2
S. K. Das et al.
the latest developments in the last few decades in the field of metal joining [3]. FSW
created revolution especially in the case of difficult-to-weld (by traditional methods)
metals, viz. aluminum (2xxx and 7xxx series), which could now be joined rather
easily and effectively. Besides, FSW gave rise to the possibility of effectively joining
dissimilar metals. Because of its huge potential, FSW technology has been readily
accepted by the fabricating industry and is now used worldwide.
FSW employs a rotating tool which has a shoulder and a pin extending below it.
The pin is plunged into the intended weld line (joint area) between the two plates
to be joined till the shoulder contacts the surface of the workpieces. Obviously,
the workpieces should be rigidly clamped to prevent their separation due to the
generated forces from the rotating tool. Frictional heat generated between the tool
shoulder and the workpiece surface softens the material. The pin that enters into
the workpiece creates a material flow by stirring action. This way the material from
the two workpieces is intermixed and gets solidified as the tool progresses forward
forming the joint. As bulk of the material melting is avoided, common issues in
fusion welding, viz. solidification and liquation crack, distortion, porosity, etc., can
be avoided in FSW.
FSW is a solid-state joining process that is capable of creating high-quality and
high-strength joints with minimal distortion. This process can create the commonly
encountered butt and lap joints and can also deal in wide range of material thicknesses
and lengths. As modern applications demand for stronger, cost-effective and efficient
joints using lesser energy, FSW seems to be a well-suited answer. In addition, FSW
offers an environmentally benign solution to these challenges and at the same time
is a very quick process. This has led to its quick advancement from initiation to
industrial acceptance.
1.2 Fundamentals of FSW Process
In FSW, a non-consumable rotating tool is employed to join two objects. The tool
comprises three parts, viz. shank, shoulder and pin (refer Fig. 1.1a. The shank
connects the tool to the FSW machine, whereas the shoulder rubs against the workpieces providing necessary frictional heating. The pin plunges into the seam line
between the workpieces (refer Fig. 1.1a, b). This plunging occurs as a result of
downward force combined with the rotation of the pin. The plunging is one of the
vital phases of the FSW process, as the thermo-mechanical conditions are initiated
in this phase setting the stage for starting of the weld. Once the pin fully penetrates
into the workpiece, the shoulder provides the necessary friction heating making the
material soft (below its melting point temperature). Penetration of the tool results in
plastic deformation in the workpiece and friction that leads to further heat production [4]. The plasticized material is contained by the tool shoulder, and the same
flows around the pin by its stirring action. As per Fig. 1.1c, the right portion of the
tool where the tool rotation direction (anticlockwise for the present case) and the
direction of tool traverse make the same vectorial sense is denoted as the advancing
S. K. Das et al.
the latest developments in the last few decades in the field of metal joining [3]. FSW
created revolution especially in the case of difficult-to-weld (by traditional methods)
metals, viz. aluminum (2xxx and 7xxx series), which could now be joined rather
easily and effectively. Besides, FSW gave rise to the possibility of effectively joining
dissimilar metals. Because of its huge potential, FSW technology has been readily
accepted by the fabricating industry and is now used worldwide.
FSW employs a rotating tool which has a shoulder and a pin extending below it.
The pin is plunged into the intended weld line (joint area) between the two plates
to be joined till the shoulder contacts the surface of the workpieces. Obviously,
the workpieces should be rigidly clamped to prevent their separation due to the
generated forces from the rotating tool. Frictional heat generated between the tool
shoulder and the workpiece surface softens the material. The pin that enters into
the workpiece creates a material flow by stirring action. This way the material from
the two workpieces is intermixed and gets solidified as the tool progresses forward
forming the joint. As bulk of the material melting is avoided, common issues in
fusion welding, viz. solidification and liquation crack, distortion, porosity, etc., can
be avoided in FSW.
FSW is a solid-state joining process that is capable of creating high-quality and
high-strength joints with minimal distortion. This process can create the commonly
encountered butt and lap joints and can also deal in wide range of material thicknesses
and lengths. As modern applications demand for stronger, cost-effective and efficient
joints using lesser energy, FSW seems to be a well-suited answer. In addition, FSW
offers an environmentally benign solution to these challenges and at the same time
is a very quick process. This has led to its quick advancement from initiation to
industrial acceptance.
1.2 Fundamentals of FSW Process
In FSW, a non-consumable rotating tool is employed to join two objects. The tool
comprises three parts, viz. shank, shoulder and pin (refer Fig. 1.1a. The shank
connects the tool to the FSW machine, whereas the shoulder rubs against the workpieces providing necessary frictional heating. The pin plunges into the seam line
between the workpieces (refer Fig. 1.1a, b). This plunging occurs as a result of
downward force combined with the rotation of the pin. The plunging is one of the
vital phases of the FSW process, as the thermo-mechanical conditions are initiated
in this phase setting the stage for starting of the weld. Once the pin fully penetrates
into the workpiece, the shoulder provides the necessary friction heating making the
material soft (below its melting point temperature). Penetration of the tool results in
plastic deformation in the workpiece and friction that leads to further heat production [4]. The plasticized material is contained by the tool shoulder, and the same
flows around the pin by its stirring action. As per Fig. 1.1c, the right portion of the
tool where the tool rotation direction (anticlockwise for the present case) and the
direction of tool traverse make the same vectorial sense is denoted as the advancing