Chinese Welding

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Chinese Welding: A few days ago, someone mentioned in a post that the Baton Welding Research Institute from Ukraine is setting up a joint venture in Guangdong. I’ll briefly talk about the welding situation in China as far as I know. The data is quite old; it reflects the situation from N years ago when I was still able to work on the front lines. It applies only to certain specific industries, and specifically to large state-owned manufacturing enterprises. Information on private and small enterprises is not available, so this data isn’t generalizable – take it with caution. 　　Generally, we use the amount of steel used in welded structures as a key indicator of an industry’s level of development and its advancement in welding technology. Currently, on average 45% of steel worldwide must be welded before it can be made available on the market. In countries such as Germany, the United States, the United Kingdom, and Japan, the amount of steel used for welded structures accounts for over 60% of the country’s total steel production. With the rapid development of industrial modernization in our country, many heavy structures such as power station boilers, pressure vessels, ships, construction projects, metallurgical equipment, and heavy machinery are becoming larger in scale, more sophisticated in design, and more efficient. As a result, the amount of steel used in welded structures has increased significantly. According to incomplete statistics, in 2010, steel used for welded structures accounted for over 45% of China’s total steel consumption, which is higher than the world average. 　　Currently, in the production of large machine tools and valves by large state-owned manufacturing enterprises, technologies that replace casting with welding, or forging-welding in lieu of casting, are widely employed. Moreover, various advanced welding techniques are also commonly used in the construction of large steel structures for buildings, railway and highway bridges, and urban transportation infrastructure. 　　Overall, apart from a very small number of processes and technologies, China’s welding technology as a whole is not far behind the world standard, placing it in the second tier after Germany, the United States, the United Kingdom, and Japan. 　　Welding is the process of joining metal materials together. It is primarily used in industries such as heavy machinery, power equipment, petrochemicals, transportation, construction, and aerospace. There is also some welding work involved in electronic devices, household appliances, medical equipment, and communication engineering. 　　The field of welding includes materials science, mechanics, heat treatment, metallurgy, automatic control, electronics, inspection, and more. 　　I. The simple course of development of welding technology in China China’s welding industry began with 156 pieces of assistance from the Soviet Union; it was the Soviet Union that taught China how to do this. Until the Soviet Union terminated its aid agreements in 1960, our country did not possess any real welding technologies or equipment; it was merely a user of Soviet welding technologies and equipment. 　　It was not until 1972 that our country independently established several welding equipment manufacturing plants. Currently, the major domestic manufacturers of general-purpose welding equipment include Shanghai Dongsheng, Shanghai Hugong, Shanghai General, Kailda, Shandong Shanda Aotai, Yuci Jingwei, and others. 　　After the reform and opening up, the key technical personnel from these large welding equipment manufacturers were poached, and many small and medium-sized welding equipment factories were established in the Jiangsu and Zhejiang regions. However, these factories mainly produced simple welding manipulators, roller frames, positioners, and turning machines, with a relatively low level of automation. Currently, the manufacturers of small and medium-sized general-purpose welding equipment include Wuxi Hanshen, Shanghai Weiteli, Shanghai Huawei, Shanghai Zhengte, Nantong Fuli, Chengdu Huayuan, Chengdu Kumagai, Chengdu Welding Technology, Chongqing Yunda, Tangshan Shuobao, Guangzhou FiberHome, Shenzhen Ruiling Shili, Shenzhen Ruiling Electric Appliance, and Shenzhen Dongshan. 　　After the 1980s, the Western countries relaxed their technological embargo against China, allowing the import of certain non-military welding equipment. Under various technological modernization projects, several state-owned enterprises in China imported large quantities of complete sets of welding equipment. These devices featured a very high level of automation (truly eye-opening; for instance, mechanical control technology, PLC control technology, and numerical control systems were widely used), as well as great precision. The introduction of these devices has led to significant progress in automated welding technology in our country. 　　In 1996, China began to import welding robots in large quantities. By 2001, the number of welding robots had reached 1,040; among them, arc welding robots accounted for 49%, while spot welding robots made up 47%. Currently, there are less than 2 million robots in use worldwide, with welding robots constituting over 45% of that total. In China, welding robots account for approximately 50% of all robots in use. In 2014, China had a total of 200,000 robots in service, of which 100,000 were welding robots—this figure comes from the China Robot Industry Alliance and may be somewhat exaggerated. 　　