What aerospace companies are there in Tianjin? What industrial equipment and raw materials are involved in the production of aerospace enterprises?

Advanced composite materials have the characteristics of light weight, high strength, high modulus, fatigue resistance, corrosion resistance, designability, good molding technology and low cost. They are ideal aviation structural materials, which have been widely used in aviation products and become the main structural materials of a new generation of aircraft bodies. The maturity of advanced technology of composite materials makes it possible to optimize its performance and reduce its cost, which greatly promotes the application of composite materials in aircraft. Some large aircraft manufacturers are gradually reducing the proportion of traditional metal processing in aircraft design and manufacturing, giving priority to the development of composite materials manufacturing. This paper aims to introduce the main processes and advanced special equipment involved in the manufacturing process of composite materials.

Application of composite materials in aircraft

With the development of composite manufacturing technology, the dosage and application position of composite materials in aircraft have become one of the important symbols to measure the advanced degree of aircraft structure. The application trend of composite materials in aircraft is as follows:

(1) Composite materials are increasingly used in aircraft.

? The amount of composite materials is usually expressed as a percentage of the structural weight of the aircraft body, and the amount of composite materials used by major aviation manufacturing companies in the world is increasing. The most representative are Airbus A380, A350 and Boeing B787. The dosage of composite materials on A380 is about 30 tons. The dosage of B787 composite reached 50%. The composite material consumption of A350 aircraft reached a record 52%. The amount of composite materials used in military aircraft and helicopters has the same growth trend, and the rapid development of unmanned aerial vehicles in recent years has pushed the amount of composite materials to a higher level.

(2) The application site has developed from the secondary load-bearing structure to the primary load-bearing structure.

At first, composite materials were used to manufacture aircraft doors, fairings, stabilizers and other load-bearing structures. At present, composite materials have been widely used in main load-bearing structures such as fuselage and wing. The application of composite materials in the main load-bearing components has greatly improved the performance of aircraft, brought remarkable economic benefits and promoted the development of composite materials.

(3) It is widely used in complex structures.

? There are more and more complex curved parts made of composite materials on airplanes, such as fuselage sections and spherical back pressure spacers on A380 and B787 airplanes, which are all made by fiber placement technology and resin film infiltration (RFI) technology.

(4) The complexity of composite components has greatly increased, and large-scale integration and * * * curing molding have become the mainstream.

The most direct effect of aircraft's extensive use of composite materials is to reduce weight. Using * * * curing and integral molding technology, composite parts can be molded into large integral parts, which can obviously reduce the number of parts, fasteners and molds, reduce the assembly of parts, and thus effectively reduce the manufacturing cost.

(5) The manufacturing methods of composite materials and advanced special equipment have been rapidly developed and widely used.

The traditional manufacturing technology of composite materials has low automation, unstable quality, large dispersion, poor reliability and high production cost, so it is impossible to produce large and complex composite materials. With the increasing size of aircraft structure, the manufacturing technology of large-size composite parts becomes extremely important.

In recent years, various highly automated manufacturing technologies have emerged, such as fiber placement, resin film transfer molding/infiltration molding, electron beam curing and so on. Advanced, efficient and low-cost special equipment development and industrial application are also emerging one after another, such as three-dimensional braiding machine, automatic tape laying equipment, tow laying equipment and so on. These high-efficiency automation equipment significantly improve the production efficiency of composite materials and the internal quality of parts, reduce the cost, and make it possible to optimize the performance of composite materials and coexist with low cost.

Manufacturing technology and main equipment of composite materials

Composite molding is a complicated process. With the emergence of various new processes and technologies, the manufacturing process of composite materials has become the key to composite materials manufacturing, covering a wide range of technical aspects and high technology content, and the cost share involved accounts for more than 80% of the total cost.

? According to the different requirements of use, batch and market, the molding technology of aviation composite products adopts manual layering, semi-automatic molding, full-automatic molding and liquid molding. The following focuses on the process methods and main equipment involved in production.

(1) laid by hand.

