Body components produced using the aluminum die-casting process are designed to reduce complexity, weight and final cost. Automakers Tesla and Volvo see this as the future, especially for electric models, what can gigacasting offer?
With the rise of electric vehicles, lightweighting is all the rage. Due to the heavy weight of battery packs in electric vehicles, weight reduction and corresponding manufacturing processes are gaining momentum. The use of aluminum die-casting processes to produce large body parts is giving new impetus to automotive manufacturing. In car construction, the process has so far been used more for the production of chassis components such as suspension strut domes or longitudinal members. It may sound tempting to cast an entire body part made of some aluminum alloy into a mold under high pressure and then further process it after it solidifies. The vision for automakers is to reduce the multitude of individual components, as is common in steel methods, to a few parts, or even one large part, removing complexity from the overall body building process.
The first report on aluminum die-casting for body parts comes from Tesla, the US electric car maker, which calls the process Gigacasting. Tesla uses this process for the rear floor of the Model Y, which requires huge equipment, with molds weighing between 80 and 100 tons. These systems are huge in size, with die casting machines up to 20 meters long and several meters high and wide. An early expert in this field was Italian machine manufacturer Indra, which called its machining system the Giga Press (domestic called Integrated Die Casting).
Volvo promises greater flexibility with Megacasting
Volvo Cars announced that it will introduce aluminum die-casting technology at its main plant in Torslanda, Sweden. From 2025 onwards, the underbody structures for future E-type car generations will be produced here using a die-casting process. Volvo calls this process Megacasting. Volvo is investing around 1 billion euros in production near Gothenburg, which will be used in a new battery pack assembly line, upgraded paint, logistics and vehicle assembly, as well as aluminium die casting.
Megacast components will be used in the underbody area of the new vehicle platform, according to Fimmel, Volvo Cars’ vehicle platform solutions designer. “It makes sense to focus the development and use of Megacast parts on this part of the body,” he said. Just look at the required seat, suspension and powertrain configuration. A corresponding system for the production of these components should provide an annual capacity of 55,000 tons with a cycle time of 140 seconds per floor.
Best of all, Megacasting has more flexibility than traditional platforms. “Megacasting will be able to produce a variety of bases for any product,” says Fimmel. In particular, Volvo wanted to reduce complexity by integrating different body components and functions into one unit. Tesla wants a 70-to-1 reduction, but Volvo wants a 100-to-1 reduction. Femmer explained that thanks to the Megacasting process, fewer parts need to be shipped and stored, and fewer machining operations are required.
That’s a plus for Volvo, and it’s also in terms of quality. Another argument in favor of Megacasting that can be seen among OEMs is the high use of recycled aluminum. All materials used in aluminum castings should be recycled on-site at the furnace. In steel processing, however, the remaining scrap must be sent back to be processed into new coils before being shipped.
According to Prof. Volcker, head of the Department of Forming Technology and Casting Engineering at the Technical University of Munich, Germany, this die-casting process is particularly suitable for the center and rear of the floor, as they do not require such high ductility in the event of a crash. He sees limited use for the craft in front of the body. According to Professor Volcker, reducing the number of parts does not in itself bring any economic advantage. Also, it doesn’t make the body lighter. In an interview with the German magazine Auto Production, he explained: “A large part requires a corresponding wall thickness, and at the same time you lose the possibility of bringing the corresponding material properties to the exact location, whereas in many cases the classic A sheet metal shell structure can be done.”
Sheet metal housing allows for smaller wall thicknesses
Tesla uses a self-hardening alloy to produce the rear floor and bypasses heat treatment with this process. According to Prof. Volcker, there is not yet a solid understanding of how the heat-treating deformation of a part of this size can be controlled. Prof Volker explained that while die casting assumes a lower limit of 2 to 3 millimeters for sheet thickness, the wall thickness of the sheet shell can be as low as 0.7 millimeters. According to him, the strength of soft deep-drawn steel today is between 140 and 1,500 MPa. In contrast, the strength of self-hardening aluminum alloys without heat treatment is only about 250 to 350 MPa at most, while the strength of wrought aluminum alloys can reach 500 to 600 MPa.
Fimmel, an expert at Volvo, is also aware of the problem of deformation after casting of large parts. Therefore, it is necessary to use an alloy that provides the desired properties of the part without heat treatment. Volvo is currently testing different alloys to meet cost, ductility and strength requirements. Volvo calls the corresponding blend the F-Temper alloy. Feimer points out that the cost is not the same as updating a set of tools or equipment for one platform or model cycle. Megacasting is an investment with a “longevity” that will support many new electric vehicle life cycles, he said.
According to media reports, Tesla has the potential to save 20% to 30% by adopting Gigacasting. Cost reductions are said to be largely due to the reduction in the use of forming presses and welding robots. Professor Volcker of the Technical University of Munich cautions that these figures should be viewed with caution. In particular, in the case of welding robots, the investment is depreciated in one model generation; in the case of forming punches, the depreciation is done in three or four generations. The term of this technical depreciation is 30 years. “It doesn’t make sense for OEMs who already use these machines in existing generations of cars to use new technology,” the foundry expert said. On the other hand, Tesla can save the typical shell construction investment thanks to the greenfield approach.
Gigacasting narrows the number of pieces
When asked about a reasonable production number, Prof. Volcker mentioned the lifespan of the die-casting mold: “The rule of thumb is that the die-casting mold has a lifetime of 100,000 to 150,000 cycles due to thermal shock.” Volcker emphasized: “On the other hand, a forming tool can handle five to six million parts. So we’re talking about a factor of 20 to 30.” Based on this, the number of pieces for this casting-intensive solution is obvious, according to the expert is limited: Therefore, he believes that in aluminum die casting, very small and very large pieces are not attractive. In particular, for mass production in the millions range, about six to seven expensive die casting molds are required. The expert also pointed out that the casting process is more complex than the cold forming process, and the scrap rate is high, likely to be 20% or more.
For car factories, Gigacasting also means a huge demand for space. Currently, die-casting molds can only be replaced vertically with the help of a crane. According to Prof. Volcker, it takes 10 to 12 hours to replace a mold weighing up to 100 tons. By comparison, the current die change time for high-efficiency servo presses in large stamping plants is around three minutes.
Prof. Volcker concluded by saying that neither Gigacasting nor Megacasting can be classified as an efficient solution per se, nor can it be classified as a lightweight solution, nor can it be classified as a higher performance process. However, this topic brings drive and passion to production. Gigacasting is suitable for rethinking car body structures, especially with an eye toward electric vehicles. So it’s still exciting to see which concepts will prevail in the future.
In Gigacasting, molten aluminum is injected into a die, a punch presses the melt into shape with several tons, and it cools