In 1917, Einstein formulated the theory of stimulated emission and laid the groundwork for the laser. In addition, laser cladding started for industrial applications during the early 80’s. A laser in welding is used for both joining, hard facing and buildup. Joining is carried out with both filler and non-filler and is used for various critical and non-critical applications. Due to its very low heat input to the substrate materials, it has the versatility to be used for very difficult to weld materials too. Laser cladding has been known for about 50 years, and in recent times, it has reached a more general industrial acceptance. At present, laser equipment requires higher investment costs compared to other coating processes like PTA, thermal spray, GMAW, etc. The benefits of laser cladding show lower heat input, lower dilution, less material consumption, and overall better. With the last decade’s development of high-power laser sources from 10 μm wavelength CO2 lasers to high-power solid-state lasers with wavelengths of around 1 μm, improved process efficiency, lower costs, and smaller footprints have been achieved. As a result, laser cladding has rapidly become more interesting for a wide variety of applications. Laser cladding is a more efficient process for sustainability, environmental effects, and consumable availability.
Laser cladding uses higher laser power in general, greater than 1 kilowatt of power as a heat source to form a cladding layer on the processing substrate. Laser cladding processes involve melting and feeding a metal stream into a melting pool generated by a laser beam while scanning through the target surface and depositing the layer of the material selected and partial melting of the substrate surface wherein the cladding is involved. Laser cladding is carried out either with a wire or powder feedstock, including hot or cold wire. Laser cladding can be achieved by appropriate selection and control of processing parameters such as laser beam, power density, laser beam travel speed, and laser beam diameter at the workpiece surface.
Four attributes which make the laser an efficient method:
Low beam divergence – resulting in very high focus. This makes the process very precise and energy-efficient
High power and high intensity – Power density at focal spot = 106 – 1017 W/cm2. At such high intensities, any material can be melted and evaporated, even formed plasma with a focused laser beam
Lasers of varied wavelengths can be formed from different laser-generating sources. The absorption and focus beam depend on the wavelength (λ) of the laser beam
Wide range of laser pulse duration
– Continuous wave (CW)
– Pulsed lasers
Millisecond pulses (10-3 s), microsecond, (10-6 s) nanosecond (10-9 s), picosecond (10-12 s) down to a few femtosecond (10-15 s).
In the process of LC, the dilution, aspect ratio, microstructure, and mechanical properties of the cladding layer are closely related to the laser power, scanning rate, powder-feeding rate, scanning method, defocus amount, and other process parameters. To obtain a cladding layer with a fine microstructure, uniform composition, and good mechanical properties, appropriate laser cladding parameters need to be derived. Mostly, it is driven by four important settings: laser power, laser scanning rate, powder feeding rate, and type of torch used.
Laser cladding brings in the versatility of using different alloys to match various application requirements; various coating thickness requirements; can be used for various types of substrates; can achieve various coating properties using different power levels, and can coat both vertically and horizontally. Most importantly, laser coating is an environment-friendly process compared to other coating processes, and powder utilisation is the highest among the commercially used processes, making it a sustainable process.
The advantages of powders
Laser cladding uses both wires and powders as consumables, but it has been observed that powder brings the best advantages.
Powder consumables are available in a far larger number of alloys than wire. Large pool of chemistry to suit your specific requirements.
The dilution or HAZ zone is considerably less and thus the requirements for coating are met with a thinner deposition layer. As finer diameter wires are very difficult to manufacture.
It is difficult to weld materials. For wire cladding, more heat input is required for melting the wire.
Lower welding consumable requirement
Accurate coating thickness. With finer powder size, coating thickness can be precisely controlled.
Minimum follow-up work or machining is required
Compared to the other coating/hard facing/surface engineering techniques, the following advantages are derived by the industry:
Lower coating thickness with the same performance. This brings a reduction in the dead weight. More power for useful work or a reduction in energy consumption.
Due to lower heat input, repair of critical or nonweldable components becomes possible
Choice of material as per your specific requirements because of the possibility of powder mixing and the huge pool of powder chemistry available commercially
Life enhancement of critical components with the use of surface engineered claddings
Conversion of high-alloy cast components to less costly surface-engineered components
More environmental-friendly and energy-efficient processes
Today, the usage of lasers has seen incredible growth and is still growing at large.
Disclaimer: The opinions expressed in this article are those of the author. They do not purport to reflect the opinions or views of Hoganas India.