1 The application of aluminum alloy in the automotive industry
Currently, more than 12% to 15% of the world’s aluminum consumption is utilized by the automotive industry, with some developed countries exceeding 25%. In 2002, the entire European automotive industry consumed over 1.5 million metric tons of aluminum alloy in a year. Approximately 250,000 metric tons were used for body manufacturing, 800,000 metric tons for automotive transmission system manufacturing, and an additional 428,000 metric tons for manufacturing vehicle drive and suspension systems. It is evident that the automotive manufacturing industry has become the largest consumer of aluminum materials.
2 Technical Requirements for Aluminum Stamping Sheets in Stamping
2.1 Forming and Die Requirements for Aluminum Sheets
The forming process for aluminum alloy is similar to that of ordinary cold-rolled sheets, with the possibility of reducing waste material and aluminum scrap generation by adding processes. However, there are differences in die requirements compared to cold-rolled sheets.
2.2 Long-Term Storage of Aluminum Sheets
After aging hardening, the yield strength of aluminum sheets increases, reducing their edge-forming processability. When making dies, consider using materials that meet the upper specification requirements and conduct feasibility confirmation before production.
The stretching oil/rust preventive oil used for production is prone to volatilization. After opening the sheet packaging, it should be used immediately or cleaned and oiled before stamping.
The surface is prone to oxidation and should not be stored in the open. Special management (packaging) is required.
3 Technical Requirements for Aluminum Stamping Sheets in Welding
The main welding processes during the assembly of aluminum alloy bodies include resistance welding, CMT cold transition welding, tungsten inert gas (TIG) welding, riveting, punching, and grinding/polishing.
3.1 Welding without Riveting for Aluminum Sheets
Aluminum sheet components without riveting are formed by cold extrusion of two or more layers of metal sheets using pressure equipment and special molds. This process creates embedded connection points with a certain tensile and shear strength. The thickness of connecting sheets can be the same or different, and they can have adhesive layers or other intermediate layers, with materials being the same or different. This method produces good connections without the need for auxiliary connectors.
3.2 Resistance Welding
Currently, aluminum alloy resistance welding generally uses medium-frequency or high-frequency resistance welding processes. This welding process melts the base metal within the diameter range of the welding electrode in an extremely short time to form a weld pool,
welding spots quickly cool to form connections, with minimal possibilities of generating aluminum-magnesium dust. Most of the welding fumes produced consist of oxide particles from the metal surface and surface impurities. Local exhaust ventilation is provided during the welding process to quickly remove these particles into the atmosphere, and there is minimal deposition of aluminum-magnesium dust.
3.3 CMT Cold Transition Welding and TIG Welding
These two welding processes, due to the protection of inert gas, produce smaller aluminum-magnesium metal particles at high temperatures. These particles can splash into the working environment under the action of the arc, posing a risk of aluminum-magnesium dust explosion. Therefore, precautions and measures for dust explosion prevention and treatment are necessary.
4 Technical Requirements for Aluminum Stamping Sheets in Edge Rolling
The difference between aluminum alloy edge rolling and ordinary cold-rolled sheet edge rolling is significant. Aluminum is less ductile than steel, so excessive pressure should be avoided during rolling, and the rolling speed should be relatively slow, typically 200-250 mm/s. Each rolling angle should not exceed 30°, and V-shaped rolling should be avoided.
Temperature requirements for aluminum alloy rolling: It should be carried out at 20°C room temperature. Parts taken directly from cold storage should not be subjected to edge rolling immediately.
5 Forms and Characteristics of Edge Rolling for Aluminum Stamping Sheets
5.1 Forms of Edge Rolling for Aluminum Stamping Sheets
Conventional rolling consists of three steps: initial pre-rolling, secondary pre-rolling, and final rolling. This is usually used when there are no specific strength requirements and the outer plate flange angles are normal.
European-style rolling consists of four steps: initial pre-rolling, secondary pre-rolling, final rolling, and European-style rolling. This is typically used for long-edge rolling, such as front and rear covers. European-style rolling can also be used to reduce or eliminate surface defects.
5.2 Characteristics of Edge Rolling for Aluminum Stamping Sheets
For aluminum component rolling equipment, the bottom mold and insert block should be polished and maintained regularly with 800-1200# sandpaper to ensure that no aluminum scraps are present on the surface.
6 Various Causes of Defects Caused by Edge Rolling of Aluminum Stamping Sheets
Various causes of defects caused by edge rolling of aluminum parts are shown in the table.
7 Technical Requirements for Coating Aluminum Stamping Sheets
7.1 Principles and Effects of Water Wash Passivation for Aluminum Stamping Sheets
Water wash passivation refers to removing the naturally formed oxide film and oil stains on the surface of aluminum parts, and through a chemical reaction between aluminum alloy and an acidic solution, creating a dense oxide film on the workpiece surface. The oxide film, oil stains, welding, and adhesive bonding on the surface of aluminum parts after stamping all have an impact. To improve the adhesion of adhesives and welds, a chemical process is used to maintain long-lasting adhesive connections and resistance stability on the surface, achieving better welding. Therefore, parts requiring laser welding, cold metal transition welding (CMT), and other welding processes need to undergo water wash passivation.
7.2 Process Flow of Water Wash Passivation for Aluminum Stamping Sheets
The water wash passivation equipment consists of a degreasing area, an industrial water washing area, a passivation area, a clean water rinsing area, a drying area, and an exhaust system. The aluminum parts to be treated are placed in a washing basket, fixed, and lowered into the tank. In the tanks containing different solvents, the parts are repeatedly rinsed with all working solutions in the tank. All tanks are equipped with circulation pumps and nozzles to ensure uniform rinsing of all parts. The water wash passivation process flow is as follows: degreasing 1→degreasing 2→water wash 2→water wash 3→passivation→water wash 4→water wash 5→water wash 6→drying. Aluminum castings can skip water wash 2.
7.3 Drying Process for Water Wash Passivation of Aluminum Stamping Sheets
It takes about 7 minutes for the part temperature to rise from room temperature to 140°C, and the minimum curing time for adhesives is 20 minutes.
The aluminum parts are raised from room temperature to the holding temperature in about 10 minutes, and the holding time for aluminum is about 20 minutes. After holding, it is cooled from the self-holding temperature to 100°C for about 7 minutes. After holding, it is cooled to room temperature. Therefore, the entire drying process for aluminum parts is 37 minutes.
8 Conclusion
Modern automobiles are advancing toward lightweight, high-speed, safe, comfortable, low-cost, low-emission, and energy-efficient directions. The development of the automotive industry is closely linked to energy efficiency, environmental protection, and safety. With the increasing awareness of environmental protection, aluminum sheet materials have unparalleled advantages in cost, manufacturing technology, mechanical performance, and sustainable development compared to other lightweight materials. Therefore, aluminum alloy will become the preferred lightweight material in the automotive industry.
Edited by May Jiang from MAT Aluminum
Post time: Apr-18-2024
