What's laser cladding technology?

What's laser cladding?

Laser cladding technology refers to the process of placing the selected coating material on the surface of the substrate with different fillers, melting it with a shallow layer on the surface of the substrate simultaneously by laser irradiation, and forming a surface coating with very low dilution and metallurgical bonding with the substrate material after rapid solidification, thus significantly improving the wear resistance, corrosion resistance, heat resistance, oxidation resistance and electrical characteristics of the surface of the substrate material.

Classification of laser cladding

Laser cladding can be divided into powder-feeding laser cladding and wire-feeding laser cladding depending on the feeding method (powder or wire).

Wire feeding laser cladding: The wire is fed directly into the spot through the wire feeding mechanism, which melts and solidifies together with the substrate to achieve laser cladding. Compared with powder coating, wire feeding can achieve no waste of coating material, which is much higher than powder coating, but the disadvantages are that the heat affected zone is too large, good gas protection cannot be achieved, many defects in coating, and difficulty in adjusting process parameters.

Powder feeding laser cladding is more widely used than wire feeding. According to the different ways of powder feeding, it can be divided into side-axis powder feeding and coaxial powder feeding. Coaxial powder feeding means that the laser is output from the center of the cladding head and the powder is distributed in a ring around the laser or in multiple circumferential directions (commonly three or four ways). Side-axis powder feeding is similar to wire feeding, except that the wire feed is replaced by a powder feed. The powder feed tube is located in front of the laser processing direction, and the metal powder accumulates on the substrate surface in advance by gravity, and then the rear laser beam is scanned on the pre-deposited powder to complete the laser cladding process.

Advantages of side-shaft powder feeding：

Compared with coaxial powder feeding, the powder utilization rate of side shaft powder feeding is high, which can reach more than 95%.

The rectangular spot solution (i.e., broadband melting) can be used for side-axis powder feeding laser melting, which allows for a significant increase in melting efficiency by increasing the spot length and width.

The gravity feeder is used to feed the powder on the side shaft, which can reduce the consumption of inert gas.

Disadvantages of side-shaft powder feeding：

Due to the lack of protective gas, the melt pool is poorly protected; it cannot be blown, and the airflow will affect the preset powder.

Because of the gravity feed, it is not suitable for sloping workpieces or internal hole cladding, so the application is limited.

The surface of the cladding layer is very obvious and the subsequent grinding and processing costs are high.

Advantages of coaxial powder feeding：

Compared with the side shaft feeding, the coaxial feeding surface is flatter, and the post-processing process is simple and small.

The powder can be fed in any direction at different angles, and the surface can be coated in any path with the industrial robot.

The melt pool is protected by inert gas, the melt layer has less oxide inclusions and high quality.

Disadvantages of coaxial powder feeding：

The inert gas blows the metal powder to the excitation pool, and part of it is blown outside the pool to be wasted, and the powder utilization rate is about 70% on average.

Powder feed channel is narrower, easy to uneven powder distribution, powder outlet channel blockage phenomenon, in serious cases need to replace the nozzle.

General cladding VS High-speed cladding

It becomes molten or semi-molten and then falls into the molten pool on the surface of the workpiece, and then melts with the base material. In this way the powder absorbs most of the energy and the powder temperature is close to the melt pool temperature. In this way, most of the energy is absorbed by the powder, so the heat input to the base material is less, and the heat affected zone and thermal deformation are relatively smaller, which is more effective for thin wall and thin plate. Since the surface quality of the coating is significantly higher than that of ordinary laser cladding, it only requires simple grinding or polishing for application. Therefore, material waste and subsequent processing are greatly reduced, and ultra-high speed laser cladding has irreplaceable application advantages in terms of cost, efficiency, and thermal impact on parts.

Laser cladding equipment

Laser cladding equipment with laser as the core, and with the cladding head, water chiller, powder feeder, motion control system and other key functional units: the laser provides a high-energy laser heat source, which determines the cladding performance of the whole set of equipment; the cladding head is used to output laser and powder, which also determines the effect of cladding to a certain extent; the water chiller guarantees the stable operation of the laser and the laser cladding head; the powder feeder provides continuous raw materials for laser cladding; the motion control system (such as slide rail and rotary table) is used to control the cladding head and the parts to be processed, which determines the processing accuracy.

?GW Fiber lasers for laser cladding

GW Laser Tech, as a global leader in high brightness fiber lasers, has a product line covering the full power range from low-power air-cooled lasers to high-power 10,000-watt lasers. Among them, the P series 6KW lasers fully meet the current demand for laser cladding and are widely used in this field.

Main features of GW Lasers:

Power Reliability

New optical structure design with 976nm pumping technology, longer pump diode life, higher energy density and better beam quality. Long time operation power stability <2%, able to withstand ultra-long time laser melting.

Structural reliability

The environment of laser cladding is usually dusty, once it enters the laser, it will damage the internal optical devices, and in serious cases, it will also lead to short circuit of the circuit board, which will endanger personal safety. The laser structure is fully enclosed, with IP65 protection level, which greatly reduces the requirements of the laser on use of the environment, and can continue to operate in the harsh environment of high temperature, high humidity and high dust.

Energy Distribution

Gaussian spot temperature distribution is different, with stronger energy in the middle than on both sides and faster heat dissipation at the edges, which will produce an uneven molten layer. GW Laser HBF-high brightness flat top mode distribution can utilize energy more efficiently compared to Gaussian mode distribution. In Gaussian beam profile, the energy below the threshold requirement in its two wings are wasted and can damage the surrounding area beyond the target area, thus extending the heat-affected zone; while the middle energy is too high for the melt channel, which is very likely to cause over-burning in the middle and under-melting on both sides. Compared with Gaussian beams, flat-top beams do not have two wings in the profile, but have steeper edge transitions, so the energy transfer is more efficient and the melt channel is smoother.

Light spot size

The optical fiber core diameter of the GW laser can be customized up to 800μm to meet the requirements of different melting processes. At the same time, GW laser can be configured with an external optical coupler to couple the laser from the output fiber to the operating fiber, greatly expanding the laser's functionality. The output fiber core diameter of ordinary lasers is usually 50/100μm, while the coupler has a variety of different output core diameters to choose from. For example, a 100μm laser for cutting can be coupled to an output of 800μm for fusing applications; when the operating fiber is damaged, it can be easily replaced without damaging the laser body.

Application areas for laser cladding

The application of laser cladding is very wide, almost covering the entire machinery manufacturing industry, including but not limited to mining, petroleum, electric power, railroads, automobiles, ships, etc.: mining coal machines set a large amount of wear and tear, due to its harsh working environment, parts damage faster; power equipment non-stop operation, the chance of damage to its parts is also relatively high.

The petrochemical industry basically adopts a continuous mass production mode, in the production process, the machine works for a long time in a harsh environment, resulting in damage, corrosion and wear of components in the equipment.

Oil drill pipe repair

These devices are expensive and involve many types of parts, most of which have a variety of shapes and are difficult to repair, but because of the advent of laser cladding technology, these problems are no longer a problem.

GW P6000 laser for internal wall repair

With excellent beam quality and output stability, GW high power fiber lasers have been widely used in heavy machinery manufacturing industry. In the future, GW Laser will continue to make efforts in the field of laser cladding, through independent innovation, product iteration and upgrade, and continue to provide customers with high-quality fiber lasers, as well as strong technical support.

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