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P. Sarkar et al.
the pin. A tilt of 2°–4° towards the trailing edge is required to exert the forging force
along the weld line properly. Generally, linear welds are produced with a concave
shoulder. The demand for maintaining a tool tilt around the concavity makes it
difficult for performing non-linear welding with a simple FSW machine [7].
The convex shape propels material off the pin. The convex shoulder is generally
used with scrolls that help the flow of material from outer to the inner side of the
shoulder and perform sound welding. Due to the convex shape, the user can set the
required amount of surface contact of the shoulder by controlling PD, thus, a more
precise weld line is created [8].
Various features like scrolls, grooves, concentric circles can also be machined into
the shoulder (concave, convex, or flat) of an FSW tool [8]. These features enhance the
deformation of the materials produced by the shoulder. Consequently, the mixing of
material is increased, and hence the weld quality gets improved. The most common
feature is the scrolled shoulder, which not only directs the material for better mixing
but also helps to avoid the requirement of the tilt angle. The scrolled shoulder can
significantly reduce the undercut, flashes, and the amount of tool lift seen when using
a concave shoulder. However, precise control of the position of the tool must be
maintained in case of scrolled shoulder to avoid excessive flash generation. Scrolled
shoulder geometries cannot join two plates with different thicknesses or plates having
thickness variations along the weld line.
Various pin geometries have been developed to enhance the process quality and
material mixing to increase joint strength and to enable the process to join numerous
hard-to-weld materials [7–11]. Initially, FSW was conducted with a round bottom
cylindrical threaded pin. The threads present in the pin excavated material from the
mating shoulder surface and deposited them at the bottom of the pin. Tool wear, in
this case, was less because of the presence of the round dome. The efficiency was
the maximum with a dome having a radius equal to 75% of the pin diameter.
However, the low velocity of the round bottom led to the discovery of a flat bottom
pin, the velocity of which was increased to approximately 30 times by providing a
suitable α [12]. The ease of manufacturing a flat bottom versus a curved pin provides
an additional advantage. Both these pins were mainly used for thin plates. The need
for welding of thicker plates necessitates further tool developments, and hence truncated cone pin tools were developed [13]. With this pin, aluminium plates with
thicknesses greater than 12 mm can be welded with a faster v [14]. Lower F z and
higher moment load at the base of the truncated pin than that of the cylindrical pin
made it a better option for joining thicker materials [14].
The need for welding of high-temperature materials further motivated the development of new tools. Threads that were used in the initially developed tools may get
distorted by these high-temperature materials. On the other hand, a thread-less pin
profile cannot produce enough material flow. The use of a stepped spiral tool was
successful for welding high-temperature materials that can sustain temperatures up to
1000 °C [15]. The possibility of grinding the stepped spiral feature into a ceramic tool
like polycrystalline cubic boron nitride (PCBN), increases the deformation volume
of materials [16].
P. Sarkar et al.
the pin. A tilt of 2°–4° towards the trailing edge is required to exert the forging force
along the weld line properly. Generally, linear welds are produced with a concave
shoulder. The demand for maintaining a tool tilt around the concavity makes it
difficult for performing non-linear welding with a simple FSW machine [7].
The convex shape propels material off the pin. The convex shoulder is generally
used with scrolls that help the flow of material from outer to the inner side of the
shoulder and perform sound welding. Due to the convex shape, the user can set the
required amount of surface contact of the shoulder by controlling PD, thus, a more
precise weld line is created [8].
Various features like scrolls, grooves, concentric circles can also be machined into
the shoulder (concave, convex, or flat) of an FSW tool [8]. These features enhance the
deformation of the materials produced by the shoulder. Consequently, the mixing of
material is increased, and hence the weld quality gets improved. The most common
feature is the scrolled shoulder, which not only directs the material for better mixing
but also helps to avoid the requirement of the tilt angle. The scrolled shoulder can
significantly reduce the undercut, flashes, and the amount of tool lift seen when using
a concave shoulder. However, precise control of the position of the tool must be
maintained in case of scrolled shoulder to avoid excessive flash generation. Scrolled
shoulder geometries cannot join two plates with different thicknesses or plates having
thickness variations along the weld line.
Various pin geometries have been developed to enhance the process quality and
material mixing to increase joint strength and to enable the process to join numerous
hard-to-weld materials [7–11]. Initially, FSW was conducted with a round bottom
cylindrical threaded pin. The threads present in the pin excavated material from the
mating shoulder surface and deposited them at the bottom of the pin. Tool wear, in
this case, was less because of the presence of the round dome. The efficiency was
the maximum with a dome having a radius equal to 75% of the pin diameter.
However, the low velocity of the round bottom led to the discovery of a flat bottom
pin, the velocity of which was increased to approximately 30 times by providing a
suitable α [12]. The ease of manufacturing a flat bottom versus a curved pin provides
an additional advantage. Both these pins were mainly used for thin plates. The need
for welding of thicker plates necessitates further tool developments, and hence truncated cone pin tools were developed [13]. With this pin, aluminium plates with
thicknesses greater than 12 mm can be welded with a faster v [14]. Lower F z and
higher moment load at the base of the truncated pin than that of the cylindrical pin
made it a better option for joining thicker materials [14].
The need for welding of high-temperature materials further motivated the development of new tools. Threads that were used in the initially developed tools may get
distorted by these high-temperature materials. On the other hand, a thread-less pin
profile cannot produce enough material flow. The use of a stepped spiral tool was
successful for welding high-temperature materials that can sustain temperatures up to
1000 °C [15]. The possibility of grinding the stepped spiral feature into a ceramic tool
like polycrystalline cubic boron nitride (PCBN), increases the deformation volume
of materials [16].