Welding is the most widely used and most important method of permanent connection of materials. It has unique advantages in improving material utilization, reducing structural weight, and reducing costs.
Laser welding is the most advantageous welding method
Laser welding is the welding method with the fastest application development in the past ten years. It uses a focusable and controllable high-energy density laser beam as a heat source to achieve fusion welding of materials. The laser beam has excellent directivity, monochromaticity and coherence. The light intensity is 1010 times that of ordinary light, and the pulse power can reach 1014 watts. Therefore, the heat effect is concentrated, the welding deformation is small, the welding structure is manufactured with high precision, and the flexible automation is well implemented. Combined with advanced technology modes such as robotics, process database and expert system management, it can realize digital intelligent manufacturing. It is an indispensable key technology in the manufacturing of modern equipment structures. It is obtained in automobiles, ships, high-speed trains and aerospace structures. Successfully applied, in which the automotive industry has identified laser welding as a standardized process for structural manufacturing, and laser welding technology is considered internationally as an advanced welding technology with the greatest development potential.
development of laser welding applications
The development of laser welding applications With the development of laser,powder metallurgy, materials, mechanics, measurement and control, information, electromechanics and other disciplines, it is a comprehensive reflection of the application of modern science and technology in the field of material processing, especially high-power laser welding technology above the kilowatt level. , Almost with the progress of lasers. From the CO2 laser and YAG laser in the 1980s, semiconductor lasers and fiber lasers have been expanded. The laser power has been increased from 1kW to 100kW. The characteristics of typical welding lasers are shown in Table 1. Among them, fiber laser welding is the current new laser welding process. Research hotspots.
Holmium laser welding application prospects
It is different in the form of heat action and can be suitable for product objects. The key problems to be solved are also different according to needs. The most widely used laser welding is thin-walled structure laser welding. The most typical in the aviation structure is the aluminum fuselage lower wall plate of the European Airbus series passenger aircraft. This welding structure will reduce the aircraft fuselage weight by nearly 20%. To reduce manufacturing costs by about 20%, Airbus A318, A380, and A340 series aircraft have been used to weld the panel structure, of which the number of panels will reach 18 pieces, and the total length of the weld seam will reach 1,000 meters. With the development of aviation structure application requirements, an application development of laser welding technology is the laser composite heat source welding technology for medium thickness structures. The purpose is to expand the application scope of laser welding technology and solve the high-precision and high-efficiency welding of medium-thickness structures in future equipment structures. Need, followed by pulse laser welding for micro-nano structure precision welding, using pulse lasers such as microseconds and nanoseconds to solve dissimilar metals such as copper and aluminum, metal matrix composites, non-metal materials such as ceramics, and laminated materials related to aviation structures ( Glare), carbon fiber reinforced composite (CFRP) weldability issues.
the United States, Europe ,China and other development
At present, the United States, Europe and other developed countries have issued national plans in the field of military manufacturing to promote the research and application of advanced laser welding technology. Airbus Europe is the first aviation manufacturer to use laser welded structures instead of traditional riveted structures for the connection of aircraft aluminum alloy wall panels and beams. It will also be used in the welding of A350 aircraft wall panels in the future. Laser welded metal sandwich panels have begun to be widely used in the manufacture of missile cabins, large aircraft wall panels, and lightweight structural parts for light ships. Compared with traditional solid core structural parts, they can reduce weight by more than 50% and reduce space required. 2 / 3. Aircraft’s hybrid laminar flow control structure is also the object of future laser welding technology applications, and Germany has been conducting research in this area. The new aluminum-lithium alloy is a metal structural material that can compete with composite materials in the design of aircraft weight-reducing structures. Many research institutions in the European Union have been conducting basic research on laser welding technology of aluminum-lithium alloy wall panels. In the Turboprop90pax weight-loss project, Carry out research on 2198 aluminum-lithium alloy laser welding technology. Framework projects of the European Union, such as ECO-01-060, ECO-01-065, and ECO-01-069, all involve research on aluminum-lithium alloy laser welding technology. Europe and the United States have listed aluminum-lithium alloy laser welding technology as the research plan for the next 20 years. In terms of engine structure, Pratt & Whitney in the United States completes automatic laser welding of parts required for turbine blades. The United States GE has also successfully completed laser welding of engine guide vane components, effectively solving the problems of laser welding deformation and cracks of nickel-based alloy parts. Many foreign countries have also done a lot of research work on laser welding of special materials such as intermetallic compounds and memory alloys.
