The cold chamber die casting, hot chamber die casting and other processes such as vacuum die casting cannot solve the safety and environmental problems in the die casting industry. The Semi Solid Metal casting process is a variant of die casting and is used to mold casted alloy featuring thin wall components of up to 2 millimeters thick. In this method, the selected non-ferrous metals such as copper, aluminum, or magnesium get cast inside a cool chamber, instead of a hot chamber.
Semisolid metal forming (SSM semisolid metallurgy) combines the advantages of casting and forging, and is named after the fluid thixotropic property, which is the phenomenon that allows this process to work. Simply, thixotropic fluids flow when sheared, and thicken when standing. The potential for this type of process was first recognized in the early 1970s by MIT researchers. There are four semisolid metal casting processes being used today: thixomolding, thixocasting, rheocasting, and stress induced melt activation (SIMA).
Semi-solid metal casting maintains all the advantages of diecasting, while eliminating all (or most) of the residual porosity, thereby producing high-quality, thin-walled castings with excellent mechanical properties. Instead of using a fully liquid metal to produce the castings, semi-solid casting uses a high-viscosity feed material that is about 50% solid and 50% liquid.
There are a number of different techniques to produce semi-solid castings. The special structure of semi-solid structure gives it special advantage. For aluminum alloys the more common processes are thixocasting and rheocasting. Other process such as strain induced melt activation (SIMA) can also be used with aluminum alloys, although are less common commercially. With magnesium alloys, the most common process is thixomolding.
● Castings can be produced without splashing, oxide formation and entrapment of air, as long as the rheocasting process is carefully chosen.
● The viscous semi-solid alloy flows only when forced, and will not cascade into lower cavities of the die.
● High pressures (up to 100 MPa) can allow the complete feeding of solidification shrinkage porosity.
● SSM cast products have exceptional soundness, and therefore have excellent strength, ductility and fatigue resistance, and are fully weldable.
● The fast cavity-filling time allows semi-solid alloys to fill extremely thin sections (2- 3 mm and less), minimizing casting weight.
● SSM reduces cycle time, thereby maximizing productivity.
● SSM significantly extends tool life, so a die life of hundreds of thousands of shots is possible.
Semi-solid processing is ideally suited for the production of large volume die casting components, including light weight, high strength components for automobiles. For aluminum alloys typical parts include engine suspension mounts, air manifold sensor harness, engine blocks and oil pump filter housing. For magnesium alloys, semi-solid casting is typically used to produce extremely thin walled castings, such as frames for consumers device and camera bodies. Because of this the process can be applied to mass production.
Our development plan for Semi-solid metal casting:
● 2021 - Vacuum-assisted systems will be coupled to all Al and Mg die casting machines. SinoForming will begin Magnesium Thixomolding and Squeeze casting in 2021.
● 2022 - Begin Rheocasting of Aluminum Alloys.
● 2023 - Begin Thixocasting of Aluminum Alloys.