Automotive Parts Forming: Process Analysis and Technological Evolution
As a core link in the automotive manufacturing industry, the molding of automotive parts directly affects the performance, safety, and manufacturing costs of vehicles. From the engine cylinder block to the interior panel, different components require diverse molding processes due to differences in functional requirements. With the transformation of the automotive industry towards electrification, lightweighting, and intelligence, molding technology is constantly innovating, promoting breakthroughs in material utilization, production efficiency, and environmental performance of components.
Mainstream molding process: applicable scenarios and technical characteristics
Injection molding: the mainstream choice for precision components
Injection molding, with its high degree of automation and high dimensional accuracy (tolerance up to ± 0.02mm), is widely used in automotive interior parts (such as instrument panels and door panels), electronic components (such as connectors and sensor housings), and structural components (such as engine covers). The process principle is to inject molten plastics (such as PP, ABS, PC/ABS alloy) into a closed mold through a screw, and after cooling and shaping, obtain a product that is consistent with the mold cavity.
In the automotive field, key technologies for injection molding include:
Gas assisted injection molding: By injecting nitrogen into the melt, the shrinkage marks and internal stress of the plastic parts are reduced. After adopting this technology, the surface defect rate of the dashboard of a certain car company is reduced by 70%, and the material consumption is reduced by 15%.
Dual color injection molding: Two different colors or materials of plastic are molded at once, such as the grip area of a car steering wheel (TPE soft material) and the skeleton (PP hard material), which are integrated to improve the feel and aesthetics.
Micro foaming injection molding: Introducing supercritical fluid (CO ₂ or N ₂) into the melt to form tiny bubbles, reducing the weight of components by 10-20% while maintaining structural strength. It has been applied to battery brackets for new energy vehicles.
Stamping forming: the core process of metal structural components
Stamping is the main forming method for metal components (accounting for 60-70% of the weight of a car), suitable for processing materials such as steel plates and aluminum alloys. It can produce body coverings (such as doors and engine covers), chassis components (such as crossbeams and longitudinal beams), and structural components (such as crash beams). The process applies pressure to metal sheets through punching machines and molds, causing them to undergo plastic deformation and obtain the desired shape.
The development of modern stamping technology is reflected in:
Hot stamping forming: Heating boron steel to 900-950 ℃ and rapidly stamping and quenching to obtain ultra-high strength steel components with a strength of 1500MPa, which can be used for vehicle safety structures, reducing deformation during collisions and reducing weight by 30%.
Servo stamping: The slider is driven by a servo motor to achieve precise control of stamping speed and stroke. After a joint venture car company introduced a servo stamping line in its stamping workshop, the production cycle increased from 15 times/minute to 18 times/minute, reducing energy consumption by 20%.
Aluminum alloy stamping: In response to the lightweight requirements of new energy vehicles, a cold stamping process for 6 series aluminum alloys has been developed. By optimizing the die fillet (R ≥ 5mm) and lubrication scheme, the forming rate of the car door inner panel has been increased from 85% to 98%.
Die casting: an efficient solution for complex metal components
Die casting is particularly suitable for the production of complex non-ferrous metal components such as zinc alloys, aluminum alloys, etc., such as gearbox housings, motor end caps, steering knuckles, etc. The process involves injecting molten metal (aluminum alloy die-casting temperature of about 650 ℃) into the mold cavity at high speed under high pressure (5-150MPa), and rapidly forming dense metal parts.
Technological breakthroughs in the automotive field include:
High pressure die-casting: Using a large die-casting machine with a locking force of over 4000 tons, the traditional body structure components welded by dozens of parts are integrated and die cast. After adopting this technology, the rear floor of Tesla Model Y reduces the number of parts by 70 and increases production efficiency by 300%.
Semi solid die casting: Metal slurry is die cast in a semi-solid state to reduce porosity and shrinkage defects. After adopting this process, the airtightness qualification rate of the motor housing of a certain new energy vehicle increased from 90% to 99.5%.
