Is Unibody Die-casting The End Game For Car Manufacturing?

"Die-casting is made of iron," said one investor.

However, the income of "blacksmiths" has risen in the past two years: in 2020, the average monthly income of a technician with 5 years of die casting experience in the Pearl River Delta region is about 10,000 yuan, and now it has risen to 15,000 yuan, and the supply is in short supply.

"Now I think (the popularization of integrated die-casting/high-pressure die-casting will be) very fast." Luo Yan, a researcher at the Intelligent Manufacturing and Equipment Research Center, told "Electric Vehicle Observer": "As far as I know, some traditional OEMs have New models with one-piece die-casting components will be released, and basically most of the new models from other OEMs will be released next year.”

One-piece die-casting, FSD, and CTC are regarded by investors as Tesla's three major technological killers. They are also the basic technologies for Musk's vision of building cars like Lego. Mercedes-Benz has begun to develop and deploy a new manufacturing process.
But some people are not optimistic. The founder of Qiantu Automobile, Lu Qun, recently released a picture of a 3D-printed integrated body, with an annotation: "This is more than Musk's 'one-time die-cast aluminum body' NB. Technically, there is no need to engage in personality cult."

SAIC, BYD, GAC and many other companies have paid attention to integrated die casting as a cutting-edge technology, but have not yet had a clear investment application plan.

Is one-piece die-casting a technological revolution for weight reduction, cost reduction, and efficiency enhancement, or is it an over-the-top myth?
Why do some people flock to it, and some people stand on the sidelines?
In the process of turning cars into LEGOs, what technical barriers are still to be broken for one-piece die-casting?

This article is divided into three parts: "How Tesla reinvented the one-piece die-casting", "Why some people do it and some don't", and "The current core technical barriers of one-piece die-casting". The difficulty of reading increases in turn. I wish you a happy reading.

01
Tesla re-invents unibody die-casting

Because of Tesla, "one-piece die-casting" has become a "hot word" in public awareness in the past two years. But just like Volvo has already tried autonomous driving technology on the road as early as 2012, one-piece die-casting has long been used in car manufacturing.
Simple illustration of high pressure die casting


Engines, gearbox housings, subframes of chassis, control arms, and steering knuckles are small in size and complex in structure, all of which are fabricated at one time by casting (including low-pressure casting and high-pressure die casting).

Even die-cast aluminum alloy body parts technology has long been used in mass-produced models: the Cadillac CT6, which went on sale in 2018, uses larger die-cast aluminum alloy parts, reducing body parts from 227 to 31. Only the central part of the cabin is made of steel. The number of body frame parts is reduced by 20%, and the weight is reduced by 99 kg.
 

Cadillac CT6 body components

"Before Tesla came out, CT6 was the benchmark for one-piece die-casting, representing the highest level of aluminum casting in body applications, and it was used very reasonably." A head of research and development at an OEM told Electric Vehicle Observer.

And the "heat-free material" that is regarded as the basis of one-piece die-casting has long been available.

The Mn (manganese) Mg (magnesium) series 560 heat-free cast aluminum alloy developed by Alcoa in 2008 has been applied to die-cast Nissan GT-R door parts, with a projected area of 0.5 square meters, a wall thickness of 2-3 mm, and a weight of only 0.5 square meters. 5.5 kg, 35% weight loss.
 

Domestic heat-free aluminum alloy die-casting shock tower

During the 13th Five-Year Plan period, China has established a key project for the development of die-casting aluminum alloy materials for body parts, which can die-cast parts with a projected area of less than 0.5 square meters at one time, and has been successfully applied to aluminum alloy shock towers.

Projection area of 0.5 square meters Audi A8 shock tower die-casting equipment, and Lijin 6000-ton die-casting island

However, when the integrated die-casting parts are upgraded from 0.5 square meters of doors and shock towers to more than 1 square meter, the rear body floor weighing 50-60 kg, or even a 3 square meter battery housing, the game is completely different.

From the die-casting machine, heat-free materials to the integrated die-casting process at this scale, everything is blank.

"It (Tesla) can think of using 6,000 tons, or even 8,000 tons (high pressure to do an integrated die-casting process), and it's really awesome." The above-mentioned R&D person in charge said: "This is in our traditional die-casting people. In my eyes, it’s something that you don’t even think about. When making traditional cars, you will consider process performance and equipment performance. The materials and die-casting machines (used by Tesla’s all-in-one die-casting technology) have broken through the cognition of the traditional automobile industry. ."

Yes, when Tesla wants to complete the "game mission" of integrated die-casting large-scale body components, it needs to collect key materials such as materials and machines from scratch, and greatly upgrade its craftsmanship skills.

1.1 Collect key "materials" for the task

The story begins in 2015, when Alcoa released EZCast (an aluminum alloy material with high flow, thermal stability and low shrinkage porosity) developed for high-pressure casting thin-walled parts.

In the same year, Musk hired Charles Coyman, the head of research and development of the integrated aluminum alloy body of Apple's Mac notebook.

As the vice president of materials technology for Tesla and SpaceX, Koyman carried out secondary development of Alcoa's aluminum alloy materials, enabling them to obtain correspondingly better strength, toughness and other key factors without secondary heat treatment. performance.

Tezhila heat-free aluminum alloy die-casting material Get!

The second level is: the machine.

