In the F1 Hall of Fame, Colin Chapman, although not as famous as Enzo Ferrari, is also an indispensable figure, at the age of 20, he founded the supercar brand "Lotus", and the team under his name won the F1 championship seven times, which was invincible in the 1960s and 1970s.
Unlike Enzo Ferrari, Chapman did not like to talk about heroes with horsepower, but used engineering and the experience of driving a fighter jet to the design of the body, and it was a great success. In his words: "High horsepower can make you fast in straight lines, but lightweight can make you faster everywhere!" ”。 Translated into modern Chinese: "Ning less than ten horsepower, less than one kilogram".
But unfortunately, Chapman died of illness in 1982, and the Lotus brand has been displaced since then, successively in the hands of Americans, Italians and Malaysians, and no one would have thought that Lotus would become the "muse" of Tesla Roadster, not because of its electrification achievements, but for lightweight design.
Although electric vehicles remove the engine and gearbox, they have increased the battery as a large block, but it is heavier, and the need for lightweight is particularly urgent.
Taking the first generation of Roadster as an example, in order to achieve an endurance of nearly 400 kilometers, it carries 6831 small cylindrical batteries, which alone are 320 kilograms, plus wiring harnesses, cooling systems, BMS, trays and upper housings, the total weight of the battery pack reaches 500 kilograms, you know, an engine plus gearbox and cooling system is only about 300 kilograms.
In order to make the Roadster run farther and faster, engineers found a lot of inspiration from Lotus, such as adjusting the body structure and using carbon fiber materials, and finally achieving an acceleration of 3.6 seconds per 100 kilometers, sweeping away people's stereotypes of electric vehicles that are "not ugly or bad".
In the automotive industry, weight loss has immediate results: for every 10% reduction in body weight, fuel consumption can be reduced by 6-8%, acceleration time can be reduced by 8%, emissions can be reduced by 10%, and braking distance can be reduced by 5%. But it's expensive, requiring changes to the material, structure, and process at the same time, and involving the whole body.
In the era of fuel vehicles, only luxury brands or performance cars have the capital to pursue the "devil body", as if answering a question of Olympic number plus points. In the electric era, due to the weight gained by hundreds of kilograms out of thin air, weight loss has become a mandatory question in front of car companies.
01
Body: Liposuction body
In 1985, at the Hannover Fair in Germany, two slender women effortlessly lifted the all-aluminum body of the Audi 100 and pushed open the first arbitrary door of the lightweight body.
Prior to this, aluminum alloy was mainly used in the aviation field, and its composition was once regarded as a state secret by Germany, and then slowly entered the automotive field. Compared with traditional low-carbon iron, aluminum alloys are one-third lighter, more flexible and plastic, and can better absorb collapse (that is, disperse the collision kinetic energy by deformation).
However, a new material wants to be accepted by the mass production car, but the performance is not enough, replacing the new material requires a new process or structure, only the three can achieve a balance between "quality - cost - performance".
Eight years later, Audi officially unveiled the ASF (Audi Space Frame) concept car at the Hannover Show, an unpainted car that shines with dazzling silver and is also the prototype of the A8. In 1994, the first-generation Audi A8 with an all-aluminum body was officially mass-produced, and its weight was 248 kilograms lighter than the previous generation of flagship cars.
This is mainly due to the structural design of ASF, and the core logic is to put the right material in the right place. For example, in positions such as A-pillar, B-pillar and stringer, high-strength materials are used to select lower-cost steels in other places, so as to minimize the weight of parts under the premise of meeting the crash requirements and not affecting the performance of the vehicle.
With the all-aluminum body and ASF structural design, the process is poor.
The traditional low carbon steel is mainly welded by resistance, which is low cost and fast, but it does not match the aluminum alloy. Until 1999, the Audi A2 car used laser welding for the first time, which greatly solved the problem of connecting the aluminum alloy material and promoted the application of the all-aluminum body.
With the passage of time, more and more lightweight materials have also been put on the car, including high-strength steels, magnesium alloys, titanium alloys and carbon fiber composites. For car companies, the richer the materials on the body, the more difficult the connection in the process, and the more complex the structural design.
