Four Typical Structures and Development Direction of Additive Manufacturing in Aerospace Field

--- Reprinted from 3D Technical Reference
In the article "China Southern Airlines: Systematic Discussion on Three Typical Materials and Application Challenges of Aerospace Additive Manufacturing", we have introduced Professor Gu Dongdong's summary of high-performance metal materials in the aerospace field. Light-weight high-strength alloys represented by aluminum and titanium, and load-bearing heat-resistant alloys represented by Ni-based high-temperature alloys are important application materials in laser additive manufacturing; lightweight, large, integral and complex structures are the main development directions of additive manufacturing, which contains many complex and advanced scientific problems. In this issue, we continue to follow the footsteps of Professor Gu Dongdong for in-depth study.

Laser Additive Manufacturing of 1. Large Metal Components

Large metal components used in aviation, aerospace, shipbuilding, nuclear power and other modern industries are developing in the direction of complexity, integration and high performance. Laser energy deposition technology has been proved to meet the forming requirements of large metal components. However, in order to obtain more extensive industrial applications on large key components of difficult-to-process metal materials such as titanium alloys, nickel-based high-temperature alloys, high-strength steels, and refractory alloys, two key problems still need to be further solved:

1. Under the conditions of long-term intense non-steady-state cycle heating and high-speed cooling of high-energy laser, the grain morphology and microstructure of forming materials are difficult to control, and the metallurgical quality and performance control with solidified grains, internal defects and microstructure as the core is the basic problem of laser additive manufacturing large metal components;

2. The accumulation and coupling of thermal stress, tissue stress, solidification shrinkage stress and other types of complex stresses in the process of laser additive manufacturing can easily lead to deformation and even cracking of large metal components, which greatly restricts the control and control of laser additive manufacturing of large metal components.

Some studies have pointed out that the biggest obstacle to the industrial application of additive manufacturing technology is the thermal stress and various structural defects in the formed parts. Academician Wang Huaming of Beijing University of Aeronautics and Astronautics believes that internal stress and deformation cracking are the bottlenecks that restrict the development of laser additive manufacturing technology for metal components for a long time. Titanium alloy has been widely used in aircraft engine components, main bearing components, landing gear and so on because of its low density, high specific strength and strong corrosion resistance, but its poor processing performance restricts its engineering application range.

After years of research, Academician Wang Huaming's team has broken through the laser additive manufacturing of key components such as large-scale titanium alloy main bearing components of aircraft, titanium alloy reinforced frames of large-scale complex integral structure main bearing aircraft such as TA15, TC4 and TC11, and A- 100 ultra-high strength steel aircraft landing gear, and has realized the installed application of main bearing components.

Fabrication of Large Monolith Metal Components by Laser Melting Deposition

(a) Titanium alloy aircraft large key main bearing members;

(B) Aero-engine gradient performance titanium alloy bladed discs;

The team of professors Huang Weidong and Lin Xin of Northwestern University of Technology, facing the demand of China's C919 medium-sized passenger aircraft, used laser energy deposition technology to manufacture TC4 alloy system C919 aircraft wing rib flange with a length of 3100mm. The flaw detection and mechanical performance test results all meet the design requirements of COMAC.

(a)LMD formed C919 titanium flange

(B) SLM forming titanium alloy fan blade edging

(c)SLM forming nickel-base superalloy engine case

In addition, the development of large SLM equipment in recent years has opened up a new way for the forming of large integral metal components with more complex structures. The wrapping length of titanium alloy fan blades based on SLM forming can reach 1200mm, with complex spatial curved surface structure and high forming dimensional accuracy. The size of the nickel-based superalloy engine casing based on SLM forming reached Ф 576mm × 200mm, it provides important technical support for the design, manufacture and application verification of key engine components.

