With the advancements in lightweight automobile technologies, the use of aluminum automotive casting parts has gained significant attention and rapid development in both domestic and foreign automotive industries. These casting parts serve as essential load-bearing components in vehicles and are closely related to automotive safety. Structural components in automobiles are often interconnected to form strong frames that resist deformation. These structural components usually have large sizes, thin walls, and complex structures. Due to the need for reliable car safety during driving, there is a high requirement for the mechanical performance of these structural components. This article provides a brief overview of the production process for large aluminum alloy structural components, serving as a reference for readers.
1. Rough Production
1.1 Die Casting
Major European vehicle companies have casting subsidiaries dedicated to the research, development, and production of large and complex castings. To reduce costs, they outsource the remaining processing processes to “post-processing” enterprises. This method has refined the market division of labor, improved the specialization and automation of automotive component production.
1.2 Packaging and Transportation
Vehicle factories, as end-users of the products, design dedicated material frames based on the product’s shape and the size of the truck carriage. These parts are secured in the frame using clamping mechanisms to prevent contact and collision, ensuring the economy and safety of the raw materials during transportation. The truck used for transporting the parts is a standard side curtain box truck, which is compatible with loading and unloading platforms. The side curtains of the carriage are easily removable, allowing for unloading from both sides and the rear. The body and front of the truck can be separated, eliminating the need for waiting during loading and unloading, thus improving safety and efficiency in transportation.
2.1 Entry Inspection
Once the box truck enters the factory, the material frame filled with blank parts is unloaded to the loading point buffer area of the production line using a forklift. Workers visually inspect the parts based on the delivery note and personnel inspection form, checking for any obvious casting defects, damage, or pollution during transportation.
2.2 Heat Treatment
To enhance the mechanical properties, corrosion resistance, dimensional stability, cutting performance, and welding performance of castings, heat treatment is necessary for the die-casting blanks. Ordinary die castings cannot undergo high-temperature treatment due to their high gas content. However, with high-vacuum die-casting, the gas content in the castings can be significantly reduced, allowing for T7 heat treatment, which improves strength and toughness simultaneously.
2.3 Bubble Inspection and Repair
After the completion of the solid solution treatment, the parts are inspected for bubbles, bubble size, bubble group size, bubble spacing distance, and crack size. Unqualified products are determined according to inspection standards. Small bubbles on qualified products can be gently eliminated by tapping with a hammer. After inspection and repair, the data is uploaded to the ERP system.
2.4 Correction and Testing
Parts may deform during the air-cooling quenching process, but the deformation is minimal during the subsequent artificial aging process. Aluminum parts become softer and more plastic after quenching. The parts are shaped and then artificially aged to stabilize their size and reduce further deformation.
2.5 Heat Treatment (Stabilization Treatment)
After quenching, the part structure produces a supersaturated solid solution, resulting in an unstable structure. To maintain dimensional stability for long-term use, stabilization is required. After complete artificial aging, the parts obtain high toughness and strength due to the precipitation of Mg2Si strengthening phase. The parts undergo manual aging treatment according to the designated temperature and time, and their mechanical properties are spot-checked, including yield strength, tensile strength, Brinell hardness, and riveting performance.
2.6 Automatic Polishing
All mating surfaces, contact surfaces, and installation parts need to be smooth and free of burrs. The polishing process is automated and may involve the use of mechanical hands in high production situations. A completely enclosed polishing compartment is used to isolate dust and noise, with a dust removal system collecting all dust.
Robotic arms handle the workpieces and place them in the machining center. Several 5-axis high-speed machining centers are equipped to match the production capacity. The workpieces are clamped, and all machining surfaces, deep holes, and tapping are processed. The machining center used is the Chiron Mill 2000 vertical 5-axis milling machine, selected for efficiency, accuracy, and reliability.
The cleaning process is also automated, with the robotic arm placing the machined parts onto a conveyor roller support. The parts are then cleaned using a 50 ℃ cleaning solution with a pH value of 7-11 at a specific pressure. After cleaning, the parts are dried using heated compressed air and moved to the assembly station by the robotic arm.
Before assembly, a manual inspection station checks the cleaned products for errors and surface cleanliness. The parts are assembled, using fully automatic installation for internal threads and blind rivets. Robotic arms equipped with automatic detection equipment ensure that any non-conforming products are manually repaired.
2.10 Electrophoretic Coating, Packaging, and Shipping
To improve corrosion resistance and appearance, the inspected products are cleaned, electrophoretically coated, and dried. The coating layer thickness, surface morphology, adhesion, and corrosion resistance are tested. After a final factory inspection, the qualified products are packaged and shipped to the vehicle factory.
In summary, the post-treatment of aluminum alloy die castings in China follows a production method organized by functional zones. However, dedicated production lines are still limited. Dedicated line production requires a large output of a single product, offering advantages like high automation, low labor demand, high production efficiency, and stable quality. However, it also poses challenges in terms of investment costs, flexibility, and organizational production and equipment management requirements. The European automotive industry faces high labor costs, making dedicated line production less common.