At present, most of the welding equipment in use at large state-owned manufacturing enterprises in our country is equipped with automatic control systems, intelligent control systems, and network control systems. Welding robot arms are widely used as operating units to form welding centers, welding production lines, and integrated manufacturing systems. 　　Currently, in China’s large-scale manufacturing industry, welding has evolved from a simple method for joining components or producing blanks into one of the precision processing methods used in manufacturing. Welding processes and technological solutions that require no direct human involvement have been developed; likewise, the structure and configuration of welding machinery and systems have also been optimized. Moreover, the automation of welding inspection and assembly inspection has been achieved (that is, an automated welding process without any direct human intervention has been realized). 　　Of course, in small enterprises and private businesses, the use of manual welding is still a widespread practice. 　　At present, welding technology in our country has evolved from a mere processing technique to a comprehensive engineering discipline, encompassing a wide range of technical processes such as materials, structural design, welding methods, welding equipment and process tools, welding materials, welding preheating treatments, cutting and material preparation, groove preparation, the development of welding processes and related standards, welding production, monitoring and management of the welding process, post-welding treatment and coating, inspection, environmental protection in welding operations, and the performance of welded joints. 　　II. Progress in welding technology in China’s large state-owned manufacturing industries 1. Welding robots and laser welding technology are widely used in large state-owned manufacturing enterprises. In China, medium- and low-end arc welding robots are now largely produced domestically (including sensors, CNC systems, reducers, and servo motors), and industrial network control is employed to enable precise and intelligent adjustment of the welding current from a distance. High-end welding robots currently have no competitiveness; this is mainly due to a significant gap in CNC systems, as well as huge disparities in product precision, lifespan, and reliability. 　　Currently, China is also promoting the welding process using a combined laser and laser-arc heat source. 　　This process features high energy density, high energy efficiency, high arc stability, lower requirements for tool preparation precision, and lower surface quality of the workpieces to be welded. It combines the advantages of two separate heat sources: laser and arc. The laser heat source features high energy density, excellent directivity, and the ability to penetrate transparent materials, while arc plasma offers high thermoelectrical conversion efficiency, low operating costs due to inexpensive equipment, and mature technical development. It overcomes the disadvantages of each of these sources – such as the loss of laser energy due to the high reflectivity of metal materials on lasers, the high cost of laser equipment, and the low electro-optical conversion efficiency – as well as the lower energy density of arc heat sources and poor discharge stability when moving at high speeds. 　　Currently, the lasers that can be used for welding in China include CO2 lasers, YAG lasers, and semiconductor lasers. The arc welding heat sources that can be used for welding include TIG, MIG, MAG, and plasma arcs, all of which can be manufactured entirely domestically. 　　However, AC arc welders still account for a large proportion among arc welders; high-energy-consuming rotary DC welders also hold a certain share, while the proportion of CO2 welders needs to increase. 　　2. Inverter-type welding machines are widely used in large state-owned manufacturing enterprises. Inverter-type welding machines can save 20%–30% in energy and 80%–90% in materials; they also facilitate the realization of multi-functionality, automation, and intelligence. 　　In China, the research, development, and production technologies for inverter-type welding machines are well-established; their output and variety have seen rapid growth. Currently, they are approaching world-class standards. Among them, the invertor transformer, which is a key component in inverter welders, represents China’s strength in this field. At present, high-power inverter welders in China generally use amorphous iron cores, while most foreign welders still use ferrite cores; amorphous iron cores offer advantages in terms of material costs and technical performance compared to ferrite cores. 　　Moreover, in large state-owned manufacturing enterprises, high-power inverter technology has been widely adopted, with current levels rising to 1000A for submerged arc welding ； Processes such as arc gas gouging and 250A air plasma cutting are widely used ； Inverter-based CO2/MAG/MIG DC, pulse, and AC square-wave welding equipment reduces spatter and improves weld quality by employing techniques such as increased power (up to 630A), waveform control, unified adjustment, and arc start/stop control, thereby meeting the requirements of high-end welding applications to some extent ； Digital control technologies represented by DSP are now widely used in invertor-type high-performance welding machines in our country. 　　High-efficiency arc welding processes are widely used, such as gas-shielded arc welding (including TIG welding which uses argon as the shielding gas for the welding area, and MIG welding which uses carbon dioxide as the shielding gas, etc.) ； Tungsten inert gas welding (commonly used for welding stainless steel and superalloys) ； 　　Plasma arc welding, and so on. 　　3. In the large state-owned manufacturing sector, wave control, intelligent and automatic, as well as semi-automatic welding technologies are now widely adopted. At present, China is capable of fully producing domestically automatic and semi-automatic gas shielded welding machines, submerged arc welding machines, resistance welding machines, and other such products. 　　