Previously, the maximum clamping force of die-casting machines in the die-casting industry was only 4,400 tons. To make the alloy solution fill the mold cavity of parts with complex structure and larger than 1 square meter before the crystallization time, the "district" clamping force of 4400 tons is not enough. Starting from 6000 tons - a "big machine" that has never been seen in the die casting machine industry.

According to rumors, Musk approached six mainstream die-casting machine manufacturers in the world at that time, and five of them chose to refuse due to the cost of technology development or because they felt that they would not make money. Only the die-casting machine giant from China, Lijin, got on the "chariot" of Tesla's one-piece die-casting.
LK 6000 ton die-casting island

Industry insiders told Electric Vehicle Observer that with the sharp increase in clamping force, the mechanical, hydraulic and electronic control systems inside the die-casting machine need to be completely redeveloped. LK has achieved complete independent intellectual property rights in the process.

Tesla's world's first 6,000-ton super-large die-casting machine Get!

With materials and core equipment, it is only the beginning, and the upgrading of integrated die-casting process skills is the ultimate challenge.

1.2 Practice extreme craft skills

"Such a large-scale product is stepping on the limit. It is necessary to use the entire process parameters and set the parts to the limit state of the equipment." Liang Zhenjin, technical director of Guangzhou Guangzhuang Mould Co., Ltd., who has served North American new energy vehicle companies Speaking to Electric Vehicle Spectator.
Tesla's integrated die-casting factory assembly process

An integrated die-casting unit (die-casting island) includes two core equipment: die-casting machine and die-casting mold, as well as smelting furnace, holding furnace, spraying equipment, pick-up equipment, casting cooling water tank, edge trimming casting peripheral cleaning, cylinder lining conveyor belt, It consists of peripheral equipment such as mold temperature machine and water temperature machine, with a total of 20-30 equipment.

As a project manager, Tesla needs to grind the newly developed heat-free aluminum alloy materials, large-scale parts molds and these twenty or thirty pieces of equipment into a mature set of equipment without precedent or experience. mass production system.

First of all, the limit that must be stepped on is the width of the craft space.

The properties of the metal solution will change with time and cavity

Process space: The size of the impact of process parameter changes on the key quality attributes of the product is called the process space. A larger process space means that when the process parameters change greatly, the impact on the key quality of the product is small, and vice versa.

Under the combination of mature technology and equipment, the process space is often large, each process parameter has a wide process band, and the process "fault tolerance rate" of the entire system is high. For Tesla's one-piece die-casting system, where everything is "new", the fault tolerance rate of the entire process system becomes extremely low.

Secondly, it is the torturous running-in of equipment and systems.

 

One-piece die-casting process demonstration at Tesla's Texas factory

Because of the standard equipment of more than 6,000 tons, all equipment suppliers in the die-casting island are redesigned. The equipment of the entire die-casting island comes from more than ten suppliers, and it is necessary to run-in the software and hardware, process flow and on-site design.

"It is the first time to explore such a large part in craftsmanship, and it is intertwined with molds, equipment, materials, and design. It takes a long time to try and identify which link has a deviation. So the early stage planning is really important.”

The above-mentioned industry insiders said that compared with traditional die-casting workshops, such large-scale equipment of 6,000 tons requires too much equipment coordination, and problems can be eliminated one by one, and all of this must be completed within the mass production timeline, and the pressure of all parties involved. As you can imagine. "If you don't have experience, just bite the bullet and do it."

1.3 One-piece die-casting tuyere

"Bite the scalp" has achieved remarkable results, and the "hard worker" has become a hot object in the capital market.

In terms of materials: In 2019, Alcoa's upgraded EZCast-NHT alloy, NHT is the abbreviation of Non-Heat Treatable.

In terms of machines: In 2019, LK Group released the world's first super tonnage press with a clamping force of 6,000 tons, becoming the only company in the world that mass-produces large-scale integrated die-casting machines. At present, more than 10 die-casting islands have been arranged on the mass production side.

Thanks to its valuable experience in mass production engineering, LK has accumulated important team resources of R&D, management and construction personnel, and has become a general contractor of integrated die-casting process, which can provide turnkey services for foundry companies and car companies.

Lijin's stock has also gained a hundredfold in three years.
Lijin 9000 ton die casting machine

The "player" Tesla has proved its ability as a manufacturing company by upgrading the integrated die-casting process.

"About five or six years ago, we said we wanted to be the best manufacturer in the world, which is a bit counterintuitive. (But) actually (manufacturing) is our strongest competitive advantage." On July 21, Musk said in said at the financial report.
Tesla's patent for an integrated mold

In 2019 and 2021, Tesla has successively applied for a mold for one-piece die-casting large components and patents for integrated energy-absorbing castings.

In September 2020, Musk announced that the Tesla Model Y will use a one-piece die-cast rear floor assembly, which can reduce the weight of the lower body assembly by 30% and reduce manufacturing costs by 40%.

In 2021, Tesla demonstrated Tesla's one-piece die-casting chassis at the Berlin factory open day. It plans to replace the lower body assembly consisting of 370 parts with 2-3 large die-casting parts, reducing the weight by 10% and improving the cruising range. 14% increase.
Tesla's front and rear body process changes

In Q2 2022, Musk said that Tesla's Texas and Berlin factories will reduce the number of body welding robots per unit of production capacity by 70%, and that integrated die-cast parts are lighter, cheaper, and perform well in NVH performance. And future Tesla's electric pickup, the Cybertruck, will bring "another level of simplicity and manufacturing improvements."

