Pipe joining by Friction Stir Welding Process

Friction Stir Welding is one of the most common welding processes in pipe fabrication industry in which two work pieces are joined together by coalescence created by friction of mechanically driven tool. Due to heat generation as the result of applied friction, work piece becomes softer and transforms to plastic state. The soft material near to the tool, gets blended by mechanically applied pressure, making a solid state bond between two work pieces. Friction Stir Welding process is widely utilized to weld aluminium structure and pipe. It requires no filler material but uses base metal material to make joint. Unlike other arc welding processes, friction stir welding requires;

Below video is about how pipes are being joined using FSW.

FSW process was introduced to minimize many problems that happen in using conventional welding processes. The intended use of this process was to produce high strength welds in lighter materials and now it has wide applications in automotive, aerospace, rolling vehicles, off-shore, fabrication, even the electronics and other lightweight structures. Following are the points that describe the usefulness of Friction Stir Welding Process.

  • A solid-state joining technique, means no high energy is required as compared to arc welding processes.
  • It does not involve the transformation of liquid phase to solid and thus defects like porosity, blow holes and cracking do not arise.
  • The process involves the use of base metal to make joints, means no additional filler wire and gas supply is required.
  • Lower Cost.
  • Use of friction heat (created by mechanical tool), to provide coalescence of joint metal. No use of arc and formation of by-product hazardous gases, makes the process environmental friendly.
  • It can be employed to weld butt and lap joints.
  • Due to the process of solid state bonding, it can be operated in all positions.
  • No additional cost for post weld heat treatment.
  • Unlike arc process, less affected by environmental factors.

Comparison between TIG and FSW

In TIG welding, a non-consumable electrode is used to make weld by melting and feeding of a filler rod while in case of friction stir process, a rotating tool instead of electrode is used to melt and blend part of parent metal instead of a filler metal to produce a high quality and strong joint. The tool is allowed to rotate constantly on the joint, which transforms the parent material into soft plastic form due to the heat produced from friction force. After which the tool blends the soft material of joint, consolidating it by applied welding pressure. 
1. Non-Consumable electrode.
1. Non-Consumable rotating tool.
2. Arc is produced by electrode.
2. Friction heat is produced by tool.
3. Additional filler metal is fed.
3. Filler is parent metal itself.
4. Post weld treatments are required.
4. No Post weld treatments are required.
5. Process is manipulated by a welder.
5. Automatic.
How FSW works?

During FSW, following are the forces which actually facilitate the process of welding.

  • Clamping force – required to keep the joining work pieces intact.
  • Friction force – required to produce frictional heat by applying specific downward force on tool. 
  • Rotating force – required to make the tool spin continuously.
  • Forward force – required to traverse the tool.

After the pipe pieces are clamped, the spinning tool traverses the joint due to which parent material gets softer by frictional heat without going to melting state. The tool is rotated at the specific rate due to torque set into the equipment. The plasticized material is stirred by mechanical mixing action of tool and is allowed to merge by clamping force that is why it is named as Friction Stir process.  

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