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3D Printed Pistons – Porsches New Innovation

The car industry as a whole has stagnated for quite some time in terms of innovation until the sudden boom of electric vehicles overtook the market. From the sudden emergence of Tesla causing competition from the traditional big manufacturers such as Chevy and Ford to produce their own hybrid and electric vehicles, one is left to wonder if that is the new way forward for all production cars. Even law makers are now setting deadlines for states to only sell electric vehicles, causing car enthusiasts to worry about the future of internal combustion engine cars. What if there was a way to keep up with the EV market by taking what we already know and have with internal combustion engines, and refining them to be faster, stronger, lighter, and more efficient? Thankfully, companies like Porsche are still innovating and finding ways to improve their line up of internal combustion engine cars in ways that not many other car makers have dared to explore with additive manufacturing, giving car enthusiasts hope that performance cars are here to stay. Digging down into the heart of the engine, Porsche had targeted the pistons first to be the test bench of this new production and design method.

Pistons and How They Work

The pistons in an internal combustion engine are the main driving force that turns combustion energy into mechanical rotational force. They are a plunger like component that moves up and down in an engines cylinder that comprises of four strokes: Intake, compression, combustion, and exhaust. The number of pistons a car has is determined by its configuration, such as V6, V8, 4 cylinder engine, or W16. Pistons are exposed to billions of rotations in their life and at 6000 RPM, can have 10 tons of force exerted on them every 0.02 seconds. These pistons travel 27 meters per second while creating heat from fiction up to 310 Celsius.

Traditionally, pistons are made by either forging the piston from a heated block of aluminum and shaping them in a press or casting them by taking molten aluminum and pouring it into a mold to shape. Forged pistons are inherently stronger due to the consistent grain flow of the metal due to being shaped out of one single block of aluminum whereas casted pistons form a random metal grain throughout its structure. This results in a 10-20% increase of tensile strength in forged pistons than cast pistons but are generally a bit heavier. That is generally the reason enthusiasts prefer forged pistons in higher performance engines despite the price increase compared to their casted counter parts.  

A New Future, Layer by Layer

We all have heard of 3D printing, whether it’s from the International Space Station using FDM (Forced Deposit Manufacturing) 3D printing to help resolve some concerns for long duration space travels to perhaps your cousin printing nick-nacks off their Ender 3 printer. While this technology isn’t new, additive manufacturing is starting to be implemented in many manufacturing processes around the world. The biggest advantage of additive manufacturing is the ability to rapidly prototype in a way that saves both time and money by allowing designers to make multiple iterations of a design while producing them much faster, for cheaper due to the low cost of filament, and allows them to make changes overnight to a design if needed to meet strict deadlines.

Working with partners Mahle and Trumpf, Porsche is bringing this process beyond the prototyping by using high precision Trumpf TruPrint 3000 machines to weld a fine metallic powder layer by layer in a laser metal fusion process (LMF), also known as laser powder bed fusion (LPBF), to build their pistons. This creates an object from bottom to top based off the parameters made by the engineers using CAD software with great accuracy in a way that other manufacturing processes cannot. This allows engineers to expand their design potential to create and reinvent objects that were deemed impossible to manufacture with traditional methods. While this technology is exciting, it does come at a cost.

These metal 3D printers can cost upwards of $250,000 per machine, not including the material needed to be consumed during the printing process. The products made by these printers must be analyzed to meet quality control requirements as well. Another cause of concern is the grain structure inside of these printed parts and how they will hold up to real world tests. Fortunately, researchers are developing new control strategies for the lasers to create a more uniform grain inside of the printed part, thus improving its durability and fatigue resistance. This is especially important for a component as durability demanding as the engine piston. Porsche understood these risks and has partnered with Zeiss to analyze their pistons using multiple quality assurance tests, along with inspections by light microscopes, scanning electron microscopes, and X-ray microscopes.

Accuracy is the name of the game when it comes to printing out Porches pistons. Using the Trumpf TruPrint 3000, they were able to build 1,200 layers with 0.02 to 0.1 millimeters of accuracy due to the precision of the powerful lasers built into the printer. The dust used to be welded from that very laser is a proprietary aluminum alloy called M174+, developed my Mahle. This all came together to create a product that Porsche classified as comparable to its casted counterpart. While as the exterior of the raw product would be rough as one would expect, CNC machines are used to cut the metal into its exact specifications while leaving behind a very smooth finish worthy of being installed in Porsche’s engines.

Bionic Architecture and Topological Optimization

Often when we hear the word “bionic”, we think robotic human parts, cyborgs, and cool sci-fi arm mounted cannons. In the case of bionic architecture, it brings this idea of mixing biological organisms and mechanical structures to create designs that are not only organic in structure, but also extremely optimized for durability and strength. It stems from the belief that nature doesn’t waste resources when creating a structure. Designers have taken this principal and have incorporated it into their design software, now called topology optimization, which creates a structure with the least amount of material needed and the strongest configuration based on the parameters provided.

