Aluminum alloy stud welding
(1) features of aluminum alloy stud welding
The stud welding process is an arc welding process in which the stud welding surface and the base metal contact surface are fused by lifting the arc and drawing the arc. Ordinary steel stud welding has been widely used in automobile manufacturing industry, while aluminum alloy stud welding has emerged in recent years along with the development of lightweight body. Different from ordinary steel stud welding, aluminum alloy stud welding must adopt ac stud welding machine to ensure the metal melting ratio on both sides and effectively reduce the porosity. When welding, as aluminum is a reactive metal, it must be protected from oxidation by a high purity mixture of argon or argon helium. The surface of the aluminum material shall be treated with de-oxidized layer and oil stains.
(2) application of aluminum alloy stud welding -- Emhart aluminum alloy stud welding machine
At present, the domestic application of aluminum alloy stud welding is very few. The main aluminum stud welding equipment adopts the German Emhart Tucker automatic aluminum stud welding machine, as shown in figure 4 (a). As the aluminum alloy stud welding requires high purity argon protection, there is a gas shield at the head of the aluminum stud welding gun, as shown in FIG. 4 (b), to ensure that the welding pool of aluminum screws is fully protected by argon during stud welding. In addition, since aluminum has a higher magnetic resistance than steel, aluminum alloy stud welding is more vulnerable to arc instability due to the influence of magnetic bias blowing. Therefore, ceramic rings must be used on the aluminum stud welding gun with additional protective gas to shield the influence of magnetic bias blowing. In the structure of aluminum stud welding fixture, try to make the stud welding gun far away from the two ends of the electrode, the welding gun is located in the middle of the two ends of the electrode symmetrical structure or use other media for magnetic bias blowing compensation, in order to balance the impact of the magnetic field on the arc, to ensure the quality of aluminum stud welding.Four, FDS hot melt self - tapping screw connection
(1) features of FDS technology
FDS softening process by high speed rotation screw connection plate, and under the effect of large axial pressure extrusion sheet and screwing in stay connected, finally formed between the plate and screw thread connection, while the center hole of the parent metal being squeezed out and at the bottom of the lower plate form an annular casing, FDS specific process as shown in figure 5 (a). This process can be applied to the connection between al-al and steel-al.
The advantages of FDS process are :(1) it can connect any material and heterogeneous material including ultra-high strength steel, al-mg alloy and composite material; (2) it can realize unilateral connection with small deformation, which is easy to operate; (3) the rivet is removable and easy to recover.
The disadvantages of FDS process are :(1) due to the drilling of the lower plate, the anti-corrosion ability of the joint will be reduced. In addition, the longer screw size will increase the body weight, and the exposed screw front end will affect the subsequent assembly of the body. (2) single-side construction of FDS process has a great impact on the workpiece and the robot during operation, so it is necessary to use a robot with a large and stable load capacity. During the tightening process, the screws must be vertical to the workpiece, and sufficient support for the workpiece should be considered in fixture design.
(2) FDS process application -- Weber RSF robot-assisted fastening system
German company Weber has developed the RSF series robot automatic fastening system, as shown in figure 5 (b). RSF system has realized the automatic production of FDS process. At present, RSF system has been widely used in high-end vehicle manufacturers in Europe and America. In recent years, some domestic automobile enterprises have also started to adopt this equipment and process.
Under the development trend of new materials and new energy, the automobile industry will be confronted with industrial upgrading. In the process of industrial upgrading, the application of aluminum alloy materials in the connection technology of body parts will become the key factor for the development of the automobile industry. In this paper, five new techniques of aluminum alloy connection with high frequency in recent years are studied and analyzed.