The research of high-power laser welding technology in China was first aimed at automobile blank welding, and it has been applied in various fields. Based on the industry-university-research alliance, Harbin Institute of Technology has carried out a lot of research on titanium alloy and stainless steel lightweight components in spacecraft, and established related laser welding platforms. Harbin Welding Research Institute and Shanghai Jiaotong University have carried out research on laser welding and laser arc welding technology for ship structures. Beijing Institute of Aeronautical Manufacturing Engineering takes laser welding of aircraft structures as its core, and conducts basic research on laser welding with Huazhong University of Science and Technology, Beijing University of Technology, and Xi’an Jiaotong University. Through more than ten years of efforts, laser welding technology has been applied to aircraft titanium Alloy ventral fins, siding and other structures. At the same time, based on independent research and development, the CO2 laser flight optical path four-axis automatic control laser cutting and welding system, the YAG laser welding manipulator automatic welding system, and the fiber laser multi-axis numerical control dual-beam laser welding platform have been established. As well as the dual-robot dual-beam laser welding platform, China has taken the lead in forming a system of experiments and small batch production with a variety of high-power laser welding. In terms of basics, on the one hand, it is committed to basic research on laser welding process of new materials and analysis of welding joint performance and welding thermal efficiency, such as laser welding of intermetallic compounds such as Ti3Al, Ti2AlNb, TiNi; on the other hand, aluminum alloys for aviation structures, Titanium alloy has carried out in-depth laser welding process optimization, defect control and detection, and automatic control. It has also carried out a lot of basic research on welding metallurgy and mechanical properties. It has not only established a laser welding process signal detection system for plasma characteristics, molten pool behavior, and small Research on the process mechanism of hole characteristics, and developed invention patents such as titanium alloy laser active agent welding technology. Based on laser welding of aluminum alloy and titanium alloys for aircraft components in the industry, we will prepare 5 laser welding related process standards (HB). In the future, we will gradually improve the Chinese aviation structure laser welding process standard system.
Laser welding also has inherent disadvantages:
- Laser welding of alloy-reinforced metals, such as high-strength aluminum alloys, leads to welding cracks due to solidification crystallization, which is liable to form low-melting eutectics.
- The dynamic instability of small holes in the laser welding process is prone to lead to weld seams;
- The size of the laser spot is small, and the assembly accuracy of the welding part is required to be high;
- Laser welding of highly reflective materials, laser reflection is not only easy to cause personal injury, but also easy to damage laser welding equipment, affecting the reliability of equipment work. These issues are the research topics that laser welding engineers outside China have been working on. From the process innovation using the inherent characteristics of laser welding to the research of combined laser welding process technology and laser composite heat source welding technology, the laser welding process has become more precise and efficient. Development; laser welding equipment is developing towards intelligence and information; welding assembly is developing towards digitization and flexibility.
Each step of the development of laser welding technology involves new materials, new structures and new processes. On the basis of overcoming existing engineering problems, it also generates new scientific and engineering problems for the welding of new materials and new structures. Future aircraft and engines will place more emphasis on long life, high maneuverability, low cost, and damage tolerance design. Manufacturing technology has a stronger demand for lightweight, integrated structural parts manufacturing, precision manufacturing of new structural parts, and low cost and efficient new processes. Laser welding technology will still play an important role, and its development trends are:
- Efficient, automated and intelligent laser welding, and the development of electronic technology, automatic control technology, sensor detection and information processing technology, also provides a favorable way for the welding process to move towards flexibility, automation and intelligence. Technical Support;
- Fully digital laser welding, including welding process simulation, welding quality monitoring, and reliability evaluation of welding structure mechanics, which will greatly improve the quality of aviation products;
- Integrated and integrated laser welding, and the CNC machining concept of “one-time clamping and complete completion” is also being introduced into the welding field. Traditional single-function welding equipment is gradually being replaced by composite equipment. The engine manufacturing industry has had a revolutionary impact.