Precise and efficient: automated optical measurement for determining the roughness and micro structure of piston ring running surfaces
Federal-Mogul Powertrain and NanoFocus AG (Oberhausen, Germany) have jointly developed an automated process for non-contact, optical-confocal measurement of the roughness and micro structure of piston rings. This joint development for production control and quality assurance in piston ring manufacturing at Federal-Mogul Powertrain in Burscheid, Germany is a specific combination of an optical measuring system from NanoFocus and software and a piston ring product database from Federal-Mogul.
Piston rings play a decisive role in regard to the function and emissions behaviour of engines in vehicles. The piston ring solutions from Federal-Mogul Powertrain, with their optimised friction, wear and durability properties, enable reduced fuel consumption and CO2 emissions and a longer engine service life. As components subjected to strong mechanical stresses in the tribological system of piston, piston ring and cylinder, their friction and wear behaviour is defined by functional surface structures.
A tactile roughness measurement on DuroGlide®-coated LKZ® oil control rings with their conical-cylindrical running surfaces as well as on steel rails is relatively complex. In addition, operator influence cannot be ruled out in regard to the selection of the right measuring points. Therefore, a measurement solution that was better and more efficient than tactile methods was needed.
“With NanoFocus AG, we have found the right measuring technology partner for developing a robust, non-contact measuring process for determining the roughness and micro structure of piston ring running surfaces which optimally meets our requirements with regard to precision, quality and efficiency,” said Ulrich Lenhof, Manager Metrology Lab Burscheid and head of the project team at Federal-Mogul Powertrain.
“The optical-confocal µsurf measuring system from NanoFocus AG has been adapted both in terms of hardware and software especially for the analysis of piston ring running surfaces at Federal-Mogul Powertrain and offers the option to carry out production-related measurement of large quantities,” explained Marcus Grigat, COO of NanoFocus AG. This is realised through user-friendly and efficient sample handling, as piston rings can be quickly inserted and precisely positioned for measurement. In addition, the measuring process and the evaluation of the data are fully automated.
The target measuring position on the piston ring running surface is approached semi-automatically by the system and measured over a defined measuring spot (0.8 x 0.8 mm2). This is followed by an automatic analysis and evaluation using Federal-Mogul Powertrain proprietary special software that draws upon the information regarding Rk (core roughness) and Rpk (reduced peak height) roughness parameters stored in the in-house piston ring product database.
In addition to Burscheid, there are also plans to use this efficient solution over the coming years at other Federal-Mogul Powertrain development and production sites for piston rings.