Abstract： To decrease the development cycle of blades of gas turbines, the present research situations, as well as the application both at home and abroad of metallic three-dimensional printing technology used in the fields of rapid manufacture and the repairment method of laser cladding technology for gas turbine blades, are elaborated based on summarizing the main three-dimensional printing technology and its forming principle at present. The advantage of metallic three-dimensional printing technology compared with traditional manufactural technology is analyzed. The research progress of three-dimensional printing technology in investment casting fields to manufacture gas turbine blades is introduced. The result shows that the three-dimensional printing technology has broad application prospects in the rapid manufacture of blades for gas turbines.
Keywords： gas turbine blades；3D printing technology； rapid manufacture and repairment； investment casting
Gas turbine blade manufacturing is a high-tech manufacturing field. Currently, only a few industrially developed countries have mastered the core technology. The main reason is that gas turbine blades require high material properties, special geometries, and stringent dimensional accuracy requirements. Traditional manufacturing processes can only improve the processing quality of blades by focusing on the control of blanks, selection of tool materials, setting of cutting parameters, and tool feeding methods, which increases the manufacturing cost and production cycle of the blades, and also reduces the stability of product processing quality. Hard to guarantee.
As the most cutting-edge and leading emerging technology, 3D printing technology has a profound impact on traditional manufacturing methods and production processes with its revolutionary “significant saving of raw materials” and “manufacturing flexibility”. It is the key to the third industrial revolution. An important benchmark that has attracted widespread attention. Currently, mainstream 3D printing technologies include layered solid manufacturing (LOM), stereolithography (SLA), selective laser sintering (SLS), selective laser melting (SLM), fused deposition modeling (FDM), etc. The basic idea is based on differential The principle is to process the three-dimensional model through CAD dimensionality reduction, layer-by-layer manufacturing, and final assembly. Compared with traditional manufacturing processes, 3D printing technology has broad development prospects in new product development, rapid single-piece and small-batch product manufacturing, complex parts manufacturing, and difficult-to-process material manufacturing. Its advantage is that there is no need to manufacture molds in advance and no need to A large amount of raw materials are removed during the manufacturing process, and there is no need to go through complicated casting and forging processes. J. P. Kruth and L. Froyen conducted in-depth research on laser beam energy control, residual stress, and deformation analysis of melted materials in laser selective melting technology, and introduced a mixed material composed of Fe, Ni, Cu, and Fe3P for this technology. ; Ben Vandenbroucke introduced the application of laser selective melting technology in the rapid manufacturing of bioactive materials in the medical field, especially for the manufacturing of products with complex geometric shapes; John Soderberg developed a desktop-level open-source 3D printer to provide collaboration for emerging companies Provide ideas for finding development space in the field of Sharing Economy; Du Yulei conducted in-depth research on 3D printing materials, including engineering plastics, rubber, metal materials, ceramics, photosensitive resins, colored gypsum, ceramics, artificial bone powder and biomass
Bioactive materials, it is proposed that my country should establish relevant standards for 3D printing materials, increase investment in material research and development, and change the industrial pattern of imported printing raw materials from abroad.
3D printing technology has three main applications in the field of gas turbine blade manufacturing.
(1) Directly print the gas turbine blade model. Different from the traditional “subtractive” manufacturing method, it greatly saves production costs and shortens the product cycle. The blade model information can be adjusted in real-time during the manufacturing process to quickly adapt to the performance requirements of different blade products.
(2) Repair the blades. Gas turbine blades will suffer fatigue damage during long-term operation. The production cost of the blades is high and the processing cycle is long. Replacing new blades is not conducive to the production needs of the power plant. Using 3D printing technology to repair damaged blades can reduce costs and increase the life of the blades. cycle.
(3) Investment casting field of high-temperature hollow blades of gas turbines. Using 3D printing technology instead of molds to make wax models of blades can be used directly for investment casting, or to make molds, which can reduce the mold production cycle and adjust the investment casting model in real time.
1. Metal 3D printing technology to manufacture gas turbine blades
1.1 Metal 3D printing technology classification and application prospects
Metal 3D printing technology is divided into two categories: directed energy deposition (DED) and powder cladding (PBF). The research hotspots of DED technology mainly focus on electron beam free-forming manufacturing and laser net forming, and focus on the key technologies of the manufacturing process, mechanical properties, and engineering applications. The main research directions of PBF technology are electron beam melting technology (EBM), direct metal laser sintering (DMLS), selective laser sintering (SLS), and selective laser melting (SLM). Among them: SLM technology uses finely focused light spots to quickly and completely melt pre-set powder materials, which can
To obtain functional materials with arbitrary shapes and complete metallurgical bonding, the density can reach 100%. The printing materials are mostly single-component metal powders such as titanium alloy, stainless steel, aluminum, etc.; the forming principle of EBM is similar to SLM, but the difference is High-energy electron beams are used as the processing heat source and are carried out in a vacuum environment to avoid metal oxidation. The printable materials are the same as SLM.
