Laser cladding: The most state-of-art coating technologyTDB Machining
What is laser cladding?
Laser cladding is a process that utilizes either wire or powder coating material, heated by laser beams, to create a molten pool on the surface of the workpiece. The material quickly cools down, creating layers that are metallurgical bond between a metal substrate and a metal coating. By using multiple powder types and adjusting the feed rate of each, it’s possible to create components deposited with multiple materials or even components with material gradients.
Laser cladding comes into play in a wide variety of industrial tasks — including applying surface coatings, rapid manufacturing and repairing worn-out parts.
Advantages of laser cladding
Thanks to the metallurgical bond, there is a low risk of separation and delamination.
Laser cladding supports a wide variety of material choices, both for the substrate and for the material being deposited.
There is limited porosity using this method.
Laser cladding also is a good fit for automation and integration into CNC operations and CAD-based processes.
Choices for deposition material include ferrous metals, such as stainless and carbon steel, plus cobalt- and nickel-based alloys, and aluminum, Inconel and titanium alloys.
Compared with traditional cladding and welding techniques, laser cladding provides a high-speed thermal cycle that makes it possible to achieve higher hardness as well as much finer microstructures — two characteristics that help to resist corrosion.
Laser cladding also offers the benefit of a limited heat-affected zone, which has numerous advantages: It reduces the amount of trauma to the part or workpiece, cuts down on the likelihood of deformations, and allows the process to take place alongside other critical areas that are less tolerant of heat, including adjacent edges and walls. That means laser cladding can add structural reinforcement to sensitive areas.
For an example of laser cladding and its benefits, compare laser-clad screws with nitrided screws. According to the Handbook of Laser Welding Technologies, screws prepared with laser cladding enjoy a service life up to 60% higher than comparable high-alloy nitrided screws.
The development of oil and gas fields requires high-performing drilling tools. These are subjected to huge stress and would not reach long lifetimes without wear protection. That is why special coatings, that are more and more frequently realized with the laser cladding technology, have become the standard for some time now. Outstanding results can be achieved from laser cladding: excellent adhesion, high precision, almost no porosity, limited crack formation, a high degree of hardness, and low deformation. In most cases, the created surface does not require any further mechanical processing.
The typical carbide layers that protect saw-blades, disc harrows, or counter blades from wear and corrosion can be optimally realized with the help of laser cladding. Distortion and mixing are kept particularly low by a quiet molten pool and minimal heat input. Coating thicknesses as well as track widths can be variably and specifically built up. Oversizes during coating are kept to a minimum, so that the economic efficiency combined with the technical advantages make a strong team for agricultural components.
Coating of hydraulic cylinders for the mining industry
A growing market is laser cladding of hydraulic cylinders in technical mining facilities for example coal extraction. The coating of the cylinder corrodes very quickly under the local atmosphere which leads to leaking hence a replacement or new coating will be necessary. Until now chrome plating was the primary method which will be replaced more and more by laser cladding due to its superior durability. The specific increase of durability can’t be quantified yet however current results show an increase in the lifetime of more than 100%.
Coating of heat exchangers
The main motivation is the protection against highly corrosive gases or liquids that come into contact with the metal heat exchanger affecting its life cycle. Therefore nickel alloys with low hardness properties are mostly used which avoids cracking and can be applied up to 1 mm thickness. Even at high temperatures, they lead to better wear protection against corrosive media. Deposition rates of 8 kg/h are possible.
Chlorine attacks metal, a fact that is known all too well by operators of biomass facilities and incineration plants. But why? The boiler walls of such plants consist of water-bearing steel pipe systems that absorb the thermal energy of the firing and then transfer it to the water-steam circuits. But the chlorine in the flue gas of the firing breaks down the pipes. Untreated, they are often no longer usable after one year. It seems reasonable then to assume that this cannot be economical.
Meanwhile, many plant operators therefore count on anti-corrosion coatings. This is already worth the effort as soon as the duration of the operation is doubled — and even more can be achieved: compared to uncoated pipes, and depending on the applied material and physicochemical load, a tripling or quadrupling of the lifespan is possible.