Resistance welding is a welding method in which a current is passed through a resistance heat generated between a workpiece and a welding contact surface to heat the weldment to a plastic or partially melted state, and then pressure is applied to form a welded joint.
Resistance welding is divided into three types: spot welding, seam welding and butt welding.
(1) Spot welding: the weldment is pressed between the two columnar electrodes, and is heated by electricity to melt the weldment at the contact to form a nugget, then power off, and solidify and crystallize under pressure to form a dense joint. .
Spot welding is suitable for welding thin plates (laps) and steel bars up to 4 mm, and is widely used in the production of automobiles, airplanes, electronics, instruments and daily necessities.
(2) Seam welding: Seam welding is similar to spot welding except that a rotating disk electrode is used instead of the column electrode. The stacked workpieces are energized between the discs and fed as the disc rotates to form a continuous weld.
Seam welding is suitable for welding thin plates with a thickness of less than 3 mm, and is mainly used for the production of sealed containers and pipes.
(3) Butt welding: According to the welding process, butt welding can be divided into resistance butt welding and flash butt welding.
1) Resistance butt welding The welding process is to apply the upset pressure (10 ~ 15 MPa), so that the workpiece joint is in close contact, heated to the plastic state, and then the forging pressure (30 ~ 50 MPa) is applied, and the power is cut off to make the welding The contact is plastically deformed under pressure and welded.
The resistance butt welding operation is simple, the joint shape is smooth, but the welding part end face processing and cleaning requirements are high, otherwise the contact surface heating unevenness will occur, resulting in oxide inclusions, welding impervious and other defects, affecting the welding quality. Therefore, resistance butt welding is generally only used for welding workpieces with a diameter of less than 20 mm, a simple cross section and a small force.
2) Flash butt welding The welding process is first energized, and then the two weldments are slightly contacted. Because the surface of the weldment is not flat, the current density of the contact points is very high, and the metal melts rapidly, vaporizes, blasts, and sparks, causing flash phenomenon. Continue to move the weldment to create a new contact point, the flash phenomenon continues to occur, when the end faces of both weldments are completely melted, pressurize quickly, then power off and continue to pressurize, so that the weldment is welded.
The quality of the flash butt welding joint is good, and the pre-weld cleaning requirements for the joint surface are not high. It is often used for welding important workpieces with large force. Flash butt welding can not only weld the same metal, but also weld dissimilar metals such as aluminum steel, aluminum copper, etc., can weld 0.01 mm wire, or weld 500 mm diameter pipe and 20 000 mm2 plate.
