Application Status and Prospect of Laser Rapid Additive Manufacturing Technology in National Defense Science and Technology

The quality and maintenance of weapons and equipment are important factors in determining the victory or defeat of wars. Especially after the Industrial Revolution, mechanical equipment has gradually entered modern wars and occupied a dominant position. The frequent use of these weapons and equipment has caused the continuous loss of equipment, making the subsequent equipment maintenance problems increasingly prominent. The diversity of equipment leads to a wide variety of maintenance equipment, and the diversity of maintenance materials will make the conditions required for maintenance more complicated and the cycle longer, causing unnecessary losses. With the continuous development of science and technology and the emergence of emerging technologies, laser additive manufacturing technology has gradually become a research hotspot in the current industrial field due to its unique technical advantages, and has gradually been applied to the rapid maintenance of weapons and equipment. The performance of equipment repaired by laser additive manufacturing technology will even be better than that of new equipment.

1 Development Background of Laser Additive Manufacturing Technology

Additive manufacturing technology (referred to as 3D printing technology) is a general term for a series of rapid prototyping technologies (Rapid Prototyping, referred to as RP). It is a new technology that converts the designed three-dimensional model into a solid object based on the principle of "discrete-accumulation" with the help of computer-aided design (CAD) and computer-aided manufacturing (CAM). Laser additive manufacturing technology is a relatively common type of additive manufacturing technology [1]. Laser additive manufacturing technology (LAM) is an advanced manufacturing technology that has been rapidly developed since the 21st century by integrating computer information technology, new material technology, numerical control technology, laser technology and other technologies [2,3]. At present, it is roughly divided into fused deposition modeling (FDM) [2], stereolithography (SLA) [3], selective laser sintering (SLS) [4], and selective laser melting (SLM) [5]. Compared with traditional manufacturing technology, the biggest advantage of laser additive manufacturing technology is that it simplifies the production process of parts as much as possible. It does not require the preparation of molds and blanks required by traditional production methods in advance, saves materials required for processing, and overcomes the problem of the production possibility of many complex parts. Laser additive manufacturing technology can be used for product development. It can easily adjust various process parameters through computers to optimize the different performance of products to meet the final requirements, instead of repeatedly producing and testing samples in large quantities as in the traditional mode, which greatly reduces the development cost and risk.

2 Research status of laser additive manufacturing technology in national defense and military

Additive technology first appeared in the 1990s. Once this technology appeared, it caused a certain impact on the traditional manufacturing industry. The manufacturing industry called it "a great technological revolution." At the beginning, due to the immaturity of science and technology at that time, additive manufacturing technology did not develop rapidly. Until the 21st century, with the rapid development of computer technology, the continuous improvement of mechanization level and the improvement of rapid prototyping technology, laser additive manufacturing technology ushered in a golden age, developed rapidly, and contributed important forces in various high-end fields, especially in military and defense technology.

2.1 Current status of foreign research

The United States has always been ahead of other countries in the world in metal rapid additive manufacturing technology. In 2000, the U.S. Naval Undersea Warfare Center (NUWC) launched and implemented a rapid manufacturing and repair (RMR) program. This program successfully completed the task of manufacturing and repairing old parts and tooling by using laser selective sintering technology, direct metal laser sintering, melt deposition molding and electron beam melting [6]. In 2001, the U.S. Army Armory also established the LENS Army Armory Repair System, which specializes in the maintenance and logistics support of various weapons and equipment [7]. Since the 2010s, the research progress of laser additive manufacturing technology has made rapid progress, and a series of breakthroughs have been made. The technology has become more mature and the level has been continuously improved. In order to adapt to the changing and complex environment of the battlefield and maximize the advantages of this technology, the U.S. military has added new processing technologies and manufacturing processes on the basis of the mobile parts hospital, and further invented the mobile expeditionary laboratory (ELM). The laboratory is actually a standard container with a length of 20 feet. The US military can use helicopters or trucks to directly transport it to any place where equipment needs to be repaired and processed. Then, various raw materials such as plastic, steel, aluminum, and copper can be used to directly process and manufacture the worn or damaged parts of the equipment on site, ensuring the emergency support of wartime equipment and maximizing the functional role of the equipment. In addition, the US Army has also invented a small, lightweight and easy-to-carry 3D printer. This small 3D printer can be put into a backpack. When equipment needs to be repaired, it can be anywhere on the battlefield. By adding the required raw materials, some small equipment parts can be directly produced, which makes maintenance more convenient and quick [7,8]. Since the beginning of the 21st century, the US Navy has been carrying out multiple additive manufacturing projects with the aim of ensuring that its naval fleet can maintain high agility and efficiency when performing missions in the oceans. For example, the US Naval Postgraduate School (NPS) has also invested in Xerox elemX metal machines to manufacture lightweight and high-quality spare parts for submarines and ships. In 2017, Oak Ridge National Laboratory (ORNL) in the United States cooperated with the Disruptive Technology Laboratory of the U.S. Navy to conduct cutting-edge technology trials and manufactured the first 3D printed submarine hull in military history (see Figure 1). The hull is a 30-foot-long conceptual ship, manufactured using ORNL's laser fused deposition (FDM) large-area additive manufacturing technology. The hull has six carbon fiber composite parts. Compared with traditional manufacturing methods, this 3D printing technology is faster and cheaper, with a manufacturing cost of only 90% of that of traditional processes. The successful manufacture of this submarine hull has great reference value for further research and development of 3D printing technology in the direction of submarine hull manufacturing [9].

