In low-pressure casting, the mold is placed on a closed furnace, and a tube (called a riser tube) is connected to the metal liquid in the furnace. If pressurized air is added to the metal surface of the furnace, the molten metal will flow from the riser into the cavity. After the molten metal is solidified, the compressed air in the furnace is released, and the unsolidified metal flows back from the riser to the furnace. By controlling the pressure and velocity of the air flowing into the furnace, it is possible to control the speed and pressure of the metal flowing into the cavity and to allow the metal to solidify under pressure. The characteristic of this process is that the casting is crystallized under pressure, the structure is compact, the mechanical property is good, and the metal utilization rate is high.
The low-pressure casting process is now quite mature in mainland China and is suitable for production management. It has been recognized by all OEMs as the mainstream process of aluminum alloy wheel manufacturing in China. The products are mainly sold to OEMs and overseas retail markets.
The aluminum alloy wheel hub manufactured by the low-pressure casting process, because the spokes are finally cooled and solidified, the spokes of some special modeling hubs are prone to shrinkage and other quality problems, and the rim portion is better in strength due to the earliest crystallization.
Squeeze casting, also known as liquid die forging, is a new process that combines the characteristics of casting and forging. The process involves pouring a certain amount of metal liquid directly into the open metal mold and applying a certain pressure through the punch. On the liquid metal, it is filled, shaped and crystallized, and a certain amount of plastic deformation is generated during the crystallization process. Squeeze casting has a smooth filling pattern, no turbulent flow and no enveloping gas, and the metal crystallizes directly under pressure, so castings do not produce casting defects such as pores, shrinkage cavities and shrinkage, and the structure is dense, grain refinement, mechanical properties Higher than low pressure castings. The product has excellent mechanical properties close to forgings, high efficiency and high precision for precision forming of precision castings, and the investment is much lower than that of low pressure casting. The disadvantage is that liquid die forged products, like traditional forged products, require milling to complete the spoke shape.
A considerable number of automotive aluminum wheels in Japan are produced by extrusion casting. Toyota has more than a dozen fully automatic extrusion casting equipment. Each piece of equipment can produce one aluminum wheel in less than 2 minutes, from pouring molten metal to taking out The entire process of casting is controlled by a computer, and the degree of automation is very high. The country has also built a modern extrusion-casting automobile aluminum alloy wheel factory in Guangdong. It has produced a variety of specifications and models of automotive aluminum wheels. The quality of the products has reached the advanced level of similar foreign products. At present, extrusion molding is one of the directions in the production of automotive aluminum wheels.
The casting spin is divided into two processes: "low pressure casting + spinning" and "gravity casting + spinning". At present, Korean car companies have adopted the trend of “low pressure casting + spinning” for the forming process of aluminum wheels. Some other cars have demand for this process. This process is the mainstream process in the spinning process, making OEM products. Most of the enterprises use this kind of technology; at the same time, a small number of enterprises doing overseas retail market adopt the process of “gravity casting + spinning”. In theory, this technology is a pass, it really puts The advantages of the two processes of gravity casting and spinning are combined and the product quality is improved. However, since the blank is produced by the gravity casting process, the economics of the process are very poor and the production cost is high. In short, the cast product, because the spoke portion is cast, has the same advantages and disadvantages as the product produced by the casting process; and the rim portion is spun out, so the airtightness is good. Casting products can theoretically reduce weight, but the effect is not obvious in practical applications.