According to foreign media reports on September 15, citing five people familiar with the matter, the American electric car manufacturer Tesla has achieved a technological breakthrough by combining a series of innovations and is expected to die-cast the underbody of its electric car in one go. This could change the way Tesla builds electric vehicles and help CEO Elon Musk achieve his goal of halving the cost of producing electric vehicles.
Tesla is the first in the industry to use a giant die-casting machine with a pressure of 6,000 to 9,000 tons, and uses a "thousand-ton level" process to integrally die-cast the front and rear bodies of Model Y. This approach significantly reduces production costs, leaving competitors scrambling to catch up.
To expand its lead, Tesla is about to launch a manufacturing process innovation that will enable the complex underbody of electric vehicles to be die-cast in one piece, rather than assembled from about 400 parts like traditional cars, people familiar with the matter said.
Sources said that this technology is the core content of the "Unboxed Assembly Process" manufacturing strategy announced by Musk in March this year. It is a key strategy for him to produce tens of millions of cheap electric vehicles in the next 10 years and still achieve profitability.
Tesla says its "out-of-the-box" manufacturing model involves the simultaneous production of large modules of the car before assembling them together. But people are speculating about the size and composition of the various modules in the car.
Terry Woychowski, president of the American engineering company Caresoft Global, said that if Tesla can successfully cast the underbody of an electric vehicle in one go, it will definitely further subvert the way cars are designed and manufactured.
Wachowski worked for American automaker General Motors for more than 30 years. "It's a stimulant and has a huge impact on the automotive industry, but it's a very challenging task," he said. "Casting is very difficult to do, especially the larger and more complex castings."
Two of the sources said this previously unreported new Tesla design and manufacturing technology means the company can develop a car from scratch in 18 to 24 months, compared with the three to four years that most rivals currently may need.
If all goes well, Tesla's small electric car could use a single large frame that combines the front and rear bodies and chassis, five people familiar with the matter said. The company aims to launch an electric car priced at $25,000 around 2025.
Tesla is expected to decide as early as this month whether to die-cast the vehicle's underbody as a whole, three sources said. Even if the company continues to advance this manufacturing process, the final product may change during the design verification process.
Neither Tesla nor Musk responded.
3D printing andindustrial sand
Tesla's technological breakthroughs focus on how to design and test giant molds for mass production of large-size parts, and how to die-cast hollow frames with internal stiffeners to reduce vehicle weight while improving crash resistance.
Five people familiar with the matter said both innovations were developed in collaboration between design and casting experts in the UK, Germany, Japan and the United States, using 3D printing technology and industrial sand.
Until now, automakers have shied away from casting larger body structures due to the "giant casting dilemma." Although using molds that can make parts of 1.5 square meters or larger can indeed improve production efficiency, it is costly and involves countless risks.
According to one casting expert, once a large metal test mold is made, it can cost $100,000 to adjust a machining operation during the design process, and it can cost $1.5 million to re-make a mold. Another expert said that the entire design process of a large metal mold usually costs about US$4 million.
Sources say the automaker considers this unacceptable. Especially from the multiple perspectives of noise and vibration, assembly and polishing, ergonomics and crashworthiness, the design may require six or more adjustments to create a relatively perfect metal mold.
But sources said Musk wanted to find a way to cast the underbody in one piece, despite the risks.
To overcome these obstacles, Tesla turned to companies that use 3D printers and industrial sand to create test molds. The 3D printer uses an input digital design file to deposit a liquid adhesive on a thin layer of sand, layer by layer, building up a mold into which the molten alloy can be cast.
Sources revealed that the cost of the design verification process for sand casting mold prototypes is the lowest. Even if multiple versions need to be iterated, it is only 3% of the cost of metal prototypes.
This means Tesla can make as many adjustments to the prototype as needed, using machines from companies like Desktop Metal and its subsidiary ExOne to reprint a new prototype in a matter of hours.
Two of the sources said that the design verification cycle for sand casting mold prototypes only takes two to three months, while metal mold prototypes take six months to a year.
Special alloy
The subframe of a car's underbody is usually hollow to reduce weight and improve crashworthiness. The current common practice among car manufacturers is to stamp and weld multiple parts, leaving gaps in between.
To cast the hollow subframe, Tesla plans to place a 3D-printed solid sand core throughout the casting mold. Once the part is cast, the sand core is removed.
But even as Tesla achieves greater flexibility in the face of complex large-scale frameworks and design processes, there's still a major hurdle that needs to be addressed.
The aluminum alloys used to produce castings behave differently in sand molds and metal molds, often failing to meet Tesla's crashworthiness and other standards.
Casting experts overcame the problem by formulating special alloys, fine-tuning the molten alloy cooling process and post-production heat treatment, three sources said. Once Tesla is satisfied with the mold prototype, it can invest in creating the final metal mold for mass production.
Sources say Tesla's upcoming small electric car is a great opportunity for it to build a complete electric vehicle manufacturing platform, mainly because of its simpler underbody.
The small electric car Tesla is developing has a small hood and a small trunk, so the front and rear overhangs are short.
"In a way, it's like a ship, a battery tray with little wings on each end. It makes sense to make it one piece," said a person familiar with the matter.
However, sources said that if Tesla decides to die-cast the underbody in one piece, it still needs to decide which giant die-casting machine to use. The choice will determine the complexity of the body frame.
People familiar with the matter said that in order to quickly stamp out such large body parts, Tesla will need a larger die-casting machine with a pressure of 16,000 tons or higher. This equipment is more expensive and requires a larger factory area.
Three of the five sources said that one problem caused by the increased pressure on the die-casting machines is that they cannot accommodate the 3D printing sand core required to create the hollow subframe.
People familiar with the matter said Tesla could solve these problems by using a different type of die-casting machine. This die-casting machine slowly injects molten alloy, a method that produces higher-quality castings and is also compatible with sand cores.
But this process takes longer.
"Tesla still has the choice of a high-pressure die-casting machine to increase productivity, or a slow-speed injection of molten alloy to improve quality and versatility," one of the people said. "At this point, it's still a 50-50 decision."