In terms of welding processes, double-wire submerged arc welding is primarily used (accounting for 50%–60% in large state-owned manufacturing enterprises). Double-wire welding offers a high welding speed; when welding thin sheets, this speed can reach 3–6 m/min, which is 5–10 times higher than that of conventional single-wire welding methods. For thick sheets, it enables an increased wire deposition rate ； The welding quality is good; for example, when welding aluminum alloys, it can significantly reduce the amount of pores ； It can also be used for welding metal materials such as low-carbon steel, ordinary low-alloy steel, stainless steel, and aluminum. 　　In addition, the plasma spray welding process has also begun to be widely used (plasma spray welding uses a plasma arc as a heat source to spray alloy powder onto a metal surface; as the spray gun and the workpiece move relative to each other, the liquid alloy gradually solidifies, thereby forming an alloy spray-welded layer). 　　New near-net-shape welding technologies are also being increasingly utilized. (Near-net-shape technology refers to a forming technique wherein, after shaping, a part requires only minimal or no further processing before it can be used as a mechanical component.) 　　4. The widespread use of digital welding machines in large state-owned manufacturing enterprises, characterized by high efficiency, energy savings, as well as digital, automated, and intelligent control of the manufacturing processes. CNC plasma cutters are also widely used (although reliable cutting power supplies of high quality still need to be imported). 　　For example, the digital control welders used in large state-owned manufacturing enterprises today have the capability to store and recall over 90 various parameter settings, including current, voltage, crater handling, and wire diameter selection. They can be connected via industrial networks to form welding production lines, and they also come equipped with data interfaces for welding expert systems. 　　5. Applications of friction stir welding Friction welding is a method that utilizes the heat generated by the mutual movement and friction between the end faces of the workpieces, bringing those ends to a thermoplastic state; subsequent rapid forcing is then used to complete the welding process. 　　Friction welding can easily join the same or different materials, including metals, some metal matrix composites, ceramics, and plastics. 　　The original friction welding method was primarily used for welding rotary components. Although other forms of friction welding techniques have been developed to overcome the limitations imposed by the geometry of the parts to be welded or to improve productivity, such as phase friction welding, radial friction welding, and linear friction welding, these are rarely used in practice. 　　Friction stir welding is a patented welding technique invented by the Welding Institute in the UK in 1991, primarily used to weld low-melting-point materials such as aluminum alloys. 　　Friction stir welding also utilizes frictional heat and plastic deformation heat as the heat sources for welding. A stir pin in cylindrical or other shapes is inserted into the joint of the workpieces; through the high-speed rotation of this stir pin, friction occurs between it and the material of the workpieces, which raises the temperature of the material at the joint point and causes it to soften. During the welding process, the stir pin rotates while remaining inserted in the joint, and the frictional heat generated between the rotating stir pin and the workpieces causes the material in front of the stir pin to undergo significant plastic deformation. As the stir pin moves, this highly deformed material gradually accumulates behind it, thereby forming a weld seam through friction stir welding – the material is simultaneously stirred and deformed to complete the welding process. 　　In addition to the advantages of conventional friction welding, friction stir welding also enables the creation of various joint types as well as welding at different positions. 　　Friction stir welding does not require sophisticated equipment; it only involves the rotational movement of the welding tool and the relative movement of the workpieces, and a milling machine can suffice to carry out small-scale flat plate butt welding. However, high rigidity is required for welding equipment and fixtures. 　　No other welding consumables such as electrodes, wires, fluxes, or shielding gases are required during friction stir welding. The only thing that is consumed is the welding stirrer. 　　The design and material of the stirring head are key to the friction stir welding process. The hardness requirement of the stirring head is much higher than that of the material to be welded, which helps to minimize wear on the stirring head during the welding process ； The shape of the stir head is key to obtaining welds with good mechanical properties. 　　Due to the relatively low temperatures during friction stir welding, the residual stress and deformation of the welded structure are much lower than those in fusion welding. In particular, during fusion welding of thin aluminum alloy sheets, out-of-plane deformation of the structure is very pronounced. Whether using distortion-free welding techniques or post-welding cold/hot shaping methods, it is quite troublesome and also increases the manufacturing cost of the structure. 　　