In February 2023, Relativity Space in California, USA, announced a technological breakthrough. The world's first 3D-printed rocket Terran1 will be launched in March. 85% of the Terran1 rocket is made by 3D printing. The launch mission is named "GLHF" (Good Luck, Have Fun). The launch time is March 8th in the United States, and the launch site is LC-16 in Cape Canaveral, Florida. When introducing Terran1, Relativity Space said that its second-stage expendable rocket is all made of 3D printing, with a height of 110 feet and a width of 7.5 feet.

In recent years, European countries other than the United States have also stepped up research on metal rapid additive manufacturing technology and made progress.

In 2017, at the Hannover Industrial Exhibition held in Germany, a propeller produced by additive manufacturing attracted people's attention. The propeller was jointly invented by the RAMLAB laboratory in the Netherlands and AUTODESK. The subsequent fine processing and surface treatment also used mechanical cutting processing methods [10]. Once this product was exhibited, it attracted the attention of many technology enthusiasts, and also promoted the further application of additive manufacturing technology in the shipbuilding industry.

In 2021, the French Naval Group used the WAAM (Wire Arc Additive Manufacturing) additive manufacturing process to print a 200-kilogram propeller and installed it on a mine-hunting ship named Andromeda. This additive manufacturing product minimizes the use of materials and increases the utilization rate of materials.

2.2 Current status of domestic research

For many years, my country has also kept up with international development trends and carried out a series of experiments and applications on additive manufacturing of weapons and equipment. The main research units include the Rapid Prototyping Laboratory of the Shenyang Institute of Automation, the National Defense Science and Technology Key Laboratory of Equipment Remanufacturing Technology of the Armored Forces Engineering Academy, etc. The main research directions of these laboratories are to use metal powder laser forming technology and additive manufacturing technology to repair and manufacture various infantry armored vehicles, parts of some models of fighter jets, engine turbines, and repair and remanufacturing of propeller blades and hull repairs of ships at sea [6,7]. In 2012, China used additive manufacturing technology to successfully print the central wing slats of the C919 large aircraft using titanium alloy raw materials, and successfully completed the test flight. The following year, the front wheel support feet of the J-15 and J-31 were printed using titanium alloy materials and successfully completed the test flight11. In 2015, the ignition device of a certain type of solid rocket engine was manufactured using additive manufacturing technology and passed the engine ground test assessment. In the same year, China North Industries Group Corporation established the "China North Industries Group Additive Manufacturing Technology Research Center"[12-14]. According to news reports, during the "Supply Operation-2015" military supplies and fuel support exercise, a unit of the Western Military Region of my country used 3D printing equipment to print out the linkage shaft of the emergency refueling truck and successfully completed the wartime emergency repair mission, ensuring the normal progress of the mission[15,16. In addition, some key parts of my country's fourth-generation stealth fighters are also manufactured using 3D printing technology[17].

3 Application Status of Laser Additive Manufacturing Technology in National Defense and Military

3.1 Application Status in the Army

In terms of metal rapid additive manufacturing technology, the United States took the lead in applying it to the maintenance and emergency backup of weapons and equipment. In 2001, at the Anniston Army Base in Alabama, the U.S. military successfully repaired the damaged gas turbine of the M1 Abrams tank using additive manufacturing technology. The performance of the repaired turbine was relatively ideal. In addition, the U.S. military also used laser near-net forming technology to repair the surface damage of the tank's compensating cantilever. The replacement cost of the cantilever is US$2,000, while the cost of laser additive manufacturing is only US$750, which greatly saves costs. After that, they also established the Army Mobile Parts Hospital (MPH) (see Figure 2). The Mobile Parts Hospital uses 3D printing technology and various CNC machining technologies to directly produce parts and repair equipment in complex geographical environments [7,18].