Tesla plans to integrate the body into 9 parts through one-piece die-casting in the future. The market has given a market valuation of 100 billion yuan for integrated die-casting.

02
Do something, do something

2.1: The perfect future of one-piece die casting

As Tesla made the impossible possible, unibody die casting became a hot manufacturing process.

Tesla Berlin factory die-casting real shot

Volkswagen, Volvo, and Mercedes-Benz have all launched integrated die-casting production lines or unveiled parts and components.
Weilai ET5 has applied an integrated die-casting rear floor;
The Wuhan industrial base project declared by Xiaopeng Motors last year included an integrated die-casting process workshop, and in January, it signed a contract with Guangdong Hongtu for a 12,000-ton die-casting unit;
In January, Great Wall Seiko joined forces with Lijin, Sevida and Longda Aluminum (Material Company: Lizhong Group Sun Company) to implement the strategic cooperation on the body structure project, and signed a contract to purchase 8,000 tons of die-casting islands;
In February, the 7,200-ton one-piece die-casting floor that Gaohe Automobile cooperated with Topology Group (a foundry enterprise) and Shanghai Jiaotong University officially rolled off the production line.

"One-piece die-casting is not only to reduce weight and reduce the number of parts, but more importantly, it is in line with the future development trend of less humanization and automation." Great Wall Seiko Automobile Co., Ltd. told the "Electric Vehicle Observer".

"The core behind the integrated die-casting is integration driven by agility. As long as the needs of users are still changing with each passing day, the integrated die-casting technology will continue to be applied." Gaohe Auto also said.

"Electric Vehicle Observer" also learned that the production capacity of super-large die-casting machines of many die-casting machine suppliers has been scheduled to June and July next year.

The industry is following this fast because the perfect one-piece die casting is perfect: lightweight, lower production costs, dramatically faster production takt time, improved product accuracy and body material recovery, shorter development cycles, and more.

Manufacturing equipment cost savings:

Guohai Securities estimated the cost of equipment, personnel, and manufacturing for the production of the rear floor of the car body using the traditional process and the integrated die-casting process. Taking a production line with an annual capacity of 500,000 vehicles as an example, the total cost of the traditional stamping and welding process is about 630 million yuan. The cost of the integrated die-casting process is about 480 million yuan, and the rear floor alone can save an average of 300 yuan per vehicle.

Luo Yan said: One-piece die casting will mainly "replace" the two major processes of stamping and welding. "The (stamping, welding) shops are combined into one forming shop. Once the lower body is done with 3-4 die castings, the welding shop may be completely replaced."

"As far as we know, for OEMs that currently plan an integrated die-casting production line, welding robots will be reduced by 15%-25%."

Shorten the development cycle:
Guosen Securities research believes that the integrated die-casting technology shortens the model development cycle to 1/3. In traditional automobile manufacturing, three rounds of comprehensive matching are required for parts such as body, interior and exterior decorations, electrical appliances, etc., to stabilize and stabilize the parts within the tolerance requirements. It usually takes 6 months, which is a long cycle, heavy workload, and repetitive. Sexual work.

One-piece die-casting simplifies the logistics and matching difficulty of components, and shortens the development cycle to 1-2 months.

He Shenghua, general manager of Ningbo Shuyi Gonglian Technology Co., Ltd., told the "Electric Vehicle Observer": "On the one hand, the improvement of efficiency by integration lies in the production cycle, and on the other hand, it reduces the system engineering of development.

It turned out that a component was made up of hundreds of parts from different suppliers. Changing the design requires extensive coordination engineering, and the one-piece die casting simplifies the entire process, shortening the supply chain considerably. "

Increase production takt time

After the one-piece die-casting process is adopted, the number of Tesla Model Y rear floor parts has been reduced from 70 to 1 (integrated) to 2 (spliced); The number of parts has been reduced from 171 to 2, and the number of welding points has been reduced by over 1,600.

The reduction in the number of punching and welding points results in a significant reduction in man-hours.
Under the traditional craftsmanship, get off the body Assembly manufacturing will go through two major workshops, stamping and welding, with a total man-hour of more than 2 hours. Previously, the die-casting time of the Model Y rear floor was about 180 seconds. In the demonstration at the Texas factory, the body manufacturing cycle has been shortened to 45 seconds.

The research of Guosen Securities believes that considering factors such as maintenance and refurbishment, the five large-scale die-casting equipment in the Shanghai plant can meet the annual production capacity of up to 600,000 pieces of body rear floors. In July, Tesla’s Shanghai plant was shut down again for technical renovations, after which it will reach a peak production capacity of 1.1 million vehicles per year by the end of the year (reported by Reuters), which is a production capacity scale that has never been achieved by a single traditional OEM.

Improve the accuracy of the body workpiece:

"The accuracy of the next-generation Model Y vehicles will be measured in microns, not millimeters." Musk said.

The improvement of the accuracy of the body workpiece not only helps to better realize the aerodynamic design, but also more effectively arranges various types of automatic driving sensors to meet the installation accuracy of the yaw angle, pitch angle, and roll angle.

In contrast, due to the accumulated error of a large number of parts splicing, the accuracy error of traditional body craftsmanship will be within 2 mm.