Parts processed using 3D printing technology can not only have complex spatial structures but also achieve good results in mechanical properties such as strength and stiffness by strictly controlling molding conditions and molding materials. Metal 3D printing is currently used in aerospace, biomedicine, complex-shaped parts manufacturing, mold manufacturing, and other fields, especially metal parts with complex surface shapes or internal structures.
1.2 Current research status of metal 3D printed blades at home and abroad
As metal additive manufacturing technology matures, it has been widely used in the manufacturing process of aircraft engine blades in the aerospace field. The German GOS company successfully manufactured aero-engine turbine blades using SLM; the Swedish Arcam company formed aero-engine multi-joint blades based on EBM technology; Italy developed γ-TiAl alloy blades based on the forming principle of EBM technology; the American General Electric Company used metal additives Manufacturing technology while using local heating and cooling processes, obtains blade products with close to forging performance, effectively avoiding the defects of traditional processing methods that are prone to deformation and micro-cracks. my country’s research in the field of metal additive manufacturing started late, and it has been involved in related fields since 1998. Therefore, currently, metal 3D printing technology to form blades is still being researched and explored, but good research progress has also been made. Wang Huaming developed coaxial powder-feeding laser rapid prototyping technology and equipment and successfully prepared titanium alloy blade products; Huang Weidong and others used laser rapid prototyping technology for additive manufacturing of hollow blades and successfully simulated the temperature field and stress of the blade during the manufacturing process. Field change rules and the deposition and growth process of the cladding layer.
1.3 Advantages of metal 3D printed blades
The advantages of the gas turbine blade metal additive manufacturing process compared to traditional manufacturing processes are:
(1) Forming blade products with complex geometric shapes. For blade models with complex shapes, traditional machining methods are difficult to ensure accuracy by only considering the deformation of the workpiece due to the influence of cutting thermal stress during the finishing process. The manufacturing process of roulette blades is complex, and the assembly accuracy of the blades and the roulette disk is difficult to guarantee. Using metal additive manufacturing, the blades are rapidly formed layer by layer from metal powder through laser beam sintering. Thermal deformation is small, and the size of the parts is almost close to the finished product size. Various types of blades with complex shapes, such as hollow blades and wheel disc blades, can be quickly formed. .
(2) The parts are lightweight and have the same strength. Using metal additive manufacturing methods, the internal form of the blade can be designed into a hollow structure, which greatly reduces the mass of the aviation blade and obtains better mechanical performance.
(3) Save manufacturing costs and shorten the production cycle. The use of metal additive manufacturing eliminates the need for cumbersome processes such as blank production, machine tool processing, and tooling fixture production, and has high raw material utilization and recovery rates, low carbon, high efficiency, and environmental protection.
2. Laser cladding technology to repair gas turbine blades
Damage to blades during the operation of a gas turbine accounts for approximately 80% of the total damage. Direct replacement and remanufacturing of damaged blades will not only greatly increase the operation and maintenance costs of the gas turbine, but will also have an impact on related production and work progress. Therefore, damage repair of gas turbine blades is another development direction of 3D printing technology with huge market demand. Laser cladding technology (LCT) is a branch of metal 3D printing technology. Its advantage is that it can reconstruct the lost material at any position of the component. Since the energy is concentrated during repair, it will have little impact on the blade to be repaired and will not cause geometric or dimensional changes. deformation, thereby ensuring the dimensional integrity and geometric accuracy of the blade to be repaired. At the same time, the cladding deposition material has excellent structural properties and high interface bonding strength, effectively ensuring the mechanical performance of the blade to be repaired under harsh working conditions.
In the 1970s, developed countries in Europe and the United States began research on this technology. Rolls-Royce applied laser cladding technology to the strengthening treatment of nickel-based alloy blades, successfully extending the blade life to more than twice the conventional length; Piya proposed to obtain A new method to reconstruct the blade model to be repaired using cross-sectional information to improve the accuracy of blade repair; General Electric used laser cladding technology to successfully repair the crown of a nickel-based superalloy blade containing 30% primary γ’ phase without preheating, and the repaired part Good fatigue properties were achieved after shot peening; Optomec Design used laser cladding technology to successfully repair T700 engine turbine blades. In the past, due to the lack of research on this technology in our country, we could only replace damaged blades or send them abroad for repair, which greatly increased operation and maintenance costs. Therefore, the country began to increase investment in scientific research in this area in 2000 and has now achieved breakthroughs. Wang Huaming has made significant research results in the repair of titanium alloy heavy-duty blades; Beijing Nonferrous Metals Research Institute has made significant progress in the research and preparation of functionally graded materials, in-situ titanium-based composite materials, and multi-principal alloy coating materials; Wang Hao, Wang Liwen A blade repair method is proposed that integrates “pre-repair inspection – blade digital model reconstruction – blade integrated remanufacturing – quality inspection”. At the same time, it also performs alignment processing, denoising, and streamlining of blade cross-section point cloud data, as well as blade leading edge, The automatic identification algorithm of point cloud data of the trailing edge, suction surface, and pressure surface was optimized, and error analysis was performed by intercepting the blade slice point cloud and using sixth-order polynomial interpolation fitting. The analysis results met the parameter performance requirements of the engine manual and provided an efficient and stable new method for blade repair.
