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At this moment, the Shanghai Lingang Tesla factory, more than 660 degrees Celsius of liquid aluminum alloy, under pressure of 6,000 tons is injected into the mold. A few minutes ago it was a pile of aluminum, and a few minutes later the mold opened, and it was already a formed Model Y one-piece rear body bottom plate.
For the first time in the history of a car, die-cast aluminum alloy parts of such sizes have been mass-produced. Since the beginning of 2021, Tesla has delivered more than 130,000 Model Ys in China alone, and the rear body baseplate of each one is die-cast in one piece.
Location and scale of die-cast parts
The Model Y in production is just the beginning, last year Tesla announced a series of new technologies on Battery Day, one of which is the die-cast front body + rear body (currently only the rear body is die-cast). With the new CTC battery pack, the overall weight reduction can be achieved by 10%, the battery life can be increased by 14%, and 370 parts can be reduced, so what will be the performance of the new Model Y that applies these technologies?
In the first half of this year, tesla factories in Texas began trial production of die-cast front body; soon after, the Model Y produced in Berlin, Germany, will be a "complete body" with 4680 battery cells, CTC battery packs, and front and rear die-cast body.
Die-cast front body + CTC battery pack + die-cast rear body
Model Y die-cast front body produced at the Texas plant
The body, or body in white, is the key and fundamental to directly defining a car's "identity" and "mission." This point Ben Hu sleeps and dreams every day, and the new friend may wish to jump to "Why do I have to care about the "car shell"?" 》。
Some of the bodywork is die-cast in one piece, and the benefits are in all aspects: higher production efficiency, lower cost, lighter weight and higher stiffness. Falling on the consumers, that is, the car price can be cheaper (just "can", the same below), the battery life can be longer, the comfort can be better, the control can be stronger...
Today's domestic Model Y can be sold from 280,000 yuan, may be by the rear body using integrated die casting, the cost of saving so many hundreds of dozens of a few cents - but do not be too little. To know that in the mainstream civilian car price, more than three digits of yuan is enough for manufacturers to break their teeth and swallow.
To understand how to die casting integrated molding how to do a good method? We'll have to talk about how the body is made.
From stamping welding to integrated die casting
As we all know, the main material of the body is metal. To process the metal raw material into body parts, it is common practice to stamp the form. Stamping, in the vernacular, is to put the sheet metal on a pre-designed mold and extrude it into the shape specified by the mold. It is similar to the mooncake mold, except that this "mooncake" only has a thin layer (plate) at the top.
However, the "pressure" in the title does not refer to the stamping of this "pressure".
No matter how complex the stamping design, the part is ultimately obtained from the plate (surface) or profile (tube), and it is unlikely to directly get a very three-dimensional structure - the complete body can be a large three-dimensional frame. Therefore, these stamping parts must enter the welding workshop and "spell" each other into a whole body.
Or, there is another way.
Instead of directly using metal raw materials, the metal is heated to a molten state, and then the liquid metal is poured into the mold "while hot", and when the metal is cooled and cured, the parts that match the shape of the mold are obtained, which is casting. Die casting is a type of casting, which relies on high pressure to force the raw material into the mold and can be used to manufacture more complex precision parts.
In the vernacular, it is to turn the metal into water, and then use a "syringe" to hit the mold, and "let it cool" out to be a solid finished product - the basic principle is as simple as that. Because it is a dynamic extrusion (die casting), the mold can be done with some complexity and some twists, and the molten metal can still fill the entire mold relatively well.
Die casting is often found
In fact, die casting is not a new thing, and it is even likely that you have die casting parts on your car - but the volume is not as large as the rear body of the Model Y.
Die casting can make more complex, three-dimensional parts at once, without having to be stamped and then welded (so most of the time the word "die casting" must be followed by "one-piece molding"). Because of this feature, die casting is particularly suitable for the manufacture of high-volume production of components that are at the same time complex and irregular.
There are many places on the body that need to be "irregular". The traditional stamping process, as long as it is made of a piece of steel plate, no matter what kind of stamping is twisted into, the thickness of different parts of the part is the same. But some places require high strength/stiffness, and some places don't need to be that high, that is, the material is bound to have redundancy.
TWB laser welding, door knockers using different thickness stitching, to achieve weight reduction effect
Weight is the enemy forever. In order to reduce this redundancy, people have invented TWB and TRB technology, which can change the material thickness of different parts of the same steel plate to a certain extent according to the preset, so as to achieve "on-demand unloading". However, this is still not flexible and free, and the weight reduction and application range are limited.
The real killer is to cast aluminum directly, taking advantage of the high flexibility of the casting mold, pre-designing the target strength for each part of the part, and allocating the corresponding thickness (of course, the aluminum itself can also reduce weight). Not only can the thickness of different parts change freely, but also the reinforcement structure in a specific direction can be designed, "four or two strokes of a thousand pounds". If ordinary plates are used, it may be much heavier to achieve the design goals.
Note that the left/rear stiffeners become transverse, reinforcing the longitudinal strength to resist rear-end collisions
Cast aluminum on the body has long been widely used in the top of suspension shock absorber towers. Because the top of the tower is the most direct part of the road stress transmission to the body, it requires extremely high local stiffness, and the shape is very complex. The traditional top of the tower is made of welded components, which in itself is not conducive to weight reduction, and to achieve high stiffness, it is almost necessary to require a great deal of thickness/weight.
What about cast aluminum? One component is solved, the process is few and simple, light weight and high stiffness.