Improve material recycling efficiency:

Because one material is used, and the high-pressure die-casting process itself is conducive to material recovery. Guosen Securities estimates. The raw material recovery rate of the traditional manufacturing process is less than 70%, and the raw material recovery rate of the integrated die-casting manufacturing process is as high as 95% or more.

2.2 One-piece die-casting is not perfect now

But the problem is that the current integrated die casting is not perfect.

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Comparison of the front and rear floors of Tesla's Texas factory with one-piece die-casting and the original parts

Tesla and the die-casting industry have run through the road of 0 to 90% of integrated die-casting. That is even more difficult, and the 10% that can truly achieve the above benefits is still in the stage of all parties. This has also become the reason why some mainstream car companies still take a wait-and-see attitude towards integrated die casting and only use it as a forward-looking topic.

"In the case where the lightweight effect does not have obvious advantages, (integrated die-casting production) does not have a very big improvement in cost, and (commissioning at this stage) is of little significance. We still have to focus on quality, cost, and technology. Three aspects Evaluation,” said the above-mentioned R&D person in charge.

Even companies that have already begun to deploy, such as Great Wall Seiko, said: "After our calculations, the current one-piece die-casting does not have an advantage in cost. However, with the continuous updating and development of industry technology, the future manufacturing cost will definitely decline, so we It is believed that the integrated die-casting process has huge development space in the future.”

The integrated die-casting technology with a completion degree of 90% is still very immature in terms of weight reduction effect, production scale, production stability, vehicle performance, and after-sales system.

Ineffective weight loss:

The fundamental purpose of Tesla's integrated die-casting process is to reduce the weight of electric vehicles by applying aluminum alloys in a large area. But from the actual effect, it is currently in the stage of ineffective weight loss.
After dismantling two generations of one-piece castings of Tesla Model Y, a car company found:

The first generation (left and right split type, middle bolt link) is 54 kg;
The second generation (completely one-piece, with the addition of a rear longitudinal member) weighs 65kg.
Compared with the same parts of the Tesla Model 3 on the same platform, the weight is reduced by 0.5 kg and 3.4 kg respectively. In contrast, under the premise of a steel wheel cover, the all-aluminum component of a self-owned brand model is 42 kg, which is even 12 kg lighter than the first-generation one-piece component of Model Y.

The problem lies in the current craftsmanship of one-piece die casting.

As a high-pressure die-casting process, one-piece die-casting is intended to use a very high injection speed so that the alloy solution can fill the mold within a limited time to manufacture thin-walled workpieces. However, with the expansion of the mold, the time and pressure of the small position at the far end are greatly expanded, so the wall thickness of the workpiece has to be thickened to reduce the difficulty of filling and realize the process.

For example, the wall thickness of ordinary steel wheel covers is only 0.7 mm, but the thickness of Tesla Model Y is 2.5 or even 3 mm. "In order to consider the craftsmanship, it was thicker (designed), which resulted in ineffective weight reduction." said the person in charge of research and development.

Great Wall Seiko also said that the one-piece die-cast rear floor weighs about 55-63 kilograms. "If you look at a single part, it does not have a great weight advantage for sheet metal parts (currently). However, according to the practical experience of domestic car companies, the changes in body design due to the use of one-piece die-casting do have an impact on the entire vehicle. weight loss.”

Material properties affect vehicle performance:

At present, both Tesla and Weilai have adopted one-piece die-casting technology in the rear floor position. Because the rear collision is mainly borne by the rear anti-collision beam and the rear longitudinal beam, the collision force is relatively small when it is transmitted to the rear floor, which has little impact on the safety of the vehicle.
The current application of ultra-high strength steel in the body

"The heat-free aluminum alloy materials used in integrated casting cannot be compared with the mechanical properties of steel plates or even hot-formed steel plates in terms of material properties. Its welding process is currently not as mature as that of steel plates." Liang Zhenjin said, "Therefore, The index value of the vehicle design and the information related to the safety design need to be re-explored, and the steel body parts cannot be completely matched.”

Previously, the overall body also obtained a certain overall performance through the splicing between parts. The main body connection process is FDS (single-sided self-tapping thread connection), and SPR (self-piercing riveting process is a cold forming process that forms a firm interlock between the rivet and the sheet).

This process has certain requirements on the plastic deformation ability of the aluminum alloy. And when the deformability becomes poor, it will also affect the performance of the connection process.
New material properties of Alcoa C611 currently used in the mainstream of surface heating materials

"The plastic deformation ability of materials is generally evaluated by bending. The bending angle of traditional die-casting aluminum alloy T7 after heat treatment is generally 60 degrees. However, there is still a certain gap between the heat-free die-casting aluminum alloys on the market." Responsible for the above R&D people said.

Therefore, models that plan to use one-piece die-casting technology need to be redesigned, or the transmission path of the crash force needs to be changed to avoid the one-piece die-cast material, or the reinforcements are made of high-strength steel.

"As far as we know, because Tesla's front floor adopts integrated die-casting technology, the force transmission design path of the vehicle needs to be re-designed, which is completely different from the transmission path of the traditional steel/steel-aluminum hybrid body." Luo Yan said .

High scale threshold and low yield:

And to deploy integrated die-casting, it is necessary to have the ambition of producing 20 million vehicles a year for several cars like Tesla.

"The core threshold of integrated die-casting is to achieve stable production." The above-mentioned industry insiders said that the one-time continuous production of 5,000 (10 days)-20,000 (30-40 days) pieces is the more economical scale for large-scale integrated die-casting components.

