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A wheel hub is a barrel-shaped, internal component of t […]
A wheel hub is a barrel-shaped, internal component of the tire that is used to support the tire and is centered on a shaft. Common automobile wheels include steel wheels and aluminum alloy wheels. Steel wheels have high strength and are often used in large trucks; however, steel wheels are heavy and have a single shape, which is not in line with today's low-carbon and fashionable concepts, and is gradually being replaced by aluminum alloy wheels. At present, the original wheels of passenger cars on the market are basically aluminum alloy wheels.
The production process of aluminum alloy wheels mainly includes the following:
Metal mold gravity casting refers to a casting method in which liquid metal fills a metal mold by gravity to obtain a casting under normal pressure, which is also an ancient casting method. Because the liquid metal cools faster in the metal mold, the casting is denser than the sand casting. The method is simple in process, high in production efficiency, low in equipment investment, and low in production cost. It is suitable for small and medium-scale production. However, the internal quality of the aluminum hub produced by this method is poor, and the shrinkage and shrinkage are serious. During the casting process, inclusions such as oxide film and slag are easily involved in the casting, and sometimes they are also involved in the gas to form pore defects. The yield is also low. Most OEMs have now rejected the wheels produced by this process, and there is a tendency to be marginalized in the aluminum wheel manufacturing industry.
Low pressure casting
Low-pressure casting is to place the mold on a closed furnace, and a tube (called a riser) is connected to the metal liquid in the furnace below the cavity. If pressurized air is added to the liquid metal surface in the furnace, the liquid metal will flow into the cavity from the riser tube. After the liquid metal solidifies, the compressed air in the furnace chamber is released, and the unsolidified metal flows back into the furnace from the riser tube. By controlling the pressure and speed of the air flowing into the furnace, you can control the speed and pressure of metal flowing into the cavity, and allow the metal to crystallize and solidify under pressure. This process is characterized by castings crystallized under pressure, dense structure, good mechanical properties and high metal utilization.
The low-pressure casting process is now quite mature in mainland China, suitable for less-manufactured production management. It has been recognized by all OEMs as the current mainstream process in the manufacturing of aluminum alloy wheels in mainland China. The products are mainly sold to OEM and overseas retail markets.
Aluminum alloy wheels manufactured by low-pressure casting process, because the spokes are finally cooled and solidified, the spokes of some specially shaped hubs are prone to quality problems such as shrinkage, and the rim part has better strength due to the earliest crystallization.
Squeeze casting method
Squeeze casting, also known as liquid die forging, is a new process that integrates casting and forging features. This process is to pour a certain amount of metal liquid directly into an open metal mold, and use a certain pressure with a punch On liquid metal, it is filled, shaped and crystallized, and a certain amount of plastic deformation occurs during the crystallization process. The squeeze casting has stable filling, no turbulence and no entrapped gas, and the metal is directly crystallized and solidified under pressure, so the casting will not produce casting defects such as porosity, shrinkage and shrinkage, and the structure is dense, grain refinement, and mechanical properties Higher than low pressure castings. The product not only has excellent mechanical properties close to forgings, but also has the high efficiency and high precision of precision castings for one-time precision forming, and the investment is much lower than the low-pressure casting method. The disadvantage is that liquid die forging products are the same as traditional forging products, which require milling to complete the shape of the spokes.
A considerable part of automobile aluminum wheels in Japan have been produced by squeeze casting process. Toyota Motor Corporation has more than a dozen fully automatic squeeze casting equipment, each of which can produce an aluminum wheel in less than 2 minutes, from pouring molten metal to removing The whole process of casting is controlled by computer, and the degree of automation is very high. China has also built a modern squeeze casting automobile aluminum alloy wheel factory in Guangdong. It has produced a variety of specifications and models of automobile aluminum wheels. The quality of the certified products has reached the advanced level of similar foreign products. At present, all countries in the world regard squeeze casting as one of the production directions of automobile aluminum wheels.
Cast spinning is divided into two processes: "low pressure casting + spinning" and "gravity casting + spinning". At present, Korean car companies have a tendency to adopt "low-pressure casting + spinning" for the molding process of aluminum wheels, and some products of other car systems also have demand for this process. This process is the mainstream process in the casting and spinning process and is used as an OEM product. Most of the companies use this process; at the same time, a small number of companies in the overseas retail market use the "gravity casting + spinning" process. In theory, this process is feasible, it really The advantages of gravity casting and spinning are combined, and the product quality is improved. However, because the blank is produced by gravity casting, the economics of this process are very bad and the production cost is very high. In short, the cast-spinning product has the same advantages and disadvantages as the product produced by the casting process because the spoke part is cast; and the rim part is spun out, so the airtightness is better. The weight of the product can be reduced in theory, but the effect is not obvious in practical application.
Forging is one of the earlier forming processes for aluminum wheels. Forged aluminum wheels have the advantages of high strength, good corrosion resistance, accurate dimensions, and small processing volume. In general, their weight is only equivalent to 1/2 or less of the same size steel wheels. The grain flow direction of the forged aluminum hub is consistent with the direction of the stress, and its strength, toughness and fatigue strength are significantly better than that of the cast aluminum hub. At the same time, the performance has good reproducibility, almost every wheel has the same mechanical properties. The typical elongation of forged aluminum wheels is 12% ~ 17%, so it can absorb the road vibration and stress well. Usually cast wheels have a relatively strong ability to withstand compressive forces, but the ability to withstand impact, shear and tensile loads is far less than forged aluminum wheels. Forged wheels have a higher strength to weight ratio. In addition, the forged aluminum hub has no pores on the surface, so it has a good surface treatment ability, which not only can ensure uniform coating, reliable combination, but also good color. 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.
Casting and forging method
It is a method of using castings as blanks in the forging process and plastically processing them. Because forging is used as the final forming process of parts, it can eliminate casting defects, improve the structure of products, and greatly improve the mechanical properties of products compared with castings. At the same time, it takes full advantage of the casting process in forming complex parts, making the shape complex The product forging process is reduced, the material utilization rate is greatly improved, and the production cost is reduced. Casting and forging technology is used to produce aluminum wheels, its performance can fully reach the mechanical performance index of forgings, but the production cost can be reduced by 30% compared with ordinary forgings.
Semi-solid die forging process
The so-called semi-solid die forging is the process of heating the semi-solid billet to a semi-solid state with about 50% of the liquid phase in a semi-solid state to obtain the required close-sized finished parts. This is a process between solid forming and A new process between liquid forming.
The advantages of semi-solid die forging: the parts shrink less in the mold, which is easy to be finalized, and the amount of machining is reduced; the surface of the semi-solid die forging is smooth and smooth, the internal structure is dense, the grain is fine, and the mechanical properties are higher than that of die casting and extrusion Castings; forming is not easy to entrap air, macro pores and micro-loose are much less than those in conventional castings; forming temperature is low, mold life is long.
In the past 10 years, semi-solid forming technology has been widely used abroad, and it has gradually become a new field of development in advanced industrial countries. It is called a new generation of emerging metal forming technology in the 21st century by experts and scholars. The use of semi-solid die forging instead of low-pressure casting to produce ZL101 aluminum alloy wheels can not only reduce the amount of machining and increase productivity, but also improve mechanical properties and reduce quality.
Compared with high-end forming technology, the advantage is that the product has good internal quality and the product strength is high quality and light; the disadvantage is that the equipment cost is high, and the spoke shape of the product manufactured by the traditional forging process can only be completed by milling, the metal utilization rate is low and the production efficiency is not high. Forging is divided into traditional forging and rolling forging, which can directly forge the shape of the spokes.