Laser welding enables use of steel pistons in car diesel engines

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Mahle, a development partner and supplier to the automotive industry, has developed a new production process involving laser welding that will enable steel pistons to be used in the diesel engines of passenger cars.

The steel pistons will useable in place of aluminium pistons, the current standard for powerful diesel engines, and will lead to lower fuel consumption and reduced
CO­
emissions from the vehicles.

The new production technology solves a problem that Mahle says has existed since the invention of the cooled piston itself: ‘Thick [piston gallery] walls have poor heat dissipation and produce high temperatures at the bowl rim,’ the company said in its announcement of the new process. ‘On the other hand, thin walls can lead to undesired high temperatures at the inner wall of the piston gallery, causing a layer of oil carbon to form. This acts as a thermal insulator and promotes – due to excessive operating temperatures – undesired wear and damage to the piston and cylinder liner.’

These issues can be addressed using a piston gallery with a kidney-shaped cross section, which guides the flow of cooling oil in an optimal hydraulic path, and ensures a uniform dissipation of heat that makes overheating impossible. Such a design is only feasible, however, using the laser welding process developed by Mahle, which enables maximum design freedom for the piston gallery. Typically, friction welding is used to produce pistons, however the resulting material build-up in the cooling channel hinders controlled guidance of the cooling oil flow.

The kidney-shaped cross section will enable steel pistons to be used in the diesel engines of a passenger car in place of currently used aluminium pistons, which will lower the fuel consumption and reduce the CO2 emissions of the vehicle. This is due to the lower expansion of steel compared to aluminium, which has a positive effect on frictional losses, and ultimately reduces oil entry into the combustion area of the engine  leading to lower particle emissions. Steel pistons can also have a shorter top land and allow for a longer connecting rod with their low overall height. The smaller pivoting angle of the longer connecting rod results in smaller lateral forces and lower friction in the region of the piston skirt.

The Mahle group generated sales of approximately €12.8 billion, in 2017, and at the time had approximately 78,000 employees.

Image caption: Mahle has developed passenger car diesel pistons made of aluminium as well as diesel pistons made of steel. (Credit: Mahle)

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