? At present, hand-laying is still a widely used traditional molding method, and even in the manufacture of B-2 bombers and some general-purpose aircraft, hand-laying technology is widely used. Because the order quantity of these products is often single digits, and the quality requirements are very high. The advantages of manual paving method are that the skin thickness can be greatly changed, local reinforcement can be carried out, and metal reinforcing sheets for joints can be embedded to form reinforcing ribs and honeycomb sandwich areas.

At present, many special equipment are used to control and ensure the quality of manual laying, such as the automatic cutting and blanking system for composite prepreg and the laser positioning system for laying, that is, using special numerical control cutting equipment to cut prepreg and auxiliary materials, thus transforming the manufacturing process that depends on templates into a manufacturing process that can be operated completely according to the data files generated by composite design software.

? The disadvantage of manual laying is that it requires the laying personnel to have higher skills and construction experience, and manual laying is labor-consuming and time-consuming, so it is inefficient and costly (1/4 of the total cost), and it is difficult to meet the production requirements of mass production and large-scale complex composite parts. Therefore, in the early 1960s, after several years of laying composite materials by hand, automatic tape laying (ATL) technology was developed.

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Even in the United States, manual tape laying is still used, which is operated by workers of American Free Aerospace Company.

(2) automatic tape laying (ATL).

? Automatic tape laying technology adopts unidirectional prepreg tape with isolation liner, and its cutting, positioning, palletizing and winding are automatically completed by numerical control technology and realized by automatic tape laying machine. The multi-axis gantry manipulator completes the automatic control of tape laying position, and the tape laying head is equipped with a prepreg tape conveying and cutting system, which automatically completes tape laying and cutting in a specific shape and position according to the boundary contour of the workpiece to be laid. When the prepreg tape is in a heated state, it is laid on the surface of the mold under the pressure of the press roller.

? Automatic tape laying machine can be divided into plane tape laying and curve tape laying according to the geometric characteristics of laid parts. With the further development of automatic tape laying equipment, programming, computer software, tape laying technology and materials, automatic tape laying has become more efficient, reliable and humanized. Compared with manual operation, advanced tape laying technology can reduce the manufacturing cost by 30% ~ 50%, and can form composite parts with oversize and complex shapes, with stable quality, shortened tape laying and assembly time, near-net forming of workpieces, and reduced consumption of cutting and raw materials. At present, the most advanced fifth-generation tape laying machine is 10 axis tape laying machine, which adopts double ultrasonic cutting knives and slit optical detectors. The maximum tape laying width can reach 300mm, and the production efficiency can reach dozens of times that of manual tape laying.

? Automatic tape laying machine needs to use narrow band to form complex hyperboloid surface, which will reduce work efficiency, and the price of a tape laying machine needs 3 million to 5 million dollars, which is too high. Therefore, Hercules took the lead in developing automatic tow laying (ATP) equipment.

(3) Automatic tow placement (ATP).

? Automatic tow laying technology combines the advantages of automatic tape laying and fiber winding technology. The beam laying head combines the independent transportation of different prepreg yarns used in winding technology and the functions of compaction, cutting and retransmission used in tape laying technology. A plurality of pre-impregnated yarn bundles are gathered into a pre-impregnated tape with variable width by the beam laying head below the press roller, and then laid on the surface of the mandrel. During the laying process, the pre-impregnated yarn bundle is heated, softened, compacted and shaped.

? Compared with automatic tape laying, automatic tow laying technology can form more complex structural parts with lower material consumption rate, which is the peak of automatic manufacturing technology. ATP equipment is as important to composite materials as milling machines are to metal materials. It is a laminating method between automatic winding and automatic tape laying, and is especially suitable for the manufacture of complex components. The basis of automatic mounting technology is the design and development of mounter.

? Take the Agkistrodon fiber paving and loading system of Cincinnati Machine Tool Company as an example. Viper fiber placement system combines winding, special tape placement and computer control to automatically produce complex parts that need a lot of manual placement, thus shortening the placement and assembly time, and reducing the consumption of cutting and raw materials due to the near-net forming of the workpiece.

