1 Status of assembly methods for light alloy materials such as aluminum alloy
At present, major international automobile manufacturers are promoting the aluminum alloying of body materials according to the viewpoint of light weight and recycling. Parts such as the hood and rear door of a car are typical aluminum alloy sheet constructions that require minimal deformation during assembly. In order to improve the assembly production efficiency, the production plant must adopt the point combination method. The main method used now is the resistance spot welding method.
In the resistance spot welding method, a copper alloy electrode is used to contact a welded object, and an electric current of tens of thousands of ampere or more is used to fuse the interface between the plate and the plate into one body. Therefore, the method is suitable for welding of materials such as carbon steel and stainless steel having large electrical resistance. However, the electrical resistance of aluminum alloy is smaller than that of steel. In order to generate enough heat, the current used must be three times that of steel. Therefore, it takes more electric energy to weld them, and an aluminum alloy special resistance welding system capable of using large current is required. . In order to achieve light weight of vehicle materials, it is sometimes necessary to update and increase the power supply equipment of automobile manufacturers. Since the electric resistance welding is a large current passing between the upper and lower poles, the thermal deformation is large, and large marks are left on both sides of the welded portion. In addition, the surface of the electrode is extremely fast, and the surface must be ground and cleaned at a maximum of tens of points to more than one hundred points. At the same time, it takes a lot of time to replace the electrode, and dust and sparks are generated during welding. The working environment is very bad.
Although there are other bonding methods for aluminum alloys, such as self-piercing riveting using rivets, and binding of two plates to the undercut. However, there are many problems in the cost of the auxiliary material such as the rivet, the strength of the joint portion, the processing efficiency, and the like, and it is suitable only for processing of a small part of the automobile casing.
2 Using frictional heat to soften and stir the contact points
In order to develop a new aluminum alloy spot welding method, KHI (Kawasaki, Japan) and MAZDA (Japan Mazda) jointly developed the Friction Spot Joining Technology (FSJ). (patented).
The basis of this technology is the Friction Stir Welding Technology (FSW) in the continuous bonding method developed by the British welding research institute TWI in early 1990. This method uses a friction head to move along the joint surface while rotating, by the friction head. Rotation generates frictional heat to soften the welded substrate and produce plastic flow after agitation, thereby achieving material integration.
"FSJ" is a modified and developed FSW. The cylindrical friction head with threaded protrusions on the top rotates (2000~2500 rpm for 1 minute) and applies pressure of 400~500kg/cm2 to the material. The heat softens the material and plastically flows around the protrusions to bond the two sheets.
Since the friction head friction substrate only reaches 400 to 500 ° C, and the melting point of the aluminum alloy is 630 ° C, the material is not melted but softened. “It's different from stirring and melting, and it's more like stirring ice cream.â€
There are many advantages to using an FSJ method to weld aluminum alloys:
* Energy saving
The main energy consumption of the FSJ spot welding method is on the two motors that drive the friction head, which is one-twentieth of the energy consumption of conventional resistance spot welding.
* Simple
The welding equipment is extremely simple, does not require a variety of auxiliary machinery, and even does not use cooling water and compressed air substantially, which greatly reduces equipment costs.
* high quality
The strength of the welded part is not inferior to the resistance spot welding and the quality is stable. The material has almost no thermal deformation because it does not withstand the frictional heat of melting.
* long life
The friction head used in the FSJ method has been used without loss for 100,000 times.
* Clean
The workplace is clean because there is no dust and sparks from resistance welding. In addition, electromagnetic wave noise caused by the use of a large current does not occur.
The FSJ welding technology won the special review committee of the 33rd Japan Industrial Technology Award. Mazda Japan is using FSJ welding technology to build the hood and rear door of the new sports car RX-8. Because of the wide applicability of this new technology, it can be applied to the construction of plates and reinforcing materials for vehicles, ships, airplanes, etc., and may also be used in the manufacture of traffic signs, home appliances, cooking appliances, and the like. The new aluminum alloy spot welding method of FSJ is very likely to become a worldwide standard.
(Zhao Zhijian, Department of Biotechnology, Department of Design, COSCO Kawasaki Ship Engineering Co., Ltd., Nantong, Jiangsu, China) |
