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Shrinkage then introduces residual stresses and distortion. Distortion can pose a major problem since the final product is not the desired shape. To alleviate certain types of distortion, the workpieces can be offset so that after welding, the product is the correct shape. [19] The following pictures describe various types of welding distortion ...
It can also stabilize the arc when welding aluminium and high-alloyed stainless steel. Other gases can be used for special applications, pure or as blend additives; e.g. sulfur hexafluoride or dichlorodifluoromethane. [10] Sulfur hexafluoride can be added to shield gas for aluminium welding to bind hydrogen in the weld area to reduce weld ...
Vibratory Stress Relief, often abbreviated VSR, is a non-thermal stress relief method used by the metal working industry to enhance the dimensional stability and mechanical integrity of castings, forgings, and welded components, chiefly for two categories of these metal workpieces:
During the welding process, residual stresses can present themselves in the area of the weld, either in the heat affected zone or fusion zone. The mean stress a welded joint may see in application, can be altered due to the welding processes implementing residual stresses, changing the fatigue life and can render S-N laboratory testing results. [2]
Most weld purging is carried out on joints made by the TIG or GTAW arc welding process. [6] When the laser welding process is chosen, joints or welds being made on reactive materials will need to be carried out and in the case of electron beam welding, this is carried out in a vacuum, in which case purging takes place by complete evacuation of all gas.
Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses.
Arc blow tends to occur if the material being welded has residual magnetism at a certain level, particularly when the weld root is being made, and the welding current is direct current (DC positive or negative). Magnetic arc blow is popularly attributed to a change in the direction of current as it flows into and through the workpiece.
In addition to residual stresses, microstructural changes occur due to the high temperatures induced by the welding process. [1] These changes can increase hardness of the material and reduce toughness and ductility. The use of PWHT can help reduce any increased hardness levels and improve toughness and ductility to levels acceptable for design ...