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CoatingStruc – Innovative Hybrid Manufacturing P rocess of Textured, Thermally Sprayed Surface Systems to Improve Friction Coefficients by up to 10%

Coatings based on tungsten carbide (WC) applied by thermal spraying are well established in the field of surface technology to enhance wear resistance of tribologically stressed surfaces. WC-based coating systems such as WC-Co or WC-CoCr with added cobalt/chromium are applied mostly using high velocity oxygen fuel spraying (HVOF). Compared to uncoated tempered steel, HVOF-sprayed WC-coatings exhibit substantially higher wear resistance when under stress of sliding contact. Because initial surface roughness of HVOF-coatings is high, additional treatment after spraying is necessary for many applications. Thus, a multi-step process consisting of grinding and polishing is often used in industrial production.

Friction occurring between tribologically stressed surfaces like bearing surfaces can be significantly reduced using liquid lubricants for most applications. To allow for continuous lubrication of sliding surfaces, the fluid film needs to be maintained, which can be enhanced using tailored surfaces. The application of surface textures forming lubricant pockets can benefit hydrostatic and -dynamic bearings by significantly reducing the coefficient of friction compared to plain surfaces.

Laser-based processes, which are the most common method used for surface texturing at present, involve unfavourable burr-forming and thermally induced defects. WC-coatings, especially those consisting of sub-microscopic and nano-scale particles, are thermally sensitive and tend to undergo unwanted phase-transitions reducing the surface’s mechanical properties and its service life when exposed to cyclic mechanical stress. Machining technologies like milling implicate these disadvantages to a much lesser extent.

The project’s goal, i.e. to apply bionic and technical textures to thermally sprayed coating, is to be achieved by combining HVOF-spraying and machining with geometrically defined cutting edges (e.g. micro milling) in a novel hybrid manufacturing process. Hereby, the disadvantages of established processes mentioned above can be avoided and the tribological properties of the surface (e.g. coefficient of friction) can be tailored to the application. While maintaining the mechanical properties like wear resistance that are necessary for the application, it is necessary to optimize the composition and microstructure of the coatings for machinability and to adapt the machining process for texturing the difficult to machine coating. In addition to avoiding the shortcomings of laser-based processes, the application of machining can potentially induce compressive residual stresses into the coating to further enhance fatigue strength.

Cross section of coating on substrate / surface structure produced by means of micro milling © ISF ​/​ LWT
Main project goals of CoatingStruc

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Location & approach

From A1

Take exit Kreuz Dortmund/Unna to merge onto A44 toward Dortmund, which changes into the B1. Exit Dortmund-Dorstfeld toward Universität (onward see map).

From A 45

Exit Dortmund-Eichlinghofen toward Universität (onward see map).

Alternatively, you can calculate the route here: Google Maps.

 

Arrival by Deutsche Bahn to Dortmund or Bochum central station.

From Dortmund central station, take the S1 city train in the direction of Düsseldorf to the "Dortmund Universität" station (7 minutes journey time).

From Bochum central station, take the S1 city train in the direction of Dortmund to the "Dortmund Universität" station (14 minutes journey time).

The city train runs regularly every 20 minutes in both directions.  From the city train station, take the Skytrain (S-Universität stop) to the Campus Süd stop (1 stop, runs every 10 minutes).

From Dort­mund Airport

By taxi to TU Dortmund University, Campus South (approx. 20 min and 30 €, see  Map)

From Düsseldorf Airport

Take the city train S1 in the direction of Dortmund to the "Dortmund-Universität" station (approx. 60 min). From here, take the Skytrain in the direction of Campus South or Eichlinghofen (runs every 10 minutes and takes approx. 3 min.).

 

The H-Bahn is one of the hallmarks of TU Dort­mund Uni­ver­sity. There are two stations on North Campus. One (“Dort­mund Uni­ver­si­tät S”) is directly located at the suburban train stop, which connects the uni­ver­si­ty directly with the city of Dort­mund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.

 

The facilities of TU Dort­mund Uni­ver­sity are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the uni­ver­si­ty are located in the adjacent “Technologiepark”.

Site Map of TU Dort­mund Uni­ver­sity (Second Page in English).