Laser cladding has gained momentum in the field of material processing
the process of using laser and adding materials to realize rapid prototyping and repair of parts is usually called laser cladding manufacturing. After decades of research and development, together with the improvement of laser system performance and the market demand for sustainable environmental protection projects, all these factors are promoting the wider application of laser cladding technology
laser cladding (also known as laser additive manufacturing or coating manufacturing) is a process of depositing additive materials on the surface of the substrate by laser, or creating a new three-dimensional object by establishing a material layer. At present, laser cladding is increasingly gaining extensive development power in the field of material processing. The industry is highly interested in laser cladding technology, and it is expected that at least two laser cladding processing stations will be established in the world this year. 
although the use of laser and additive materials for parts repair, surface hardening, rapid manufacturing and other applications has experienced decades of development, laser cladding technology has just been widely used in industry and commerce. Similar to the situation that laser welding technology has been widely used, the emergence of a directed graph laser system with higher power, higher beam quality, improved part quality and service life, the market demand for sustainable environmental protection projects, as well as the reduction of energy consumption, toxic gas emissions and material waste, have jointly promoted the wide application of laser cladding technology
definition of related terms
cladding refers to adding a thin layer (usually 3mm or 4mm) on the surface of existing parts to improve the surface properties of parts; And additive manufacturing (AM) is to add specific materials to the existing structure, or create free structure materials
Stewart Williams, Professor of welding science and engineering at the welding engineering research center of the University of Cranfield in the UK, said: "for example, laser cladding applications include coating corrosion-resistant materials on the inner wall of pipes to protect the base material, thereby avoiding the use of expensive corrosion-resistant alloys in pipe manufacturing. Common additive manufacturing applications include the repair of high-value parts (such as the repair of turbine blades and engine sealing elements, that is, adding high-performance materials to the end of turbine blades) and parts manufacturing. Because the added manufacturing parts can be manufactured directly through the CAD system, each part can be easily changed to meet any demand, which is extremely important in medical applications (such as medical transplantation). "
williams pointed out that laser additive manufacturing is the field with the largest growth, and a large number of laser additive manufacturing research activities have been carried out in the UK and throughout Europe. "At present, carbon fiber composites are more and more widely used in civil aircraft. In the latest aircraft, the proportion of carbon fiber composites has been as high as 50%. The remaining materials are mainly titanium, which is to avoid corrosion problems." Williams said, "the standard mechanical manufacturing method of processing parts with solid billet usually turns 90% of the starting material into debris, and the material waste is serious. If the laser addition manufacturing method is adopted, the material waste is usually only 10%, and the energy consumption and carbon dioxide emissions are also greatly reduced."
James W. Sears, head of additive manufacturing at South Dakota Institute of mining and technology, pointed out that although the past parts manufacturing field may be a market for laser additive manufacturing to gain growth, the real exciting growth point of laser additive manufacturing applications is some large-scale applications, such as the cladding application of booster pipes for oil drilling, And applications such as cladding repair and component remanufacture in large companies such as Caterpillar forklift company in the United States. "Many of these applications will consume several tons of materials per month, rather than one ton of materials per year." Sears said
laser cladding is to first apply powder materials or additive materials to the surface of the substrate through a nozzle, and then under the scanning of the laser beam, these materials are sintered or melted on the surface of the substrate to form a coating
the laser power range used in laser assisted metal repair and cladding is usually 1 ~ 4kw. "The most typical cladding application is to coat hard surface materials such as tungsten carbide on nickel matrix materials to improve the wear resistance of parts. These parts are usually used in oil and gas drilling applications, or for blades and cutting disks in agricultural applications." Christian foehl, product manager of tongkuai company in Germany, said, "compared with traditional coating technologies such as thermal spraying, laser metal deposition technology provides real metallurgical fusion advantages, which can create higher quality coatings while avoiding some common defects. Using two or more powder containers, different powders can be mixed together to meet specific coating needs." (see Figure 1)
Figure 1: laser cladding applications usually use a nozzle to blow out the powder and use the heat from the center of the laser beam to realize surface cladding
recently, IPG photonics has launched 2kW, 3KW and 4kw laser products specifically for cladding, welding and annealing applications. In addition, the high light series semiconductor laser system of coherent company has an electro-optical conversion efficiency of 40%, and can output 808nm or 975nm near-infrared light, with a total output power of kW level