SLM fabrication 2. complex monolithic structures

With the increasing requirements for the service performance of hot end components in the aerospace field, more and more attention has been paid to the design and manufacture of the overall structure, which contains complex internal flow channels, porous lattice and other difficult-to-process structures, which has exceeded the manufacturing capacity of traditional processes, and the rapid manufacturing of these complex overall structures based on SLM technology can be made possible.

Additive manufacturing of monolithic structures has proven critical to the future of space exploration, and NASA has set a goal to "manufacture the core components of rocket engines 10 times faster and reduce production costs by more than 50 percent. It uses SLM technology to realize the overall manufacturing of hydrogen rocket booster, and then realizes the structural weight reduction, manufacturing efficiency and service performance. The printing and application of copper alloy liner integral components in rocket engine combustion chamber is another successful practice in recent years. This case overcomes the multiple challenges of high reflection of copper materials, optimization of fine flow channel structure and laser additive manufacturing forming quality. The overall manufacturing of such large and complex structures puts forward higher requirements for the development of additive manufacturing technology.

NASA SLM-based copper alloy monolithic components and performance testing.

(a) Laser additive manufacturing component ignition trials conducted by NASA and AerojetRocketdyne;

(B) Rocket engine combustor copper alloy liner monolith

GE has developed a new type of fuel nozzle for engines based on SLM technology, which is the most famous case of complex integral structure additive manufacturing in aviation industry in recent years. As a typical complex assembly, fuel nozzle has many processes, many tooling, time-consuming and high cost, and it is difficult to meet the requirements of processing accuracy and stability, whether it is forming manufacturing or assembly assembly. It is a big challenge for traditional manufacturing technology. In response to this problem, GE adopts SLM technology to process IN718 nickel-based superalloy, realizes the overall design and manufacture of fuel nozzle, and turns the original "assembly" of 20 small parts into a whole component. This not only eliminates redundant connections between different components, but also optimizes the fuel nozzle structure. In the end, the overall design and manufacture of the fuel nozzle achieved a weight reduction effect of 25%, while shortening the manufacturing cycle, reducing production costs, and increasing the service life by more than 5 times.

Aircraft engine fuel nozzle components manufactured by GE based on SLM technology.

(a) Advanced turboprop engine (ATP);

(B) The working principle of the fuel nozzle in the engine;

Additive Manufacturing of 3. Lightweight Lattice Structure

For aerospace vehicles, weight loss is an eternal theme, and traditional manufacturing methods have brought the possibility of weight loss to the extreme. The combination of lattice structure optimization design and additive manufacturing technology can make the component have excellent mechanical properties such as high specific strength and high specific stiffness. Laser additive manufacturing, due to its process characteristics of laminated free manufacturing, gives complex lightweight structures a high degree of design and forming freedom, and can form lightweight complex dot matrix structures that are difficult to form by traditional processing methods.

Lattice structure is widely used in many fields

In recent years, laser additive manufacturing of complex lightweight lattice structures has become one of the hot research directions, bringing new opportunities for breakthroughs in the performance and function of lightweight metal components in aerospace and other fields. Traditional classical structure, innovative structure and lattice structure based on topology optimization can bring breakthrough for component performance improvement.

Additive manufacturing technology has shown certain development and application potential in the field of aerospace lattice structure product design and manufacturing, and takes lightweight and high performance as the main assessment objectives. Moreover, laser additive manufacturing lattice components have been applied in the field of international civil aircraft manufacturing. The bionic lattice structure cabin partition designed and manufactured by Airbus based on SLM technology is a new type of light and high-strength aluminum alloy. In the structural design, the cross-scale bionic lattice structure design is realized based on biological enlightenment. In the macro scale, the main structure design is realized based on the algorithm of "slime mold adaptive network". In the micro scale, the biological inspiration of bone growth is borrowed, the arrangement of more than 66000 grids was completed, and the microscopic grid density was matched with the stress distribution. Finally, the displacement of the cross-scale bionic lattice component was reduced by 8%(9mm) compared with the original honeycomb composite partition structure under the same impulse force, which is expected to be applied to A320 passenger aircraft in batch.

