What are the problems with technology and alu alloy panels for automobiles?
What are the problems with technology and aluminum alloy panels for automobiles?
With the development of the modern automobile industry and China's increasingly stringent requirements in terms of energy, environmental protection and safety, the application of aluminum alloy sheets in the field of automobile manufacturing can be effectively saved by improving the light weight of automobiles and saving fuel consumption and reducing displacement. It is also more and more extensive. Aluminum has the advantages of low density, light weight, good moldability, recyclability, energy saving and environmental protection, as well as improved vehicle driving performance and safety and comfort performance, reduced fuel consumption, reduced emissions and reduced environmental pollution. As a result, aluminum alloys are recognized as one of the ideal materials for future cars.
First, the application of aluminum alloy on the car body
At present, 12% to 15% of the world's aluminum consumption is used in the automotive industry, and some developed countries have more than 25%. In 2002, the entire European automotive industry consumed more than 1.5 million tons of aluminum alloy in one year, of which about 250,000 tons were used for body manufacturing, 800,000 tons for automotive transmission systems, and another 428,000 tons for automobile driving mechanisms. And suspension mechanism. It can be seen that the automobile manufacturing industry has become the most important consumer of aluminum materials.
Second, the process requirements of aluminum alloy stamping sheet in stamping
(1) Aluminum alloy sheet forming and mold process requirements
After investigation, the forming process of aluminum alloy is consistent with that of the cold plate. It can reduce the amount of scrap knives and increase the production of aluminum swarf by increasing the number of processes, but the mold requirements are different from those of the cold plate.
(2) Precautions for long-term storage of aluminum alloy sheets
1 The post-yield strength of aluminum sheet failure hardening increases, and the edge processing property is reduced. When the mold is made, it is considered to use the upper limit material that meets the specification requirements, and the feasibility confirmation is made before production;
2 The drawing oil/rustproof oil used for production is easy to volatilize, and the sheet material should be used immediately after opening, or cleaned and oiled before stamping;
3 The surface is easily oxidized and cannot be placed in the open air. Special management (packaging) is required.
Third, the process requirements of aluminum alloy stamping plate parts in welding
The main processes in the process of welding aluminum alloy body are resistance welding, CMT cold transition welding, tungsten argon arc welding, riveting, rushing and polishing.
(1) Aluminum alloy plate parts without riveting connection process
The non-rive joint of the aluminum plate is formed by cold extrusion of two or more metal sheets by pressure equipment and special molds, and then forms an internal mosaic joint with certain tensile and shear strength. The thickness of the connecting plates may be the same or different, and may have an adhesive layer or other intermediate layers, and the materials may be the same or different. The connection is good and no auxiliary connectors are required.
(2) Aluminum alloy parts punching and riveting connection process
The punching and riveting connection of the aluminum plate parts is to use the punching and riveting equipment to press the punching rivets into the connected materials to form a stable, firm and beautiful connection point. Features of the punching and riveting process:
1 High-strength, shear-resistant and tensile strength, fatigue resistance, and impact resistance are higher than or equal to the strength of the spot welding joint;
2 can visually measure the quality of the connection. The rivet is completely driven into the workpiece, and a convex joint is formed on the other side of the connected workpiece, which is considered to be qualified;
3 The material to be connected does not need to be drilled beforehand, and the process is simple;
4 The connection point is sealed and will not enter the gas or liquid, causing corrosion of the material;
4 pairs of metal, non-metal, different materials, different thickness, different strength of metal can be connected.
(3) Resistance welding
At present, the resistance welding of aluminum alloys generally adopts medium frequency or high frequency resistance welding technology. This kind of welding process only melts the base metal in a very short time and forms a molten pool in a very short time, and the welding point is rapid. Cooling forms a connection, and the possibility of producing aluminum-magnesium dust is extremely small. Most of the welding fumes produced are oxide particles of metal surfaces and surface impurities. During the welding process, there is a local exhaust at the station, which can discharge the particles into the atmosphere through the air cylinder in time, and basically no deposition of aluminum-magnesium dust is generated.