For example, the latest generation of Audi A8 is no longer an all-aluminum body, but uses 4 kinds of materials including carbon fiber and magnesium alloy, aluminum alloy accounts for only 58%, and even the weight is about 50 kg heavier than the previous generation. But that doesn't mean that lightweighting is no longer important, but there's another reason.
On the one hand, because materials like carbon fiber are still somewhat unattainable, about 120 to 200 yuan per kilogram, equivalent to 4 times that of aluminum alloys, and the efficiency of production is much lower than that of stamping. On the other hand, car companies continue to make breakthroughs in structure and connection process, which can use different materials to the extreme, enhance stiffness and safety while reducing costs, so as to obtain a "perfect body", which is more cost-effective than all-aluminum.
The new generation of Audi A8 body material composition
In other words, the process can make up for the defects of the material itself by means of combined processing.
With the popularity of electric vehicles, car companies can not only pursue the ultimate performance, but also consider the issue of making money. For example, in 2018, BMW launched a new i3, in order to expand sales, the body changed from carbon fiber to aluminum alloy; the body of Tesla Model 3 also changed from the previous all-aluminum to steel-aluminum hybrid (aluminum accounted for about 20%).
Then it's the turn of the process to come into play.
02
Die casting: eight-pack abs
On September 22, 2020, Musk announced that Model Y will adopt a one-piece die-cast rear floor assembly, with parts from 80 to 2, solder joints reduced from the previous 700-800 to 50, and the raw material recycling rate can reach more than 95%. After one operation, the total weight of the body is reduced by 30%.
To some extent, Tesla's choice of integrated die casting technology is both a helpless move and a risk.
The die-casting process has long existed in automobile manufacturing, and its principle is simply similar to injecting molten metal into the abrasive, waiting for cooling to get a molded metal casting. However, because the thermal expansion and contraction in the molding process is prone to errors, the scope of application is relatively limited, and the die casting parts of traditional car companies are often replaced by non-structural parts, and the integrated die casting is tested on large structural parts, which is the first time.
Tesla's process upgrade this time is equivalent to directly pressing out an eight-pack abs from a bulging belly, eliminating the link of fitness running.
Integrated die casting combines stamping and welding processes, simplifying the manufacturing process of body-in-white, and the sharp reduction in the number of parts also reduces mold development and assembly costs, and greatly reduces the use of robots. At the same time, a die casting machine covers an area of only 100 square meters. According to Musk, tesla factory footprint after the use of large die casting machines has been reduced by 30%, and manufacturing costs have been reduced by 40%.
This approach not only hedged the adverse impact of the Model 3 body from all-aluminum to steel-aluminum hybrid weight gain, but also further improved production efficiency and expanded sales.
Although integrated die casting is a new technology, there are uncertainties and challenges in equipment, materials, processes and costs, but this does not prevent the automotive industry from blowing up a die casting storm in the past two years, including new forces such as Weilai, Xiaopeng and Huaren Express, as well as Volvo, which is more radical in electrification transformation, are actively embracing this new technology.
Overall, integrated die casting is a huge change in traditional automotive manufacturing processes. Its role is not limited to reducing the weight of the car body, but a systematic upgrade of the production efficiency of the car.
03
Sandian: Optimize the skeleton
In an electric car, batteries, motors and electronic controls account for 20-40% of the total weight, and with the urgent need to reduce weight, this "elephant in the room" came to the front of the stage.
According to traditional thinking, the first reaction is to change the material. For example, the battery Pack housing is changed from steel to aluminum. As early as 2019, CATL announced that the aviation-grade "7 series aluminum" would be used in the box under the battery pack, which could reduce the mass of the vehicle by 250 kg and increase the energy density of the battery system by 50% [12].
The second is structural design, turning zero into wholeness. For example, BYD's "eight-in-one" electric drive system can reduce the volume of parts by 20% and reduce the weight by 15% under the same power by integrating different modules. In addition, GM's Ultium all-electric platform can also reduce the wiring harness arrangement by 90% through the wireless BMS system.
But these do not touch the core of the battery pack weight reduction. The battery pack has two significant characteristics: one is that the battery cell weight occupies more than 60% of the weight; the other is that its level is complex, including not only hundreds of modules packaged from thousands of cells, but also BMS, cooling systems, high-voltage wiring harnesses and housings.
