P/M opportunities abound with evolving engine designs - Materials - powder metal technology

Diesel Progress North American Edition, March, 2002 by Rob Wilson

"Any change in engine design is an opportunity for powder metal technology," commented Eckart Schneider, director Product Management-Powertrain, GKN Sinter Metals, in a recent interview with Diesel Progress. "Engine designs continue to evolve to higher performance levels, but every performance-related decision has to take into account the economic tradeoffs. Cost analysis is an integral part of the design process and powder metal technology is a proven low-cost alternative."

Powder metal can be either a near-net shape technology, requiring very little machining, or a net-shape technology, requiring no machining. Advancements in low-cost, green machining and high-density warm compaction (which take place prior to sintering) are making it possible to address even more complex, more highly stressed components with P/M production techniques.

P/M practitioners like GKN Sinter Metals are now producing parts with densities approaching 7.3 grams per cubic centimeter via a single warm pressing and sintering technique that greatly enhances the mechanical properties of components. Whereas a decade ago yield strength was in the range of 600 MPa for conventionally sintered P/M parts, today's components can have yield strength of 1000 MPa and higher. With powder forging grades, that number is in the 900 to 1500 MPa range.

"It's a huge playground for tailoring alloys. You could even produce a yield strength of 2000 MPa, but you always have to factor in the machinability of the resulting part, when a particular application requires it," explained Schneider. The continuing improvement in mechanical properties brings more highly loaded parts and systems within the range of powder metal capability.

"We now have much greater potential for diesel engine parts," said GKN's Schneider. "There certainly is a need for higher strength with diesel applications. The significantly higher combustion pressures of state-of-the-art diesel direct injection technology make for a greater challenge, but there are still many opportunities."

One component group marked with high potential is engine timing systems, Schneider believes. P/M has been widely applied to timing components such as pulleys and sprockets for spark-ignition engines. In Europe, the trend in diesels is toward the chain drive timing system and the sprockets could be produced with powder forgings. Direct gear driven timing systems have been developed recently and may be growing in popularity for smaller engines. Straight and helical gears also have high P/M potential for balancer shaft mechanisms.

Powder metal helical gears have had only limited success in the past, but recent advances in CNC compaction presses and multi-platen tool technology make them more feasible today.

Though we move toward a more global technology base, there are still significant differences in approach. And within regional markets, various market segments adhere to the status quo. An example noted by Schneider is that conventional forging has been the predominant process used in Europe and still rules the roost. Straight conventional forgings have close to 100 percent of the market share in diesel. However, powder forged connecting rods are extremely common in U.S. gasoline engines and, if GM made small diesels, they very well might have powder forged connecting rods.

"There is still great potential for powder forged connecting rods in European diesels, and the cost as well as the technical benefits of applying the latest best-in-class forging technology are apparent and compelling," said Schneider. "We can tailor precisely the alloy for the required strength and performance. So once we have a successful application, the market is likely to follow rapidly."

A P/M application that has been very well received in the marketplace is the crankshaft main bearing cap. Initial success came in the U.S. and spread first to Europe and then to Japan. But now there is a new twist. Ferrous alloy-based powder metal bedplate inserts are being cast into aluminum engine blocks. They serve as the mating surface for the main bearing caps and secure the crankshaft to the block. Traditionally, these bedplate inserts were cast iron. Now they are migrating to P/M technology

Bedplate inserts increase the yield strength of the casting, locally, and provide a rigid, high-strength support for the crankshaft. Because the alloy can be tailored precisely and the inserts are very near-net shape, there is much less need for machining. Additionally, the alloy is optimized for dual material (aluminum and P/M steel) machinability.

The ferrous insert, combined with the aluminum alloy block, produces a machining condition much like an interrupted cut, which is plain havoc to the machining world. The introduction of a customized alloy significantly alleviates this potential problem.

Schneider explained that the alloy offers properties needed for high performance in its application environment while retaining its machinability during the production process: "We've taken our experience from main bearing cap applications and transferred it to the production of bedplate inserts," he said.