The welded tower top of the Mercedes-Benz C-Class W204 requires four components to be welded together
The new C-class cast aluminium front tower top with stiffeners is clearly visible
The top of the tower is almost the lowest threshold cast aluminum part, and at present, above the medium-sized luxury car, the cast aluminum tower top is almost standard. Even new cars such as the zero-run C11 that take the cheap stacking route, in addition to the double wishbone front suspension, the front tower roof also uses cast aluminum. Larger cast aluminium parts are at a higher level, as previously mentioned that the Audi A7 used cast aluminum parts to compensate for the "joint" at the top of the C-pillar in order to reduce the stiffness of the hatchback door ("Why do hatchback sedans always go into the flow?"). 》）。
Note that the red-marked front tower top is also cast aluminum
Before the Model Y, the largest component of the one-piece cast aluminum process was almost the front and rear stringers of the body. This is the rear body rail of the Cadillac CT6, and the dense reinforcements reflect that it is a cast aluminum component.
Cast aluminium rear axle beam of Mercedes-Benz's predecessor C-class
Large castings are not common
When it came to the Model Y, Tesla made a large part of the entire rear body floor, rear wheel arch, rear cross-stringer, etc., into a cast aluminum part - this part of the body needs 70 parts on the Model 3, not to mention the new version of the Berlin factory, the front body is also made into a one-piece cast aluminum part.
In fact, it is conceivable that large cast aluminum components have not been preemptively applied by Tesla until today, and there is no reason for this.
A famous figure, from 70 pieces of Model 3 to 2 pieces of Model Y, the latest version is more integrated
The die-casting process is good, on the one hand, the parts are formed in one piece, reducing the number of parts and the connection process; on the other hand, the cast aluminum achieves a high degree of flexibility in thickness and structure, which easily balances lightweight and high stiffness. However, in the past, cast aluminum was a small part, and the reason was naturally that once the volume of cast aluminum parts became larger, there would be problems that were difficult to solve.
The first is the need for larger die casting machines. The rear body weight of tesla model Y is about 80kg, which requires a die casting machine to be able to press into 80kg of liquid aluminum alloy at one time. Only when such a large-scale die casting machine is developed and matured, it is possible to manufacture cast aluminum parts of this size, and the world's largest die casting machine can inject 200kg of raw materials at one time.
The model Y's cast aluminium front body at the Berlin factory is said to weigh 130kg, which means that the die-casting machine must be able to press in 130kg of aluminum water at one time. The reason why Tesla first cast aluminum body (80kg) and the front cast aluminum parts were first introduced in the new Berlin and Texas factories should be that they are waiting for a larger die casting machine to be in place and shipped directly to the new factory.
The second is that casting such a large part is a big challenge in itself. The principle of die casting seems simple, nothing more than to press liquid metal into the mold, but in order to obtain high-quality large parts, it is full of problems, and it is no exaggeration to say that the large-scale die casting machine with stable production is a big country heavy instrument (the Die casting machine in Shanghai factory comes from the domestic Lijin Group).
Liquid metals are not "obedient", and turbulence, impurities and other abnormalities may occur during the process of being pressed into the mold by high pressure. The more complex the part/mold, the more prone to problems such as underfilling. The gases that are originally in the mold and the gases that enter with the material may cause porosity inside the part. Component defects always revolve around the casting process, and the larger the part, the more problems there are, and the car body is obviously not tolerant of defects.
Finally, there is the contradiction between large volume and high intensity. Large body parts are more likely to be required to bear the task of resisting collisions, and they are more likely to require high strength. However, the general cast aluminum parts need to undergo heat treatment (solid solution, aging, similar to quenching in steel) in order to obtain high hardness and high strength, and heat treatment will inevitably bring about the volume change of thermal expansion and contraction, the larger the volume of the part, the greater the impact of this deformation error.
Tesla finally found a special aluminum alloy material that did not require heat treatment to achieve the Model Y's large cast aluminum rear body. In October this year, NIO announced that it has successfully validated heat-free treatment materials that can be used for large die castings and will be applied to the second generation of platform models. Finding materials that don't require heat treatment (the subtext is still meeting strength requirements) is key to large die casting applications.
Tesla specializes in dà li bǐng, terrible four directions simultaneously die-cast, note that the intermediate finished product is a complete body
The Model Y, which is die-cast in front and rear, has not really been mass-produced, and Tesla has long been looking forward to a farther future. A long time ago, Tesla filed a patent for the overall die-casting of the body.
It should be known that the "rear body" mentioned above is actually only "a part of the rear body (of course, it is the lower part of the more critical part)", and it must be connected with other body components after all. Tesla's more ambitious future is that the entire body is formed by a single die-casting - truly achieving a literal "one-step in place".
Such a sci-fi integrated die-casting body is still far away, and it will take some years just to accommodate hundreds of kilograms of raw materials, not to mention how to design such a complex mold, how to ensure that there are no defects under such a complex flow field, how to ensure that the vehicle has sufficient strength after die-casting, and so on.
In fact, the integration of body parts and the casting of aluminum of key components have always been the direction of the automotive industry. Tesla, as a spoiler, kicked the ball that had been rolling forward a lot, and naturally attracted a lot of catchers. It is said that several car companies, including Weilai, are already seeking large-scale cast aluminum parts, when Tesla gradually relies on integrated cast aluminum to get more advantages, new car manufacturers are hungry for product breakthroughs, maybe they will really kick this ball faster and farther.