The rim is a barrel-shaped metal part with the center of the tire mounted on the shaft.
- Classification by material
According to the material, the wheels are mainly divided into iron wheels and light alloy wheels, and light alloy wheels are mainly made of aluminum alloy and magnesium alloy products. In today’s automotive market, iron wheels are rare, and most models use aluminum alloy wheels and aluminum wheels.
Aluminum alloy materials used in the manufacture of aluminum rims include A356, 6061, etc. Among them, A356 is widely used in cast aluminum wheels. A356 aluminum alloy has the characteristics of small specific gravity and good corrosion resistance. It is mainly composed of aluminum, silicon, magnesium, iron, manganese, zinc, copper, titanium and other metal elements. Aluminum accounts for about 92%. It is a mature aluminum alloy. material.
A356 aluminum ingot, the raw material for manufacturing aluminum alloy wheels ↑↑
- Production process of aluminum alloy wheels
Aluminum alloy rims are more suitable for passenger cars than steel rims. At present, the manufacturing process can be basically divided into three types. The first is casting. Currently, most automobile manufacturers choose to use the casting process. The second type is forging, which is mostly used in high-end sports cars, high-performance cars and high-end modified markets. The third one is more special. It is the MAT spinning technology first put into use by Japan Enkei Company. At present, the application of this technology in China is not as many as the first two.
- Gravity casting method
Gravity casting simply said, mainly relying on the gravity of aluminum melt to fill the mold, which is an early casting method.
The method has low cost, simple process and high production efficiency. However, during the casting process, inclusions are easily involved in the casting, and sometimes gas is also involved, forming pore defects. The wheels produced by gravity casting are prone to shrinkage and shrinkage and poor internal quality. In addition, the limitation of the liquidity of aluminum liquid may also lead to a low-yield wheel with complicated shapes. Therefore, this process is rarely used in the automobile rim manufacturing industry.
- Low-pressure casting method
Low-pressure casting is a process in which molten aluminum is filled into a mold under pressure and solidified and crystallized under pressure. In the same situation, compared with gravity casting, the internal structure of the low-pressure casting hub is denser and stronger. In addition, low-pressure casting utilizes pressure filling and supplementation, which greatly simplifies the structure of the pouring system and enables the yield of molten metal to reach 90%. At present, low-pressure casting has become the first choice for the production of aluminum rims, and most domestic aluminum alloy rim manufacturers use this process. However, the low-pressure casting method also has its shortcomings: long casting time, long time for feeding and changing molds, and large investment in equipment.
- Forging method
Hot forging → RM forging → Cold spinning → Heat treatment → Machine work → Shot blast → Surface finishing
Forging is a solid-to-solid change. The shape of the hub is formed by means such as patting, pressing, and forging. This process does not change the liquid phase, which is a solid change. Therefore, its mechanical properties are higher than those of casting, and it has the advantages of high strength, good corrosion resistance and precise dimensions. The grain flow direction is consistent with the direction of the stress, so the strength, toughness and fatigue strength are significantly better than the cast aluminum rim. At the same time, the typical elongation of forged aluminum wheels is 12% to 17%, so it can well absorb the vibration and stress of the road.
In addition, the surface of the forged aluminum rim has no pores, so it has a good surface treatment ability.
However, the biggest disadvantage of forged aluminum wheels is that there are many production processes and the production cost is much higher than that of casting. Although the performance of forged rims is better, automobile manufacturers still mainly use cast rims on most vehicles, and only a few luxury cars are equipped with forged rims. However, CITIC Dicast, a leading domestic rim manufacturer, has successfully entered the passenger car forged rim production line and compressed the cost of forged rims to a thousand yuan, and has begun to supply domestic joint ventures as the original rims.
- Squeeze casting method
Squeeze casting, also known as liquid die forging, is a process method that combines casting and forging features-pouring a certain amount of metal liquid directly into an open metal mold, and acting on liquid metal with a certain pressure through a punch , So that it is filled, shaped and crystallized, and a certain amount of plastic deformation occurs during the crystallization process. Advantages: The mold filling is stable, the metal crystallizes and solidifies directly under the pressure, so the casting will not produce casting defects such as porosity, shrinkage and shrinkage, and the organization is dense, the mechanical properties are higher than the low pressure casting and the investment is much lower than the low pressure casting method. Disadvantages: As with traditional forged products, milling is required to complete the shape of the spokes. A considerable number of automobile aluminum wheels in Japan have been produced by squeeze casting technology. The entire process from pouring molten metal to removing castings is controlled by a computer, and the degree of automation is very high. At present, all countries in the world regard squeeze casting as one of the production directions of automobile aluminum wheels.
- Special molding: spinning technology
Spinning technology * was first put into use in Japan. Strictly speaking, it should be regarded as a type of casting. It refers to the use of special equipment to rotate and pressurize the stressed place after the overall rim is cast. The molecular arrangement within the location metal has changed, and the specific segmentation surface has a higher density of fibrous shape than the general cast product, thereby changing the overall metal mechanics process. The quality, strength, elongation and other characteristics of the rims manufactured by the spinning technology are close to forged rims, and now it is easier for forged rims to produce. In general, MAT spinning technology can not only ensure the manufacturing cost of the hub, but also make the cast rim have a weight and strength similar to the forged rim. It’s just that the domestic technology is immature and the cost is high, so it is not widely used.