Laser Cladding is a novel method of surface modification. It generates a metallurgically bonded additive cladding layer on the surface of the base material by adding cladding material to the surface of the base material and fusing it with a thin layer on the surface of the base material using a high-energy-density laser beam.
Read More : Laser Cladding Unlimited Guide In 2023
Laser cladding, like PTA cladding, allows for metallurgical connection between the coating and the substrate. Except in a few circumstances, the coating can be applied to most iron- and nickel-based substrates.
What Is Laser Cladding Process？
Laser cladding process can be used to improve component wear resistance or to restore damaged surfaces. This procedure is quite adaptable. Two or more powders can be consistently mixed throughout the cladding process by adjusting the varied powder feeding rates of the double-barrel powder feeder.
Laser Cladding Process Working Range
- Deposition rate: up to 8 kg/hour
- Deposition thickness: 0.5 – >4 mm
- Deposition hardness: up to 68 HRC
Type Of Laser Cladding
Laser cladding can be divided into powder-fed laser cladding and wire-fed laser cladding according to the feeding method (powder or wire).
According to the technique of cladding material delivery, laser cladding may be split into two categories: preset laser cladding and synchronous laser cladding.
Powder Feeding Method In Laser Cladding
Wire-Fed Laser Cladding
Wire-fed laser cladding is a method of generating a protective or useful covering by melting a metal wire and depositing its substance onto a substrate. It differs from previous cladding processes in that it uses wire rather than powder as feedstock. It may be used to restore old or damaged components, include wear-resistant coatings, and build complicated geometries.
Powder-Fed Laser Cladding
Powder-fed laser cladding is an additive manufacturing technique that includes utilizing a laser to melt and deposit powdered material onto a substrate. Because the material is given in powder form, it varies from wire-fed laser cladding. It can be used for coating, repair, and prototyping.
Powder feeding may be classified into two types: side-shaft powder feeding and coaxial powder feeding. The laser is output from the center of the cladding head in coaxial powder feeding, and the metal powder is disseminated in an annular form around the laser or in a multi-channel circumferential distribution (often three or four channels).
Powder feeding on the sideshaft is identical to wire feeding, except that the wire is replaced by powder feeding. In front of the laser processing direction is the powder feeding tube. The metal powder is deposited on the surface of the substrate in advance by gravity, and the laser beam at the back scans the pre-deposited powder to finish the process.
|Side-axis powder feeding
|Side-axis powder feeding has a higher powder usage rate than coaxial powder feeding, which can reach more than 95%.
A rectangular spot scheme (i.e. broadband cladding) can be used for side-axis powder feeding laser cladding. The cladding efficiency is considerably increased by expanding the length and breadth of the spot.
A gravity powder feeder is used for side-shaft powder feeding, which reduces inert gas usage.
|The molten pool’s capacity to defend itself is inadequate due to a lack of protective gas; air cannot be blown, and the air flow will damage the preset powder.
Because gravity feeding is employed, it is not appropriate for inclined workpieces or inner hole cladding and has a limited application range.
The melt channels on the cladding layer’s surface are quite visible, and the subsequent grinding and processing costs are significant.
|Coaxial powder feeding
|The coaxial powder feeding surface is comparatively smooth compared to the side-shaft powder feeding surface, and the subsequent processing steps are easy and the processing volume is modest.
Powder may be supplied in any direction at any angle, and surface cladding can be done using industrial robots in any path.
The molten pool is shielded by inert gas, and the cladding layer is of good quality with minimal oxide inclusions.
|The inert gas pushes the metal powder into the molten pool, and some of it is blasted out and wasted. The typical usage rate of powder is around 70%.
Because the powder feeding channel is small, it is prone to uneven powder distribution and powder output channel clogging. In severe circumstances, the nozzle must be replaced.
Technique Of Cladding Material Delivery
Preset Laser Cladding
Preset laser cladding involves placing the cladding material on the surface of the substrate in the cladding section beforehand, and then using laser beam irradiation scanning melting, the cladding material is added in the form of powder or silk, with powder being the most typically utilized.
Preset laser cladding’s basic process flow is as follows:
- base material cladding surface pretreatment
- preset cladding material
- laser cladding
- post heat treatment.
Synchronous Laser Cladding
During the cladding process, synchronous laser cladding feeds powder or wire cladding materials via the nozzle into the molten pool at the same time. The cladding material is applied as powder or silk, with powder being the most typically utilized.
The main process flow of synchronized laser cladding is:
- substrate cladding surface pretreatment
- synchronous laser cladding
- post heat treatment.