In July 2012, the U.S. Rapid Mobile Force completed the construction of the first mobile laboratory and put it into use for the first time (as shown in Figure 3-5). In January 2013, the US military delivered a second mobile expeditionary laboratory in Afghanistan [1,19].

In recent years, with the continuous improvement of metal additive manufacturing technology, direct manufacturing of parts has developed rapidly in the field of additive manufacturing, and has once become the fastest growing direction. The US military has also begun to use additive manufacturing technology to directly produce firearms, light drones and other weapons and equipment. In 2017, the US military successfully and quickly manufactured a grenade launcher using additive manufacturing technology. The launch tube and receiver of the grenade launcher are both made using laser selective sintering technology, and are directly made using laser sintering aluminum powder [19]. This manufacturing method greatly reduces the cost of equipment production, effectively improves the utilization rate of materials, and avoids a large amount of waste of production materials. The US military also uses additive manufacturing technology to directly manufacture swarm micro drones. This drone is extremely small, with a wing width of only about 2.54 cm, and is specifically used for reconnaissance work. Swarm micro-UAVs can be launched by F-16 and FA/18 fighter jets, or launched by ground-dropping. They are extremely convenient in war environments. After launching, they can form swarms to carry out various reconnaissance missions [21].

3.2 Application Status in Air Force and Aerospace

In the air force and aerospace fields, modern research ideas are based on ensuring safety and reducing equipment quality and manufacturing costs as much as possible to achieve the best flight results. In the 2001 Afghanistan War, the US military used the laser near-net shaping technology (LENS) for the first time to successfully repair the engine blades of the Black Hawk fighter jets damaged in the war. The performance of the repaired blades even exceeded that of the original blades [22,23]. Additive manufacturing is not only widely used in the repair of air force equipment, but also in aerospace. In 2014, NASA sent the first zero-gravity 3D printer to the International Space Station. The printer was developed by the American Space Manufacturing Company. The maturity of its 3D printing technology has reached level 8, which can be competent for printing in a space environment. The tasks of this printer include the maintenance, upgrade and extension of the service life of the space station, application payload improvement, hardware space manufacturing, etc. [24]. In September 2017, NASA used chromium-nickel-iron alloy and copper alloy to print rocket engine igniters, solving various technical problems of metal additive manufacturing [23,25,26].

In 2016, an engine named "Rutherford" was developed. It is the world's first liquid engine that uses an electric pump to deliver propellant [14]. "Rutherford" was developed by Rocket Lab, USA. Its highlight is that all 75 parts of this engine are produced by additive manufacturing technology. It does not require the mass production of various complex parts. It only needs to provide the raw material metal powder required for the production of parts, and it can be produced and processed in 3 days, which greatly shortens the production cycle and reduces the workload of manufacturing complex parts [27].

Other countries in the world are also developing rapidly in the direction of additive manufacturing. In particular, many European countries have extensive applications in additive manufacturing. The Spanish Air Force has begun to try to use additive manufacturing to manufacture various parts of helicopters, including leakage control measurement tools for helicopter landing gear that are difficult to manufacture using traditional processes and customized keys for helicopter main rotors [201. Compared with traditional manufacturing, additive manufacturing can reduce the difficulty of manufacturing complex parts and greatly reduce the workload of research and development and production.

3.3 Current application status in the navy

Navy ship equipment is a general term for equipment, devices, instruments, tools, instruments and their accessories required to maintain naval ships. The technical support of ship equipment is an important basis for measuring a country's naval strength [28]. The US Navy actively promotes the rapid integration of additive manufacturing and maritime combat platforms to achieve free manufacturing of parts under special circumstances. At present, the repair and maintenance of the main hulls of various ships have been achieved, such as the catapult guide cover of the aircraft carrier, the vertical launch tube wall (VLS tube) of the Los Angeles-class nuclear submarine, etc., and the power devices of various ships have also been successfully repaired, such as the propulsion shaft sealing surface of the Los Angeles-class nuclear submarine (SSN-668), the propulsion main shaft of the Virginia-class nuclear submarine, etc. [291, and the parts manufacturing and repair of underwater weapons have also been achieved, such as the cylinder block and connecting rod of the torpedo [30]. In May 2013, the US military hoped to use additive manufacturing technology to produce low-cost, light-weight drones that can meet combat requirements, so as to replace aircraft carriers with drones.

