Porsche AG, a German high-performance sports car manufacturer, recently developed 3D printed pistons for its 911 GT2 RS sports car with help from its collaborators Mahle, a German parts supplier, Trumpf, a 3D printer manufacturer and Zeiss, a German manufacturer of optical systems and optoelectronics. The resulting 3D printed pistons have proved to be 10% lighter and thereby improving efficiency.
Porsche manufactured a set of six 3D printed pistons through a powder-bed fusion technology from Trumpf.
According to a statement released by Porsche, Frank Ickinger, a member of Porsche’s advance drive development department said, “Thanks to the new, lighter pistons, we can increase the engine speed, lower the temperature load on the pistons, and optimize combustion. This makes it possible to get up to 30 horsepower more from the 690-horsepower, twin-turbocharged engine [in the 911 GT2 RS] while at the same time improving efficiency.”
PORSCHE 3D PRINTED PISTONS
Porsche decided to experiment with 3D printing as the technology provides the freedom to create complex structures that are impossible with conventional manufacturing processes. It is because of 3D printing technology that Porsche was able to optimise the piston structure to correspond to load conditions and also to integrate a cooling duct, while at the same time reducing each piston’s weight by 10 percent in comparison with a production forged piston.
Ickinger also stated, “This has allowed us to increase engine speed, lower the temperature load on the pistons and optimise combustion. The result is more power and greater efficiency. This means that a power increase of up to 30 PS is possible for the 515 kW (700 PS) Porsche 911 GT2 RS.”
The 911 GT2 RS is equipped with forged pistons but as the world moves towards futuristic high-performance engines, the forged pistons cannot deliver the needed performance. One of the goals of this project was to reduce the weight of the pitons and with 3D printing, a topology optimised design can easily be manufactured to reduce material and ultimately the weight of the system.
Ickinger explained, “We’ve always made sure that we always err on the safe side. Our simulations show that there is a potential weight saving of up to 20 percent per piston.”
The second goal of the project was the integration of an annular cooling duct behind the piston rings. This duct has a special cross-sectional shape and is closed like a tube apart from inlet and outlet openings for oil. Such a structure can be produced only through an additive manufacturing process. Thanks to this additional cooling, the temperature of the component have been reduced by more than 20 degrees in the piston ring area, which is subject to extreme thermal loads. The combination of all these measures makes for optimised combustion with higher pressures and temperatures, resulting in greater efficiency.
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COLLABORATION WITH MAHLE & TRUMPF FOR 3D PRINTED PISTONS
For this project, Porsche collaborated with Mahle, for its Technology know-how, with Trumpf for its 3D printing expertise and with Zeiss for its measurement and testing process.
Porsche has relied on the competence of Mahle in the development of the 3D printed pistons, just as it did for the production forged pistons in the 911 GT2 RS. Mahle developed a weldable metal powder for additive manufacturing from their proprietary Mahle aluminium alloy M174+.
This powder was used in Trumpf TruPrint 3000 3D printing systems to recreate the design of the pistons into a solid part. TruPrint 3000 is a Laser Metal Fusion 3D printing technology based on the powder-bed fusion type of 3D printing and is used for industrial production.
The suitability of the powder in the 3D printer, it was subjected to multiple quality tests and results were analysed in cooperation with measurement technology specialists from Zeiss, including inspection by light microscope, scanning electron microscope and X-ray microscope.
The advanced technology company Trumpf was responsible for the development of the production process and printing. High-precision Trumpf TruPrint 3000 machines welded the powder layer by layer using the laser metal fusion process (LMF), also known as laser powder bed fusion (LPBF). In this process, the powder is fused by a laser beam in thickness in the µm range (0.02-0.1 millimeters), thus building up the piston layer by layer. The piston blanks are produced in this way with approximately 1,200 layers taking in the region of 12 hours. Testing using different non-destructive methods such as computer tomography, 3D scanning, and microscopy, as well as analysis of dissected pistons, was undertaken with partners Mahle, Trumpf, and Zeiss. These tests confirmed that the quality of the printed pistons did not differ from that of cast pistons.
WHAT NEXT AFTER 3D PRINTED PISTONS?
The cooperation with Mahle and Trumpf has already proceeded to develop an additional charge-air cooler as a further component after 3D printed pistons. This was integrated into the air pipe connecting the turbocharger and charge-air cooler. Thanks to the possibilities offered by 3D printing, the charge-air cooler has a much larger surface area for heat transfer, which permits optimisation of the flow routing and cooling. The effect is that the intake air is cooler and the engine’s power and efficiency are increased.
However, despite the rapid further development of additive manufacturing processes, there are currently still major restrictions relating to them. Firstly, there are the costs, which remain economically justifiable only for smaller quantities, depending on the component in question.
Secondly, the size of the component is a further limiting factor because it is not yet possible to manufacture larger parts in the process chamber of printers currently available. Also, it is necessary to extend the range of materials both for plastics and metals.
Finally, additive manufacturing still has to qualify itself for (small) series production processes in the automotive industry in terms of quality and reproducibility as well as economic efficiency.
Frank Ickinger concluded, “However, I am certain that additive manufacturing will be an established part of automotive development and production in 10 years at the latest.”
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