(4) CMT cold transition welding and argon arc welding
These two kinds of welding processes, due to the protection of inert gas, have insufficient contact between the molten metal and oxygen at high temperatures, and under the action of the arc jet, they can produce aluminum-magnesium metal particles with small particle size and splash into In the working environment, the deposition of aluminum-magnesium dust is formed, and there is a danger of explosion of aluminum-magnesium dust, which requires prevention and treatment of dust explosion.
Fourth, the process requirements of aluminum alloy stamping plate on the edge of the roll
(1) The aluminum alloy roll side press is different from the cold plate roll side. The toughness of aluminum is not as good as that of steel. When pressing, the pressing force should not be too large, and the pressing speed is relatively slow, generally 200~250mm. / s, each press angle can not be greater than 30 °, not V-shaped press;
(2) Aluminum alloy pressing and temperature requirements: at 20 ° C room temperature, the parts just taken back from the cold storage should not be pressed immediately.
Five, aluminum alloy stamping plate parts roll form and characteristics
(1) Aluminum alloy stamping sheet roll edge form
1 Ordinary pressing is divided into three steps: first pre-compression, secondary pre-compression, and final pressure. Usually used when there is no special strength requirement and the flange angle of the outer panel is normal;
2 European press, as shown in Figure 3, is divided into the first pre-compression, the second pre-compression, the final press, the European press 4 steps. Usually used for long side presses, such as front and back covers. European style press fit can also be used to reduce or eliminate surface defects.
(2) Roller edge characteristics of aluminum alloy stamping sheet
The bottom mold and insert of the aluminum press-bonding equipment, with 800-1200# sandpaper, regularly polish and maintain the bottom mold and insert to ensure that there is no aluminum scrap on the surface.
Six, various reasons for defects caused by the edge of aluminum parts
Various reasons for defects caused by the edge of the aluminum sheet are shown in the table.
Table A variety of reasons for defects caused by the edge of the aluminum parts
Seven, the process requirements of aluminum alloy stamping plate on the coating
(1) Principle and function of water washing passivation of aluminum alloy stamping plate
Water-washing passivation refers to the formation of an oxide film and oil stain naturally formed on the surface of the aluminum member, and a dense oxide film is coated on the surface of the workpiece by a chemical reaction between the aluminum alloy and the acidic solution. After the stamping, the oxide film on the surface of the aluminum part, the oil stain welding and the glue coating will have an influence. In order to improve the adhesion between the glue and the weld, it is necessary to maintain a long-lasting adhesive connection and resistance stability of the surface by means of a chemical process to achieve better welding. . Therefore, all parts that require laser brazing, cold metal transition welding (CMT) and other welding require water wash passivation.
(2) Aluminum alloy stamping plate parts washing passivation process
The water washing passivation device is composed of a degreasing zone, an industrial water washing zone, a passivation zone, a clean water washing zone, a drying zone, and an intake and exhaust system. The aluminum parts to be treated are placed in a washing basket, fixed and lowered into a sink. In a tank containing different solvents, the parts are repeatedly washed by all working solutions in the tank. All tanks are equipped with a circulation pump and nozzles to ensure that the bath can flush all parts evenly. The water washing passivation process is: degreasing 1 → degreasing 2 → washing 2 → washing 3 → passivation → washing 4 → washing 5 → washing 6 → drying, aluminum casting can omit washing 2 .
(3) Aluminum alloy stamping plate parts washing passivation drying process
1 The temperature of the part is raised from room temperature to 140 °C for about 7 minutes, and the time for gel hardening is 20 minutes.
2 aluminum parts rise from room temperature to holding temperature for about 10min, aluminum holding time is about 20min, aluminum parts from the holding temperature to the part temperature of 100 °C cooling time of about 7min, after the end of the insulation, cooling to room temperature, therefore, the overall aluminum The drying process was 37 min.
Eight, the conclusion
Hyundai Motor is developing in the direction of light weight, high speed, safety and comfort, low cost, low emission and energy saving. The development of the automobile industry is closely related to energy, environmental protection and safety. With the increasing awareness of environmental protection, aluminum alloy sheets have unparalleled superiority in cost, manufacturing technology, mechanical properties, sustainable development, etc. Therefore, aluminum alloy will become the preferred lightweight material in the automotive industry. .
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