Views: 42 Author: Site Editor Publish Time: 2022-07-24 Origin: Site
The friction stir welding method is similar to conventional friction welding. Friction stir welding also uses friction heat and plastic deformation heat as welding heat sources. The difference is that the welding process of friction stir welding is that a welding pin of a cylinder or other shape (such as a threaded cylinder) is inserted into the joint of the workpiece, and the high-speed rotation of the welding head makes it and welding. The workpiece material rubs, so that the temperature of the material at the connection part increases and softens. At the same time, friction stir is applied to the material to complete the welding. During the welding process, the workpiece should be rigidly fixed on the back pad, the welding head rotates at a high speed, and the edge moves relative to the workpiece along the seam of the workpiece.
The protruding section of the welding head protrudes into the material for friction and stirring, and the shoulder of the welding head rubs against the surface of the workpiece to generate heat, which is used to prevent the overflow of the plastic material, and at the same time, it can remove the oxide film on the surface.
During the welding process, the stirring needle extends into the seam of the workpiece while rotating, and the frictional heat between the rotating stirring head (mainly the shaft shoulder) and the workpiece causes strong plastic deformation of the material in front of the welding head, and then with the With the movement of the welding head, the highly plastically deformed material is gradually deposited behind the mixing head, thereby forming a friction stir welding seam.
The requirements of friction stir welding on equipment are not high. The most basic requirements are the rotation of the welding head and the relative movement of the workpiece. Even a milling machine can easily meet the requirements of butt welding of small flat plates.
But the rigidity of welding equipment and fixtures is extremely important. The stirring 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 end of the friction stir weld leaves a keyhole in the terminal. Usually this keyhole can be cut off, or it can be sealed by other welding methods. In response to the keyhole problem, a telescopic stirring head has been successfully developed, and the welding keyhole will not be left after welding.
Other welding consumables, such as electrodes, wires, fluxes and shielding gases, are not required during the welding process. The only consumption is the welding mixing head, but the consumption of the welding mixing head is limited. The functions of the mixing head are: frictional heat, so that the local material to be welded is in a plastic state; breaking the oxide film on the surface of the aluminum alloy; completing the material around the special shape Refers to the migration, extrusion and diffusion of the rod from front to back and from the top to the bottom; welding is a mechanized process, with a large axial force and a certain radial force, and cannot be welded by hand; no filler material and special Protected, Formed Welds - Solid State Welded Joints.
Due to the relatively low temperature during friction stir welding, the residual stress or deformation of the structure after welding is also much smaller than that of fusion welding. Especially when the aluminum alloy sheet is melted and welded, the out-of-plane deformation of the structure is very obvious. Whether the non-deformation welding technology or the post-weld cold and hot orthopedic technology is used, it is very troublesome and increases the manufacturing cost of the structure.
Friction stir welding is mainly used in non-ferrous metals with low melting temperature, and can complete the welding of high-strength aluminum alloy parts that cannot be welded by fusion welding, such as 2000, 7000 series aluminum alloys, etc.; and the welded joints are of high quality and good mechanical properties. This is related to the material selection of the mixing head and the working life of the mixing head. For black materials with good ductility and easy plastic deformation, it is also possible to realize friction stir welding by auxiliary heating or using its superplasticity.
Friction stir welding has been successfully applied in the connection of non-ferrous metals, but due to the limitation of the characteristics of the welding method, it is limited to the welding of simple structures, such as the welding of flat structures or cylindrical structures, and the workpiece needs to be welded during the welding process. Have good support or padding.
In principle, friction stir welding can perform welding in various positions, such as flat welding, vertical welding, overhead welding and overhead welding, that is, it has the ability to carry out all-position welding; it can complete various forms of welding joints, such as butt joints, fillet joints and lap joints. Welding of dissimilar metal materials can also be performed on joints, even structures with varying thicknesses and the connection of multi-layer materials.
As a solid-phase welding method, friction stir welding has little pollution to the environment before and during welding, and there are no defects such as pores and cracks that are easily generated by fusion welding.
The workpiece does not need strict surface cleaning preparation requirements before welding. Friction and stirring during the welding process can remove the oxide film on the surface of the weldment. There is no smoke and splash during the welding process, and the noise is low. Because friction stir welding only relies on the rotation and movement of the welding head to gradually realize the welding of the entire weld, it is more energy-saving than fusion welding or even conventional friction welding, that is, it has high efficiency and low energy consumption.
During the friction stir welding process, the heat input is smaller than that of the fusion welding process, and there is no metal melting at the joint. It is a solid-state welding process. The metallurgical properties of the base metal are maintained in the alloy, and the metal matrix composite Materials, rapidly solidified materials, etc., are used for fusion welding of materials that will have adverse reactions.
Friction stir welding is a plastic connection joint formed by materials under the combined action of heat and machine, and its joint has obvious metal plastic flow morphology.
The objects that can be welded by friction stir welding are:
1. Aluminum alloy 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000 series of aluminum alloys, even if the weldability is poor during fusion welding, unweldable aluminum alloys, such as 2000, 7000 series, can be obtained by using FSW. good weldability.
2. Welding between dissimilar aluminum alloys, such as 2024 and 6061, 2024 and 7075, etc.
3. It can complete single-pass welding with a thickness of less than 25mm.
4. Aluminum alloy materials in various states, such as aluminum die casting state, forged state; aluminum matrix composite materials.
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