For new energy vehicles, increasing range and reducing battery costs are the main contributions of lightweight. New energy vehicles have heavy batteries, high power consumption, and lower energy density than traditional fuel vehicles, which affects their range and makes the demand for lightweight more urgent for car companies. Therefore, lightweight vehicle body has become an inevitable way for new energy vehicles to increase their range, durability, and energy efficiency. The China Association of Automotive Engineers has also established direct target requirements for automotive lightweight. The introduction of the ‘vehicle weight reduction coefficient’ as the basis for measuring the level of vehicle weight reduction, which is composed of the product of three indicators: nominal density, weight to power ratio, and footprint fuel consumption. While ensuring the comprehensive performance indicators of the vehicle, it achieves relatively light weight, good power performance, and more energy-saving. According to the target plan, the overall weight reduction coefficient of fuel powered passenger cars will be reduced by 10%, 18%, and 25% by 2025, 2030, and 2035, respectively, while that of pure electric passenger cars will be reduced by 15%, 25%, and 35%, respectively.
At present, there are two main types of lightweight materials for automobiles: one is high-strength materials, mainly referring to high-strength steel, which has a yield strength of 210-550MPa and a tensile strength of 340-780MPa; One type is lightweight materials: mainly including aluminum alloys, magnesium alloys, plastics, composite materials, etc. Currently, steel accounts for up to 55% of the total weight of automobiles, and replacing it with lightweight materials is an important direction for achieving weight reduction in automobiles.
In terms of cost: The price of aluminum alloy is only higher than that of high-strength steel, far lower than that of carbon fiber composite materials, about half of that of magnesium alloy. In terms of weight reduction and performance: Aluminum alloy can achieve good weight reduction effect. In terms of density, the density of aluminum alloy is about 2.7g/cm3, which is about one-third of that of high-strength steel, equivalent to magnesium alloy, and 1.8 times that of carbon fiber; In terms of weight reduction potential, aluminum alloy is weaker than carbon fiber and magnesium alloy, and significantly stronger than high-strength steel.
Compared to steel parts, aluminum alloy has a weight reduction potential of 40%, magnesium alloy has a weight reduction potential of 50%, and carbon fiber composite materials have a weight reduction potential of 60%. In terms of manufacturing process: The aluminum alloy process is relatively mature, efficient, and cost-effective. The cost advantage of high-strength steel in terms of technology is obvious, and the manufacturing process is mature; With the application of new process technologies such as hot stamping and die-casting, the application of aluminum alloy sheets has demonstrated high production efficiency and moderate molding process costs; The magnesium alloy forming process has a high cost and is prone to oxidation, mainly using cold connection methods; The efficiency of carbon fiber material forming and connection processes is low, and the cost is also high.
In summary, aluminum alloys have higher specific strength, lower density, and greater weight reduction potential compared to high-strength steel; Compared to magnesium alloys, the cost is lower, and the forming process and connection method are more mature; Compared to carbon fiber, it has a huge cost advantage. In addition, aluminum has a large reserve, good corrosion resistance, and high recycling rate, making it the preferred material for lightweight automobiles.
The manufacturing process of traditional car bodies is mainly divided into four stages: stamping, welding, painting, and final assembly. The main car factory purchases multiple structural components manufactured by various suppliers across the country through stamping and die-casting, and assembles them together (including welding, riveting, gluing, etc.) to form the car’s body in white assembly (BIW)
Stamping: is a processing method in which metal sheets are cut or formed under pressure in a stamping die. Automotive stamping utilizes different presses to continuously press the entire roll of steel or aluminum plates into shells and small sheet metal parts using multiple large presses, completing the manufacturing of car doors, left and right side panels, engine compartment covers, front and rear floor panels, top covers, back doors, and various stamping small parts.
Welding: refers to the processing method of joining two pieces of metal together by local heating or simultaneous heating and pressure. Automotive welding involves welding the stamped body parts together, and welding the small sheet metal parts into body structural components, including the four doors and front and rear covers (engine hood+trunk cover). The welded body structural components are the white body.
Painting: includes three basic processes: surface treatment, coating process, and drying of the coated object before painting. Automotive painting is accompanied by various anti-corrosion processes for the white body, and the welded white body is sprayed with color paint, varnish, etc. to achieve coloring and surface protection and rust prevention.
Final assembly: refers to the method of connecting and combining various parts into components using connecting parts (bolts, nuts, pins, or buckles, etc.). Assemble various components (suspension and powertrain, electronic control system, interior components) on the vehicle body, and ultimately complete the entire vehicle manufacturing.