Vacuum die-casting: Vacuuming the mold cavity (vacuum degree ≤ 50mbar) to avoid the metal liquid from being sucked into the gas, thereby improving the mechanical properties of the casting by 15-20%. It is applied to high-pressure components such as engine cylinder blocks.
Vacuum Forming: Lightweight Selection for Non Metallic Components
Vacuum forming is widely used in automotive plastic parts, such as interior trim panels, trunk covers, engine heat shields, etc., especially suitable for large, thin-walled (thickness 1-3mm) and relatively simple shaped components. The process involves heating plastic sheets (such as PP, ABS, PC) to a softened state and using vacuum suction to adsorb them onto the surface of the mold for cooling and shaping.
Optimization for automotive scenarios includes:
Thick sheet vacuum forming: Using 3-8mm thick ABS/PC composite sheet to produce battery pack covers for new energy vehicles, the load-bearing capacity is increased to 500N through reinforced rib design, while the weight is reduced by 40% compared to metal solutions.
Double sided vacuum forming: Simultaneously applying vacuum to both the upper and lower sides of the sheet to obtain a more uniform wall thickness (deviation ≤ 10%). After adopting this technology, the assembly gap fluctuation of the instrument panel lower protective panel of a certain car company was reduced from ± 0.5mm to ± 0.2mm.
Integrated hot forming and cutting: Integrating the forming and cutting processes to reduce process flow. Through this solution, a certain interior supplier's production line has shortened the single piece production time from 45 seconds to 30 seconds.
The Collaborative Development of Material Innovation and Forming Technology
Adaptation of high-strength steel and forming process
The strength of automotive steel has developed from traditional low-carbon steel (200-300MPa) to advanced high-strength steel (AHSS, 500-1000MPa) and even hot formed steel (1500MPa), which puts higher requirements on the forming process:
Hot formed steel needs to be matched with specialized molds (cooling rate ≥ 50 ℃/s) to ensure sufficient martensitic transformation. The 22MnB5 steel developed by a certain steel plant has a yield strength of over 1000MPa after hot stamping.
The cold stamping of advanced high-strength steel requires the use of techniques such as stretching rib optimization and step-by-step forming to avoid cracking. The AHSS car door crash beam produced by a certain car body factory achieves complex section forming through 7 stamping processes, with a scrap rate controlled below 0.5%.
Breakthrough in the Forming of Lightweight Materials
Aluminum alloy: 6-series aluminum alloy (such as 6061) can achieve a yield strength of 110MPa after T6 heat treatment (solid solution+artificial aging) and die casting. It is used for chassis control arms and reduces weight by 40% compared to steel components.
Carbon fiber composite material (CFRP): Using resin transfer molding (RTM) process, carbon fiber fabric is placed in a mold, injected with epoxy resin and cured to produce body coverings. The carbon fiber engine hood of a certain supercar weighs only 4.5kg and has a strength five times that of steel.
Engineering plastic: PA66+30% glass fiber is injection molded and can be used for intake manifolds. It can withstand temperatures up to 150 ℃, reducing weight by 30% compared to aluminum alloy solutions and lowering intake resistance by 5%.
Application of environmentally friendly materials in molding
Recycled plastic: After crushing the PP bumper of a scrapped car and mixing it with 20% new material, the wheel arch lining plate is produced through injection molding. The utilization rate of recycled materials by a certain car company has reached 35%, reducing carbon emissions by 20%.
Bio based materials: using polylactic acid (PLA) and natural fibers composite, producing interior door panels through extrusion molding, which can naturally degrade after disposal and have been applied to a certain brand's concept car.
Technical difficulties and solutions
Molding accuracy control
Dimensional stability: In response to the issue of warpage in injection molded parts, CAE flow analysis was used to optimize the gate position and pressure holding parameters. The warpage of a certain dashboard was controlled from 2mm to within 0.8mm.
Rebound compensation: Metal stamping parts rebound due to elastic deformation, and the angle deviation of the door frame is controlled within ± 0.5 ° through mold pre compensation (such as designing an angle of 88 ° to offset 2 ° rebound).
