Two of the sources said Tesla’s previously unreported new design and manufacturing techniques meant the company could develop a car from the ground up in 18 to 24 months, while most rivals can currently take anywhere from three to four years.
The five people said a single large frame – combining the front and rear sections with the middle underbody where the battery is housed – could be used in Tesla’s small EV which it aims to launch with a price tag of $25,000 by the middle of the decade.
Tesla was expected to make a decision on whether to die cast the platform in one piece as soon as this month, three of the sources said, though even if they do press ahead the end product could change during the design validation process.
Neither Tesla nor Musk responded to questions from Reuters for this story.
3D printing and sand
The breakthrough Tesla has made centers on the how the giant molds for such a large part are designed and tested for mass production, and how casts can incorporate hollow subframes with internal ribs to cut weight and boost crashworthiness.
In both cases the innovations, developed by design and casting specialists in Britain, Germany, Japan and the U.S., involve 3D printing and industrial sand, the five people said.
All spoke to Reuters on condition of anonymity because they are not authorized to speak to the media.
So far, automakers have shied away from casting ever-bigger structures because of the “gigacast dilemma”: creating molds to make parts of 1.5 meters squared or more boosts efficiency but is expensive and comes with myriad risks.
Once a large metal test mold has been made, machining tweaks during the design process could cost $100,000 a go, or redoing the mold altogether might come to $1.5 million, according to one casting specialist.
Another said the whole design process for a large metal mold would typically cost about $4 million.
That has been deemed prohibitive by automakers – especially as a design might need half a dozen tweaks or more to achieve a perfect die from the perspective of noise and vibration, fit and finish, ergonomics and crashworthiness, the sources said.
But Musk’s vision from the start was to find a way to cast the underbody in one piece, despite the risks, the sources said.
To overcome the obstacles, Tesla turned to firms that make test molds out of industrial sand with 3D printers.
Using a digital design file, printers known as binder jets deposit a liquid binding agent onto a thin layer of sand and gradually build a mold, layer by layer, which can die cast molten alloys.
According to one source, the cost of the design validation process with sand casting, even with multiple versions, is minimal – just 3 percent of doing the same with a metal prototype.
That means Tesla can tweak prototypes as many times as needed, reprinting a new one in a matter of hours using machines from companies such as Desktop Metal and its unit ExOne.
The design validation cycle using sand casting only takes to two to three months, two of the sources said, compared with anywhere from six months to a year for metal mold prototypes.
The subframes in a car underbody are typically hollow to save weight and improve crashworthiness. At the moment, they are made by stamping and welding multiple parts together leaving a void in the middle.
To cast subframes with hollows as part of one gigacasting, Tesla plans to place solid sand cores printed by the binder jets within the overall mold.
Once the part has been cast, the sand is removed to leave the voids.
But despite that greater flexibility achieved in both the design process and the complexity of the large frames, there was still one more major hurdle to clear.
The aluminum alloys used to produce the castings behaved differently in sand and metal molds and often failed to meet Tesla’s criteria for crashworthiness and other attributes.
The casting specialists overcame that by formulating special alloys, fine-tuning the molten alloy cooling process, and also coming up with an after-production heat treatment, three of the sources said.
And once Tesla is happy with the prototype mold, it can then invest in a final metal one for mass production.
The sources said Tesla’s upcoming small car has given it a perfect opportunity to cast an EV platform in one piece, mainly because its underbody is simpler.
The kind of small cars Tesla is developing – one for personal use and the other a robotaxi – do not have a big “overhang” at the front and the back, as there is not much of a hood or rear trunk.
“It’s like a boat in a way, a battery tray with small wings attached to both ends. That would make sense to do in one piece,” one person said.
The sources said, however, that Tesla still had to make a call on what kind of Giga Press to use if it decides to cast the underbody in one piece – and that choice would also dictate how complex the car frame would be.
To punch out such large body parts fast, the people said Tesla would need new bigger Giga Presses with massive clamping power of 16,000 tons or more, which would come with a hefty price tag and might need larger factory buildings.
Three of the five sources said one problem with presses using high clamping power, however, was that they cannot house the 3D printed sand cores needed to make hollow subframes.
The people said Tesla could solve these obstacles by using a different type of press into which molten alloy can be injected slowly – a method that tends to produce higher quality castings and can accommodate the sand cores.
But the process takes longer.
“Tesla could still choose high-pressure for productivity, or they could choose slow alloy injection for quality and versatility,” one of the people said. “It’s still a coin toss at this point.”