At present, there are many manufacturing processes for composite structures, which can be applied to the production and manufacturing of different structures. However, considering the industrial production efficiency and production costs of the aviation field, especially civil aircraft, it is urgent to improve the curing process to reduce time and costs. Rapid prototyping technology (Rapid Prototyping) is a new manufacturing method based on the principle of discrete and stacked molding. It is a low-cost rapid prototyping technology. Common ones include molding rapid prototyping technology, liquid molding technology, thermoplastic composite molding technology, etc.

1. Molding rapid prototyping technology

Molding rapid prototyping technology is a process in which the pre-paved prepreg bristle is placed in the molding mold. After the mold is closed, the bristle is densely solidified by increasing temperature and pressure. The molding speed is fast, the product size is accurate, and the molding quality is stable. Uniformity, combined with automation technology, can realize batch, automated and low-cost manufacturing of carbon fiber composite structural parts in the civil aviation field.

1.1 Characteristics and performance of molded rapid curing prepreg

(1) The resin system has good viscosity-temperature characteristics;

(2) Prepreg has a long storage period and operating life;

(3) A wider process window can achieve curing requirements within a wider temperature range and can meet the prepreg molding process;

(4) High reactivity, curing time within 30 minutes;

(5) The resin and reinforcement have good interface matching

The RAPM plan proposed by the United States in 2015 aims to control the molding time of composite materials within 30 minutes. The CYCOMEP2750 epoxy resin system developed by Solvay Company is one of the main materials of the plan. Various types of parts prepared by compression molding.

In addition, Toray Composite Materials Company of the United States also announced the launch of Toray2700 prepreg system in 2021, which can be cured within 5 minutes and used to manufacture wing ribs and honeycomb panels. Domestic molding rapid prototyping technology started late, and most of it is concentrated in civil fields such as automobiles. Liu Binbin of AVIC Composite Materials Co., Ltd. uses ACTECH? The 1201/SYT45 prepreg system prepares typical body parts reinforced beams through the molding process. The rapid molding time of a single reinforced beam component is ≤8.5 minutes, and the surface quality meets the technical requirements for manufacturing acceptance.

2. Liquid molding technology

Liquid molding technology (LCM) refers to a series of composite material molding technologies that first place dry fiber preforms in a closed mold cavity, then inject liquid resin into the mold cavity after the mold is closed. The resin flows under pressure and infiltrates the fibers. , compared with the autoclave molding process, has many advantages, for example, it is suitable for manufacturing parts with high dimensional accuracy and complex shapes; it has low manufacturing cost and simple operation. In particular, the high-pressure RTM process (HP-RTM) developed in recent years is expected to control the manufacturing time of aerospace structural parts within tens of minutes by reducing the injection time, and achieve the manufacturing of parts with high fiber content and high performance.

2.1 Characteristics and performance of liquid molding resin system

(1) Good viscosity-temperature characteristics, low viscosity at injection temperature;

(2) It forms a good interface with the reinforcing fiber and can quickly fill the mold cavity;

(3) It has good curing reaction characteristics, low curing shrinkage, and no micro-cracks inside the molded parts.

2.2 Current application status of liquid molding technology

A lot of technical research and engineering applications have been carried out in low-cost liquid molding technology abroad. GKN used the RTM process to integrally mold a 17m long C-shaped trailing edge wing. Domestic research and development on the research and development and application of composite liquid molding technology have also been carried out. Discovery work. The main research institutions include AVIC Composites, COMAC, Chengdu Aircraft Corporation, etc. AVIC Composites used the BA9914 material system to form typical parts of hat-shaped reinforced wall panels and large-size reinforced wall panels. The fiber volume content of the structural parts reached more than 58%, verifying the feasibility of the VARI process to increase the fiber content of composite materials. sex.

Luo Wei and others from Chengdu Aviation Industry Corporation of China conducted research on an integrated RTM molding process for a fuselage secondary load-bearing frame structure with longitudinal and transverse reinforcements and local flanging structural features, using a full (0°/90°) The lamination plan and surface glue injection method successfully prepared a composite overall partition frame with qualified internal quality and comparable mechanical properties to the autoclave molding process.