Uniformity of wall thickness: Vacuum formed deep cavity components are prone to uneven wall thickness. By using pre stretching and multi-stage heating technology, the maximum wall thickness difference of a certain coffee machine water tank has been reduced from 0.5mm to 0.1mm.
Defect detection and prevention
Injection molded parts shortage: By increasing the number of gates and increasing the injection speed (from 50mm/s to 100mm/s), the problem of insufficient filling in complex structural parts was solved, and the shortage rate of a certain connector was reduced from 3% to 0.1%.
Cracking of stamped parts: Laser welding plates (welded and stamped with steel plates of different thicknesses) were used, and thick plates were used in stress concentration areas, resulting in a 90% reduction in the cracking rate of a certain car body side panel.
Die casting porosity: By increasing the mold temperature (from 150 ℃ to 200 ℃) and extending the holding time (from 5s to 8s), the porosity defects in the aluminum alloy shell are reduced, and the leakage rate is reduced from 500ppm to 50ppm.
Efficient production and cost control
Mold life improvement: The hot stamping mold adopts H13 hot work mold steel, which has undergone nitriding treatment (with a surface hardness of 60HRC), and the life has been increased from 50000 times to 150000 times.
Quick mold change: The stamping line adopts a magnetic quick mold change system, which shortens the mold change time from 30 minutes to 5 minutes and increases the equipment utilization rate from 60% to 85%.
Waste recycling: The recycling rate of scraps produced by vacuum forming reaches 90%, and after crushing, they are re extruded into sheets, reducing material costs by 15%.
Future Trends: Intelligence and Sustainable Development
Intelligent molding technology
Digital Twin: Constructing a digital model of the molding process in a virtual space, simulating in real-time the impact of temperature, pressure, and other parameters on product quality. A certain automotive company's injection molding workshop optimized the process through digital twin, reducing the number of mold trials from 5 to 2.
AI quality inspection: Using machine vision and deep learning algorithms, it identifies surface scratches on stamped parts (with a minimum detectable size of 0.1mm × 1mm), improving detection efficiency by 10 times compared to manual labor and achieving an accuracy rate of 99.9%.
Adaptive control: The injection molding machine monitors the temperature of the melt adhesive in real time through sensors, automatically adjusts the heating power, and controls the temperature fluctuation within ± 1 ℃, improving product weight stability by 30%.
Sustainable molding process
Low carbon die-casting: By replacing natural gas heating furnaces with electric heating, a die-casting factory has reduced its carbon emissions by 60%. At the same time, photovoltaic power supply has been introduced to achieve "zero carbon" production.
Water based coating: replaces oil-based lubricants in stamping processes, reduces volatile organic compound (VOC) emissions by 90%, and lowers environmental costs by 40% for a certain car body factory.
Near net forming: Through precision casting technology, the machining allowance of parts is reduced from 3mm to 0.5mm, the material utilization rate is increased from 60% to 90%, and energy consumption is reduced by 30%.
Integrated molding trend
Multi material hybrid molding: Integrating metal inserts with plastic through injection molding, such as molding the metal joints and plastic shells of automotive sensors in one go, reducing assembly processes and increasing connection strength by 50%.
Integrated molding of large structural components: Using a super large injection molding machine (locking force of 10000 tons), the car dashboard, center console, air duct, etc. are integrated into one component, reducing the number of parts by 60% and assembly time by 50%.
Conclusion: Molding technology drives the upgrading of the automotive industry
The molding technology of automotive parts is developing towards the direction of "lighter, stronger, more efficient, and more environmentally friendly", shifting from single process applications to multi process collaboration, and from experience driven to data-driven. In the future, with the deep integration of new materials, intelligent equipment, and digital technology, the molding process will further break through performance limits, providing core support for the range improvement of new energy vehicles and the safety guarantee of intelligent driving, and promoting the automotive manufacturing industry to move towards high-quality and sustainable direction. For enterprises, mastering advanced molding technology and achieving process innovation will become the key to gaining an advantage in fierce competition.
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