23% of the Boeing 787 fuselage manufactured by Walter Company, including 47 sections of 5.8m×7m and 48 sections of 4.3m×4.6m, adopts the automatic placement machine Viper6000 of Cincinnati Company. During the manufacturing process, Toray's 3900 series carbon/epoxy resin weftless belt is placed on a large cylindrical rotating mold, which consists of interlocking mandrels. After laying, the cylindrical part was put into an autoclave with the largest volume of 23.2m×9. 1m in the world for curing. At present, automatic tow laying machine can lay narrow-band and wide-band tow.

Robot automatic placement of prepreg tow/tape has become a powerful and efficient technology for high performance fiber reinforced composite structures. It is a comprehensive integration of electromechanical equipment technology, CAD/CAM software technology and material technology, including: automatic laying equipment technology, prepreg tow/tape cutting technology, laying CAD technology, laying CAM technology, prepreg tow/tape technology, automatic laying technology, laying quality control, mold technology, cost analysis and control and integrated collaborative digital design technology. It has the advantages of high efficiency, high quality, high repeatability and low cost.

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Viper6000 ATP machine represents the highest level of automatic tow laying today.

(4) curing and molding in an autoclave.

? Autoclave curing molding is a traditional manufacturing process of aerospace composite structural parts, which has the advantages of good product repeatability, high fiber volume content, low or no porosity and reliable mechanical properties. The disadvantages of autoclave curing are high energy consumption and high operating cost. At present, large composite components must be cured in large or super-large autoclave to ensure the internal quality of products, so the three-dimensional size of autoclave is increasing to meet the processing requirements of large composite products. At present, the autoclave adopts advanced heating and temperature control system and computer control system, which can effectively ensure the uniform temperature distribution in the working area in the autoclave and ensure the internal quality and batch stability of composite products, such as accurate resin content, low or no porosity and no other internal defects. This is also the main reason why autoclaves have been used so far.

(5) Liquid molding of composite materials.

? Liquid molding of composite materials is a very popular process, mainly resin transfer molding (RTM), including various derived RTM technologies, about 25 to 30 kinds, among which RTM, vacuum-assisted RTM(VARTM), vacuum-assisted resin injection molding (VARI), resin film impregnation molding (RFI) and resin impregnation molding (SCRIMP) are called the five main molding processes of RTM.

? The advantage of RTM is that the damage tolerance of finished products is high, and it can form complex components and large integral parts with high precision and small porosity. The key of RTM molding is to have suitable reinforced preform and resin or resin film with suitable viscosity. RTM requires low viscosity of resin at injection temperature. The viscosity of the first generation epoxy resin is required to be lower than 500 CPS(0.5 Pa·s). Previously, the viscosity of resin was required to be lower than 250 centipoise (0.25 Pa/s) for larger-sized parts. The main equipment of RTM process is various resin injection machines and integral closed molds.

? With the continuous innovation of new reinforced material structure, the combination of weaving technology, preform technology and RTM technology has formed a new technological development and application direction. For example, reinforced materials are prefabricated into 3D structures by 3D weaving technology, and then combined with RTM process, or fiber fabrics are prefabricated directly into the shape of parts by sewing or bonding, and then composite materials are formed by RTM process.

? For example, the rear pressure isolator manufactured by EADS Military Aircraft Company for the rear fuselage section of B787 is a hemispherical integral isolator interposed between the pressurized fuselage section 47 and the non-pressurized fuselage section 48 and the tail section. It is made of VARTM, and its size is about 4.3m×4.6m. Boeing 787 is the first aircraft to use composite rear pressure spacers. The manufacture of partition frame benefits from the resin permeable membrane system of Cytec company. Toughened composites have top-class flame retardant/smoke/toxic properties, and the fireproof layer can be eliminated, so the structure is lighter than that manufactured by traditional resin infiltration method. However, most of the partition frames of Boeing 787 fuselage adopt the technology of carbon fiber resin film infiltration RFI, and the composite partition frame is connected with the fuselage skin by carbon fiber composite shear hoop. Due to the design and cost, titanium alloy and aluminum alloy partition frames are still used in a few parts.