3. Investment casting of gas turbine blades based on 3D printing
Blades, as key components of gas turbines, are usually made from investment castings. Combining 3D printing technology with investment casting technology is mainly used in the following two aspects.
3.1 3D printing blade investment model
Direct 3D printing of blade investment models saves the time of manufacturing molds and greatly shortens the product design and development cycle. It can respond to changing market demands very quickly and win market opportunities and core competitiveness for enterprises in the fierce market competition. The main process flow of direct 3D printing blade investment model is: ① Design the casting process; ② Design the three-dimensional product shape; ③ Print the investment model based on 3D printing technology; ④ Bond the wax pouring system; ⑤ Make the mold shell; ⑥ Remove Wax and demolding materials; ⑦ pouring molten metal; ⑧ removing the pouring riser and cleaning the casting surface; ⑨ casting product quality inspection; ⑩ casting products are finished and delivered to the user after passing the inspection.
3.1.1 Light-cured three-dimensional molding blade investment model
Light-curing three-dimensional molding technology uses liquid model materials and support materials to solidify liquid resin materials layer by layer through ultraviolet light. The computer-controlled laser tracks the liquid model material point by point according to the predetermined layered cross-sectional profile of the part. Scanning causes photopolymerization of the thin resin layer in the scanned area to form a thin cross-section of the part. When one layer is cured, move the workbench and apply a new layer of model material on the surface of the previously cured model material for scanning and curing of the next layer. The newly cured layer is firmly bonded to the previous layer, and this is repeated until the entire part is prototyped. Light-curing molding technology can print blade models with hollow structures and mesh structures to meet the requirements of the investment casting process.
3.1.2 Fused deposition modeling blade investment model
Fused deposition technology can be used to print solid models of various materials. The most widely used material is ABS material, also known as ABS resin. It is a thermoplastic polymer material structure with high strength, good toughness, and ease to process and form. First, build the blade model in the 3D modeling software and convert it into STL format. Import the model into the 3D printer slicing software for slicing processing. In the slicing software, the key is to select the printing direction and support method of the blade model and choose to print the internal model of the blade. structure, then set the printer parameters to layer the blade model, and finally start the printer to prepare the blade model.
3.2 3D printing investment casting blade mold
3D printing investment casting blade molds can print a variety of molds of different sizes according to product characteristics for product development and finalization. They are used to form wax investment models, especially printing blade molds with special-shaped waterways, which reduces the cost and cost of manufacturing molds. Difficulty, it can achieve rapid manufacturing of molds, and at the same time it can effectively enhance the thermal conductivity of the mold. The use of composite resin materials can effectively improve the strength of the mold. First, the mold is structurally designed according to the shape of the blade, and a hollow structural mold is used.
It has a special-shaped water channel, and then uses slicing software to slice and layer the model, and then print it. During the printing process, there is a wax material support, which can be removed by heating it with warm water. The printed blade model can be used to detect the size of the resin mold using a three-dimensional optical scanner to ensure the dimensional accuracy of the 3D-printed mold [41-42]. For hollow blade investment casting, the traditional method requires the use of a ceramic core structure for the casting process. 3D printing technology can quickly and accurately manufacture blade investment casting ceramic cores, ensuring dimensional accuracy, reducing costs, and forming various complex shapes. Ceramic core construction.
4. Summary
Gas turbine blades are one of the key parts of a gas turbine. The quality of the parts directly determines the efficiency and safety of the gas turbine. The advantages of applying 3D printing technology to the field of gas turbine blade manufacturing are mainly reflected in:
(1) Using metal 3D printing technology to print blades not only eliminates the complex process of blade casting, forging blanks and machining, but also is different from the traditional “subtractive” manufacturing method, and can shape blade products with complex geometric shapes and meet the requirements of Accuracy and performance requirements greatly save production costs and shorten product cycle.
(2) Metal 3D printing technology to shape gas turbine blades facilitates the control of the product manufacturing process. Uncertain factors in the product production process are greatly reduced, especially human factors. The same model file and the same manufacturing material use high-precision 3D Printers, the quality of products can even be better than traditional manufacturing methods.
(3) In the field of blade parametric design, use CAD modeling software to parametrically modify the original blade model, use 3D printers to quickly manufacture blade products, quickly adapt to complex and changing market demands, and improve the core competitiveness of the company.
(4) In the field of repair and manufacturing of gas turbine blades, using metal 3D printing technology to repair them can increase the service life of the blades and reduce the cost of repair and remanufacturing.
(5) The use of 3D printing technology in investment casting can reduce mold manufacturing time and shorten the development cycle of new products. At the same time, the dimensional accuracy of 3D printed blade models for investment casting can be effectively controlled, ensuring the size requirements of the investment model. With the rapid development of science and technology, the market has put forward more stringent requirements for the product accuracy, service life, maintenance methods, and production efficiency of gas turbine blades. 3D printing technology is applied in the field of blade R&D and manufacturing to adapt to high reliability, long service life, The market demand for lightweight, low-cost and rapid response will inevitably have a profound impact on the field of rapid manufacturing of advanced gas turbine blades.
