It's friction stir welding!
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Friction stir welding technology was invented by the British Welding Institute (TWI) in 1991. It applied for an invention patent in the UK the following year and also applied for patent protection in various countries around the world. Since patent protection and disclosure, friction stir welding technology has been increasingly widely used first and mainly in the field of light metal structures such as aluminum alloys and magnesium alloys. It has also achieved certain development in the field of high-melting point materials.
In addition to the advantages of ordinary friction welding technology, friction stir welding can also be connected in a variety of joint forms and different welding positions. Norway has established the world's first commercial friction stir welding equipment, which can weld aluminum ship plates with a thickness of 3-15mm and a size of 6×16; in 1998, the Space and Defense Laboratory of Boeing Company in the United States introduced friction stir welding technology, using It is used to weld certain rocket components; McDonnell Douglas also uses this technology to manufacture propellant tanks for its Delta launch vehicle.
The friction stir welding method is the same as conventional friction welding. Friction stir welding also uses friction heat and plastic deformation heat as welding heat sources. The difference is that in the friction stir welding process, a cylinder or other shaped stirring needle (such as a threaded cylinder) is inserted into the joint of the workpiece, and the high-speed rotation of the welding head causes it to rub against the welding workpiece material. As a result, the temperature of the material at the joint increases and softens. At the same time, friction stir friction is applied to the material to complete the welding. The welding process is shown in the figure "Friction stir welding diagram". During the welding process, the workpiece must be rigidly fixed on the backing pad, the edge of the welding head rotates at a high speed, and the seam along the edge of the workpiece moves relative to the workpiece. The protruding section of the welding head extends into the material for friction and stirring. The shoulder of the welding head rubs against the surface of the workpiece to generate heat and is used to prevent the plastic material from overflowing, and at the same time, it can remove the surface oxide film.
During the welding process, the stirring needle extends into the joint of the workpiece while rotating. The friction heat between the rotating stirring head (mainly the shaft shoulder) and the workpiece causes the material in front of the welding head to undergo strong plastic deformation, and then as the welding head moves, highly plastically deformed material gradually deposits behind the stirring head, forming a friction stir welding seam. Friction stir welding does not have high requirements for equipment. The most basic requirements are the rotational movement of the welding head and the relative movement of the workpiece. Even a milling machine can easily meet the requirements for small flat plate butt welding. However, the rigidity of welding equipment and fixtures is extremely important. The mixing head is generally made of tool steel, and the length of the welding head is generally slightly shorter than the required welding depth. It should be noted that the friction stir weld ends with a keyhole in the terminal end. Usually, the keyhole can be cut off or sealed using other welding methods. In response to the keyhole problem, a telescopic mixing head has been successfully developed, which will not leave a welding keyhole after welding.
Application
There is no need for other welding consumable materials during the welding process, such as welding rods, welding wires, flux, and shielding gases. The only thing consumed is the welding stirrer.
Friction stir welding has been successfully used in the connection of non-ferrous metals. However, due to the limitations of the characteristics of the welding method, it is limited to the welding of simple structural components, such as straight structures or cylindrical structures, and the workpiece needs to have good support or padding. In principle, friction stir welding can be used for welding in various positions, such as flat welding, vertical welding, overhead welding, and downward welding; it can complete various forms of welding joints, such as butt joints, corner joints, and lap joints, and even structures with varying thicknesses. The connection with multi-layer materials can also be carried out for welding of dissimilar metal materials.
In addition, friction stir welding, as a solid-phase welding method, causes little environmental pollution before and during welding. The workpiece does not require strict surface cleaning and preparation requirements before welding. The friction and stirring during the welding process can remove the oxide film on the surface of the weldment, and there is no smoke or spatter during the welding process. At the same time, the noise is low. Since friction stir welding only relies on the rotation and movement of the welding head to gradually weld the entire weld, it is more energy-saving than fusion welding or even conventional friction welding.
Since the heat input during friction stir welding is smaller than that of fusion welding, there is no melting of metal at the joint. It is a solid-state welding process that maintains the metallurgical properties of the base metal in the alloy and can weld metal matrix composite materials and quickly solidify. Materials that may cause adverse reactions when used for fusion welding.
The main application industries include aerospace, defense industry, shipbuilding, railways and highways, automobile manufacturing, and electronics industries.