If the scale is not large enough, integrated die casting is not a "good business".

The above-mentioned investors calculate that the annual output value of a die-casting island with a cost of 100 million yuan is about 200 million yuan, of which the material cost is more than half, and the manufacturing cost accounts for more than 30%. And the assets are too heavy.”

The analysis of Western Securities believes that taking a 6,800-ton die-casting island with an annual output of 100,000 pieces of equipment as an example, it is necessary to ensure full-day operation and a yield rate of 80-85% in the batch stage to achieve a gross profit of 25-30%. interest rate, so as to take into account operating costs and annual output value.

At present, the yield rate of one-piece die casting has just passed the cost line.

The yield rate of traditional steel body stamping parts can reach 99%; the yield rate of die-casting parts under 4400 tons is over 95%;

The current situation of "Electric Vehicle Observer" is that Tesla, which was the first to run through the integrated die-casting technology, currently has only a 90% yield rate.

Talent and after-sales challenges:

In addition to the current material and process problems of integrated die casting, talent and after-sales problems are also key challenges for full implementation.

Die casting is a small craft category, and high-level professionals in the industry are scarce. If an enterprise wants to deploy an integrated die-casting process, it needs a high-level craft team to ensure continuous and stable production. "Tesla is still recruiting people for die casting." Luo Yan said.

In addition, after-sales is also a problem. Previously, the owner of the Tesla Model Y revealed that the repair cost was nearly 200,000 yuan due to the crash of the rear shock absorber. The vehicle itself is only 280,000 yuan.

In this regard, the industry believes that Tesla itself will reduce the occurrence of collisions by implementing high-level intelligent driving assistance capabilities, as well as its own accurate insurance system to dilute after-sales costs.

However, Luo Yan told "Electric Vehicle Observer" that some OEMs are exploring starting from the design of materials and parts, by redesigning the force transmission path, and parts do not participate or partially participate in collisions; the development of innovative die-casting aluminum alloy repair technology, to avoid/reduce the stress of aftermarket repairs for collisions.


03
Break the last 10%

"People, machines, materials, methods, and rings must be done very well." The above-mentioned industry insiders said that the yield rate of the integrated die-casting process will rise from 90% and it will depend on time.

Luo Yan holds the same view: "The difficulty of one-piece die casting lies in the cooperation of materials, processes, molds and equipment. Everyone is in the exploration stage, and Tesla has a 3 to 5-year lead."

The four major processes of punching, welding, coating and total in the automotive industry have taken nearly a hundred years to form today's complete process skills, stable production processes and yield rates that are highly suitable for mass production needs.

It has only been less than two years since Tesla released the Model Y with an integrated rear floor, and people, machines, materials, process methods, and environmental systems are still trudging on the road to 100% maturity.

3.1 Loss of benefit from heat treatment

"In theory, Tesla's patented materials cannot be directly used. In fact, Tesla's materials may not be suitable for all car models." An expert in the field of materials said at the end of 2021: "At present, we are The materials that the OEM is testing also have ingredients similar to Tesla materials. What I have learned, the actual effect is not very good. On the contrary, there are some other types of materials, and now it seems that the probability of success is higher.”

Heat-free material is the core reason that restricts the wide spread of integrated die-casting technology.
Schematic diagram of heat treatment

Heat treatment is the main means to obtain/strengthen properties (strength, plasticity, impact toughness, hardness, fatigue strength, etc.) of traditional die castings and adjust the internal crystal balance.

Die castings generally pass through T7\T6 two heat treatment methods. Specifically, T7: solution treatment plus stabilization treatment, artificial correction will be very difficult; T6: solution treatment plus complete artificial aging, the deformation of the workpiece can only be leveled after this heat treatment method.

However, the secondary thermal expansion and cold contraction caused by heat treatment will cause dimensional deformation of the product, or generate pores. Small parts can be corrected by means of shaping tooling (by means of mold shaping).

The temperature, pressure and mold flow in the die-casting process of large-scale structural parts are more difficult to control, and there will be more product deformation problems caused by heat treatment. The cost of post-shaping is extremely high, and the process is more complicated, making it difficult to achieve commercialization.

Therefore, the aluminum alloy material used in traditional die casting, which requires heat treatment to enhance its performance, does not meet the mass production requirements of large-scale integrated die casting.

Heat-free cast aluminum alloy materials with corresponding mechanical properties can be obtained without heat treatment.

However, after avoiding the "trouble" of orthopedics caused by heat treatment, heat-free materials also lose the opportunity to obtain stronger mechanical properties and adjust and balance the internal crystalline structure of the alloy through heat treatment.

Larger workpiece sizes and more complex workpiece shapes further magnify these problems.

Therefore, heat-free materials currently face two major challenges in the material itself: how to obtain higher mechanical properties comparable to stamped parts; how to reduce the sensitivity of parts performance to internal defects/internal structure of the alloy;

There are also two major problems at the process level closely related to materials: how to ensure the balance of the overall performance of large parts, and avoid the inconsistency of strength/toughness performance in one place and another; how to solve the problems caused by insufficient ductility of materials The problem of poor connection process performance.

3.2 What kind of heat-free material is needed?

However, the crux of improving the performance of heat-resistant materials currently does not lie in the material formulation, and the industry has not yet made it clear what kind of heat-resistant materials are needed.

