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2023.2.23
Tesla is a troublemaker in the traditional automobile industry. It is not only its car-building concept, but also the traditional automobile enterprises that are often “dumbfounded” in terms of automobile technology. It has led the industry with its speed-up ability, powerful endurance mileage, and advanced Autopilot driving assistance system. Now in this pure electric vehicle factory, we have seen a new technology on Model Y: the die-casting process of integrating 70 parts (currently reduced to 2 parts, and will be combined into 1 part in the future). Today, we are going to find out why Tesla uses the die casting process.
Die casting is a metal casting process. Its principle is similar to injection molding. It is to apply high pressure to molten metal and inject it into the cavity of the mold to cast the desired shape. It is essentially different from traditional sand casting, and its mold is usually made of alloy with higher strength. Don’t other auto companies have such technology? The answer is yes, die-casting technology is often seen on products with aluminum alloy body nowadays, but it is rare for cars such as Tesla to use die-casting technology on a large scale, and even Model Y can be regarded as the only one. Its integrated die-casting scope covers most of the rear body.
Tesla Model S and Model X use all-aluminum body. When the transition to Model 3, it is changed to a steel-aluminum hybrid body, and Model Y is also a steel-aluminum hybrid body. Before the revolutionary change of battery energy density, if you want to reach a long range, a pure electric vehicle needs many battery packs. The more the battery packs, the heavier the weight, and if the car is too heavy, it will affect the range in turn. Therefore, in addition to battery, the lightweight of body and chassis is particularly important for pure electric vehicles.
The choice of steel-aluminum hybrid body for Model 3 and Model Y is a decision after comprehensive consideration of lightweight and cost. There are four main materials in the body structure of Model 3, namely ultra-high strength steel, high strength steel, low carbon steel and aluminum alloy. Based on the crash safety design, the main frame is made of ultra-high strength steel, while aluminum alloy is mainly used in the energy absorption area of the front and rear of the vehicle.
The aluminum alloy material of Model 3 is widely used in the rear body, and Model Y has also made technological improvements in this part. Aluminum alloy is really helpful for weight reduction, but it also makes the manufacturing process very complicated. The connection between aluminum alloy plates is much more complex than that of steel plates. They can be welded together like steel plates, but the connection strength is far lower than that of the latter. Therefore, the connection position of aluminum alloy with large stress needs to use riveting, bolt connection or auxiliary use of adhesive and other processes.
In addition to the high cost, aluminum alloy body has many advantages, but from the point of view of production, it is more difficult to manufacture than traditional steel body. First, there is the problem of product consistency. Due to the aluminum alloy material itself, the rebound range of parts after stamping is greater than that of steel. It is a higher challenge to maintain the consistency of the precision of large batches of stamping parts; In addition, the connection between aluminum alloy parts and between aluminum alloy and steel is more complex, involving a variety of new riveting processes. The process flow is more complex, and the production efficiency is difficult to improve.
Tesla CEO Elon Musk once admitted in a media interview that the complex body manufacturing process of Model 3 affected the automation production efficiency in the factory. Therefore, targeted improvements have been made in the design of the body structure of Model Y, and one of the keys to improving efficiency is the integrated casting process we are going to talk about today.
From 70 parts to one or two, the most direct benefit is that the production efficiency has been greatly improved, which is very important for Model Y, which pursues output. Model Y adopts die casting technology. Compared with traditional sand casting, the die shaft is more suitable for mass production of Tesla body structure.
The rear longitudinal beam structure of Model Y and Audi A8 is somewhat similar in casting technology, with complex stiffener design. The difference is that the volume of the parts cast by Model Y is larger, which almost covers the whole lower part of the rear car body.
The production efficiency of die casting process is high. High speed and high pressure mold filling can hydraulically inject metal into the model in a short time, and can produce parts with complex shape, clear contour, thin wall and deep cavity. In addition, the surface roughness of die-cast parts can reach Ra0.8-3.2 μ m. In other words, the surface is smooth enough to avoid machining.
Every innovative technology is the result of thick accumulation, and behind it is an accumulation that is invisible to outsiders. Before creating the integrated die-casting process of Model Y rear body, Elon Musk invited Charles Kuehmann, an alloy expert from Apple, to develop new die-casting aluminum alloy materials, and also applied for integrated casting patents.
The die-casting process is not without shortcomings, which is why it has not been widely used in the automotive field. First, die-casting machines and die-casting molds are very expensive. If there is no scale benefit brought by mass production, it is difficult for automobile enterprises to bear their comprehensive costs; Due to the limitation of the clamping force and the size of the die, it is difficult to cast large die castings; Due to high-speed filling and rapid cooling, if the gas in the cavity is not discharged in time, the existence of pores and oxide inclusions will reduce the quality of die castings.
The basic die-casting equipment of Tesla Model Y is from Italy’s IDRA Group. This machine, named IDRA OL6100 CS, is about 20 meters long, 5 meters high and 410 tons heavy. (It is about the weight of more than 200 Model Y vehicles) Tesla and IDRA of Italy worked together to build a die-casting machine that is large enough to die cast the rear body of Model Y, which solved the problem of size limitation. As for whether the high equipment cost invested can be covered by mass production, Musk seems not to worry about the sales of Model Y, because it will cover a wide range of user groups like Model 3. Therefore, the remaining question may be whether Tesla can guarantee the precision and quality of the die-casting process.
From this plan to reduce the number of parts, it can be seen that Elon Musk is sparing no effort to pursue the automation rate of the factory and reduce the cost of personnel. Artificial intelligence is the trend of the future. The German people also put forward the concept of Industry 4.0 very early. Musk also hopes that the future Tesla factory will have a higher automation rate. The integrated casting process may face many challenges at present, but once this aluminum alloy body production mode matures, Tesla will also achieve greater capacity and lower production costs.