Friction stir welding is primarily used for welding metal matrix composites, rapidly solidified materials, titanium, low-carbon steel, composites and other materials that suffer from adverse reactions when welded by fusion methods, as well as non-ferrous metals with lower melting points, such as zinc, aluminum, copper and their alloys. For steel, auxiliary heating is required first to carry out friction stir welding, but in this case the cost of friction stir welding is higher than that of conventional fusion welding. Currently, friction stir welding is being used increasingly widely on aluminum alloys and copper alloys, with a welding thickness range of 1 mm to 75 mm. It is now widely applied to the welding of aluminum-aluminum composite materials, aluminum-magnesium composite materials, and copper-aluminum composite materials ； Welding of cast aluminum alloys and carbon-silicon composites. 　　Friction stir welding can be used for welding in various positions, such as flat welding, vertical welding, overhead welding, and underwater welding. It enables the creation of different types of weld joints, including butt joints, fillet joints, and lap joints. It is also suitable for joining structures with varying thicknesses and multi-layer materials, as well as for welding dissimilar metal materials. 　　However, friction stir welding has some disadvantages; for example, the workpieces to be welded must be rigidly fixed and should have a backing plate on the opposite side, which limits its use to components with simple structures, such as straight or cylindrical shapes. Moreover, the workpieces need to be properly supported or cushioned during the welding process ； Currently, it is not applicable when considering corrosion performance, residual stress, and deformation in certain special fields ； When performing single-pass joining on sheet metal, the efficiency is far lower than that of fusion welding ； Moreover, the cost is high, and the wear and consumption of the mixing head are too rapid. 　　Norway was the first country in the world to commercialize the friction stir welding process, which can be used to weld aluminum alloy ship plates with a thickness of 3–15 mm and dimensions of 6×16. 　　In 1998, Boeing’s Space and Defense Laboratory in the United States introduced friction stir welding technology for welding certain rocket components; this technology was used to manufacture the propellant tanks for the Delta launch vehicle. 　　In 2002, the Beijing Aeronautical Manufacturing Engineering Research Institute of AVIC in China acquired the patent license for friction stir welding from the Welding Institute in the UK. This led to the establishment of the China Friction Stir Welding Center (Beijing Safest Technology Co., Ltd.), which began the engineering applications of friction stir welding; these applications are now being put into practical use. 　　To date, Saefost has successfully developed over 60 sets of friction stir welding equipment, and has developed a variety of joining methods and technologies including longitudinal seam welding, circumferential seam welding, keyhole-free welding, variable cross-section welding, self-supporting double-sided welding, spatial 3D curved welding, friction stir spot welding, fill-type spot welding, surface modification treatment for friction stir welding, and processing of superplastic materials using friction stir welding. 　　At present, friction stir welding technology is widely used in various industrial fields in China, such as aviation, aerospace, shipbuilding, rail transportation, automotive, electronics, and power industries. It is commonly employed for welding metal materials like aluminum, magnesium, copper, titanium, and steel. For instance, this technology has been applied to aerospace cylindrical structural components, thin-walled aviation structures, wide-girder plates for ships, body structures of high-speed trains, thick radar panels, automobile wheels, wall panels made from container profiles, as well as various structural heat sinks and radiators. 　　6. High-precision and thick-sheet cutting processes are widely used in large state-owned manufacturing industries. High-precision and thick-sheet cutting mainly involves laser cutting and plasma cutting. 　　Currently, CAD/CAPP/CAM and automatic control are widely used in laser cutting. It is possible to adaptively control the laser power and mode according to the processing speed, or to establish a process database and an expert adaptive control system, thereby improving the overall performance of laser cutting machines. 　　Some large enterprises already have multi-functional laser processing centers that integrate various processes such as laser cutting, laser welding, and laser heat treatment, thereby fully leveraging the overall advantages of laser processing. 　　The laser cutting equipment currently used by China’s large state-owned manufacturing enterprises mainly consists of three-dimensional, high-precision, large-scale CNC laser cutters, which have enabled the unmanned operation and automation of laser cutting cells. 　　Plasma arc cutting is a machining method that uses the heat of a high-temperature plasma arc to locally melt (and vaporize) the metal at the cut site of the workpiece, and then utilizes the momentum of the high-speed plasma to remove the molten metal in order to form a cut. 　　Plasma cutting, when used with different working gases (commonly used plasma arc working gases include argon, hydrogen, nitrogen, oxygen, air, water vapor, etc.), can cut various metals that are difficult to cut using oxygen cutting; it is particularly effective for cutting stainless steel, aluminum, copper, titanium, nickel, and so on. When cutting metals with a not-too-thick thickness, plasma cutting offers a high speed; for example, when cutting thin sheets of ordinary carbon steel, the speed can be 5 to 6 times that of oxygen cutting, and the cut surface is smooth with minimal thermal deformation. 　　