Upset welding

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Upset welding is a special way of welding, in which two pieces of material are forged together at elevated temperatures. There are different ways to reach this temperature, but a current through the interface, friction or sometimes an external source are used. No extra weld material is added to the weld. During the forging, some material will be expelled from the weld, this material is called the upset. This removal is necessary to ensure that surface contaminants (such as oxides or oil) are removed from the weld metal. When these contaminants remain in the weld they can become initiation points for corrosion or crack forming.