3. Thermoplastic composite molding technology

In recent years, thermoplastic composite materials have become a research hotspot in the field of composite manufacturing at home and abroad because of their advantages such as high impact resistance, high toughness, high damage tolerance, and good heat resistance. The number of rivets and bolt connections in aircraft structures can be significantly reduced through thermoplastic composite material welding, which can greatly improve production efficiency and reduce production costs. Airframer Collins Aerospace, a Tier 1 supplier of aircraft structures, reports that non-autoclaved weldable thermoplastic structures have the potential to reduce manufacturing cycle times by 80% compared to metal and thermoset composite components.

3.1 Characteristics and performance of thermoplastic composite material systems

Compared with thermoset composite materials, thermoplastic composite materials have the following characteristics:

(1) It has weldable characteristics, strong versatility, short welding time, and can be applied to the connection of thermoplastic composite materials;

(2) Good toughness, fatigue resistance and high damage tolerance;

(3) Long storage and operation life, can be used for a long time;

(4) High production efficiency, usually only takes a few seconds to a few minutes;

(5) Recyclable and environmentally friendly.

At present, the thermoplastic resin systems commonly used in the aviation field mainly include PEEK, PEKK, PPS, etc. It was developed earlier abroad and has been maturely applied. It started late in China, but it has also achieved the preparation of aviation-grade CF/PPS and CF/PEEK sheets.

High efficiency and low cost have become the new development direction of composite material molding technology in the future, and are also the only way for my country's aviation composite materials field to achieve the "double carbon" goal and green aviation.

China has achieved certain results in the fields of process principles and experimental applications of this type of molding technology, but there is still a certain gap. Combining domestic and foreign developments, the following suggestions are put forward:

1. Molding rapid prototyping technology has great advantages, especially in the application and manufacturing of small aerospace structural parts. In the future, it is necessary to focus on research on rapid curing molding resin systems and prepregs. The curing time should be less than 30 minutes. The material has good processability and can meet the needs of automatic laying. For automated production needs, it also needs to have excellent temperature resistance and mechanical properties to meet the needs of aviation's primary and secondary load-bearing structures;

On the other hand, it is necessary to establish an automated molding production line, and realize the integration of material outbound, unloading equipment, molding equipment, transfer equipment, cutting equipment, testing equipment, etc. through the PLC control system to realize robotic arm loading, robotic arm pickup and transfer, Product cutting and punching, non-destructive testing and other functions, combined with alarm systems and network monitoring systems, ensure the production efficiency, safety and reliability of the automated production line; the rapid paving and molding of small-size parts prefabricated parts can be achieved through thermal isolation molding, mechanical heating Molding, etc. are used to achieve the shaping of flat prepreg roughness, focusing on studying the effects of mold temperature and compaction rate on the molding quality of preforms, suppressing the occurrence of fiber twisting and wrinkles, and achieving rapid paving.

2. The development of liquid molding technology starts with the development of advanced resin systems, which require low viscosity at the injection temperature, usually less than 10 Pa·S, and high glass transition temperature and excellent hygrothermal properties, toughness and damage tolerance. It is limited to the application of aviation main load-bearing structure;

On the other hand, it is developing automatic dry fiber placement technology. For example, the M21S wing uses ADFP dry fiber automatic placement preforming to effectively increase the fiber volume content of the final product, realizing the gradual transformation of RTM structural parts from secondary load-bearing to primary load-bearing. Structure; during the molding process, it can also be monitored through simulation methods such as curing process simulation, process numerical simulation, curing deformation simulation and control, and pressure transmission. Software such as PAM-RTM is used to select appropriate mathematical models for different resin reaction systems to describe them. During the curing process, heat transfer, resin flow and filling, fiber density, and bubble generation and migration are monitored in real time to achieve coupled calculations in multiple physical fields and multiple scales to improve the product qualification rate.

3. As more and more international aircraft models successfully apply thermoplastic composite materials and their welding technology, the feasibility of thermoplastic composite molding technology in the manufacturing of civil aircraft structures has been verified.

At present, it is expected to see thermoplastic composite materials on domestic large aircraft in the future. Therefore, our country needs to establish a complete technical system, fill in the gaps in key technologies, continue to solve the development of thermoplastic composite material systems, formulate molding process specifications, form various material standards and welding process specifications, and establish welding and weld quality evaluation plans. and standards, development of continuous automated welding equipment, etc.