Pure copper and copper alloy are one of the most widely used metal materials, second only to iron and aluminum, and are also one of the earliest metals used by human beings. Copper and copper alloys have a series of excellent characteristics: high electrical conductivity, high thermal conductivity, corrosion resistance, wear resistance, antibacterial, etc., and are widely used in electric power, electronics, communications, chemical industry, automobiles, rail transit, marine engineering, aerospace, life accessories and other fields.
Compared with traditional processing and manufacturing technology, the powder bed laser melting technology of pure copper-copper alloy can better play the excellent performance of copper, and has broad application prospects in electronics, electric power, automobiles, aerospace and other fields with high demand for thermal and electrical conductivity. The research team at home and abroad has actively carried out research on the powder bed laser melting of pure copper-copper alloys, which not only shows the great application potential of this technology, but also exposes many problems and challenges, such as the extremely low absorption rate of pure copper to infrared laser, low density of forming samples, high porosity, delamination and cracking. These problems are the main obstacles to the development of the industrial application of pure copper and copper alloy powder bed selective laser fusion (LPBF) additive manufacturing technology, which cannot carry out efficient and high-quality additive manufacturing of copper and copper alloys, which greatly limits the empowerment of LPBF additive manufacturing technology for excellent materials such as copper, which are highly reflective, highly conductive and high thermal conductivity.
The powder selective laser fusion additive manufacturing technology with single-mode CW fiber green laser as the energy is one of the ways to overcome the challenges of additive manufacturing of highly reflective metals such as pure copper and copper alloys. Recently, Xihe Additive published an article to analyze the development status of global green lasers, the unique advantages and application cases of green laser 3D printing technology in the field of pure copper and copper alloy additive manufacturing. In this issue, 3D Science Valley will share the article.
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Green laser 3D printing copper material solutions
The high reflection of pure copper and copper alloys to near-infrared lasers (such as 1064nm lasers), high thermal conductivity and low melt viscosity are the main factors affecting the printing of copper materials. The high reflection of copper makes the energy of the near-infrared laser beam more than 95% reflected, which not only does not heat the material, but also causes great damage to the core optical components of the deviceThe high thermal conductivity of copper makes the melt heat quickly transfer to the surrounding powder, which makes it difficult to form a smooth and regular melt path, and as the printing progresses, the solidified part of the bottom layer may also be remelted, which aggravates the occurrence of instabilityThe ideal powder bed selective laser melt additive manufacturing melt pool should be smooth and homogeneous, but the low viscosity of the copper melt causes the melt in the melt pool to flow around without enough heat for the surrounding powder to melt completely, resulting in slag formation around it.
Due to the excellent thermal and electrical conductivity of pure copper and copper alloys combined with the powder bed selective laser melting additive manufacturing technology and the ability of 3D printing complex structure, it has great market potential, and various research institutions at home and abroad have made various efforts to improve the forming quality and forming efficiency of pure copper and copper alloys, and promote the development of their industrial applications. For example, the addition of pre-alloying elements to pure copper will reduce its reflectivity to near-infrared lasers, or improve the laser absorption rate of the material through surface modification of pure copper and copper powder, and obtain higher density, but the addition of alloying elements greatly reduces its electrical and thermal conductivity;In addition, the molding quality can be improved by increasing the power of the NIR laser. For example, the additive manufacturing laboratory of South China University of Technology uses the self-developed LPBF additive manufacturing equipment to form pure copper with a laser power of 350W, with a density of up to 939%。Ikeshoji et al. formed pure copper by LPBF technology at a high laser power of 800W, and obtained a density of 966% cubes. JADH** et al. used an LPBF device equipped with a 1kW high-power fiber laser to form a pure copper cube-shaped prototype with a density of more than 98%. The high-power single-mode fiber laser LPBF used by Colopi and others is used to form pure copper, and the highest density of the sample reaches 991%。