A new type of bionic lattice structure cabin partition designed and manufactured by Airbus based on SLM technology.

(a) The structure of the bionic partition of the engine room;

(B) A physical drawing of the bionic partition of the engine room;

(d) Physical drawing of selected laser melting forming of engine room bionic partition parts

Additive Manufacturing of 4. Multifunctional Bionic Structure

Metal components manufactured by laser additive manufacturing are developing from high performance to multi-function. Nature published a comment on the topic of "pushing aside the limitations of 3D printing", pointing out that the creation of materials and structures will help the development of 3D printing technology, and suggested "borrowing" materials and "borrowing" structures from nature ", using natural methods, highlighting bionics and biological inspiration to realize the expected functions.

Airbus generates bionic designs for future flights

The future development of additive manufacturing will highlight material creation, structural bionics and multi-functional integrated optimization. Through billions of years of evolution and natural selection, biological systems have developed and optimized their complex multi-level organizational structures to achieve optimal performance/function in response to changes in the environment. Many biological systems have unique combinations of versatility that are often difficult to achieve with synthetic materials. Modern analysis and characterization technology has confirmed that the excellent performance or special function of natural materials is realized by its internal complex multi-level structure, and its scale range usually spans the nano-scale to the macro-scale. For performance/function-driven additive manufacturing, bionic structure design based on bio-inspiration is one of the important ways to innovate additive manufacturing structures, and is expected to achieve a leap in the performance/function of additive manufacturing structures.

However, bionic design is very simple in principle, but it is quite difficult in actual manufacturing, mainly because of the challenge of reasonable matching and layout of multi-materials and the constraint of micro/grand cross-scale bionic structure manufacturing process.

Based on the integrated and multi-functional development trends and potential engineering applications of the next generation of hypersonic vehicles, space probes and other aerospace equipment, Professor Gu Dongdong's team innovatively developed bionic structure and material layout for the comprehensive functional requirements of vibration reduction and impact resistance, heat insulation/heat protection, and realized the laser integral additive manufacturing of bionic structure and its multi-functionality, it involves the coupling, matching and integrated regulation of multiple factors such as structure, material, process and function.

Laser additive manufacturing lightweight impact-resistant bionic functional structure.

(a) Macroscopic morphology of the tail nodes of the shrimps;

(B) Bionic bidirectional corrugated plate impact resistant structure SLM processing;

(e)SLM forming bionic reticulated shell structure

Bionic design provides a new way for function-driven additive manufacturing structure optimization and multi-functionality, but "the structure is easy to imitate, the manufacturing is not easy, and the science is more difficult". The key scientific problems involved include: the mapping relationship between bionic microstructure and typical functions of components and the optimization model; Bionic design of cross-scale structure laser additive manufacturing process constraints and forming mechanism; multi-functional integrated evaluation method and response mechanism of laser additive manufacturing bionic structure. Therefore, the new technology of additive manufacturing and bionic structure design complement each other and complement each other, and the research of key scientific issues runs through the whole process of material-structure-function integration.

Thinking and Prospect: Future Research and Development Trend of Laser Additive Manufacturing Technology

The scientific connotation of laser additive manufacturing technology determines that its development trend is to realize the integration of micro-meso-macro cross-scale material-structure-process-performance/function. In the future research and development trend of laser additive manufacturing technology, the following directions deserve further attention:

(1) Laser additive manufacturing material-structure-process integration driven by high performance/multi-function, and actively realize the high performance and multi-function of components;

(2) "Multi-phase material" and "multi-material" design, preparation and shaping of laser additive manufacturing to achieve "the right material to the right place";

(3) Laser additive manufacturing innovative structural design to achieve high performance and multi-functionalization of components to highlight the "unique structure to achieve unique functions";

(4) Build key technologies and methods for laser additive manufacturing process simulation, monitoring, feedback and process optimization for full-size components and full process processes, and comprehensively improve the technical level, quality and industrial application level of laser additive manufacturing process.