(6) forming a diaphragm.

? Diaphragm molding was originally developed for thermoplastic composites, and later it was found that it has a wide range of uses for thermosetting composites. It has the special effect that the fiber is not easy to slip and wrinkle in the forming process, and is very suitable for processing the C-shaped section of the front beam of a large aircraft wing. This technology has been widely used in the C-section of the front beam of large aircraft, such as A400M, which was introduced in recent years.

? In order to form a C-shaped cross-section, the preform was unloaded from the tape laying machine and sent to the thermal envelope forming machine equipment provided by Aeroform Company in Britain for forming. In order to facilitate vacuum pumping, the preform should be sandwiched between two layers of Kapton polyimide films provided by DuPont Electronic Technology Company in Ohio. Vacuum between the films, and then infrared heating from above the parts until the temperature rises to 60℃ within 65438±0h h. This can ensure that even in the center of the thickest part of the beam root, it can be evenly heated to the same temperature. Then, the laminate between the two films is slowly pressed to form the inner surface of the light beam on the optical mode. This C-shaped section can be formed slowly within 30 minutes, and then the Kapton film can be removed.

In the ALCAS plan launched in Europe, this molding method has become a typical process method for processing the front beam of aircraft.

(7) Processing, assembly and nondestructive testing of composite parts.

? After the composite parts are formed, they need to be machined, including size machining and drilling, which requires high machining quality. Composite parts belong to brittle anisotropic materials, and conventional processing methods can not meet the processing quality requirements of composite materials. The traditional cutting method has the following shortcomings when processing fiber materials: slow cutting speed and low efficiency; Composite parts are easily deformable materials, and the cutting accuracy is difficult to guarantee; When cutting high toughness materials, the tool and bit wear quickly and lose a lot; When processing composite laminates, delamination failure is easy to occur. Therefore, the production of composite materials needs to be equipped with large-scale automatic high-pressure water cutting machine, ultrasonic cutting equipment, numerical control automatic drilling system and other special equipment to meet the requirements of non-delamination wear and assembly dimensional accuracy of composite materials after processing.

? Large wing skin laminates are generally cut by a large high-pressure water cutting machine. The world's largest cutting machine is 36m×6.5m, which is made by Flow International. This abrasive water jet cutting machine can cut thick laminates quickly without overheating. 25mm thick laminate can be cut at a speed of 0.67m/min, 6mm thin laminate can be cut at a speed of up to 3m/min, and thick skin can be cut at a speed of 0.39m/min.

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? Ultrasonic cutting equipment loads ultrasonic vibration energy on the cutter, which can effectively separate the boundaries of fiber materials, thus effectively solving the problems caused by the above traditional cutting methods. Ultrasonic cutting technology has the characteristics of excellent cutting quality, no burr, no tool wear, no carbonized material, small cutting force, difficult delamination, fast cutting speed and high precision. It has been widely used in foreign aviation enterprises.

? With the gradual transfer of aircraft metal structure to composite structure, the automation of composite manufacturing becomes more and more important. Assembly technology with high degree of automation is particularly important. The use of composite materials makes it possible for aircraft fuselage to be made of large integral structural parts. For example, in the final assembly of the 787, only six parts are docked, namely the front fuselage, the middle fuselage, the rear fuselage, the wing, the horizontal stabilizer and the vertical tail. These complete large parts make it possible to avoid using traditional giant tools and use lighter tools in the assembly process. Gantry jib cranes are not used to move aircraft structures.

? Integrated flexible assembly, automatic drilling and riveting and other advanced technologies, applied to the automatic assembly of large composite parts. Aircraft flexible assembly technology takes the characteristics of aviation products as the assembly object. Based on the digital definition of aircraft products, through flexible assembly technology, digital assembly technology, assembly tool design, assembly process optimization, automatic positioning and control technology, measurement, precision drilling, servo control and clamping technology, the rapid and accurate positioning and assembly of aircraft parts can be realized, the types and quantity of assembly tools can be reduced, the assembly efficiency and accuracy can be improved, the rapid response capability can be improved, the aircraft assembly cycle can be shortened, and the aircraft rapid development capability can be enhanced. It is an advanced assembly technology that can meet the requirements of rapid development, production and low-cost manufacturing, and meet the requirements of modular and reconfigurable equipment and tooling. For example, the movement of B787 composite wing structure adopts flexible assembly technology such as automatic guided vehicle.

