At the same time, die casting parts with the high quality, thin walls and without blow holes can be obtained through die casting, which makes die casting much more superior to other processes. 

In order to improve the competitiveness, the requirements of the wall thickness, which is a flexible index, are also becoming higher. The wall thickness of the cars' bodies in the 1980s is 2mm and it became 0.5mm in 2000. The wall thickness of the die casting parts was 2mm in the 1960s, 1mm in the 1970s, 0.7mm in the 1980s and 0.3 to 0.5mm in the 1990s.

Compacted thin-walled castings are produced based on the condition of enough metal pressure and short filling time, in other words, filling the cavity with the high flow rate of the flow gate and enough metal pressure in a very short time. It requires die casting machines to generate the high injection speed and metal pressure at the same time. According to the technological requirements of castings, die casting machines need to provide certain injection energy so as to have mold filling with high energy. To get compacted castings that have the wall thinner than 0.75mm, die casting machines with injection energy over 550 kW·h are needed.

Mold filling with high energy can adjust various technological parameters so as to produce die casting with high quality. Mold filling with high energy is the development direction of the die casting machine's injection system. For one die casting machine to have high filling energy, we should reduce energy losses caused by all kinds of frictional resistances, partial resistances, and inertia forces, that is, reducing the pressure drop. 

In addition, the advancement of die casting machines mainly reflects in the stability and reproducibility in production. But in the process of die casting, there are so many variables that will affect the stability. Static factors such as the working condition of die casting machines and molds, and the pressure of the accumulator are unchangeable after processing equipment is selected.