in the powder layer addition manufacturing, the laser beam melts and deposits the powder to form a thin layer of 20 ~ 40 m, which is used for direct metal laser sintering (DMLS); A thin layer of 100 ~ 150 m is formed for selective laser sintering (SLS); Then, the additional powder will be deposited on the surface of each solidified thin layer. By repeating this process, these thin layers can be established into three-dimensional parts. DMLS and SLS technologies were pioneered by German electro optical systems. Using DMLS and SLS technology, nylon, glass and other materials can be filled with nylon or polystyrene, with a manufacturing volume of 700 × three hundred and eighty × 580mm3 polymer type and art model; Made of stainless steel, titanium and other metal materials with a volume of 250 × two hundred and fifty × 195mm3 metal parts. In the future, 3T RPD company in the UK will use DMLS and SLS technology to develop customized parts for a wide range of applications, ranging from building models to dental implants (see Figure 2). The company even designed improved SLS nylon parts for a smart car, which can work well as factory produced parts
Figure 2: melt polymer or metal powder layer by layer with high-power laser beam to produce customized aviation turbine parts (above figure), It can even produce dental implants directly from CAD models (below)
"dental laboratories use direct metal powder laser sintering to create crowns (c our customers can calculate the mechanical property parameters of materials through experimental curves, oping) and bridges" ； Our company's eosint m 270 metal sintering equipment has customized a batch of dentures with a number of more than 200 for customers. DMLS technology has significantly improved the output of the laboratory, while meeting strict quality requirements. " Martin bulleter, medical account manager of EOS, said, "mass customization is having a certain impact in the fields of Dentistry, surgical instrument and prosthetic limb manufacturing. The application of laser sintering technology in emerging fields will become more practical and cost-effective."
pom group coo Bhaskar Dutta said that for the construction of structures with excellent performance with expensive materials, laser metal deposition can reduce production time, reduce production costs, and reduce energy consumption compared with traditional machining methods. POM group is a fast manufacturing company whose direct metal deposition (DMD) laser process is in the leading position in the industry. Dutta pointed out that in a case study initiated by NASA, a mirror room was established, which uses closed-loop feedback to control the DMD system. In the case study, the components made by DMD method are compared with those made by EDM method with solid metal plate. The results show that EDM method produces a large amount of waste (see Figure 3). "To manufacture the same parts, DMD processing requires only 1/3 of the materials required by EDM method, which can save a lot of costs. Especially for expensive materials such as nickel alloy, DMD processing advantages are more obvious." Dutta said
Figure 3: in a case study initiated by NASA, a mirror room was established for laser direct metal deposition. The case study compares DMD and EDM. The results show that DMD is much better than EDM in material saving, reducing energy consumption and improving processing speed
repair and reconstruction
aircraft manufacturers predict that their demand for engines will increase. "It is estimated that by 2025, the demand for aircraft engines will exceed 114000, which brings certain challenges for aircraft engine manufacturers to reduce the impact on the environment in the manufacturing process." Steve beech, production process director of Rolls Royce in the UK, said, "for some parts, the BTF ratio (buy to fly ratio, that is, the ratio of the amount of material required to manufacture a part to the amount of material contained in the final part) is even as high as 13:1, that is, the parts processed with 13 kg of titanium material contain only 1 kg of titanium, and the rest become waste."
laser addition and repair of the sealing parts of a high-pressure turbine aeroengine is a good example of reducing the impact of new manufacturing on the environment. "For this single crystal component, the traditional manufacturing method is to process the lattice by EDM and add wear-resistant materials to the solid substrate. When the sealing element of the turbine blade rubs against it, it is this wear-resistant substrate that is worn during engine service." Beech said (see Figure 4). In this application, traditional techniques (such as welding a new lattice on a sealing element) are not feasible, because the thickness of the lattice wall must be less than 0.3mm (and each turbine has 34 sealing elements, which is expensive). "But using direct laser deposition technology to melt the appropriate powder to establish the lattice, the repair cost will be reduced to half of the OEM cost." Beech said
Figure 4: laser additive manufacturing can be used to manufacture thin walls with a thickness of 0.3mm for lattice on aviation parts. The lattice is filled with ceramics to achieve the sealing function and avoid the wear of turbine blades
Ge aviation has used laser cladding technology for more than 20 years. "Laser cladding is suitable for cost-effective repair and case hardening of hardware returned from the field, such as high-pressure turbine and compressor blades used to improve the repetition rate of automated processes." Said Sudhir Tewari, senior engineer of the laser application division of Ge aviation. Tewari explained that generally, the thermal effect of laser cladding is small, and the properties of the treated material are good - close to the properties of refined materials, because the rapid solidification rate of the laser cladding process can obtain a good dendritic microstructure. "Ge participated in the 'aviation' for the addition and manufacturing of nickel alloy parts