Laser cladding is a new technique that may be used to make, repair, and reinforce metal objects. It has found widespread application in aircraft, vehicle manufacture, the petrochemical sector, and other industries. The performance of the powder feeder, as one of the fundamental components of cladding equipment, will directly impact the quality of the cladding layer, and it has increasingly been the focus of attention.
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.
Coaxial Powder Feeding Laser Cladding Technology
Coaxial powder feeding laser cladding technique typically employs semiconductor fiber output lasers and disk-type airborne powder feeders. The cladding head employs a circular spot pattern, with light emitted from the center. The powder is fed in an annular or multi-beam arrangement around the beam, and the Special protective air channel, powder beam, light beam, and protective air flow all converge at one place. A molten pool will form at the focus during the cladding process. A coating forms on the workpiece’s surface as the cladding head and the workpiece move relative to each other.
Advantage of 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 molten pool is tiny, the powder is evenly heated, and the cladding layer is break resistant. Coaxial powder-fed laser cladding typically has a spot size of 1-5mm. At the same time, the powder and the beam are in uniform contact, and heat transmission during the cladding process is more uniform, resulting in a crack-resistant cladding layer. It is simple to manufacture a coating with no fractures and evenly dispersed tungsten carbide for cladding of materials containing ceramic particles such as tungsten carbide.
- Low heat input and low penetration:When compared to broad spot side powder feeding laser cladding and arc welding, the cladding heat input is minimal, with a moderate dilution rate and a lesser thermal impact, due to the tiny spot diameter and high cladding linear speed of coaxial powder feeding laser cladding. zone depth, high cladding performance, and no influence on the qualities of the underlying material.
Disadvantage Of Coaxial Powder Feeding
- 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.
- Inadequate security and stability:A central output laser is used in the coaxial powder feeding cladding head. The structure of the surrounding powder path, gas path, and water path is complicated. The cladding head has a poor cooling effect. When operating for an extended period of time, the temperature of the cladding head rises, causing spilled powder to adhere.
Side-Axis Powder Feeding Laser Cladding Technology
Side-axis powder feeding laser cladding technique is also known as laser cladding technology. It often employs a semiconductor direct output laser or a semiconductor fiber output laser, as well as a gravity powder feeder. A rectangular spot + side-axis broadband powder feeding solution is used in the cladding head.
The alloy powder is delivered to the workpiece surface via the powder feeding nozzle when the cladding head is in operation. The rectangular laser beam scans the pre-positioned alloy powder and melts it to produce a molten pool, which is subsequently cooled, while the cladding head and workpiece move relative to each other. Then a cladding layer is produced.
Advantage of 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.
Disadvantage Of Side-Axis Powder Feeding
- 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.
Central Powder Feeding Laser Cladding Technology
The central powder feeding technique is known as optical powder packaging technology because it uses a single-beam powder channel in the center of the cladding head and distributes the laser beam annularly around the metal powder or circumferentially. In practice, metal powder is discharged from the center channel by gravity and pneumatics.
At one point above the substrate, the peripheral laser and metal powder intersect. The laser beam surrounds the metal powder in the center, which fully absorbs the light energy to become molten or semi-molten, and then the molten metal powder falls into the molten pool on the surface of the substrate, generating a flat and dense metallurgical cladding layer.
Advantage of Central Powder Feeding Laser
1.The usage rate of metal powder might approach 90%.
Central powder feeding differs from coaxial pneumatic powder feeding in that the powder is a single powder flow with no mutual impact or dispersion of powder flows in separate directions. Furthermore, reduced powder feeding air pressure can be employed during vertical downward cladding production. On the one hand, the powder flow speed is relatively slow, and the contact period between the powder and the laser is lengthy, allowing the powder to melt above the molten pool more easily. A reduced powder flow velocity, on the other hand, minimizes ejection between the powder flow and the substrate. In practice, the central powder feeding and high-speed cladding process considerably decreases spatter.
2.The optical route is highly stable and can emit light for an extended period of time.
The laser beam of coaxial powder feeding laser cladding technology and off-axis powder feeding laser cladding technology, on the other hand, irradiates the molten pool directly. The molten pool’s surface is exceedingly smooth and has a high laser reflectivity. As a result of these two laser cladding technologies The heat radiation of the laser molten pool has a significant impact on the optical path system, and the light output stability is poor for an extended period of time. The laser beam is typically output to the molten pool at a specified tilt angle along the periphery in the central powder feeding arrangement.
To minimize direct heat radiation from the laser action region, the light outlet is separated into numerous smaller light ports and has a certain angle with the molten pool. Optical systems are more secure. The same center-fed metal powder spills less. Furthermore, because the optical path is tilted, the impact of the splash is minimal.
3.High cladding efficiency (0.7-1.2㎡/h)
The central powder feeding technique has a high powder use rate and adequate laser energy utilization, resulting in extremely high cladding efficiency (cladding efficiency may reach 0.7-1.2m2/h when the thickness of one side is 0.5-0.7mm). The cladding layer’s dilution rate is modest. The existence duration of the molten pool is very brief due to the high cladding linear speed of ultra-high-speed laser cladding technology, therefore the cladding layer dilution rate is very low.
The ultra-high-speed laser cladding technique also has outstanding cladding layer roughness, strong fracture resistance, and little workpiece deformation. The ultra-high-speed laser cladding layer is thin, making it ideal for the creation of pre-protective coating on the substrate.
4.Benefits of central powder feeding over coaxial pneumatic powder feeding
Central powder feeding differs from coaxial pneumatic powder feeding in that the powder is a single powder flow with no mutual impact or dispersion of powder flows in separate directions. Furthermore, reduced powder feeding air pressure can be employed during vertical downward cladding production.
On the one hand, the powder flow speed is relatively slow, and the contact period between the powder and the laser is lengthy, allowing the powder to melt above the molten pool more easily. A reduced powder flow velocity, on the other hand, minimizes ejection between the powder flow and the substrate. In practice, the central powder feeding and high-speed cladding process considerably decreases spatter and sparks.
Coaxial powder feeding laser cladding technique is commonly utilized in surface cladding modification and additive remanufacturing of high-precision components and complex-shaped parts such as spindles, gears, and boxes due to the qualities listed above. Simultaneously, metal 3D printing based on coaxial powder-feeding laser cladding technology is mostly employed for net near-forming of big components and gradient material preparation.
Side-axis powder feeding laser cladding technique is commonly used in surface cladding and additive remanufacturing of products with huge surfaces and simple forms, such as hydraulic cylinders and rollers, because to its great efficiency and cheap cost.
To conclude the above study, side-shaft powder feeding and coaxial powder feeding have been created for a long time but have not been generally pushed or utilized due to their unique technological features and limitations. Central powder feeding method may compensate for both of their technological drawbacks and offers several technical advantages. High-efficiency and high-quality laser cladding effects will undoubtedly conquer additional areas with the optimal combination of high-speed laser cladding and central powder feeding technology. market.
We think that with more firms applying and promoting high-speed laser cladding + central powder feeding technology, it will become the mainstream application of laser cladding in the near future, and that this technology will also occupy a bigger market share in the metal surface industry.