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GT2 RS gains 30 hp with 3D-printed pistons Porsche endurance-tested for 200 hours

Tuesday, July 14, 2020

Above: A worker blows excess aluminum alloy powder away from a set of printed pistons.

Article by Damon Lowney
Photos courtesy Porsche

As 3D printing technology has progressed over the past couple decades, it has become more widespread, with applications ranging from backyard hobbyist to the production of a supercar. While Porsche hasn’t printed a car yet, it’s several steps closer after successfully printing and testing a set of special pistons for a 992 GT2 RS.

Above: Note the more intricate design of the printed piston (right) versus the original forged piston.

The numbers you need to know: The pistons are 10% lighter than the car’s original forged pistons, stay cooler with a new closed oil duct in the piston crown, and allow the engine to safely rev 300 rpm higher and produce 30 more horsepower — that’s 730 hp! Furthermore, Frank Ickinger of Porsche's Advance Drive Development Department says, “Our simulations show that there is a potential weight saving of up to 20 percent per piston.” He erred on the side of reliability rather than print lighter pistons. The car would need to endure more than 200 hours of testing.

Above: The printed piston (right) has an oil duct to cool the piston crown, a feature not possible on a forged or cast piston.

Without the need for tooling specific to the parts being produced, the basics needed to print six GT2 RS pistons are as follows: 1) Weldable powdered metal, in this case Porsche worked with longtime collaborator Mahle, which supplied its proprietary aluminum alloy M174+. Apparently, this stuff is available in both “solid” or powder form. 2) A 3D printer, this one supplied by Trumpf, a company that’s been in the 3D printing game since 1999. The TruPrint 3000 employs the Laser Metal Fusion (LMF) process, which uses laser beams to melt layer by layer of the powdered alloy into pistons. 3) A way to measure the pistons after they’re printed but before they’re put into an engine for testing. Zeiss, known for its camera lenses, provided the equipment used to visually measure the pistons.

Above: 3D-printed piston.

Porsche could have made printed replicas of the forged pistons and call it a day, but the automaker decided to push the envelope and explore how a main advantage of additive manufacturing — the ability to produce more complex shapes than through forging (a form of subtractive manufacturing) or casting — could build a better piston. For example, Porsche says making a piston with an oil duct in the crown would have been impossible using traditional manufacturing techniques, as would the production of the twin-jet nozzle that supplies oil to the crown, as on the original piston, but also the duct in the crown in the printed piston. “Production [of the twin-jet nozzle] using conventional technology would have become very complex due to the geometry,” explains Porsche engineer Marco Klampfl.

The LMF printing process works similarly to that of the small hobbyist printer in your uncle’s garage, but instead of heating and pushing out a stream of melted plastic and building an object layer by layer, a laser beam melts hundreds if not thousands of layers of powdered metal into a shape. A GT2 RS piston is the result of 1,200 layers of metal, heated and cooled and stacked over the course of 12 hours. The TruPrint 3000, with a single laser, can print up to five pistons at a time, though the 5000 model has three lasers and could speed up the process. Take a look at the image below to see the printer in action.

Above: A piston in the beginning stages of printing. LMF printing method uses a laser to melt powdered metal, layer by layer, until it forms a piston.

The downside of 3D printing is that it’s time intensive and not ready to be used to make parts for series production vehicles. However, the small scale of manufacturing prototype parts for testing purposes lends itself well to 3D printing. A change in programming allows engineers to revise parts relatively quickly, in all types of materials.

Above: A GT2 RS twin-turbocharged flat six fitted with 3D-printed pistons was tested under varying conditions for 200 hours.

The fourth company to play a role in this experiment was Zeiss, which provided imaging technology to visually confirm the pistons’ quality and performance capability. Zeiss, delving far away from its more mainstream camera lens business, made the light microscope, scanning electron microscope, and x-ray microscope needed for the visual tests. What Porsche learned was the printed pistons have similar characteristics to cast alloy pistons. They’re about the same hardness and react to stresses such as high temperature and all kinds of forces.

Above: The printed pistons after a 200-hour endurance test.

Finally, the pistons were installed into a GT2 RS engine and then tested on a rig for 200 hours. By Porsche’s account, the engine spent 135 of those hours at full throttle! A variety of other conditions were simulated as well. In typical understatement, the automaker states in a press release: “The end result was that all pistons passed the test.”

3D printing isn’t yet common throughout Porsche, but there are ways to get your hands on genuine 3D-printed Porsche parts today. Porsche Classic recently started making printed parts where it makes sense, such as the small clutch release lever for a 959, which is no longer available (NLA), or other small, rare parts. In May, the automaker started to allow customers to option body-formed bucket seats for 911 and 718 models. The center cushion and seatbacks are partly 3D printed, and have a unique styling cue as a result of the exposed 3D-printed lattice structure in the seatback.

Though 3D printing is far away from becoming a common form of manufacturing at Porsche due to cost and limited size of printable components, Ickinger says: “I am certain that additive manufacturing will be an established part of automotive development and production in 10 years' time at the latest."

Source: Porsche

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