This creates weight saving and structural support, which is crucial in so many different applications including automotive. Porsche has taken this design concept and has put it into practice with their pistons to shave off 10% of its weight. While 10% may not seem like a lot of weight to save, it has allowed Porsches engineers to increase the redline of the engine by 300 RPMs causing an increase in 30 peak horsepower. Porsches senior engineer Frank Ickinger has stated “Our simulations show that there is a potential weight saving of up to 20% per piston”, indicating that Porsche has been playing it safe with their first batch of pistons.

Weight saving wasn’t the only goal that Porsche had in mind for their new pistons. An oil gallery has been added into the design of the piston that allows oil flow through an annular cooling duct behind the piston rings, something that is impossible to do without the help of additive manufacturing. This has proven to reduce the temperature in the piston ring area, which is subjected to extreme thermal loads, by 20 degrees Celsius.

Combining both the weight and temperature savings leads to higher efficiency as well as a smaller torsional vibration damper to make a much more optimized, free-revving engine as Ickinger explained. Paired with the newly designed annular ducts was a twin-jet nozzle made specifically to feed oil into straight into them. This design was also incredibly complex and was a result of 3D printing with stainless steel. “Production using conventional technology would have become very complex due to the geometry,” explains Porsche engineer Marco Klampfl, reiterating the benefits of using such a new design method.

Testing Pistons

Car engine” by Markus Spiske is marked with CC0 1.0.

Forged by 1500 tons of force or casted by flames hotter than 600 degrees Celsius, these metal slugs are molded to become the driving force of your cars engine that undergoes hundreds to thousands of pounds of force, multiple times a second for hours on end. A true engineering marvel that requires precision and vigorous testing to achieve the incredible mechanical properties and reliability that are demanded by your engine.  Porsche is no stranger to developmental testing as their 3D printed pistons were subjected to a multitude of testing requirements to ensure it’s a worthy component for their halo car, the 911 GT2 RS.  

The first step is to be analyzed by Zeiss’ precision equipment with the collaboration of Mahle and Trumpf by using the same methods for the first material samples. They scanned the blank and compared it to the CAD drawing to ensure the physical product had not changed its geometry during the manufacturing process. The engineers concluded that all deviations were within acceptable tolerances and moved onto scanning the cooling ducts of the piston. Initial concerns were powder residue left from the printer that could become detached when under load; fortunately, the adapted design prevented such a mistake from happening in the first place. Ziess then took these pistons to be scrutinized under their high-resolution computer tomography inspection to pinpoint defects and cracks before the real testing would occur. The smallest of defects were then marked safely using a method called the microdefect history so that they can later be re-evaluated after the first tests if needed.  

Next came the more exciting testing. With the help of Mahle a hydropulser was used to support the experimental pistons at their pin bore and load it with more and more force until it failed and sheered. With the results being above what is standard for cast pistons, it had passed and sent to the next phase: the boss tear-off test. This is where the engineers measure the force needed to rip the pin boss from the piston with the use of a steel bar within the housing. Force is then pulled on the piston from this bar until it is sheered off. As expected, the pistons had passed this test and found the force value to be in the same range as typical cast pistons.

After determining that their pistons were performing as they expected, Porsche then installed those pistons into a GT2 RS motor and bolted it to a test stand to put it to see if it was worth the effort. The development engineers then ran it for 200 hours total, simulated the conditions of a 24-hour race including breaks for pit stops, ran the engine at varying loads for 25 hours, then finally ran the engine at full load for 135 hours. Once these tests were completed the engine was stripped and the pistons were re-evaluated, resulting in all 6 to pass all post inspections. This is a huge step forward for not only Porsche, but for the entire automotive industry.

A New Beginning

The proof of concept that we can take a tried-and-true component and refine it even more to see exceptional gains in power and efficiency should spark more engineers to think outside of the box with new manufacturing techniques. Even the cost of these prized printers should be coming down as patents are soon to expire, allowing other industries to build up on what is already produced and create competition to bring the cost of barrier down and accessible for many other companies. We are already seeing other automotive companies taking the dive into the 3D printing world, such as BMW with their custom parts for its “Mini Yours” program or Bugatti and their 3D printed titanium brake calipers. Porsche also uses 3D printing technology for customized bucket seat inserts in their vehicles as well. The limits for this type of manufacturing have yet to be discovered and will only progress as far as engineers are willing to take it. We could soon be seeing EV’s with bionic architecture to decrease weight and drag to better improve efficiency. Thankfully, his technology will inevitably make its way down to typical consumer grade vehicles and will presumably be affordable for car enthusiasts alike, giving a very hopeful future of more efficient and reliable automobiles.

This entry was posted on November 1st, 2022 and is filed under Automation, Electrical, Robotics, Technology, Uncategorized. Both comments and pings are currently closed.

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