The difference between plasma cladding and laser cladding

       With the rapid development and wide application of laser technology, laser cladding equipment has gradually begun to be used in various industries. Laser cladding seems to be very tall in everyone's eyes. However, some plasma surfacing equipment manufacturers take advantage of this and even advocate that their plasma surfacing equipment is laser cladding. Another part of the manufacturers of laser cladding equipment infinitely exaggerates the advantages of laser and depreciates plasma cladding as a backward technology. In view of this, it is necessary to comprehensively compare the differences between the two here.



1. Technical features

The plasma arc used in plasma surfacing welding uses various restraint mechanisms to give full play to the high temperature and high penetration ability of the arc plasma area, which makes the characteristics of the arc change qualitatively. The compression arc has a high temperature, and the shape of the arc changes from a conical shape to a cylindrical shape, so that plasma surfacing has a series of favorable process characteristics. Plasma cladding generally works continuously, and the cooling rate of the workpiece is relatively slow, and the transition area formed is deeper than that of laser cladding. For cemented carbide materials, the stress will be released better.

Laser cladding is to add cladding material on the surface of the substrate, and use a high-energy density laser beam to melt it together with the thin layer on the surface of the substrate. Surface coating, thereby significantly improving the wear resistance, corrosion resistance, heat resistance, oxidation resistance and electrical properties of the surface of the basic material. The most important features of laser cladding are heat concentration, fast heating, fast cooling, and small heat affected zone. Laser cladding, a special process of fast heating and cooling, produces a special structure in the casting area, and can even produce amorphous structures, especially for pulsed lasers. This is the so-called laser cladding without annealing. cause of deformation,

2. Equipment Features

Plasma surfacing equipment is generally composed of plasma spray welding power supply, electrical control system, mechanical device, gas circuit system, water cooling system, plasma welding torch and other parts. The design of plasma surfacing equipment is to meet the process requirements as the starting point, and the performance of the main components and basic circuits that make up the equipment will affect the quality of the surfacing welding layer and process stability. With the advancement of electrical technology, my country's plasma arc welding power source technology level has sufficient support capabilities. In addition, the plasma surfacing equipment is small in size and weight, and the welding torch can be equipped with or hand-held, which makes it more flexible and convenient to use, and the cost of auxiliary tooling is cheap.

There are currently two types of laser cladding machines used in China: CO2 laser and YAG laser. The former is continuous output, and the cladding power is generally above 3KW; the YAG laser is pulse output, generally around 600W. For equipment, due to the high threshold of laser technology, it is difficult for ordinary users to understand and rely heavily on the service of the manufacturer. Laser equipment is complex, expensive to purchase, maintenance costs and parts and components are high, and the stability and tolerance of equipment are generally far from foreign countries. Therefore, laser cladding machines are generally used in special fields such as high-value products (aero-engine blades), and it is difficult to generate economic benefits in the fields of general industrial manufacturing and maintenance.

3. Process characteristics

(1) Pre-processing

Plasma surfacing only needs to remove rust, decontamination and fatigue layer.

Laser cladding generally requires polishing, degreasing, rust removal, decontamination and fatigue layer removal of the workpiece, which is more refined than plasma surfacing.

(2) Powder feeding

Plasma surfacing uses argon gas as the powder feeding gas, and the powder feeding outlet can have a certain inclination through the internal or external powder feeding of the welding torch nozzle. This facilitates manual plasma surfacing operations, and is more suitable for on-site repair of workpieces.

The power of the CO2 laser is high, and argon gas is generally used to feed the powder; the power of the YAG laser is low, and the natural powder drop is generally used. Due to the linearity of the laser, the molten pool is basically formed in a horizontal position during cladding. If the inclination is slightly larger, the powder cannot be delivered to the molten pool normally, and the scope of use is greatly limited, especially for YAG lasers.

(3) molten pool state

The stability of the plasma surfacing welding is good, the formation of the molten pool is also easy to control, the surfacing alloy material is fully integrated with the body, and the regional transition is good.

Due to the high control accuracy of the laser, the constant output power, and no arc contact, the size and depth of the molten pool are consistent, and the heat-affected zone of the molten pool is much smaller than that of plasma surfacing.

4) Material selection

Plasma surfacing welding, the use of plasma arc heating method has fewer restrictions on materials, and the choice of materials is more extensive. Generally, iron-based, nickel-based, cobalt-based, copper-based and high-temperature ceramic materials can be used, and the surfacing welding of carbide, oxide and other materials Relatively easier.

Laser cladding, due to the different absorption capabilities of different materials for different wavelengths of laser light, has a large limitation on the choice of laser cladding materials. Laser is more suitable for some materials such as nickel-based self-fluxing alloys, and is more suitable for carbide and oxide cladding. more difficult