Read More : Laser Cladding Powder Feeding Method Guide
The process parameters of laser cladding mainly include laser power, spot diameter, cladding speed, defocus amount, powder feeding speed, scanning speed, preheating temperature, etc. These parameters have a great impact on the dilution rate, cracks, surface roughness of the cladding layer, and the density of the cladding parts. Each parameter also affects each other, which is a very complex process. Reasonable control methods must be used to control these parameters within the range allowed by the laser cladding process.
Laser cladding has three important process parameters
The more powerful the laser, the more cladding metal is melted, and the greater the likelihood of porosity forming. As the laser power increases, the depth of the cladding layer grows, the surrounding liquid metal swings wildly and dynamically hardens and crystallizes, progressively reducing or even eliminating the number of pores and fissures.
When the cladding layer approaches the ultimate depth, the surface temperature of the substrate rises, and the deformation and cracking events become more severe. If the laser intensity is too low, just the surface coating melts, but not the substrate. At this point, localized phenomena develop on the cladding layer’s surface. voids, piling,voids, etc. cannot achieve the purpose of surface cladding.
Laser beams are typically round in shape. The breadth of the cladding layer is mostly determined by the laser beam’s spot diameter. The cladding layer grows wider as the spot diameter rises. varied spot sizes will result in varied energy distributions on the cladding layer’s surface, and the morphology and structural characteristics of the resulting cladding layer will be considerably diverse.
In general, when the spot size is small, the cladding layer quality improves. The quality of the cladding layer degrades as the spot size grows. However, the spot diameter is too tiny, which makes acquiring a broad area of cladding layer difficult.
The cladding speed V has an impact equivalent to the laser power P. If the cladding speed is too fast, the alloy powder cannot be entirely melted, and the high-quality cladding effect is lost; if the cladding speed is too slow, the molten pool exists for too long, the powder is overburned, and the alloy components are lost. At the same time, the matrix’s heat input is high, which increases the amount of deformation.
Laser cladding parameters do not impact the macro and micro quality of the cladding layer individually, but rather interact with one another. The idea of specific energy Es is presented to describe the overall impact of laser power P, spot diameter D, and cladding speed V, namely:
In other words, the irradiation energy per unit area may be examined alongside parameters such as laser power density and cladding speed.
Reduced specific energy is conducive to reduced dilution rate, and it is also connected to cladding layer thickness. When the laser power remains constant, the cladding layer’s dilution rate falls as the spot width grows. When the cladding speed and spot diameter remain constant, the cladding layer’s dilution rate increases as the laser beam power increases. Furthermore, when the cladding speed rises, the melting depth of the matrix reduces, as does the rate of dilution of the cladding layer by the matrix material.
The overlap rate is the primary factor influencing the surface roughness of the cladding layer in multi-pass laser cladding. The surface roughness of the cladding layer diminishes as the overlap rate rises, but the uniformity of the overlapped section is difficult to ensure. The depth of the overlapping areas between the cladding channels is different from the depth of the center of the cladding channels, which affects the uniformity of the entire cladding layer. Moreover, the residual tensile stress of multiple lap cladding layers will be superimposed, increasing the local total stress value and increasing the sensitivity of the cladding layer to cracks. Preheating and tempering can reduce the cracking tendency of the cladding layer. 
Laser Cladding Advantages
- The cooling rate is fast (up to 106K/s), resulting in a quick solidification process. Fine-grained structures are easily formed, as are novel phases that cannot be obtained in equilibrium, such as unstable phases, amorphous states, and so on.
- The coating has a low dilution rate (usually less than 5%) and a strong metallurgical bond or interface diffusion bond with the substrate. A excellent coating with a low dilution rate may be achieved by modifying the laser process settings, and the coating composition is consistent with Dilution can be controlled.
- Because the heat input and distortion are modest, especially when employing high power density and quick cladding, the deformation may be limited to the part’s assembly tolerance.
- There are essentially no constraints on powder selection, particularly for depositing high melting point alloys on the surface of low melting point metals;
- The cladding layer thickness range is broad, with a single coating thickness of 0.22.0mm using single-pass powder feeding.
- It can conduct selective welding, uses less material, and has a great performance-price ratio;
- Beam aiming can weld inaccessible places; and (8) It is simple to automate.
What Type of Laser Is Used in Laser Cladding?
For the deposition process, laser cladding typically uses a high-power solid-state laser. The following is a list of laser types used in laser cladding:
Fiber lasers generate laser beams using optical fibers and are known for their efficiency and reliability.
Diode lasers emit laser beams through semiconductor diodes and offer precise control in a compact package.
Carbon dioxide lasers, CO2 lasers, produce laser beams through a gas mixture and are suitable for cladding larger areas.
Neodymium-doped yttrium aluminum garnet lasers generate laser beams using solid-state crystals. They are versatile for various cladding applications.