Large water platforms such as the USS Essex are used as mobile offshore 3D printing factories, and they hope to improve the space utilization of ships by installing high-quality 3D printers to complete the on-demand production of parts and ammunition casings [23]. In 2014, the US Navy installed a 3D printer on the Essex amphibious assault ship, and successfully manufactured a series of parts such as oil cap boxes and flight deck models using 3D printers.

In addition, the US military has also developed a mobile additive manufacturing laboratory (X FAB) (see Figure 6), which is deployed on various ships to ensure the normal service and rapid maintenance of ships [31].

The University of Southampton in the UK used additive manufacturing technology to print the world's first additive manufacturing drone named "SULSA". The four important components of this drone were made on land by EOSINT P730 3D printers, and the manufacturing material is nylon. This type of drone is propeller-driven, has a wingspan of 1.5 meters, and weighs about 3 kilograms[32]. It was successfully tested at sea in 2015, with a maximum flight speed of about 100 km/h and a flight time of about half an hour. It was officially put into service in 2016. Compared with traditional military drones that cost millions of dollars, the cost of the "SULSA" drone is only 7,000 pounds, which is a significant reduction in cost. This type of drone was used in the Antarctic expedition mission of the British Royal Navy's "Protector" icebreaker[33].

In March 2022, the University of Maine developed a logistics support ship for the US Marine Corps. The Advanced Structures and Composites Center in Orono used 3D printing to manufacture two large ships, one of which is the largest additively manufactured ship ever. It is used to provide material reserves for the US Marine Corps and conduct tests for field use by the armed forces. The larger one can carry two 20-foot large transport containers, and the other can provide the marines on board with food, fresh water and other resources for three days.

The continuous application and development of laser additive manufacturing in weapons and equipment such as submarines and ships indicates that additive manufacturing technology is no longer at the conceptual stage, but is becoming more and more perfect, and is shining in many fields, especially in the field of military equipment, providing strong support for the country's national defense and military cause.

4 Existing problems of laser additive manufacturing technology

The long-term use of weapons and equipment will inevitably lead to various failures and damages, especially large weapons and equipment, equipment and high-precision equipment. At present, the main way to solve this problem is to carry a large number of spare parts so that weapons and equipment can be quickly repaired and restored to normal use when they are damaged. Although this method can meet the needs of rapid maintenance in a short period of time, with the diversification of equipment types and the increasing complexity of parts, even some equipment parts are too large in size and weight, which makes this method a serious waste of resources. There are too many spare parts. Once weapons and equipment are eliminated, a large number of spare parts will also be eliminated. In addition, many parts used in modern weapons and equipment have higher requirements for the maintenance process, generally requiring special maintenance equipment, and some even require special maintenance tools and professional technicians [34]. In addition, in air defense and coastal defense equipment, due to the limited internal space of aviation equipment and ship equipment, it is not realistic to carry a large number of spare parts, and excessive mass will also affect combat maneuverability. Laser additive manufacturing technology can effectively solve the above problems, so it is more and more widely used in national defense science and technology, but correspondingly, many problems and shortcomings have also appeared in the actual application process, such as: high production cost, the unit price of metal powder required for printing is more expensive than the corresponding metal material, and its production efficiency is low compared to the large-scale manufacturing of traditional molds. In addition, in some special cases, laser additive manufacturing technology is also difficult to achieve rapid production of some parts. For example, under the conditions of undesirable external environment on land battlefields and swaying and vibration of ships, the stability of the laser additive manufacturing process cannot be fully guaranteed, which leads to errors in the accuracy of repaired or remanufactured equipment and parts, and is prone to deformation. In addition, in actual military applications, the powder required for laser additive manufacturing technology is mostly made of metal. During the manufacturing process, these powders will inevitably spheroidize, resulting in uneven pores in the printed parts, which will affect the quality of the final product to a certain extent, and thus shorten the actual service life of the printed parts; secondly, the huge temperature difference generated by the laser in a short period of time before and after the rapid scanning of a certain printing area will cause the probability of deformation or cracking of the printed parts, thus affecting the actual use effect of the finished product. In addition, the support of the printed parts is difficult to remove directly by simple processing, and generally requires wire cutting and then grinding. Generally speaking, laser selective melting technology (SLM) and selective laser sintering technology (SLS) belong to the field of laser powder bed melting, which are suitable for manufacturing or repairing small and high-precision equipment and parts; laser fused deposition manufacturing technology (FDM) is suitable for the production of large-sized equipment and parts with low precision requirements. At present, it is impossible to take into account both large-sized manufacturing and high-precision production at the same time.

