Upset Butt Welding | Diagram , advantages and Application
Upset Butt Welding
For making upset welding, edges of the workpiece should be cleaned perfectly and flatten. The parts to be welded are clamped in copper jaws as shown in Figure . The jaws act as electrodes. Both work pieces edges are prepared and butted together. There may be some gap between parts but it should be such that no arcing takes place. Then the jaws are brought together in a solid contact when the current flows through the point of contact of jaws to form a locality of high electric resistance. At this point, the applied pressure upsets or forges the parts together.
Upset welding (UW)/resistance butt welding is a welding technique that produces coalescence simultaneously over the entire area of abutting surfaces or progressively along a joint, by the heat obtained from resistance to electric current through the area where those surfaces are in contact. Pressure is applied before heating is started and is maintained throughout the heating period. The equipment used for upset welding is very similar to that used for flash welding. It can be used only if the parts to be welded are equal in cross-sectional area. The abutting surfaces must be very carefully prepared to provide for proper heating. The difference from flash welding is that the parts are clamped in the welding machine and force is applied bringing them tightly together. High-amperage current is then passed through the joint, which heats the abutting surfaces. When they have been heated to a suitable forging temperature an upsetting force is applied and the current is stopped. The high temperature of the work at the abutting surfaces plus the high pressure causes coalescence to take place. After cooling, the force is released and the weld is completed.
Advantages of Upset Butt Welding :
1. Upset butt-welding is more suitable for welding many alloys which are difficult to weld using fusion welding. The metal retains base metal characteristics because the base metal does not melt during welding.
3. The welded joint is stronger because the hot working structure is maintained.
4. The introduction of composite materials and inclusion of secondary materials on the base metal are almost minimal.
5. Upset welding is mainly adapted to fabricate very large structures compared to conventional resistance welding.
Applications of Upset butt Welding :
1. This process is mainly used for welding nonferrous materials of smaller cross section such as bars, rods, wires, tubes etc.
2. Upset welding is used to make closure of capsules, small vessels and containers,
3, It is applied in welding steel-rails.
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