Because in order to clarify the material properties required by the heat-free material, it is necessary to redesign and study the structural properties of the integrated parts from the initial original design; after that, the required strength of each part and the impact resistance under collision are judged through simulation analysis. What is the elongation requirement?

And this can only start from the OEM. Material experts said: "At present (by the end of 2021), some of the demands put forward by domestic OEMs are very rough and inaccurate. Car companies are also trying one-piece die-casting, and material factories are even more unclear about the specific situation. ."

Great Wall Seiko said: "One-piece die-casting materials are different from conventional products in terms of strength and toughness, mainly due to differences in product functions. As a body part, the main consideration is the improvement of the strength and stiffness of the body, but in terms of toughness Mainly based on body shock absorption and connection process requirements.”

At present, some companies have made breakthroughs in relatively formed heat-free aluminum alloy casting materials.

Germany Rheinfelden, Alcoa, China Lizhong Group and Shanghai Jiaotong University material team have patents for heat-free materials. However, some experts told "Electric Vehicle Observer" that Lizhong Group's heat-free materials are still mainly used in small castings. At present, the mainstream commercial heat-free materials for one-piece die casting are still concentrated on the material basis of Alcoa.
In specific applications, Tesla's grasp of the performance of heat-free materials is more advanced.

Luo Yan said that after secondary development, the strength of Tesla's materials used in the front cabin may be more than 50% higher than that of the rear floor. "Normally (after the strength is increased) the toughness will be slightly reduced, but according to our current understanding, the toughness of the aluminum alloy material in the front cabin is now better controlled."

In addition, many domestic car companies and foundry companies have announced that they have the ability to develop heat-free materials.

In October 2021, NIO and Shuaiyichi jointly developed the EZCAST series of integrated die-casting heat-free and toughened die-casting aluminum alloy materials, which will be applied to the second-generation platform models.

In December 2021, Human Express Auto and National Engineering Center for Light Alloys of Shanghai Jiaotong University reached a strategic cooperation in the development of new materials and low-carbon light alloys.
TechCast™ Low Carbon Aluminum Alloy for Oversized Casting. In February this year, the foundry company Topp and Human Express Gaohe jointly mass-produced the off-the-line body rear cabin. The long model reached 1700mm*1500mm, achieving a weight reduction of 15-20%.

In China, Luo Yan said that the high-performance one-piece die-casting heat-free casting aluminum alloy of Shanghai Jiaotong University, Tsinghua University, Beijing University of Science and Technology and other material teams has passed the laboratory test, and the technical maturity has reached the level of 5 and 6. In the production testing stage, actively seek mass production opportunities.

In view of the insufficient performance of heat-free materials and the impact on the performance of the connection process (mainly SPR), some car companies have developed technologies to ensure the connection performance under the condition of low material elongation.

"Currently, the development of aluminum alloy materials for integrated die casting is still in the initial stage.Factories, R&D institutions, material suppliers, and die-casting suppliers are all contending to promote their own materials, but the final selection of materials still depends on the comprehensive consideration of the basic performance, manufacturing performance and cost of the material by the target parts of each OEM. "Gaohe Automobile:" In the long run, the aluminum alloy materials used for integrated die casting will definitely form a differentiated and serialized grade system to meet the individual needs of various OEMs and parts. "

Liang Zhenjin said, "The key to controlling the development goals and reasonably improving the product qualification rate is to grasp the demand for parts for the performance of the vehicle."


3.3, reducing the standard to meet the process

According to the process, after the heat-free alloy material is confirmed, the alloy liquid is poured into the mold and pressed with a die-casting machine. But the current status quo is that there is no perfect integrated die-casting gating system and matching mold.

"At present, the development system of integrated die-casting in the whole industry is not perfect, and the research and refinement of the basic principles still need to be further explored." Liang Zhenjin said: "The existing development projects are still on the road of imitation, and a lot of information may not be That's what happened."

The reason for "it's not like that" is that in order to deploy the integrated die-casting technology, it is necessary to re-learn from the underlying principles of die-casting.

As mentioned earlier, the stamped steel wheel can be 0.7 mm thick, and the wall thickness of the one-piece die-cast Tesla Model Y is 2.5-3 mm. The increased wall thickness eliminates the weight savings brought about by the aluminum alloy material, resulting in ineffective weight savings.

Tesla's 6,000-ton die-cast rear body

The reason is to form the Model Y integrated component structure with the current capability of the die-casting island system. "To ensure the filling of the distal end of the component and the mechanical properties after forming, it is necessary to appropriately thicken the product wall thickness in some areas." Liang Zhenjin express.

At present, the clamping force of the die-casting machine and the projected area of the die-casting parts are used as a quantitative standard for what kind of machine can do large-scale workpieces. For example, a clamping force of 6000-7000 tons can die-cast parts with a projection area of 1 square meter; if the floor projection area of a pure electric pickup including a battery compartment is greater than 1.5 square meters, a clamping force of 12,000 tons is required.

But this simple correspondence does not apply to process practice.

In the process of practice, Liang Zhenjin deeply realized that the projected area only involves bulging force: in the process of die casting, when the filling ends and turns to the supercharging stage, the supercharging specific pressure acting on the solidifying metal is poured through the metal casting. The row system transmits the cavity wall, which is called the bulging force. The process parameters need to be arranged so that the mold is just able to withstand this force.

