Thixomolding
Thixomolding emerged as a novel technology for magnesium alloy die-casting in the 1990s, blending die-casting and injection processes. It leverages the rheological behavior of metals within specific temperature ranges. The method closely resembles injection molding.
Molding Process
Initially, magnesium alloy is finely cut into particles via a pellet machine. These particles are loaded into a hopper and propelled into a pellet cylinder. Within this cylinder, a rotating screw propels the magnesium alloy particles toward the mold. The heating component within the particle cylinder employs a combined resistance and induction heating process. The alloy particles are heated to temperatures ranging between 560 to 630°C, forming a thixotropic slurry in a partially molten state. Once the solid phase volume reaches 60%, Argon gas is introduced. The screw-driven alloy, characterized by a dendritic structure, forms a semi-solid alloy with a thixotropic structure. This semi-solid alloy flows under external force and, upon reaching a specific volume, is injected at high speed (approximately 5.5m/s) into a vacuum within the preheated mold cavity, resulting in net-shape or near-net-shape parts.
Fig. 1. Schematic of a Thixomolding machine.
Reproduced from Decker, R., LeBeau, S., 2008. Thixomolding. Advanced Materials & Processing 166 (4), 28–29.
The process for injection molding magnesium alloys
Similar to vacuum die casting, this process results in less porosity and improved fatigue strength over conventional die casting. The thin wall capability (0.5–1 mm) and the similarity with plastic injection molding process have resulted in successful applications of magnesium Thxiomolding in computer and electronics industries
Advantages
In contrast to traditional cold and hot die casting, which yield a 50% product rate alongside waste and byproducts, thixoinjection molding fosters a worker and environment-friendly atmosphere. The production process is clean, safe, and energy-efficient. Gas entrainment during molding is significantly reduced, leading to part porosity of around 0.07%.
When compared to engineering plastics and die casting, magnesium alloy thixoforming excels in producing thinner, lighter, and stronger parts, substantially reducing raw material consumption per formed unit. Moreover, it offers considerable cost advantages.
Magnesium thixoforming has become the preferred technology for manufacturing a diverse array of products across various markets. The burgeoning demand for durable, lightweight products has fueled substantial growth in magnesium alloy thixoforming. It has become an ideal choice for producing automobile components, consumer goods, defense equipment, electronics, handheld devices, and sports equipment.
Thixoforming Processes Innovation
Presently, widely utilized thixoforming processes encompass thixocasting, thixoforging, thixorolling, thixoextrusion, and thixoforming. These different processes present challenges such as microstructure evolution, heating, and exploratory studies on parameters like pouring temperature, mold temperature, mechanical properties, viscosity, and final product quality. Each process offers a diverse range of end product properties, thereby presenting numerous possibilities for component innovation.
Yizhimi's semi-solid magnesium alloy injection molding equipment
The latest magnesium alloy equipment produced by Chinese companies is a 3200-ton semi-solid magnesium alloy injection molding machine. Its most outstanding feature is its injection pressure of up to 100 megapascals, which effectively solves the weakness of large component molding during the semi-solid injection process. The equipment has a high-flow, high-speed response hydraulic system, which brings strong filling capacity. It is equipped with a 160mm screw, and the maximum stable displacement exceeds 11 kilograms. Key parameters such as injection capability, melt supply capability, and clamping force have all reached the global leading level.
The 3200-ton semi-solid magnesium alloy injection molding machine from China
The semi-solid magnesium alloy injection molding machine integrates injection molding and die-casting into a unified "one-piece" molding process. Injection molding is similar to plastic injection molding; magnesium alloy is heated to a near-liquid state near its melting point and then injected into the mold under high pressure. Die-casting is a metal casting process characterized by applying high pressure to molten metal within a mold cavity. After forming, the material cools and solidifies in the mold. Since magnesium alloy is prone to oxidation, oxidation control is necessary during the injection molding process to prevent deterioration of product performance. Therefore, the process is usually conducted under an inert gas atmosphere.
The machine utilizes advanced technologies such as high-speed mold opening and closing, sensor measurement and control, real-time control, and features like remote monitoring, information storage and memory, security keys, and automatic alarms. It is a high-end intelligent equipment that integrates material technology, automatic control technology, internet technology, hydraulic control, and mechanical design. The equipment is mainly used in the production of large key components for new energy vehicles, such as motor parts and the crossbeam of central control dashboards.
With the promotion of new energy vehicles, the rise of new consumer trends driven by high-precision 3C products, outdoor sports products, and medical and health products, as well as the actual needs for energy saving, emission reduction, and green development, magnesium alloy lightweight components are increasingly coming into focus. The semi-solid magnesium alloy injection molding process, with its excellent performance and safety, as well as environmental benefits, is gaining more attention and application.
This mechanical equipment has greatly promoted the more environmentally friendly and efficient production and use of large parts.