All of them are aluminum alloy wheels, why is there such a big difference?

There is a saying in the automotive modification industry that goes, ‘It’s better to be ten pounds lighter on the spring than one pound lighter off the spring.’ Due to the fact that the weight off the spring is related to the response speed of the wheel, upgrading the wheel hub will have a significant impact on the performance of the vehicle in the currently allowed modifications. Even for wheels of the same size, there will be significant differences in their mechanical properties and weight when using different materials and processing techniques. Do you know about various processing techniques for aluminum alloy wheels?

 
Gravity casting
Casting is the most fundamental technique in the metalworking industry. As early as prehistoric times, people knew how to use copper to manufacture weapons and other vessels using casting methods. It is a technology that heats metal to a molten state and pours it into a mold to cool it into shape, and the so-called “gravity casting” is to fill the entire mold with liquid aluminum under the action of gravity. Although this production process is cheap and simple, it is difficult to ensure the consistency inside the wheel rims and is prone to producing bubbles. Its strength and yield are relatively low. Nowadays, this technology has been gradually phased out.

Low pressure casting
Low pressure casting is a casting method that uses gas pressure to press liquid metal into a mold and causes the casting to crystallize and solidify under a certain pressure. This method can quickly fill the mold with liquid metal, and because the air pressure is not too strong, it can increase the metal density without being sucked into air. Compared with gravity casting, the internal structure of low-pressure casting wheels is denser and has higher strength. Low pressure casting has high production efficiency, high product qualification rate, good mechanical properties of castings, high utilization rate of aluminum liquid, and is suitable for large-scale supporting production. At present, most of the mid to low end cast wheel hubs use this process.

 
Spinning casting
Spinning casting is a bit like the drawing process in ceramic technology. It is based on gravity casting or low-pressure casting, and gradually elongates and thins the wheel rim through the rotation of the aluminum alloy itself and the extrusion and stretching of the rotary blade. The wheel rim is formed by hot spinning, with obvious fiber flow lines in the structure, greatly improving the overall strength and corrosion resistance of the wheel. Due to its high material strength, light product weight, and small molecular gaps, it is a highly praised process in the current market.

 
Integrated forging
Forging is a processing method that uses forging machinery to apply pressure to metal billets, causing them to undergo plastic deformation in order to obtain forgings with certain mechanical properties, shapes, and sizes. After forging, the aluminum billet has a denser internal structure, and the forging process can better heat treat the metal, resulting in better thermal properties. Due to the fact that forging technology can only process a single piece of metal blank and cannot form a special shape, aluminum blanks require complex cutting and polishing processes after forging, which are also much more expensive than casting technology.

Multi piece forging
Integrated forging requires cutting a large amount of excess dimensions, and its processing time and cost are relatively high. In order to achieve mechanical properties equivalent to those of integral forged wheels, while reducing processing time and costs, some automotive wheel brands have adopted a multi piece forging processing method. Multi piece forged wheels can be divided into two pieces and three pieces. The former consists of spokes and wheels, while the latter consists of front, rear, and spokes. Due to seam issues, the three piece wheel hub needs to be sealed to ensure airtightness after assembly. There are currently two main ways to connect the multi piece forged wheel hub with the wheel rim: one is to use specialized bolts/nuts for connection; Another way is welding. Although the cost of multi piece forged wheels is lower than that of one-piece forged wheels, they are not as lightweight.

 
Squeeze casting
Forging technology facilitates the processing of complex shaped parts, giving them better mechanical properties, while squeeze casting combines the advantages of both. This process involves pouring liquid metal into an open container, and then using a high-pressure punch to press the liquid metal into a mold, filling, forming, and cooling it to crystallize. This processing method effectively ensures the density inside the wheel hub, with mechanical properties close to those of an integral forged wheel hub, and at the same time, there is not too much residual material that needs to be cut. At present, a considerable number of wheel hubs in Japan have adopted this processing method. Due to the high degree of intelligence, many companies have made squeeze casting one of the production directions for automotive wheel hubs.