LOOKING FORWARD TO THE FUTURE…
Mahle’s new Topweld steel pistons, the first of their kind, are designed to improve fuel economy and reduce CO² emissions, as well as cut production costs. “The Topweld piston is the industry’s first laser-welded steel piston for high-volume series production,” said Jochen Adelmann, head of Light Vehicle Product Technology at Mahle. “The technology initially was developed for use in mid-range and high-per- formance diesel-powered passenger cars, but there will be commercial-vehicle applications for it as well.”
Mahle’s laser process is up to twice as fast and consumes considerably less energy than friction welding, the joining technology traditionally used to produce steel pistons Adelmann added that laser welding also enables a variety of piston design modifications that permit higher peak cylinder pressures, increase engine efficiency and reduce operating temperatures. A solid-state laser is used to join the upper and lower portions of Mahle’s Topweld high-strength piston. Compared to friction welding, laser-welded seams can be positioned for optimal performance. In addition, weld seams—which hinder oil flow in a piston’s cooling gallery—can be eliminated. The result is a better, less expensive diesel piston that achieves the impossible: better emissions and improved fuel economy, while also being stronger and lighter!
3D printed pistons are actually a thing! Why, you ask, would anyone want to print pistons? According engineering company IAV, printing stainless steel pistons using 3D additive manufacturing technology is needed to meet emissions requirements and increasing in-cylinder loads of up to 300 bar. Their solution, the not-so-novel part, is to improve the mix of fuel and air in the combustion chamber. To get there required a new type of piston geometry, one with under-cuts to extend the length of injector spray. The piston has a starshaped recess as a result, and it’s there that the undercuts occur. Additionally, these pistons have a lightweight honeycomb structure and include built-in sodium-filled cooling channels. While that concept worked well in the com- puter, such innovation required 3D printing to actually build.
Pistons are normally cast or forged from steel or an aluminum alloy, and each design iteration takes weeks and months. 3D printing requires only days from the CAD (computer aided design) phase until a finished prototype of stainless steel is completed. IAV says the prototype has the same quality as a production piston. The company notes that these prototypes are also stronger and stiffer thanks to the honeycomb structure, as well as lighter. For now, 3D printing is too expensive for production volumes. However, prices have been falling for five years, so it’s not out of the realm of reality to expect to see something in a production engine sometime relatively soon. For now, 3D printed pistons live only in prototype engines.
Mahle is now on its second iteration of this much-improved steel piston designed specifically for small-medium-large diesel engines. As you see, piston designs vary considerably based on engine size and demand.
Given all the advances in engine technology, particularly diesel engines, pistons like these from engineering company IAV may hold a place in the future. For that to happen, additive manufacturing must become mainstream.