Can we control friction?

Novel micro-architectures created by laser structuring

Friction plays an important role in many areas of day-to-day life. Whenever two surfaces move against each other, this creates friction and wear. In Germany alone, this potentially costs the economy billions of euros every year. And in the automotive sector in particular, a lot of energy is wasted due to friction. Take diesel engines: no more than 30 per cent of their fuel is directly converted into drive energy. With this in mind, the Steinbeis Research Center Material Engineering Center Saarland (MECS) is investigating methods for controlling friction.

Controlling friction is incredibly important across a variety of applications. While this often focuses on reducing friction, increasing friction can also be desirable – such as when developing new braking and clutch systems.

Over previous decades, a variety of methods have been developed to minimize friction in both dry and lubricated situations. These include mechanical methods such as honing, lithographical methods such as UV lithography, high performance coatings like DLC, and surface structuring methods. Laser-structured surfaces appear to be particularly promising candidates for tribological applications in both dry and lubricated conditions.

The main benefits of using lasers as a tool include their high processing speeds, their cleanliness and ease of use, and their universal applicability for different material surfaces. Based on this, the Steinbeis Research Center Material Engineering Center Saarland (MECS) developed a new technique to create almost tailor-made material surfaces. In laser interference structuring, multiple laser beams are superposed on the surface of the workpiece, creating interference. This makes it possible to simultaneously create geometrically precise microarchitectures over an area of several square centimeters.

To do this, the energy from the laser is applied extremely locally. This means that a metal like tungsten, which has a melting point of almost 3500 °C, can be melted in a precise area less than one-tenth the width of a human hair – while just a few thousandths of a millimeter away, the neighboring area remains unchanged. The laser transfers all of its energy to the material in a few millionths of a second. This means both the inner structure of the material and its surface topography can be modified in a highly specific manner, allowing precise control of friction and wear properties.

This solution has proven especially efficient for oil-lubricated systems. Tiny recesses created by the laser act as lubricant reserves, ensuring excellent failsafe properties in the event of inadequate lubrication. Together with the faculty for functional materials at the University of Saarland, the MECS is working on the theoretical basis needed to understand these effects, and is testing these theories in realistic systems.

Using a variety of laser sources – some of which release their energy in even briefer bursts – plus characterization techniques which allow detailed investigation of the target material’s surface and inner structure, the Steinbeis Research Center in Saarbrücken is investigating a wide range of issues in this area.

Ultimately, the main advantage of the laser interference method is the high speed with which it can create precise micro- and nanostructures on macroscopic surfaces. This also means the technique is easy to integrate into production processes. Other advantages come from the well-defined interactions between the high-intensity laser pulse and the different classes of material. The laser interference method is highly versatile, making it possible to generate a wide range of geometrically exact periodic structures and thus ensuring materials have the right properties in the right place.


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