Innovative piston ring casting technology results in lower friction,higher durability piston rings.
Federal-Mogul Corporation’s Powertrain Segment has developed an innovative, highly optimised casting process for piston rings that will provide to engine manufacturers higher quality and stronger, more wear-resistant piston rings.
The process uses a highly automated vertical moulding process that delivers enhanced material integrity and improved manufacturing process control. Additionally, Federal-Mogul has developed a new casting simulation process that provides more precise data in order to optimise the material flow, pressure and filling of the piston ring casting moulds.
Federal-Mogul’s piston ring manufacturing center in Burscheid, Germany, is the site of the new moulding process
“As engine manufacturers continue to pursue strong engine downsizing and more advanced injection strategies to reduce fuel consumption and CO2 emissions, the thermal, mechanical and tribological demands on components around the combustion chamber – particularly piston rings – increases. While engine friction can be reduced through the use of thinner piston rings, a stronger ring material is necessary in order to maintain the proper bending strength,” explained Dr. Steffen Hoppe, director of technology, Rings and Liners, Federal-Mogul Powertrain. “To achieve these requirements, we have developed new materials, casting and simulation processes.”
New casting process
Federal-Mogul’s extensive expertise in stack casting over the past 80 years has helped the company achieve consistently high quality within the constraints of a manual or semi-automated casting process. However, with stack casting, horizontal arrangements of multiple moulds are stacked above each other in layers, so the design of the runner system is compromised because the pressure and flow velocity of the molten metal varies across the different levels in the stack. The one-piece moulds used in the stack casting process also reduce the range of piston ring design options.
Casting a new steel alloy for piston rings at Federal-Mogul’s Burscheid, Germany, ferrous foundry
To overcome these limitations, Federal-Mogul’s new, highly automated, vertical casting process uses a special mould design which provides new opportunities to optimise the design of the blanks and gating systems, improving control of material flow. The new casting form allows the feeding around the complete circumference of the casting, which improves the uniformity of the graphite formation of the grey cast iron significantly. Fully automatic moulding and casting, with extensive monitoring and in-process documentation of all relevant parameters ensures more reproducible molten material flow rates and more thorough mould filling, resulting in greater consistency in ring quality.
High-speed cameras, not FE modelling
Federal-Mogul also developed a new casting simulation method using high-speed cameras to overcome the limitations of conventional finite element (FE) modelling. “FE simulation has one major drawback,” explained Hoppe. “No matter how fine a network is selected, the ‘macro process’ is still simulated. How close the simulation is to reality always depends on how well the simulation parameters are chosen and set.”
Federal-Mogul said its Slow-Motion Casting Simulation (SMCS) technique provides a more detailed analysis of mould filling, enabling more precise optimization of the complex gating and feeder systems that control molten material flow. It means molten metal flow at different temperatures and casting speeds can be tracked more effectively, improving understanding and control of pressure fluctuations and the reactions of mould gases.
New casting material
The optimised casting process provided the opportunity to simultaneously develop a more highly refined cast steel material. Traditionally, a high strength martensitic grey cast iron containing nodular graphite would be used for diesel engine rings, with good ductility and strength up to around 1200MPa. Federal-Mogul’s new cast steel material, GOE70, is characterised by a martensitic matrix structure with embedded chromium carbides and strength of at least 1800MPa. This formulation can be further improved for extremely high wear resistance by adding nitriding, providing a surface hardness of up to 1300 HV.
Federal-Mogul’s Slow-Motion Casting Simulation technique using high-speed cameras to provide a more detailed analysis of mould filling, enabling precise optimization of the gating and feeder systems that control molten material flow
Piston rings made from GOE70 were subjected to a high number of endurance tests on heavy-duty diesel engines and showed exceptionally low side face wear and high robustness, enabling reduced exhaust gas blow-by and lower oil consumption. Series production of rings made from GOE70 began in 2012, with the first application on a highly loaded heavy-duty engine meeting EU6 emissions standards.
“Through the development of innovative casting, moulding and simulation technologies that provide enhanced control of key process parameters, we have achieved improved product quality and increased strength and wear resistance,” said Hoppe. “We believe this new ring process technology will further strengthen Federal-Mogul’s leading position in the light and commercial vehicle piston ring market.”
For further details visit www.federalmogul.com.