Laser Metal Deposition with Diode Lasers

Laser metal deposition (LMD) refers to the coating of parts by welding using additive welding materials. The LMD process can be used to repair or create surfaces with specific functions. The application of coatings with materials more resistant to wear relative to the base material is called hardfacing.  When coating with materials to increase the chemical resistance of surfaces, one also speaks of plating.

Laser Metal Deposition

One of the most important industrial applications of diode lasers in the industrial sector is laser cladding. It is an established process for producing or restoring high quality laser coatings. Components refined by diode laser deposition welding are used in a wide variety of areas: from heavy industry to vehicle production and agriculture.

In laser metal deposition welding, the laser beam creates a melt pool on the workpiece surface, to which the coating material is fed and melted by the laser at the same time. The additional material, supplied as wire or powder, produces a layer on a base material after melting by the laser. The short reaction time causes only slight distortion, the cooling takes place quickly. The result is a layer that is metallurgically bonded to the base material. It is more hard-wearing than coatings produced by thermal spraying and, unlike hard chromium plating, harmless to health.

Surface protection and construction of complex structures

Diode lasers are an ideal tool for all variants of deposition welding. Basic advantages are high flexibility and short processing times, low distortion of treated workpieces as well as fine-grained coatings with excellent adhesion. The extremely hard-wearing surfaces require hardly any reworking. The motivation for the additional layers is very different. All coatings that protect heavily stressed surfaces of metal workpieces from wear and corrosion, repairs of high-quality components, but also the generative production of complex structures can be carried out very effectively with the laser.

Corrosion resistance

Laser coating is very suitable to prevent creep corrosion as well as crevice corrosion with the additional layers. For this purpose, stainless steels as well as nickel alloys are applied to low-alloy steels. When diode lasers are used as an energy source, the mixing of the materials is typically less than 5%. Thus, one layer of approx. 1 mm is sufficient for good corrosion protection, while alternative and conventional processes require two layers.

Motivation wear protection

Another motivation is the protection of surfaces against wear. Here, laser cladding is in competition with thermal spraying, among other things. Since laser deposition welding creates a metallurgical bond between the base material and the additional layer, it achieves a much longer service life than the purely mechanical spraying process. The materials are often Ni-based alloys (In 625) with tungsten carbides. These can amount to up to 60 weight percent of the applied layer.

The repair of components

In addition to initial coatings, repair welding is also carried out as wire or laser powder deposition welding. After removal of the old coating and cleaning of the workpiece surface, extremely stable new coatings can be produced in which the applied material is metallurgically bonded to the base material.  In contrast to wear or corrosion protection, the same materials are usually applied to the base material to repair a worn surface, broken pieces or other damage to components. As long as the material in question is weldable, there are practically no limits.

The generative manufacturing

The last major area of laser deposition welding is the generation of components, often referred to as additive manufacturing (AM) or 3D printing. Here, too, layers of identical materials are applied. Mixing is therefore not to be considered separately. Layer by layer, components with complex structures can also be generated with appropriate programming of the processing system.  In addition to stainless steels, aluminium, titanium and superalloys are increasingly being used here, as they are used in turbines, fuselages and wings in aircraft construction.

Laser powder cladding

The laser beam connects the metal workpiece with the applied powder. Various steels, cast iron, copper, aluminium, nickel-based and cobalt-based alloys can be used as the base material. The layers are formed from iron-based alloys (low-alloy steels, tool steels, stainless steels), nickel-based alloys such as Inconell (625, 718, 738), cobalt-based alloys such as stellites, high-temperature alloys, aluminium alloys, titanium alloys and materials containing carbides as additional wear protection. The decisive factor is the availability of the filler material in powder form, with a typical particle size of 40-120 µm, to enable the use of a coaxial powder nozzle. Laserline LDM and LDF diode lasers achieve excellent results when melting metal powder: Excellent adhesion, high precision, virtually no porosity and limited cracking with a high degree of hardness and minimal deformation. In most cases, the surface resulting from mixing does not require any further machining. Conventional hardfacing processes, such as plasma powder deposition welding, on the other hand, do not achieve a sufficiently long service life for many applications. 

Laser metal deposition with wire

In this process, the laser beam melts a supplied wire and the material of the component to be coated. Wire with diameters of approx. 0.8 to 1.6 mm is used, which is conveyed to the build-up welding process with commercially available wire feeders. Today it is estimated that 90 % of the applications are coated with powder and 10 % with wire. Areas of application for laser deposition welding with wire are the repair of components and the functionalisation of surfaces. The process is particularly economical, clean and reworking is reduced to a minimum.