Integrated die-casting improves integration efficiency and reduces production costs in automotive manufacturing
Integrated die-casting uses a large tonnage die-casting machine to highly integrate multiple individual and dispersed aluminum alloy components, forming 1-2 large aluminum castings once again, replacing the traditional method of stamping and welding multiple components together.
1.Integrated die-casting greatly improves the production efficiency of automotive bodies compared to traditional processes
The one-time die-casting of integrated assembly components greatly improves the production efficiency and integrated quality of automobiles. According to Tesla data, Model Y, which adopts an integrated die-casting rear floor assembly, has reduced the number of parts by 79 compared to Model 3 due to the one-time die-casting of all parts. Due to the use of new heat-free alloy materials, the heat treatment process is eliminated, and the manufacturing time is reduced from 1-2 hours in traditional processes to 120-180 seconds. And with only one part, there is no need to develop too many tooling equipment, which greatly reduces the accumulation of errors caused by the connection of a large number of parts and improves manufacturing accuracy.
2. Integrated die-casting greatly simplifies production costs
On the one hand, integrated die casting significantly reduces production line costs. Under the existing production technology cost framework (stamping, welding, painting, final assembly), the traditional production of 70 components requires the placement of machines and molds for each component, as well as machine arms, transmission lines, fixtures, etc. around the production line; And the integrated die-casting molding only requires a large die-casting machine and a set of molds. After the process is simplified, other consumables and equipment are reduced, machining is simplified, material transportation, and die-casting costs are all smaller; Moreover, it eliminates heat treatment equipment and processes, molding equipment [to repair deformation after heat treatment] and processes, passivation equipment and processes, and structural adhesives, resulting in better overall economic performance. In addition, a large die-casting machine covers an area of only 100 square meters. According to Elon Musk, the use of a large die-casting machine has reduced the factory’s area by 30%.
On the other hand, integrated die casting significantly reduces labor costs. A welding and assembly factory in a mainstream domestic automobile factory is equipped with approximately 200 to 300 production line workers. After adopting integrated die-casting technology, the required technical workers will also be significantly reduced. According to Tesla’s 2020 Battery Day press conference, the integrated die-casting process for the modelY rear base plate has reduced manufacturing costs by 40% compared to the original plan.
The current integrated die-casting aluminum body single vehicle material+manufacturing cost is 10600 yuan, far lower than the 14400 yuan for all aluminum stamping welded body and the 12000 yuan for steel aluminum mixed welded body, which is basically close to the steel welded body.
The cost of integrated aluminum die-casting body can be divided into material cost and manufacturing cost. Taking the integrated body of a typical B-class car as an example, the core assumption is:
Material cost: Lightweight degree: Based on the density and performance parameters of steel and aluminum, it is assumed that replacing an all steel body with an all aluminum body will result in a 35% reduction in mass. Among them, the weight of the steel white body is 350kg, the all aluminum welded body is 280kg, and the integrated aluminum die-cast body is 228kg. Direct material prices: Calculate the cost of raw materials by taking the current prices of steel and aluminum as of March 2022.
Manufacturing cost: mainly including depreciation of die-casting machines and die-casting molds. And other materials, electricity bills, labor, etc. Based on the typical B-class vehicle structure, the investment in the production line of the integrated die-casting body requires nearly 500 million yuan. Depreciation is calculated based on an annual production of 100000 units and a 7-year life cycle. The mold has an investment of 150 million yuan and is depreciated with an annual production of 100000 pieces and a life cycle of 100000 pieces. At the same time, in terms of other manufacturing costs, due to the poor toughness and surface adhesion of aluminum alloys, the aluminum stamping and welding process is complex and material consumption is high. The die casting process is simple and can significantly reduce additional manufacturing costs.
According to the calculation results, the current use of aluminum integrated die-casting for the full body bottom plate is close to the cost of steel welded body, which is 12.32% lower than the cost of steel aluminum mixed welded body; Compared to all aluminum welded body, the cost is reduced by 26.40%.
The current aluminum price is rapidly rising unilaterally due to the influence of the international situation. It is expected that in the long run, with the further stabilization of aluminum prices, the cost reduction effect of aluminum integrated die-casting will be further enhanced.
With the development trend of lightweight and intelligent automobiles, the shortcomings of traditional body manufacturing processes are becoming increasingly prominent. Integrated die casting has become a new process choice for efficiency improvement, lightweight, and cost reduction due to its relative advantages.