Welding Methods for Micro and Small Parts Laser welding is an efficient and precision welding method that uses a high-energy-density laser beam as the heat source. It is one of the important applications of laser material processing technology. In the 1970s, it was mainly used for welding thin-walled materials and low-speed welding, and the welding process belonged to the heat conduction type. Specifically, the laser radiation heats the surface of the workpiece, and the heat on the surface diffuses inward through thermal conduction. By controlling parameters such as the width, energy, peak power, and repetition frequency of laser pulses, the workpiece is melted to form a specific molten pool. Due to its unique advantages, it has been successfully applied to the precision welding of micro and small parts. China’s laser welding technology ranks among the world’s advanced levels. It has the technology and capability to form complex titanium alloy components over 12 square meters using laser, and has been applied in the prototype and product manufacturing of multiple domestic aviation research projects. In October 2013, a Chinese welding expert won the Brook Award, the highest academic award in the field of welding, which confirmed China’s world-class laser welding level.
## Development History The world’s first laser beam was generated in 1960 by exciting ruby crystals with a flash lamp. Limited by the thermal capacity of the crystal, it could only produce very short pulsed beams with low frequency. Although the instantaneous pulse peak energy could reach up to 10^6 watts, it still belonged to low-energy output. A neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal rod, with neodymium (Nd) as the excitation element, can generate a continuous single-wavelength laser beam with a power of 1-8KW. The YAG laser, with a wavelength of 1.06μm, can be connected to the laser processing head through a flexible optical fiber, featuring flexible equipment layout and suitability for welding workpieces with a thickness of 0.5-6mm. The CO₂ laser, using carbon dioxide as the excitant (with a wavelength of 10.6μm), can achieve an output energy of up to 25KW and realize single-pass full-penetration welding of 2mm-thick plates. It has been widely used in metal processing in the industrial sector. In the mid-1980s, laser welding, as a new technology, attracted widespread attention in Europe, the United States, and Japan. In 1985, ThyssenKrupp Steel AG (Germany) and Volkswagen AG (Germany) collaborated to successfully adopt the world’s first laser-welded blank on the Audi 100 body. In the 1990s, major automobile manufacturers in Europe, North America, and Japan began to widely use laser-welded blank technology in automobile body manufacturing. Practical experience from both laboratories and automobile manufacturers has proved that laser-welded blanks can be successfully applied in the production of automobile bodies. Laser tailor-welding uses laser energy to automatically splice and weld several steels, stainless steels, aluminum alloys, etc., with different materials, thicknesses, and coatings into an integrated plate, profile, or sandwich panel. This meets the different material performance requirements of components, and achieves equipment lightweight with the lightest weight, optimal structure, and best performance. In developed countries such as Europe and the United States, laser tailor-welding is not only used in the transportation equipment manufacturing industry but also widely applied in fields such as construction, bridges, home appliance plate welding production, and steel plate welding in rolling lines (plate connection in continuous rolling). World-renowned laser welding enterprises include Soudonic (Switzerland), ArcelorMittal Group (France), ThyssenKrupp TWB (Germany), Servo-Robot (Canada), and Precitec (Germany). The application of laser-welded blank technology in China has just started. On October 25, 2002, China’s first professional commercial production line for laser-welded blanks was officially put into operation. It was introduced by Wuhan ThyssenKrupp Zhongren Laser Tailor Welding from ThyssenKrupp TWB (Germany). Later, Shanghai Baosteel Arcelor Laser Tailor Welding Co., Ltd., FAW Baoyou Laser Tailor Welding Co., Ltd., and other enterprises were successively put into production. In 2003, foreign countries realized the double-beam CO₂ laser filler wire welding and YAG laser filler wire welding for the A318 aluminum alloy lower wall panel structure. This technology replaced the traditional riveted structure, reducing the weight of the aircraft fuselage by 20% and saving 20% of the cost. Gong Shuili believed that laser welding technology would play a significant role in the transformation and upgrading of China’s traditional aviation manufacturing industry. He immediately applied for a number of related pre-research projects, organized a research team, and took the lead in introducing the “double-beam laser welding” technology into research projects in China. From the very beginning, he planned to apply this technology to aircraft manufacturing. The Chinese expert team reported the preliminary technology to an aircraft design institute and promoted the advantages and feasibility of double-beam laser welding. After multiple verifications and evaluations, the design institute decided to apply this technology to the manufacturing of ribbed wall panels for a certain aircraft, achieving the initial goal of applying “double-beam laser welding” technology to aircraft manufacturing. It broke through key technologies such as precision control of laser welding filler wire for lightweight alloys, developed an integrated and innovative double-beam laser filler wire hybrid welding device, established China’s first high-power double-beam laser filler wire welding platform, realized the double-beam and double-sided synchronous welding of T-joints in large thin-walled structures, and successfully applied it to the welding manufacturing of key structural parts of aviation ribbed wall panels for the first time, playing an important role in the development of China’s new aircraft. In 2003, the first domestic large-scale online strip welding complete set of equipment provided by HG Laser passed the offline acceptance. This equipment integrates laser cutting, welding, and heat treatment, making HG Laser one of the world’s fourth enterprises capable of producing such equipment. In 2004, the project “High-Power Laser Cutting, Welding and Combined Cutting-Welding Processing Technology and Equipment” by HG Laser Farley Laserlab won the Second Prize of National Science and Technology Progress Award, making it the only laser enterprise in China with the R&D capability of this technology and equipment. With the rapid development of the industrial laser industry, the market has put forward higher requirements