Friction stir welding,principle,working, advantages and disadvantages.
FRICTION STIR WELDING :
Friction stir welding (FSW) is a solid state welding precess in which a rotating tool is fed along the joint line between two work pieces. During welding, heat is generated due to friction and the metal is mechanically stirring to form the weld seam. FSW differs from normal friction welding in such a way by generating friction heat by a separate wear-resistant tool instead of the parts between them.
In friction stir welding process, the rotating tool consists of a cylindrical shoulder and a smaller probe projecting beneath it. During welding, the shoulder rubs against the top surfaces of the two parts thereby developing friction heat and the probe simultaneously generates additional heat by mechanical mixing of the metal along the butt surfaces. At the same time, the probe has been designed m order to perform the mixing perfectly. The heat is produced by the combination of friction and mixing but the metal will not melt but it softens. The softening of metal takes place up to a highly plastic condition. When the tool moves forward along the joint, the leading surface of the rotating probe is forcing the metal around it. Then the developed force forges the metal into a weld seam. So, the shoulder helps to limit the plasticized metal flowing around the probe.
FSW process is used in: aerospace, automotive, railway, and shipbuilding industries. The main applications are butt joints on large aluminium parts. Sometimes, steel, copper, and titanium, as well as polymers and composites are also joined by using FSW.
Advantages:
1. It ensures the good mechanical properties of the weld joint.
2. It avoids toxic fumes, warping, shielding issues, and other problems associated with arc welding.
3. It permits less distortion or shrinkage on joints.
4. 1t Provides good weld appearance.
Disadvantages:
1. An exit hole remains the same after the. tool is Withdrawn from the work.
2. Heavy-duty clamping of the parts is required.
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