It is more important to get a filling process that is fast enough. This means that a fast enough speed is required - involving the equipment flow Q, and a large enough driving force at the corresponding speed - the dynamic injection force P.

If the average wall thickness of parts about 1 square meter is too thin, or the modeling channel is complicated, the current level of dynamic injection force and flow of the 6000-7000 ton press often cannot fully achieve the goal.

"Because the power provided by the equipment system during the filling process is not enough to ensure that it can overcome the resistance (in a complex cavity)," Liang Zhenjin said: "For factors such as the shape of the parts during the filling process, the distribution of wall thickness and other factors, the gating system The shape design is a more important factor to measure the matching degree of parts and equipment."

3.4, learn the principle, re-understand the casting process

However, the premise of considering the above important elements is a deep understanding of the underlying principles of the die-casting process.
For example, a very critical process parameter in the die casting process: filling time - the alloy cavity filling is completed within this time.

Because the fluidity of the alloy has a certain time/temperature range, it will enter the crystallization zone after exceeding the range. Once the crystallization begins to form, the fluidity of the alloy will be greatly reduced, it is difficult to fill the cavity, or the surface quality of the part will be affected.

There is already a mature calculation formula for filling time: NADCA (North American Die Casting Association) filling time formula - which is one of the underlying principles of the casting process.
Example of how the NIADCA formula is applied

However, the accuracy of formula calculation depends on the accurate grasp of surface elements. Such as the solid liquidus temperature of the alloy, the working temperature of the mold, the average wall thickness of the product design, etc.

The accuracy of surface elements is based on the grasp of physical properties. Such as physical properties of heat exchange, material fluidity, textured structure during molding, cooling shrinkage state of alloy molding and corresponding temperature range, etc.

The multi-layer properties and feature conditions will form a mathematical model that ultimately outputs an accurate fill time range through the fill alloy formula.

"The principle of the old beauty has been studied for a long time, but the research on the basic principles of the domestic die-casting industry is relatively slow, and now only about 30% of enterprises have begun to pay attention to it." Liang Zhenjin said.

Like all principles and the accumulation process of knowhow, the underlying principles of the casting process are also based on a large number of experimental analysis. Numerous laboratory explorations and time accumulation are required.

The reason why domestic die-casting enterprises have less research on the principle level is that they were "unusable" in the past. Previously, the die-cast parts were smaller and had a large process space for existing die-casting equipment - for example, a die-casting machine could provide an injection speed of 5 m/s to 12 m/s. When the parts are small, the equipment has enough capacity that the process adjustment can fully control the filling of the product.

However, when the die-casting parts change from the products of the stringer level to the parts of the size and complexity of the rear floor, the process space will be instantly reduced to the upper limit of the equipment capacity.

"Therefore, the requirements for the accuracy of basic principles and underlying calculations/checks are very high." Liang Zhenjin said: "You must first understand the underlying calculations/checks before you can realize the process required for components on the surface layer."
The lack of understanding of the underlying principles is also reflected in the industrial division of labor.

Based on the part design, it is related to how the alloy solution enters the mold and discharge pressure, and adjusts the forming gating system
It is designed and completed by the foundry engineers of the die-casting factory in the European, American and Japanese systems. The mold company is only responsible for designing the mold structure, and then taking care of the machining of the mold.

However, domestic customers often require mold companies to participate or have the ability. The reason is that mold companies have more contact with each link and have more experience to learn from.

However, as the integrated die-casting of ultra-high pressure and large-size parts pushes the process space to the limit, not only material suppliers, but also all chain links in the process will need to learn and make breakthroughs at the principle level from scratch, especially the OEMs.

To this end, the body designer of the OEM needs different materials such as steel, steel-aluminum mixture, and heat-free casting aluminum alloy, the basic principles of the collision force deformation of different parts of the body components, and the overall collapse, and the basic know how of the bottom layer. In-depth mastery and understanding. It even requires a certain understanding and understanding of manufacturing processes such as die casting.

Fortunately, in the past six months, with the continuous enhancement of the equipment capacity of the die-casting island, the process space of the integrated die-casting has begun to be larger.

In November last year, China's first self-developed and designed two-section spliced whole body project came out, and it has entered the fourth round of debugging, and its performance has basically met the requirements for mass production. "The appearance quality and operational stability of this casting are much stronger than similar foreign products." The above-mentioned industry experts said that the elongation of the parts produced by the integrated die-casting front and rear cabin molds that have entered the experimental stage reaches 10% and 10% of the front cabin. 8% in the rear cabin.

3.5, Accumulate simulation data

"Aluminum alloy casting itself is a very complex forming process. At present, it is difficult to accurately predict the mechanical properties of various parts at the beginning of part design. There is still a lot of work to be done." Liang Zhenjin said, "This work is done well. After that, the accuracy of the structural design of the parts can be reversely promoted, and the mechanical properties of each part and the focus of each body part can be clarified, so as to improve the effectiveness of the part design and ensure its economy.”

"Now many of our designs are redundancy arranged to ensure the achievement of the integrated die-casting process. The accuracy is improved and the redundant moisture is reduced, so that weight reduction and energy saving and emission reduction can be truly achieved."

"This work" refers to the collection and analysis of test and practice data in all aspects of integration, and the establishment of an integrated die-casting professional team and simulation database.

