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Porsche tests 3D-printed pistons for its 911 GT2 RS

While they're not quite ready for production, the printed parts were lighter, ran cooler and unlocked more power than the standard forged pistons.

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- 05:07
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The prototype pistons are lighter than a cast part, but just as strong thanks to their 3D printing optimization and "bionic" structure.

Porsche

Porsche has completed its first endurance test of 3D-printed pistons in the engine of the 911 GT2 RS. Not only did the part survive, but the automaker's research found that the printed aluminum alloy pistons match (and even exceed) that of comparable cast or forged parts.

Porsche's been at the 3D printing thing for a while now. The automaker says it has been using 3D printing for rapid prototyping and parts development since the '90s, and currently sells about 20 plastic, steel and alloy-printed "Porsche Classic" production parts for heritage cars. Recently, full bucket seats orders opened for 911 and 718 motorsport variants, allowing customers to specify firmness, color and shape of the 3D-printed cushion and backrest surfaces. These pistons, however, might be the most ambitious automotive application of 3D printing tech yet.

The process starts with redesigning the piston with the advantages of 3D printing in mind. Porsche used computer simulation and artificial intelligence to optimize the piston's supporting shape and underlying topology, removing material where not necessary and adding where needed. The result is what the automaker calls a "bionic" design utilizing an organic structural shape. Part of the 3D printing optimization includes minimizing support material that needs machining away later. I'm told the only support that needs removing is the hole for the wrist pin.

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Like their cast and forged counterparts, the printed pistons still undergo heat treating and machining to add strength and precision fit.

Porsche

Porsche was also able to integrate a cooling duct into the piston's structure and separately engineer special twin-jet oil nozzles. These additive manufacturing feats would be impossible -- or at least extremely difficult -- to pull off with machining or casting, the automaker claims. With the design sorted and tested many times in simulation, the moment had come to actually print the part, which required much more specialized hardware than the plastic filament hobbyist printer in your shed.

The pistons are created in a high-precision Trumpf TruPrint 3000 laser 3D printer that basically builds the parts one 0.02 to 0.1 millimeter layer at a time by welding a fine metal powder with powerful, accurate lasers. The material used is a proprietary aluminum alloy called M174+, developed and provided by partner and parts manufacturer, Mahle. Each piston is composed of about 1,200 layers of the fused alloy, taking about 12 hours to print. Fortunately, they're able to print them in batches.

Porsche and its partners claim the properties of the final product are comparable to those of casted material for production pistons, but to make sure the automaker also worked closely with Zeiss, a German manufacturer of optical systems, to test and measure the material with light microscope inspection, electron microscope scanning, X-ray microscope and 3D scanning. Examples of the printed pistons were also torn down and analyzed.

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The prototype pistons were fitted to a Porsche 911 GT2 RS engine and subjected to 200 hours of grueling endurance testing.

Porsche

Six pistons were then slapped into a 911 GT2 RS' 3.8-liter, twin-turbocharged flat-six engine in a lab to begin a practical endurance test. The evaluation included 24 hours of simulated high-speed driving, replicating the rigors of the race track over 3,728 miles (6,000 km) at an average speed of 155 mph (250 kph). Porsche even went so far as to include simulating stops for refueling. Next, the engineers ran the pistons for 135 hours at full load and 25 hours under drag load at a variety of speeds. Two hundred hours later, the test was deemed a success with all six pistons passing.

Each 3D printed aluminum piston is 10-percent lighter than the forged piston that the GT2 RS normally uses and runs more than 20 degrees cooler in the piston ring area thanks to the new duct. That means the engine can rev higher, unlocking additional power. According to Frank Ickinger of Porsche's Advance Drive Development Department, "an extra 300 rpm equates to around 30 [horsepower] more."

And that's with Porsche playing it safe. Already, the automaker is thinking down the road about the butterfly effect these lighter, cooler 3D-printed pistons can have on engine design.

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Partners Mahle, Trumpf and Zeiss made sure that the strength, density and precision of the parts were up to par throughout development.

Porsche

"We've always made sure that we err on the safe side," says Ickinger. "Our simulations show that there is a potential weight saving of up to 20 percent per piston."

"The torsional vibration damper can then be made smaller," he continues, "thereby making the engine even more free-revving. Increased thermal resistance due to the lower temperature permits higher combustion pressures and even more advanced ignition timing -- both factors that increase power and efficiency."

The 3D-printed GT2 RS pistons are still in the early development stage without concrete production plans locked in just yet. However, Porsche is clear that the tech is here to stay and has a roadmap for more 3D-printed parts making their way into special series cars and, eventually, large scale series production vehicles. And, with research going into copper as a 3D printing material, there's even potential for the tech to find interesting new applications in electric car manufacturing.

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These pistons are the most ambitious application of additive manufacturing for auto parts I've seen.

Porsche

"I am certain that additive manufacturing will be an established part of automotive development and production in 10 years' time at the latest," says Ickinger.

Porsche isn't the only automaker developing additive manufacturing parts. BMW has invested in metal 3D printing and experimented with 3D-printed customization parts for its Mini Yours program. Meanwhile, French hypercar builder, Bugatti, has demonstrated (and spectacularly torture tested) 3D-printed titanium brake calipers.