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Laser Cladding: Multifunctional and Very Promising

Industry and research benefit from the potential provided by the Oerlikon Metco Laser Center of Competence with its modern gantry system for laser cladding and additive technologies.

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Industry and research benefit from the potential provided by the Oerlikon Metco Laser Center of Competence with its modern gantry system for laser cladding and additive technologies.

By Dr. Arkadi Zikin

Laser cladding has received increased attention from the industrial and scientific communities in recent years as one of the most promising technologies in the world of modern surface engineering. This is because in addition to creating high-quality coatings with a metallurgical bond to the substrate, laser cladding is a multifunctional process, even to the point of enabling additive manufacturing.

Although it has been on the market for more than 40 years, laser cladding can still be considered one of the newcomers among the coating methods. The high cost of lasers and components made its use relatively unattractive until a recent drop in prices dramatically altered the equation.

Precision parameters for the material

In laser cladding, a laser beam creates a spot on the surface of the substrate. The heat causes formation of a molten pool into which a metallic material is introduced as a powder or wire. The material melts and the coating is built up. The component or the working head moves during the process, which causes formation of weld seams that typically have a width equal to the size of the laser beam’s spot.

 

With the assistance of optical elements (fibers, lenses, collimators), the geometry and the dimensions of the spot that is created can be defined and controlled with precision — which is one of the primary advantages offered by laser cladding. If a larger surface must be coated, several passes are required so that the weld seams overlap.

In laser cladding, the geometry and size of the spot, and thus of the weld seam, can be controlled with precision.

Development work is focused on faster, better additive

Laser cladding is much more than “just” a coating process and is multifunctional not only in terms of the application. The current focus of development work and research by the scientific and industrial communities falls within three main areas: High-power laser cladding, high-speed laser cladding (also known as EHLA, or extremely high-speed laser application) and the process of building up 3D structures. Thanks to very high coating rates (more than 5 m²/hour is possible), laser cladding can compete successfully with processes such as thermal spraying or hard chrome plating. Moreover, the process makes it possible to build up 3D structures layer by layer directly on the surface of components and thus modify their design. This is why laser cladding is also considered one of the additive manufacturing processes in the areas of Directed Energy Deposition (DED) or Laser Metal Deposition (LMD).

Dr. Arkadi Zikin

Oerlikon Metco Laser Center of Competence for Customer Service and R&D

In Oerlikon Metco’s unique Laser Center of Competence in Wohlen, Switzerland, a team of experts is working on further developing the laser cladding process. The focus of their efforts is a new gantry portal system that opens up a wide variety of process options. It has been specially modified and, among other things, equipped with a custom, newly developed tilting rotary table. The high-precision 7-axis portal and a multifunctional selection of laser processes (including wire cladding, EHLA/high-speed laser cladding and additive manufacturing) make it possible to test the newest generation of materials and applications. Moreover, the center is available to customers for coating jobs ranging from prototype fabrication to large-scale orders as well as for exclusive joint R&D projects. The range offered covers the entire process chain from concept development to pilot production and on to industrialization.

The Oerlikon Metco Laser Center of Competence team, from left to right: Patrick Spapens, Kemal Coskun, Dr. Arkadi Zikin, Jörg Spatzier, Peter Öhninger.

Additive manufacturing (AM) with laser cladding:

Wire or powder is used in additive manufacturing with laser cladding, a still relatively unknown process called DED (Directed Energy Deposition) or LMD (Laser Metal Deposition).

Dipl.-Ing. Jörg Spatzier, Senior Process Engineer, explains: “Laser cladding offers the unique possibility of building up structures on the freeform surface of existing components and is ideally suited for the production and repair of applications in the aerospace industry, which typically requires a high degree of accuracy and customer-specific modification of parts. In combination with our multiaxial CNC gantry system, this method of additive manufacturing can be scaled for extremely large components quite easily, while also enabling high manufacturing speeds. We are currently working on different strategies to deliver additive manufacturing products to our customers in which the DED process is monitored and integrated in an automated CAD-CAM delivery chain.”

High-speed laser cladding

In high-speed  or extremely high-speed laser cladding (EHLA), the powder is melted before it interacts with the surface. Accomplishing this uses more than 80% of the laser energy, and the substrate itself is subject only to local melting on the surface, which results in thin coatings with low surface roughness and outstanding properties.

Kemal Coskun, Senior Process Engineer, says: “The high deposition rates of up to 5 m²/hour for rotationally symmetric bodies and the high deposition efficiency of 90% are making EHLA an alternative to thermal spraying or hard chrome plating that must be taken seriously. It is versatile with respect to materials, makes coating thicknesses of 50 µm to 500 µm possible, and, for rotationally symmetrical parts, can replace hard-chrome, anti-corrosion and wear-protection coatings. The best examples are wear and corrosion protection coatings on brake discs and hydraulic piston rods. The EHLA technology is very exciting because it eliminates every upper boundary in the laser cladding process and enables upscaling very well. This means it can compete with every other coating process for rotationally symmetrical parts.”

Wire cladding in laser cladding

A further application of laser cladding is wire cladding. Its main advantage is 100% deposition efficiency (DE): The metal that is introduced is used in its entirety for the formation of the coating. This represents a promising alternative  not only from an economical point of view, but especially for industry sectors in which operations with toxic powders are restricted.

These three examples reveal only a few of the possibilities that are contributing to the success of this multifunctional technology. Consequently, it will continue to be worthwhile to keep an eye on this newcomer in the future as well.

About the author: Dr. Arkadi Zikin is a materials scientist and head of Oerlikon Metco’s Laser Center of Competence in Wohlen.

Main advantages of laser cladding

  • No heat-affected zone (HAZ);
  • Low heat input and therefore negligible distortion;
  • Only approx. 5% mixing with the substrate, enables better coating properties;
  • Large range of processes with high process reliability and reproducibility;
  • High deposition efficiency (80-95%) with powders and up to 100% with wire;
  • Metallurgical bond with very high impact strength.
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