Before the blank is designed and manufactured, the structural engineer fully communicates with the cold and hot process engineers to determine the optimal blank shape, achieve near-net forming in local areas, improve material utilization, reduce machining allowances, and shorten the processing cycle. Common blank precision forming manufacturing technologies mainly include the following 5 types.
Precision casting
A processing method that heats and melts solid metal, pours it into a molding mold shell, and solidifies it into a casting blank. At present, precision casting technology is widely used in turbine blades, and its flow path surfaces are all zero-residue castings, and the flow path surface profile is ±0.2 mm.
Sand casting
Precision forging
A processing method that applies pressure on a press to cause the raw material to undergo plastic deformation in the mold, thereby obtaining a precision forging with little or even no allowance. This process has been widely used on compressor blades, which can improve material utilization and reduce or eliminate machining. At present, the blade body of the precision forged blade adopts zero-residue forging, and the material utilization rate reaches 80%.
Precision spinning
A processing method that processes a sheet or preformed annular blank into a thin-walled hollow rotating body by high-speed rotation and applying a certain pressure. It is currently widely used in parts such as fairings, combustion chamber cones, and compressor casings. At present, hot spinning can achieve 1-2 mm margin control, and cold spinning can achieve ±0.2 mm margin control.
Powder metallurgy
A process technology that uses metal powder (or a mixture of metal powder and non-metallic powder) to make materials and products through sintering and molding processes. This process is mainly used in the field of aviation engines to manufacture rotating parts such as turbine disks that withstand high temperatures and high loads.
Powder metallurgy flow chart
Rapid prototyping
Decomposing complex three-dimensional parts into multiple layers of simple two-dimensional structures, and reconstructing complex three-dimensional parts by manufacturing simple two-dimensional structures is a process from "complex" to "simple" and then to "complex". The fuel nozzle with a relatively complex structure in the engine combustion chamber uses rapid prototyping technology.
2. Special processing technology
Special processing (sometimes also called non-traditional processing) refers to the process that does not require a tool harder than the workpiece, nor does it require the application of obvious mechanical force. Instead, it directly uses electrical energy, thermal energy, chemical energy, light energy or a combination of them to remove the workpiece material or change its performance to achieve the required shape, size and surface quality requirements. The following 6 special processing technologies are currently commonly used.
Electrodischarge machining
Special processing that controls the removal of workpiece material and deforms the material and changes its performance through discharge between the workpiece and the tool electrode. At present, the air film holes on the turbine guide blades are mostly processed by electrospark small hole forming, and the fan-shaped segments of the compressor stator blades are also processed by electrospark wire cutting.
Schematic diagram of electrospark machining
Electrochemical machining
Special processing that removes workpiece material through electrochemical reactions. Some difficult-to-process materials, such as high-temperature alloy integral blades, are difficult to achieve through traditional processing, and can be processed using electrolytic machining technology.
High-energy beam processing
Use high-energy-density laser beams, electron beams or ion beams to remove or connect workpiece materials. Laser beam processing can be mainly used for drilling, cutting, welding and marking. Femtosecond laser drilling is one of the methods for processing air film holes on turbine blades.
Abrasive flow
Use a semi-fluid viscoelastic abrasive medium containing abrasives to force it to flow over the processed surface under a certain pressure, and remove the microscopic uneven materials on the workpiece surface by the scraping action of the abrasive particles, thereby achieving the purpose of surface polishing or deburring. Abrasive flow technology has been applied to integral closed blades.
Schematic diagram of abrasive flow processing
Vibration finishing
Put the workpiece, abrasive, water and chemical additives into a container according to a certain formula. Relying on the regular vibration of the container, the abrasive and the workpiece produce relative movement and mutual friction, grind off the burrs protruding from the surface and periphery of the workpiece, and round the sharp edges of the workpiece and polish the surface. It is an efficient surface finishing technology, which has been widely used on parts with high fatigue strength.
Abrasive water jet machining
Using high-speed water flow as a carrier, a high-speed and concentrated abrasive flow is driven to impact the surface to be machined, realizing a regular and controllable removal process of the material. Due to its characteristics of no cutting thermal deformation, the ability to cut any material, high flexibility in cutting direction and very small cutting force, it is widely used on difficult-to-machine materials such as ceramics and reinforced composite materials.
3. Advanced welding technology
Welding is a high-quality and efficient process for connecting metal materials. It belongs to the low-cost advanced structural manufacturing process technology and is also one of the most widely used processing technologies in the advanced manufacturing industry. Commonly used welding technologies mainly include the following 4 types.
Electron beam welding
A process that uses high-speed, high-energy density electron beams as heat sources for welding. It has the characteristics of large aspect ratio, small welding residual deformation, easy to achieve precise control of welding process parameters, pure welds in a vacuum environment, good repeatability and stability. These advantages are difficult to match with other fusion welding methods, so it is widely used in the welding of important structures such as the integral rotor, casing and shaft of the engine.
Electron beam welding
Inertia friction welding
A type of solid phase welding that generates heat through friction between the materials to be welded, and causes the materials to undergo plastic deformation and flow under the action of the upsetting force, thereby achieving material connection. It has the advantages of good weld joint quality, high dimensional accuracy, and good connection effect of dissimilar materials. It has become the main welding process for connecting aircraft engine fan disks, high-pressure compressor rotor assemblies, and high-pressure turbine disk shaft assemblies.
Brazing
A method of heating the materials to be welded at a temperature lower than the melting point of the parent material and higher than the melting point of the brazing material, and filling the gap with liquid brazing material to achieve connection. It has the characteristics of less impact on the properties and structure of the parent material and less welding deformation. It is suitable for a variety of materials and structures, including aircraft engine honeycomb sealing structures, turbine blades, compressor blades, and combustion chamber components. For some complex components, brazing is the only feasible connection method.
Brazing diagram
Argon arc welding
Under the protection of inert gas, the arc generated between the electrode and the materials to be welded is used to melt the materials to be welded and the filler material, thereby achieving connection. It has great advantages in portability and cost, and is widely used in welding of engine casings and combustion chambers.
4. Surface treatment technology
In order to improve the surface state of parts, meet the special functional requirements of parts such as corrosion resistance, wear resistance, oxidation resistance and high temperature resistance, and improve the service life of parts, it is necessary to perform surface treatment on parts. The commonly used surface treatment technologies in aircraft engines mainly include chemical treatment, surface strengthening and coating technology.
Chemical treatment
A surface modification process that improves the surface state of materials through chemical treatment methods such as corrosion, electroplating, anodizing, and chemical cleaning.
Plasma spraying
Surface strengthening
Through plastic deformation of the surface layer, high residual stress is formed on the surface of the part to increase the "cold deformation" process of surface stress concentration. Mainly used for shot peening of the surface of the integral blade.
Coating
According to different uses, it can be divided into sealing, wear-resistant, thermal barrier and other coatings. Among them, sealing coatings can be used for casing components, wear-resistant coatings can be used for shaft parts, and thermal barrier coatings can be used for turbine blades.
Aircraft engine parts can be said to be quite "suffering". For turbine blades alone, the operating temperature can reach 1700℃ - a temperature that is nearly 150℃ higher than the melting point of iron!
In order to make these parts "healthy", researchers have to use "telescopes" to focus on the forefront of technology. At the same time, they also have to use "microscopes" to explore the technical details and strive to make the technology better adapt to the needs. On the journey of "casting the heart", Shangfa people's pursuit of superior "material" art will never end!
