1 Friction Stir Welding
31
trailing edge is also aided by the tilt of the tool. In general, a tilt angle between
0 and 3° is selected for optimum weld quality [40]. Takahara et al. [63] reported
that the tensile strength of the welded joint is sufficiently maintained by limiting the
backward tilt up to 3°.
1.7.4 Other Parameters
1.7.4.1 Forces
Considering the forces in three direction w.r.t. the tool in a FSW system (refer
Fig. 1.1c), the down force acting on the tool (Z-force) is the most important one
which affects the welding. It is to be noted here that normally, FSW machines can be
operated in two modes, viz. position control and force control. In case of the former,
the machine tries to maintain the position command given to the tool (plunge depth)
while recording the forces as a response. In the force control mode, the machine
tries to maintain the force given as the input. As already mentioned, Z-force value
is normally specified while the plunge depth can vary. Higher Z-force results in
increased plunge depth as well as greater heat generation, thus playing its part in
the material softening and the corresponding phenomena. The other two forces,
viz. longitudinal force or transverse force (X-directional force) and lateral force (Yforce), are normally recorded as response. However, these forces give an indication
regarding the quality of the weld produced. In some cases, defects in the weld can
be predicted by observing the trends in the force values recorded during the FSW
process.
1.7.4.2 Plunge Depth
The plunge depth is also an essential parameter for FSW. Whether the tool has fully
penetrated into the workpiece is ensured by the plunge depth. Moreover, it ensures
necessary vertical force needed for the heat generation. Excessive plunge depth may
cause the pin to reach up to the reverse side of the workpiece resulting in its welding
with the backing plate.
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trailing edge is also aided by the tilt of the tool. In general, a tilt angle between
0 and 3° is selected for optimum weld quality [40]. Takahara et al. [63] reported
that the tensile strength of the welded joint is sufficiently maintained by limiting the
backward tilt up to 3°.
1.7.4 Other Parameters
1.7.4.1 Forces
Considering the forces in three direction w.r.t. the tool in a FSW system (refer
Fig. 1.1c), the down force acting on the tool (Z-force) is the most important one
which affects the welding. It is to be noted here that normally, FSW machines can be
operated in two modes, viz. position control and force control. In case of the former,
the machine tries to maintain the position command given to the tool (plunge depth)
while recording the forces as a response. In the force control mode, the machine
tries to maintain the force given as the input. As already mentioned, Z-force value
is normally specified while the plunge depth can vary. Higher Z-force results in
increased plunge depth as well as greater heat generation, thus playing its part in
the material softening and the corresponding phenomena. The other two forces,
viz. longitudinal force or transverse force (X-directional force) and lateral force (Yforce), are normally recorded as response. However, these forces give an indication
regarding the quality of the weld produced. In some cases, defects in the weld can
be predicted by observing the trends in the force values recorded during the FSW
process.
1.7.4.2 Plunge Depth
The plunge depth is also an essential parameter for FSW. Whether the tool has fully
penetrated into the workpiece is ensured by the plunge depth. Moreover, it ensures
necessary vertical force needed for the heat generation. Excessive plunge depth may
cause the pin to reach up to the reverse side of the workpiece resulting in its welding
with the backing plate.