With the needs of the development of the automobile industry, aluminum alloy wheels are developing in the direction of large diameter, light weight, and beautiful appearance. Forged aluminum alloy wheels have the advantages of light weight and beautiful appearance, and are widely used in important automobile parts. However, the current level of production technology of aluminum alloy wheels in my country is not mature, and there are certain defects, which directly affect the development of the automobile industry. Therefore, this article starts from the characteristics of forged aluminum alloy wheels, analyzes the defects of forged aluminum alloy wheels and the detection methods of main defects, and provides technical support and reference for the development of good quality aluminum alloy wheels.
The wheel hub is a force-transmitting element of the automobile, which plays the role of bearing, steering, driving, braking, etc., and its structure is complicated. The manufacturing method of this part generally selects the forging method. The high performance of wheels and their selection of materials are constantly changing. In recent years, forged aluminum alloy wheels have been widely used and have shown the advantages of light weight. From forging processed workpieces to qualified auto parts, many errors will inevitably occur, leading to some defects in forged aluminum alloy wheels, which require further research and improvement of production technology. 1 Features of forged aluminum alloy wheels
1.1 Good heat dissipation Due to the large heat capacity of aluminum, the thermal conductivity of aluminum alloy occupies an important position in metal materials, and this is of great significance to the increase of vehicle speed. Due to the high thermal conductivity of aluminum alloy, it can quickly dissipate the frictional heat of the tire and reduce the heat of the tire, that is, reduce the squeezing work of the tire, thereby helping to reduce the wear of the tire, and also by reducing the heat of the brake device. Load can extend the life of tires and improve the safety of car driving.
1.2 Lightweight Forged aluminum alloy has a lower density. Compared with steel wheels of the same size, forged aluminum alloy wheels are lighter in weight, strong and durable. When the car is running, the light weight causes the inertia to increase, which reduces the acceleration and braking functions of the car, especially when the car is driving in a curve, it can reduce the centrifugal force acting on the wheel hub, and the higher strength is less In order to reduce the energy consumption of the car, the use of aluminum alloy wheels improves the overall performance of the car.(1) Easy to process. Due to the low melting point of aluminum alloy, it has good forgeability, good cutting performance, beautiful shape and easy processing. In actual production, it can be easily processed into a standard wheel hub shape and appearance according to customer requirements, and has high-precision geometric dimensions.(2) It has certain economic benefits. With the advancement of science and technology in my country, it is easier to obtain aluminum. The continuous maturity and development of aluminum alloy wheel production technology has led to lower prices. Moreover, the use of aluminum alloy wheels greatly reduces the weight of the car compared with other materials, so the car is reduced. The cost of production has brought higher economic benefits. 2 Research on the defects of forged aluminum alloy wheels
In actual production applications, it is found that forged aluminum alloy wheels are prone to the following defects: (1) Folding: Folding is the most destructive defect for forged aluminum alloy wheels. After this defect occurs, the wheel becomes a waste product. In actual production, it is found that 60%-70% of the waste product is due to folding. The main reasons for folding are: the shape of the wheel hub forging is relatively complicated, especially the shape and size of the cross section change too much, which causes the metal flow trajectory to be complex and changeable; the preform and pre-forging are not used in the production, and the direct forging process is too complicated. ; The design of the preform and the pre-forging die is unreasonable; during forging, operation errors, uneven lubrication, and too fast pressing speed.
(2) Overburning: This is a very common defect during heat treatment, mainly due to the limitation of the heating temperature of aluminum alloy forging. When the quenching temperature is very close to the eutectic melting temperature of the alloy, aluminum alloy forgings are prone to overburning. The main manifestation of overburning is that the surface is dark and easy to have bubbles. The overfired billet can be processed again but only once, and the overfired billet cannot be used as a defective product.
(3) Large grains: mainly appear on special parts of forgings, such as the surface of the wheel hub, the parts with small deformation and large size of the forging, the area with large deformation, and the vicinity of the flash area.
(4) Cracks: The main causes are insufficient heating of the billet, insufficient holding time, forging temperature is too high or too low, the degree of deformation is too high, the deformation speed is too high, and the bending and folding generated during the forging process are not eliminated in time. Forging, surface cracks may occur. At the same time, the die and the forging equipment are not preheated, or the preheating temperature is not enough, it may cause cracks in the forged aluminum alloy wheel.
(5) Irregular streamlines, eddy currents and penetrating flow: The causes are basically the same as folding, and they are also caused by metal convection or flow turbulence, but in some parts, even though there are streamline irregularities and vortex phenomena, they have not been developed to As serious as folding. Through flow and eddy current significantly reduce the plastic index, fatigue performance and corrosion resistance.
(6) Mold sticking and peeling: Aluminum alloy is soft and easy to stick due to its low density at a certain temperature, which will cause the wheel hub to peel and cause the surface to be rough, and even affect the entire production process due to the lack of mold release. The cause of the sticky mold defects of the forging blank is caused by insufficient lubrication of the forging or failure of the lubricant. The incidence of this defect is low, and the control method of this defect has been studied.
3 Detection methods for defects of forged aluminum alloy wheels
According to a lot of practical experience, the detection methods of forged aluminum alloy wheel hub defects have been researched and analyzed, and the following detection methods have been summarized.
3.1 Visual inspection method This is the most intuitive method to detect wheel hub defects. The visual inspection method is mainly for the detection of large cracks caused by folding or internal defects of the blank during production. Because the cracks are large, visual inspection can be found. Normally The geometric length of the crack is about 30-50 cm. The visual inspection method is intuitive and reliable. Through this method, we can find defective products in time, avoiding defective products from entering the next process, wasting production costs, or even interrupting production. In production, this visual inspection method puts forward higher professional quality requirements for technicians. They must not only have professional quality inspection technology, but also have a relatively strong sense of responsibility and a good working attitude. Each product is inspected one by one. So as not to affect production.
3.2 Ultrasonic testing method Ultrasonic testing is a relatively new detection method applied this year. This method is simple to monitor, safe and environmentally friendly, and has high economic efficiency. It mainly uses the propagation of ultrasonic vibration in the medium to detect whether there are defects in the wheel hub according to the fluctuation curve of mechanical vibration. It has the advantages of quantitative, accurate and qualitative description, but the technical application is not mature and needs to be further improved.
3.3 Eddy current flaw detection method This method mainly detects whether there are defects on or near the surface of the wheel hub. It uses the magnetic field generated by the alternating current around the coil to detect. During the detection, the coil will move along the surface of the hub, and the corresponding high-frequency current will be generated in the hub. This is the eddy current. The change of the induced vortex flow inside the hub is used to evaluate the defects of the hub. This detection process is also a process using the principle of electric induction and ultrasonic detection.