Studies have shown that the use of high-power lasers to form copper parts will increase the recoil pressure and produce undesirable phenomena such as vaporization and spatter. At the same time, due to the high reflectivity of pure copper, increasing the laser power will accelerate the damage of optical components such as lasers. Therefore, increasing the laser power can improve the forming quality of pure copper and copper alloys to a certain extent, but it is not the best forming solution. For example, the Hong Kong Polytechnic University uses a very small focused spot (25 m), a very small layer thickness (10 m), a very small particle size copper powder (5-25 m) and a small scanning distance (50 m) for printing, with a density of up to 996%。However, such printing efficiency is lower. In order to find a higher quality and more efficient way to form copper materials, researchers at home and abroad compared the absorption rate of copper materials to different wavelength lasers, and found that the absorption rate of copper to blue and green lasers is more than ten times higher than that of infrared lasers, and it will be simpler and more efficient to use short-wavelength lasers such as blue light and green light for high-quality pure copper and copper alloy LPBF. At the same time, because the high-power blue laser is mainly coupled to the multi-mode large-core fiber output through the beam combination of several blue semiconductor chips, it cannot achieve the same high beam quality as the currently commonly used infrared CW fiber laser (m2 105), high brightness and long-term power stability (annual power attenuation ratio of 5%), while the single-mode CW fiber green laser that benchmarks single-mode infrared CW fiber laser has achieved 500W-1000W, which can meet the high-quality and high-efficiency pure copper and copper alloy LPBF manufacturing in terms of laser power, beam quality and stability. Samira Gruber et al. in Germany used green laser LPBF equipment to print pure copper samples with a density of up to 9995%, conductivity up to 100% IACS;Sung-Gyu Kang et al. also achieved good results in printing pure copper lattice structures using green laser equipment. Therefore, LPBF equipment with single-mode CW fiber green laser as the energy is the most reliable way to manufacture pure copper and copper alloys with high quality and high efficiency.
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With the continuous breakthroughs in the power and beam quality of short-wavelength lasers, especially the power of single-mode CW green lasers reaching 500W, 700W, and 1000W, and the forming strategies and forming conditions of pure copper and copper alloys have been optimized, the problem of additive manufacturing of copper materials has been broken. It has laid a solid foundation for its broad application in electronic and electrical, automotive, aerospace and other fields with high demand for thermal and electrical conductivity.
TRUMPF: At the end of 2019, TRUMPF launched the world's first commercial green laser metal 3D printing equipment, pioneered the connection of the new TruDisk 1020 disk laser with the TruPrint 1000 3D printer, and successfully realized the overall printing of pure copper RF quadrupole accelerator (RFQ), a key copper component. Disk laser, also known as disk laser, is essentially different from traditional solid-state lasers in the shape of the laser working substance, changing the rod-shaped crystal of the traditional solid-state laser to a disk crystal. It has the advantage of high power stability, but because it is a multimode fiber output (50um na01) The diameter of the focused spot is larger than that of the single-mode beam.
Figure 1TRUMPF 3D printed RF quadrupole accelerator (RFQ).
IPG: As early as the end of 2015, IPG released single-mode QCW (pulsed) green fiber lasers with output powers of up to 500W. At present, the mainstream of metal 3D printing is single-mode continuous fiber laser, because the pulse laser can not continuously produce light, theoretically can not fully adapt to the needs of LPBF process, the metal 3D printing market rarely uses QCW single-mode fiber laser related reports. It is reported that at present, some metal 3D printing manufacturers at home and abroad are in the test, but the test results have not yet been made public.
Figure 2IPG QCW green single-mode fiber laser.
Xihe Additive: The parent company Gongda Laser is currently the only manufacturer in China to achieve batch production and delivery of high-power green fiber lasers above 100W, single-mode CW green fiber lasers for 3D printing, with laser power covering 500W, 700W, and 1000W, Xihe Additive has launched the first market-oriented green laser metal printer XH-M160G for the global market in September 2023.
Figure 3Gongda laser single-mode CW green fiber laser.
Figure 4Xihe Additive Green Laser Metal Printer XH-M160G
The high-power single-mode CW green laser has obvious advantages in the additive manufacturing of copper and copper alloys due to its short wavelength and excellent beam quality, and the high laser absorption rate and small focused spot make it have higher forming efficiency, better forming quality, higher printing resolution and larger process window in the additive manufacturing of copper and copper alloys.
Figure 5The absorption rate of a typical powder material for each wavelength of laser.