? Automatic drilling and riveting machine is widely used in the automatic assembly of large composite parts, such as A380 wing assembly using automatic mobile drilling equipment. The essential difference between these drilling equipment and traditional metal drilling equipment is that in order to maintain the structural integrity around rivet holes, delamination will not occur during drilling, so hard tools are generally used to drill holes and multi-step drilling methods are adopted. In view of the different manufacturing methods of composite materials, their machinability is also different. For example, the fabric with cross weave structure is easier to cut than the unidirectional fabric belt, which has greater wear force and is easy to delaminate and break fibers when drilling. Therefore, different drilling parameters, materials and shapes of drill bits should be selected according to different molding methods of composite components.

Italian automatic drilling and riveting machine

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? The nondestructive testing equipment for composite parts mainly needs to be equipped with large ultrasonic C scanning equipment and X-ray nondestructive testing equipment. In addition, laser shearing photography and laser ultrasonic detection are also the main development directions.

? One of the most important advances in ultrasonic testing technology is the development of phased array testing. Compared with traditional ultrasonic detection, phased array ultrasonic detection improves the detection probability and obviously accelerates the detection speed.

? Traditional ultrasonic testing needs many different probes to conduct comprehensive volume analysis, while phased array testing can achieve the same result with one multi-element probe. This is because each unit probe can perform electron scanning and electron focusing, and the start of each unit probe has a time delay. Therefore, the incident angle and focal depth of the synthesized ultrasonic beam can be changed, which means that the speed of volume inspection can be much faster than that of traditional methods. Because when using the traditional method, the probe must be replaced in time, and it must be multiplexed to get different incident angles and focal depths. In addition, the phased array probe can provide a wider coverage, so it has higher production efficiency than the traditional probe.

(8) Integration of digital design and manufacturing of composite materials.

? The unique technological characteristics of composite parts determine that they are quite different and more complicated from metal parts in design and manufacture.

Digital design and manufacturing of composite components are based on composite design/manufacturing platform and digital manufacturing equipment. The traditional design/manufacturing method of composite materials has been changed, and the products are comprehensively described and data are transmitted in the form of digital quantities, thus realizing the seamless integration of design and manufacturing.

The integration of composite design software and existing CAD system provides a powerful platform for designing/manufacturing composite components. It includes four stages: preliminary design, detailed engineering design, detailed manufacturing design and manufacturing output.

? The digital manufacturing process of composite components includes prepreg blanking, laying and curing. At present, the digital manufacturing of composite components is mainly reflected in the automatic blanking of prepreg, laser placement positioning and automatic fiber placement.

? For example, in the B787 project, all composite parts are digitally designed by FiberSIM software, and the design data are distributed to global partners, thus ensuring the uniqueness and accuracy of composite parts data. Because B787 adopts a large number of digital designs, its research and development cycle is shortened by three years compared with B777.

Digital design and manufacturing of composite components make it possible to implement concurrent engineering, solve manufacturing problems in the early stage of design, and greatly reduce workshop modification and repetitive work. Settings? The seamless integration of accounting and manufacturing data shortens the manufacturing time, reduces the errors caused by manual programming and improves the quality of parts.

Concluding remarks

? To sum up, with the increasing application of composite materials in aircraft, composite materials manufacturing industry has quickly become the main component of aircraft manufacturing industry. In the future, more than 50% of aircraft structural parts will be converted from metal to composite materials, and composite material manufacturing will become the basic means of aircraft manufacturing. Composite manufacturing technology and special equipment are one of the key technologies of advanced composite materials, and it is worth investing a lot of manpower and material resources in research and development and application. If you master the advanced composite manufacturing technology, you will master the advanced manufacturing technology of future aircraft.