5 Future development trends and prospects

With the continuous development of science and technology, laser rapid additive manufacturing technology will increasingly tend to:

(1) Miniaturization and lightweight of weapon maintenance equipment. The smaller the printing equipment, the easier it is to carry. In particular, it can be used to quickly repair and replace equipment parts in complex environments and small spaces, so that weapon maintenance is not affected by the external environment and the normal service of the equipment is ensured. Custom design of unit structure is carried out according to the different structural characteristics of the required parts. Under the condition that the original shape characteristics of the required parts remain unchanged and the performance is almost the same, the internal redundant structure is removed as much as possible and replaced with an approximate structure that can be simply manufactured, so as to achieve the requirements of rapid manufacturing in wartime and rapid use as temporary spare parts.

(2) Establish a material numerical model library, fast printing speed and short production cycle. The advantages of laser additive manufacturing in the application of national defense and military are fast speed and short production cycle of parts. Especially in a wartime environment, the required maintenance time is even more limited, which makes the requirements for maintenance equipment continue to increase. Laser additive manufacturing technology can make it only take a few or dozens of hours from design to processing of parts, and the production process is fully digitized without the need for complex programs [35]. A digital model library can be established by computer to establish models of the parameters of various weapon equipment parts and provide digital model technical support for maintenance models. When weapons and equipment fail or are damaged, the required parts can be selected anytime and anywhere for production and replacement. The greater advantage of establishing a digital model library is that the various parameters of the required parts can be changed at will, and there is no need to manufacture multiple parts maintenance equipment according to different models of parts. In the future, with the rapid development of computer technology and the increasing maturity of support-free printing technology, multi-dimensional stereo molding technology may be realized, and rapid manufacturing may be directly realized.

(3) High printing accuracy. With the continuous improvement of powder making technology, the quality of powder is getting better and better, and the types of printing materials are increasing. With the promotion of carbon fiber materials, high-strength and high-toughness composite metal materials, and the continuous optimization of process parameters such as laser source energy density, scanning speed, and scanning power, the printing accuracy of 3D printers will become higher and higher. The maintenance accuracy requirements of high-end weapons and equipment are high, so the required 3D printing technology must not only be fast but also have good quality parts. It can meet the normal use of equipment, and the service life of parts should reach or even exceed the life of original parts as much as possible.

(4) Combine with emerging science and technology to create new scientific and technological products. For example, combined with the emerging bionics, bionic structures often have complex and difficult-to-manufacture structural features. The characteristics of additive manufacturing three-dimensional manufacturing can be used to manufacture structures that cannot be produced by traditional manufacturing to achieve bionic design and gradient design. Print electronic components directly into weapons and equipment. Use additive manufacturing technology to achieve equipment structure integration19] For example, small electronic components such as antennas, radars, and signal detectors are directly printed in helmets and combat uniforms to achieve real-time communication on the battlefield and timely collection of battlefield information.

6 Conclusion

With the continuous development of science and technology, additive manufacturing technology will continue to improve. In an environment where the price of raw materials for manufacturing some complex parts is gradually decreasing, additive manufacturing will inevitably replace traditional manufacturing, especially in the aerospace industry. Laser additive manufacturing technology will also occupy an increasingly high weight in military defense. With the maturity of technology, troops will be able to "go into battle lightly", reduce the carrying of various heavy and complex spare equipment parts, make full use of additive manufacturing technology, quickly manufacture on site, save time and effort, and save costs, and achieve a great improvement in national military strength.

About Stardust Technology

Stardust Technology (Guangdong) Co., Ltd. is a national high-tech enterprise specializing in the research, development, production and sales of high-end spherical powder materials for 3D printing, powder metallurgy, surface engineering and other fields. The company insists on taking radio frequency plasma spheroidization powder making technology as the core, and provides internationally advanced powder products and application solutions.

The company's main products include high-end rare refractory metals such as tungsten, molybdenum, tantalum, niobium, vanadium, rhenium, chromium and their alloys, compound spherical powders, and also provides radio frequency plasma spheroidization, plasma rotating electrode atomization, 3D printing, hot isostatic pressing, injection molding, powder metallurgy and other technical services. Stardust Technology not only provides high-quality powders, but also brings integrated molding solutions for additive manufacturing, helping innovative intelligent manufacturing and leading future technology!

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2023 Issue 4 · Total Issue 131

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