7. Breakthroughs have been achieved in the welding of special materials under special engineering conditions. Under such conditions (high temperature, low temperature, petrochemical industries, marine environments, nuclear energy, aerospace, acid and alkali corrosion, etc.), breakthroughs have been made in the welding techniques for special engineering materials (ultra-high strength steels, aluminum alloys, titanium alloys, etc.), enabling tasks to be completed largely with domestically produced equipment and welding materials. 　　8. Batch production of complete sets of specialized welding equipment has been achieved; breakthroughs have also been made in the production of basic and auxiliary components. In terms of general-purpose products, we are now close to or have reached foreign advanced levels. Currently, the welding equipment produced by China’s large enterprises can be used for:
- Welding of new heat-resistant steels used in supercritical and ultra-supercritical thermal power generating units;
- Welding of ultra-low carbon bainitic high-strength steels and ultra-high strength steels used across various industries;
- Welding of cryogenic steels used in storage tanks for liquefied petroleum gas (LPG) and liquefied natural gas (LNG);
- Welding of high-strength pipeline steels such as X70, X80, and X100;
- Welding of high-performance, high-strength steels and high-strength atmospheric corrosion-resistant steels used in steel structures of high-rise buildings and long-span steel bridges;
- Welding of new high-strength heat-resistant steels used in petroleum refining equipment and hydrocracking units ； 　　As well as the welding of high-performance ferritic stainless steels and duplex stainless steels. 　　It is also capable of producing various high-performance welding materials. 　　9. The production level of welding materials has seen rapid growth, with significant changes in product structure. China has long held the world’s top position in welding wire production. In recent years, the product structure has been optimized: the output of welding wires with low added value has decreased, while the production of welding wires used for semi-automatic and automatic welding has increased. Currently, among the welding materials consumed in large state-owned manufacturing enterprises, the proportion of welding electrodes is less than 20%, while the usage rate of gas-shielded welding wires exceeds 50%. 　　The main issue with welding materials in our country at present is the gap in quality stability compared to world standards; as a result, some key infrastructure projects and defense projects are reluctant to use domestically produced welding materials and are forced to rely on expensive imported ones. This includes gas-shielded solid wires and submerged-arc welding wires for high-alloy steels, nickel-based alloys, and other alloys, as well as welding materials used in ultra-high-pressure vessels and boilers for supercritical power plants. 　　The quality stability of welding materials is determined by the manufacturing equipment, testing methods, and quality management systems used by the welding material manufacturers; it is actually a management issue rather than a technical one, nor is it related to equipment or processing techniques. 　　At present, the ratio of welding material production to steel production in our country is around 0.9%, which is already close to the level of developed countries. 　　10. Progress has been made in the automation of welding processes and welding production. Currently, the welding automation systems in the laboratory stage in China can achieve the following: (1) The system’s controller and software have a very high information processing speed; the electromechanical devices exhibit excellent control precision (the positioning accuracy of robots and welding manipulators must reach 0.1 mm, while the control accuracy of their movement speed must be 0.1%). 　　(2) The system is designed in a modular manner, allowing modules to be combined according to the different requirements of users regarding system functions, thereby providing various control options. 　　(3) The system can utilize sensing technology, computer technology, and intelligent control technology to enable high-quality, efficient automatic welding in various complex environments and under changing welding conditions. It is not only capable of carrying out the automatic welding process based on instructions, but it can also determine the number of weld passes per layer as well as related parameters and the position of the cover layer, based on continuous measurements of the groove width of the workpiece. All weld passes, from the bottom of the groove to the cover layer, are automatically executed by the welding machine, which adjusts the path as needed. 　　(4) The system can also be integrated into a flexible manufacturing system, enabling full utilization of the equipment’s capabilities to meet the production needs of workpieces of different specifications for similar products. 　　(5) The system enables integrated control through industrial networks, integrating production management with automatic welding process control, and supports offline programming as well as remote monitoring, diagnosis, and maintenance. 　　(6) The system architecture, hardware circuit chips, and interfaces have been standardized and generalized, enabling system expansion and peripheral compatibility, as well as facilitating system maintenance.