For example, in the design of the gating system, the size of the parts is too large, the structure is complex, and the aluminum alloy solution has a sensitive crystallization time period. In order to ensure that the aluminum alloy can fill the cavity within the specified time, the flow of the fluid in the mold requires very accurate simulation to optimize the design of the runner including the liquid inlet and exhaust port.

Not only the gating system, but also the design of body parts and the casting process all require such a highly accurate simulation process. "High-pressure die-casting has the following technical difficulties and problems due to its high temperature, high pressure and high flow rate, and the technical barriers are relatively high. Moreover, integral die-casting components often have porosity defects and bubble problems."
Luo Yan said: "These are a brand-new exploration stage for OEMs and parts companies. Simulation is based on the prediction of the future after the accumulation of big data in the early stage. Therefore, in the absence of accumulation in the early stage, the predictions are all inaccurate. Accurate (causing problems such as lower yield).”

"As the OEM slowly masters the data accumulation, and even the basic methods of mold trial, adjustment of process parameters, optimization of runner design, etc., under the coordination of the whole industry chain, the yield will increase."

The accumulation process of simulation data will depend on the collaborative advancement of the foundry team and industrial big data software.

Industry insiders said: Although there are now die-casting machines and die-casting plants to provide teams, it does not mean that the main engine factory can completely rely on the supplier's turnkey projects, but needs to master the KNOW HOW of integrated die-casting: on the one hand, to achieve high yield rate stable production; on the other hand, it accumulates experience for subsequent parts development.

"The number of equipment and operation complexity of the integrated die-casting island have increased significantly, and it is difficult for process engineers from ordinary die-casting plants to get started quickly." There is a deep understanding of the characteristics of each equipment. If it is one or two people, it will be a lot of pressure. The team is larger, and it is more scientific for each person to be responsible for several process equipment."

At the same time, industrial big data software will also accelerate the maturity of the integrated die-casting industry chain technology.

He Shenghua said, "Casting has high requirements on process parameters. From 90% to higher, it is impossible to rely only on the experience of the master. Instead, it depends on the big data analysis platform of process quality, the data collection of the Internet of Things, and even a lot of deep learning. algorithm."

At present, the digital factory built by Shuyi Gonglian connects all equipment in the die-casting island to the Internet by adapting digital software to collect all process parameters and the result data of subsequent product quality inspections. After this, the data model of the process quality big data analysis platform is established.

"With the accumulation of data, we can look at the composition of raw materials, mold temperature, molten aluminum temperature, process parameters of the die-casting machine, spraying liquid composition, spraying path, etc., so that the qualified rate of integrated die-casting products can be higher." He Shenghua said.

In April, the fully transparent die-casting industry digital factory project of Haiwei and Shuyi Industry Federation was officially launched.

The system will include 14 modules and 35 functions, including planning report management, mold management, quality management, equipment management, and exception management, etc., to achieve real-time acquisition of equipment IoT, real-time acquisition of production report data, real-time transparency of inventory data, and complete quality assurance. Traceability and other goals, build process control quality standards with built-in quality improvement, and create a digital and intelligent factory with traceable processes and traceable quality.

3.6, the die-casting island goes in a larger direction

Compared with the heat-free materials, pouring systems, and overall processes that are still struggling to overcome difficulties, the technological maturity of equipment such as die-casting machines and die-casting islands is relatively higher, and they are moving in a more "big" direction.

Luo Yan told "Electric Vehicle Observer" that as a leading enterprise of large-scale die-casting machines, LK's market share in the field of integrated die-casting has reached more than 50%. The large-scale die-casting machine sold to Tesla before is still a three-platen type. At present, the direct-pressure die-casting machine developed by it has entered the mass production stage.
At present, the mainstream structural design of die casting machines is divided into two-platen and three-platen presses.

Among them, the clamping force of the three-plate die-casting machine is only one. The two-plate type can flexibly control the clamping force within a range due to the use of servo motor driving control. Swiss Bühler excels in two-platen press designs.

Luo Yan said that in addition to the advantages of equipment life, stability and die-casting machine size, the biggest advantage of direct pressure and two-platen presses compared to the past is that the production line is more flexible.

"The die-casting process involves the design of a series of parameters such as injection speed, filling time, mold temperature, etc., which are closely linked and will directly affect product quality.

The price of the direct pressure type and the two-platen type of the same tonnage is not much different from that of the three-platen type press. "The difference between the direct pressure and the two-plate type and the third version is mainly that the requirements for the basic parts of the press are higher, and the requirements for the structure design of the press are also higher."

At the market application level, LK currently has a considerable first-mover advantage.

It is understood that Buhler, Yizumi, and Haitian have all received orders for high-pressure die-casting machines of 6,000 tons and 8,000 tons respectively, but they have not yet been delivered. LK has more than 10 integrated die-casting islands running at the terminal.

After delivering the 6,000-ton machine to Tesla, Lijin's 9,000-ton and 12,000-ton machines have both received purchase contracts and entered the stage of mass production.
One-piece die-casting already has a foothold in the car factory, and in the long run, could transform the car factory.

Combined with other materials and process innovations, one-piece die-casting may make cars as highly integrated and easy to splicing as Lego, making the most difficult sector of human industry - automobile manufacturing, a breeze.

This is Musk's dream, an awesome dream.

However, a technology, from scratch to excellent, often requires a long time and painful running-in process. For a mature, reliable and complete car manufacturer, it is a difficult choice to deploy or not to deploy integrated die casting at this moment.