for laser processing technology. Laser technology has gradually shifted from single application to diversified applications. In terms of laser processing, it is no longer limited to single cutting or welding. The market demand for integrated laser processing equipment that combines cutting and welding is increasing, and thus integrated laser cutting and welding equipment has emerged. HG Laser Farley Laserlab developed the Walc9030 integrated cutting and welding machine, with an ultra-large format of 9×3 meters, which is currently the world’s largest format integrated laser cutting and welding equipment. The Walc9030 is a large-format cutting and welding equipment that integrates laser cutting and laser welding functions. It is equipped with a professional cutting head and a welding head, and the two processing heads share one beam. Numerical control technology ensures that they do not interfere with each other. The equipment can complete two processes that require cutting and welding simultaneously. It can switch freely between cutting first then welding, or welding first then cutting, realizing both laser cutting and welding functions with one equipment without the need for additional equipment. This saves equipment costs for application manufacturers, improves processing efficiency and processing range. Moreover, due to the integration of cutting and welding, the processing accuracy is fully guaranteed, and the equipment performance is efficient and stable. In addition, it has overcome the difficulties of thermal deformation of plates during the tailor-welding of ultra-large plates and the stable realization of ultra-long flying optical paths. It can weld two flat plates of 6 meters in length and 1.5 meters in width at one time, and the welded surface is smooth and flat without additional post-processing. At the same time, it can cut plates with a width of 3 meters, a length of more than 6 meters, and a thickness of less than 20mm in one forming process without secondary positioning. The Shenyang Institute of Automation, Chinese Academy of Sciences, conducted international cooperation with IHI Corporation (Japan). Following the national scientific and technological development strategy of “introduction, digestion, absorption, and re-innovation”, it overcame several key technologies of laser tailor-welding, developed China’s first set of complete laser tailor-welding production lines in September 2006, and successfully developed a robotic laser welding system, realizing laser welding of planar and spatial curves. In October 2013, a Chinese welding expert won the Brook Award, the highest academic award in the field of welding. The Welding Institute (TWI, UK) recommends and nominates candidates every year from more than 4,000 member units in over 120 countries, and finally awards this prize to one expert in recognition of their outstanding contributions to the science and technology of welding or joining and its industrial application. This award is not only a recognition of Gong Shuili and his team but also an affirmation of AVIC’s role in promoting the progress of material joining technology.
## Structural Parameters
### Working Equipment It is composed of an optical oscillator and a medium placed between the mirrors at both ends of the oscillator cavity. When the medium is excited to a high-energy state, it begins to generate in-phase light waves, which reflect back and forth between the mirrors at both ends, forming a photoelectric concatenation effect. This amplifies the light waves, and when sufficient energy is obtained, the laser is emitted. Laser can also be defined as a device that converts primary energy sources such as electrical energy, chemical energy, thermal energy, light energy, or nuclear energy into electromagnetic radiation beams of specific optical frequencies (ultraviolet light, visible light, or infrared light). This conversion can be easily carried out in certain solid, liquid, or gaseous media. When these media are excited in the form of atoms or molecules, they produce a light beam with almost the same phase and nearly a single wavelength—laser. Due to its in-phase property and single wavelength, the divergence angle is very small, and it can be transmitted over a long distance before being highly concentrated to provide functions such as welding, cutting, and heat treatment. ### Classification of Lasers There are mainly two types of lasers used for welding, namely CO₂ lasers and Nd:YAG lasers. Both CO₂ lasers and Nd:YAG lasers are invisible infrared light to the naked eye. The beam generated by the Nd:YAG laser is mainly near-infrared light with a wavelength of 1.06μm. Thermal conductors have a relatively high absorption rate for light of this wavelength, and for most metals, the reflectivity is 20%-30%. The near-infrared beam can be focused to a diameter of 0.25mm using standard optical lenses. The beam of the CO₂ laser is far-infrared light with a wavelength of 10.6μm. Most metals have a reflectivity of 80%-90% for this type of light, so special optical lenses are required to focus the beam to a diameter of 0.75-1.0mm. The power of Nd:YAG lasers can generally reach about 4,000-6,000W, and the maximum power has now reached 10,000W. In contrast, the power of CO₂ lasers can easily reach 20,000W or even higher. High-power CO₂ lasers solve the problem of high reflectivity through the keyhole effect. When the material surface irradiated by the light spot melts, a keyhole is formed. This keyhole filled with vapor is like a black body, which absorbs almost all the energy of the incident light. The equilibrium temperature inside the keyhole reaches about 25,000°C, and the reflectivity decreases rapidly within a few microseconds. Although the development focus of CO₂ lasers still focuses on equipment development and research, it is no longer about increasing the maximum output power, but about how to improve the beam quality and its focusing performance. In addition, when argon is used as the shielding gas for CO₂ laser welding with a power above 10kW, it often induces strong plasma, which reduces the penetration depth. Therefore, helium, which does not generate plasma, is often used as the shielding gas for high-power CO₂ laser welding. The application of diode laser combinations for exciting high-power Nd:YAG crystals is an important research and development topic, which will greatly improve the quality of laser beams and form more efficient laser processing. The use of direct diode arrays to excite and output lasers in the near-infrared region has achieved an average power of 1kW and a photoelectric conversion efficiency of nearly 50%. Diodes also have a longer service life (10,000 hours), which helps reduce the maintenance cost of laser equipment. The development of diode-pumped solid-state laser (DPSSL) equipment is also advancing.
Post time: Aug-27-2025
