134
P. Sarkar et al.
4.1.3 Principles of FSW
The heat generated due to the friction between the tool and workpiece and the dynamic
recrystallization due to the stirring of the pin leads to the joining by FSW. To achieve
welding, FSW undergoes the following stages, as shown in Fig. 4.1:
i. Stage 1: Plunging—This is the stage where the pin and a pre-set depth of the
shoulder progress into the adjoined surface of the workpieces to be welded. The
material is initially at room temperature and hence is not soft enough to reduce
the force. Therefore, the axial resistance force encountered by the tool in this
stage is the maximum.
ii. Stage 2: Dwelling—Sufficient heat must be generated for softening the material
preceding the pin to initiate the welding. Initial heating is achieved by rotating
the tool in the starting spot for a specific period fixed by the operator.
iii. Stage 3: Traversing—The tool then traverses along the weld line of the parts to
be joined, prompting the material to flow from the front edge to the back edge
of the tool by stirring action. As a consequence, the mixing of the material takes
place, and it forms the joint.
iv. Stage 4: Retracting—After traversing through the desired distance, the tool is
withdrawn from the workpiece with an exit hole at the end of the joint line.
Recent developments in the FSW process enables the exit hole to be sealed [5].
In FSW, both frictional and mechanical (SPD) heating cause the temperature to
reach around 0.6-0.8 times the melting temperature of the materials to be joined.
Since the temperature rise exceeds the recrystallization temperature, the formation
of new grains takes place. It is observed from the literature [6] that the action of the
pin to stir continuously and the local heating of the material alter the strain, strain
rate, and temperature at different sections of the weld zone. In a cross-sectional view
of an FSWed sample, shown in Fig. 4.2, the weld region can be partitioned into four
Fig. 4.1 Stages in FSW process
P. Sarkar et al.
4.1.3 Principles of FSW
The heat generated due to the friction between the tool and workpiece and the dynamic
recrystallization due to the stirring of the pin leads to the joining by FSW. To achieve
welding, FSW undergoes the following stages, as shown in Fig. 4.1:
i. Stage 1: Plunging—This is the stage where the pin and a pre-set depth of the
shoulder progress into the adjoined surface of the workpieces to be welded. The
material is initially at room temperature and hence is not soft enough to reduce
the force. Therefore, the axial resistance force encountered by the tool in this
stage is the maximum.
ii. Stage 2: Dwelling—Sufficient heat must be generated for softening the material
preceding the pin to initiate the welding. Initial heating is achieved by rotating
the tool in the starting spot for a specific period fixed by the operator.
iii. Stage 3: Traversing—The tool then traverses along the weld line of the parts to
be joined, prompting the material to flow from the front edge to the back edge
of the tool by stirring action. As a consequence, the mixing of the material takes
place, and it forms the joint.
iv. Stage 4: Retracting—After traversing through the desired distance, the tool is
withdrawn from the workpiece with an exit hole at the end of the joint line.
Recent developments in the FSW process enables the exit hole to be sealed [5].
In FSW, both frictional and mechanical (SPD) heating cause the temperature to
reach around 0.6-0.8 times the melting temperature of the materials to be joined.
Since the temperature rise exceeds the recrystallization temperature, the formation
of new grains takes place. It is observed from the literature [6] that the action of the
pin to stir continuously and the local heating of the material alter the strain, strain
rate, and temperature at different sections of the weld zone. In a cross-sectional view
of an FSWed sample, shown in Fig. 4.2, the weld region can be partitioned into four
Fig. 4.1 Stages in FSW process