Figure 6Single-mode continuous green fiber laser printing pure copper (Xihe additive) (density 99.).5%）
Figure 7Advantages of single-mode CW green lasers for additive manufacturing of copper and copper alloys.
Green laser 3D printing not only enables efficient and high-quality printing of pure copper and copper alloys, but also expands the range of printable materials for the LPBF additive manufacturing process, providing more possibilities for 3D printing of composite materials. 3D printing using multiple materials with different physical properties will provide unprecedented design freedom for the manufacture of highly complex, lightweight components, thus creating new heights of development for industrial applications. For example, the integrated steel-copper heat exchange radiator, the thrust chamber composed of copper alloy and Inconel alloy, etc., can provide huge thrust for the development of the industry.
Figure 8Multi-material 3D printed parts created by foreign companies.
Green laser 3D printing copper material case introduction
Pure copper (red copper) is second only to silver in electrical conductivity and thermal conductivity, and is the most suitable electrical and thermal conductor, which is widely used in the manufacture of conductive and thermal management equipment. Pure copper also has excellent corrosion resistance, and has good corrosion resistance in the atmosphere, seawater and some non-oxidizing acids (hydrochloric acid, dilute sulfuric acid), alkali, salt solution and a variety of organic acids (acetic acid, citric acid), and is widely used in chemical industry and other fields. With the empowerment of additive manufacturing technology, pure copper can exert greater efficiency, and Xihe Additive uses a single-mode CW green fiber laser as a light source, which has been integrated and optimizedThe density of 3D printed pure copper parts is more than 995%, conductivity over 98% IACS, passedAfter simple annealing, the conductivity is more than 100% IACS, reaching 1015%iacs。For example, pure copper 3D printing heat exchanger, heat sink, inductor for induction heat treatment, motor winding and other directions have been applied, and reflect its unique advantages, such as 3D printing pure copper heat exchanger, heat exchanger excellent heat dissipation, heat exchange performance, and excellent integration, miniaturization, lightweight ability, all bring obvious competitive advantages to the product. Another example is the complex inductor for heat treatment printed by pure copper, which is integrated forming, highly conformal with the heating product, high dimensional accuracy and high consistency, which effectively solves the problems of the traditional manufacturing method of complex inductor requiring a large number of welding, low overall conductivity, high cost, low dimensional accuracy and poor consistency. It is more capable of manufacturing inductors with excellent structure but difficult to manufacture by traditional methods, which not only improves the quality of heating products, but also increases the life of complex inductors by 2-4 times.
Figure 9(A) EOS 3D printed new pure copper heat sink, (B) Xihe additive 3D printed new pure copper heat sink.
Figure 10(A) Trumpf 3D printed pure copper heat sink, (B) (C) Xihe Additive XH-M160G 3D printed pure copper heat exchanger.
Figure 11Xihe Additive XH-M160G 3D printed pure copper heat treatment sensor.
Figure 12Xihe Additive XH-M160G 3D printed pure copper motor winding.
CUSN10 alloy has high strength, excellent wear resistance and corrosion resistance, and can be used to manufacture wear-resistant parts such as blades and gears, and is often used for handicraft printing, such as playing an increasing role in the protection, restoration, reproduction, and display of bronze cultural relics. It is also one of the copper alloy materials that are currently used for LPBF printing.
Figure 13Bronze statue of a horse rider printed by Concept Laser.
Figure 14AMCM uses a copper alloy printed E-1 rocket engine combustion chamber.
CucrZR alloy is a precipitation-hardening alloy with excellent mechanical properties, which is widely used as combustion chambers, walls of thermonuclear experimental reactors, liquid rocket engine parts, etc. In recent years, domestic and foreign aerospace units have carried out more research and development work around the additive manufacturing of rocket engine thrust chamber parts, and CUCRZR is the current optional material. It is worth mentioning that the copper alloy materials used in rocket engine parts are still being updated and iterated, and CUZR, CUCR, CUAGZR, CUCRNB and other materials have been applied and researched one after another, especially the GRCOP-42 (CU-4CR-2NB AT%), which is being verified by NASA in additive manufacturing, which is expected to upgrade the rocket engine combustion chamber material to a new level.
Fig.15 (a) Copper rocket nozzle lining printed by SPEE3D (b) Copper combustion chamber lining printed by Xihe additively.
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