Therefore, the most effective weight loss is the right medicine. Compared to marginal improvements on the housing and BMS, the skeleton can be optimized by changing the shape of the battery cell and the way the entire pack is grouped. In addition, the simplest and most effective way to increase the energy density of the system is to deintermediate and reduce the number of intermediate structural parts.
In 2020, BYD launched a blade battery, a long and thin single cell shaped like a blade, directly skipping the module link and integrating the battery cell into a battery pack, which is called CTP (Cell To Pack). Other peers such as CATL and Hive Energy have adopted the same design idea.
Although CTP omits the module, but the shell weighing hundreds of kilograms still exists, at this time there is a bolder idea in the industry: since the battery is tiled at the bottom of the vehicle, why not simply use the body floor as a battery shell, integrate the body, battery and chassis into a whole, and make the battery directly into the whole vehicle structural parts.
This idea is somewhat "first principles", equivalent to thinking of the battery as gasoline, and the space between the body and chassis as the fuel tank. In Musk's words: "There's no need to put another box inside the box." ”
In 2020, Tesla officially announced CTC technology. Musk said that after adopting this technology, 370 parts can be saved, the weight of the body can be reduced by 10%, and the cost of batteries per watt-hour will also be reduced by 7%. At the Berlin Gigafactory conference last October, Tesla unveiled the 4680 battery pack, which can be directly used as part of the body structure.
Compared with CTP, CTC can not only improve the energy density of the system to a higher level, but more importantly, its emergence can allow battery factories to break through the scope of battery packs and directly extend the technology to the chassis development, which is the most critical component of the whole vehicle.
The first person in China to propose this idea was Zeng Yuqun. At the beginning of 2021, CATL announced that it will launch CTC (Cell To Chassis) technology around 2025, integrating the battery cell and chassis together, which can make the range of electric vehicles reach more than 800 kilometers.
If changing materials and structural design is likened to finding ways to make a person's clothes lighter, then CTP and CTC, which have been mass-produced, are trying to reduce the body fat rate of the person itself.
04
End
Someone once asked a question: "How hard is it to improve the 100-meter dash by 0.1 seconds?" ”
Su Bingtian, who was most qualified to reply to this question in China, personally replied: "That is too difficult." 0.1 seconds is great, and increasing 0.01 seconds is a bit difficult. I went from 9.99 to 9.91 (0.08 seconds up) for 3 years. ”
The same principle can also be applied to the energy density and weight reduction of electric vehicle systems, the endurance from 300 km to 600 km is relatively easy, but the more difficult the technological breakthrough, the higher the cost of marginal improvement.
But this does not mean that there is no need to gnaw on this hard bone, on the contrary, the more difficult things must be done, because the new energy vehicle revolution can never be achieved overnight, but from quantitative change to qualitative change in bit by bit.
[1] Automotive Lightweight and Integrated Die Casting Industry Analysis, Orient Securities
[2] A question that many people are concerned about: What is the difference between a pure electric vehicle and a gasoline car? , pure electric car EV
[3] [Car dismantling] To tell the truth, aluminum body is a new technology? You can go punch in the face, the car demolition workshop
[4] The lightweight technology of the Audi A8 bull fork, strictly speaking
[5] Tesla is changing what the automotive industry is about "all-in-one die casting," Reger Assets
[6] Zhongding shares in-depth report: intelligent chassis business force, rubber parts leader to usher in a new growth period, Western Securities
[7] The skateboard chassis is too hot, and Tuopu Group also wants to enter the game, the Gestapo auto community
[8] Tesla Model S Weight Distribution，Teslarati
[9] Automotive industry integration die casting thematic aluminum die casting to large-scale integration development, Guosen Securities
[10] Punch output? No! "Cast" production is sexy! Garage number 42
[11] Manufacturing is the first productive force, and all-in-one die casting is the cost code, have you mastered it? The heart of the car
[12] Pack lightweight Ningde era chooses "7 series combat aluminum", high-tech lithium battery
【Live Preview】
At 8:00 p.m. on April 28 (Thursday), Lei Ming, chief planner of the "Company Case Class" of the Investment Academy, and two other producers shared macro and industry insights under the epidemic and took stock of 24 companies.