Revolution in Production Technology Demands New Design Concepts

Prototype gasoline and diesel engine pistons by IAV show the potential of 3D printing

3D printing will revolutionize manufacturing technology in the medium term. Additive manufacturing has already become the established method for prototypes, with small-batch series soon to follow. IAV has been using 3D printing for engine components such as pistons and cylinder heads for more than two years now. The long-term aim is mass production ready from the first part.

3D printing offers developers completely new degrees of freedom in design and opens up possibilities for using new materials, such as aluminum reinforced with ceramic. The innovative production technology is capable of integrating more functions in engine components and shifting load limits higher. Take pistons in gasoline engines, for example. “Today they are cast or, particularly for high power outputs, even forged”, explains Matthias Krause, Head of the Base Engine Development department at IAV. “This imposes restrictions, especially when designing the cooling ducts.”

Lower HC emissions, less knock tendency

IAV’s prototype for a gasoline engine piston illustrates what 3D printing can do. The piston consists of an aluminum alloy reinforced with about ten percent ceramic particles. The material has nearly twice the tensile strength of usual piston alloys with 30 percent less heat expansion. Additive manufacturing gave the designers scope for noticeable optimization of the piston: filigree cooling ducts at the piston top land reduce hydrocarbon emissions, with a decrease in engine knock tendency.

There is also less deformation at high temperatures. “Material accumulation within the component differs greatly in cast and forged pistons”, says Roger Budde, Senior Technical Consultant for Cranktrains at IAV. “This causes varying expansion at higher temperatures so that the piston never fits perfectly in the cylinder.” 3D printing permits a lattice structure within the piston with relatively uniform distribution of the material. Together with lower thermal expansion, this leads to far lower, more regular deformation which is reflected in reduced friction and thus lower fuel consumption. Another positive effect is the reduced weight of the piston, which weighs about 25 percent less than its conventional equivalent with the same load-carrying capacity. “The reduced mass forces in the cranktrain permit higher engine speeds”, says Krause. “Sports car manufacturers could thus increase engine output without any need for radical changes to the design of the cranktrain.”

Better mixture formation in diesel engines

Pistons in commercial vehicles with heavyduty diesel engines also benefit from 3D printing, with the new design freedom again playing a major role. While conventional pistons today have an axially symmetrical recess that looks like the Greek letter omega, additive manufacturing will permit a star-shaped design in future. “This gives the fuel spray more space to interact with air, resulting in better mixture formation”, reports Budde. “The size of the piston recess will gain in significance in future. We expect further increases in injection pressure, which is why the fuel spray will need even more free spray length due. Unburnt fuel must not be allowed to hit the piston recess wall.”

As with gasoline engines, piston cooling can be optimized in diesel engines as well. Here IAV champions a two-stage cooling system with fine ducts transporting liquid sodium to the first ring groove and to the piston recess, in other words, points exposed to special thermal loads of more than 300 degrees Celsius. A volume partly filled with oil (“shaker") absorbs the heat from the sodium and transfers it to the engine’s oil cooling system. This diesel piston also weighs less: thanks to 3D printing with highly resistant tool steel, it weighs up to 15 percent less with the same performance capability.

“We have already started concrete discussions with customers about using the new diesel piston”, says Krause. “We might be fitting one into a single-cylinder engine before the end of the year for better validation of the potential.” In addition to new pistons, the IAV experts also have other engine components on their list. For example, 3D printing could reduce the weight of cylinder heads by about 30 percent and also improve some of the functions, such as an optimized cooling system. One conceivable approach here consists in a hybrid design with the base plate and combustion chamber part of the components printed onto the cast part.

3D printing for cylinder heads, turbocharger housings and crankshafts

Other candidates for 3D printing include exhaust manifold modules with integrated turbocharger housing and crankshafts for prototypes. Although additive manufacturing is currently still too expensive for volume production, falling costs could change this already in the medium term. “And so we’re already thinking about what could be mass-produced this way in future”, says Krause. “Among others, we have developed a specific design catalogue which we use to develop components that make full use of the potential offered by 3D printing and are ideal for this production method”. It is even conceivable in future that the first prototypes will have the same quality as subsequent volume production. And at the end of the vehicle’s life cycle, spare parts could simply be printed on demand instead of keeping them in stock for years.