1 Friction Stir Welding
7
eliminated reducing the associated costs. Besides, chances of production of harmful
gases are also reduced.
Some of the limitations of FSW include:
• Presence of ejection hole/exit hole
In FSW technique, ejection hole remains on the workpiece when the tool is withdrawn
from. In many applications, the presence of this ejection hole is not acceptable, viz.
marine industries and aerospace industries. A runoff tab can be used to eliminate
this hole or a suitable workpiece being attached at the end of the process so that key
hole can be placed on that extra workpiece material. This involves the requirement
of extra arrangement increasing the cost.
• High initial investment
During FSW, high forces are produced by the machine. The fixture design and the
equipment cost increase to handle this level of forces. The tool used for this technique
is also very costly. All these make the cost of the machine quite high pushing it beyond
the reach of smaller companies. Besides, for manufacturing single product or lesser
number of products, this technique may not be economical.
• Less flexible
This joining technique is less flexible compared to manual arc welding process, and
it is difficult to join different plate thicknesses together.
1.4 Friction Stir Welding Tools
The tool plays an important part in the successful welding through FSW process. As
already mentioned, the tool consists of three main parts, viz. the shank, shoulder and
the pin. Broadly, the tool has a couple of functions: (a) heating in a localized area and
making the material soft and (b) flow of the softened material. Friction generated (at
shoulder and pin) due to the rotation of the tool provides local heating that leads to
material plasticization (softening) around the tool pin. Rotation of the tool together
with its translation (tool traverse) helps in the flow of the soft/plasticized material
from the leading side to the trailing side. This transfer of material helps in filling the
hole which is generated by the pin, thus forming the joint. The shoulder supplies the
majority of the frictional heat and also prevents the escaping of softened material
out of the weld zone. Thus, the quality of the weld depends a lot on the design
of the shoulder and that of the pin. However, the microstructure and mechanical
properties of the stir zone and HAZ zone of FSW also depend on the tool material
and its properties. For welding aluminum alloys and soft metals, these techniques
gained practical success. However, the design and selection of the tool became very
important while welding hard alloys, viz. steel, nickel alloys and titanium alloys, as
the life of the tool is shortened considerably and the cost increased. Thus, there has
been a concerted effort to develop cost-effective tools for the purpose which at the
7
eliminated reducing the associated costs. Besides, chances of production of harmful
gases are also reduced.
Some of the limitations of FSW include:
• Presence of ejection hole/exit hole
In FSW technique, ejection hole remains on the workpiece when the tool is withdrawn
from. In many applications, the presence of this ejection hole is not acceptable, viz.
marine industries and aerospace industries. A runoff tab can be used to eliminate
this hole or a suitable workpiece being attached at the end of the process so that key
hole can be placed on that extra workpiece material. This involves the requirement
of extra arrangement increasing the cost.
• High initial investment
During FSW, high forces are produced by the machine. The fixture design and the
equipment cost increase to handle this level of forces. The tool used for this technique
is also very costly. All these make the cost of the machine quite high pushing it beyond
the reach of smaller companies. Besides, for manufacturing single product or lesser
number of products, this technique may not be economical.
• Less flexible
This joining technique is less flexible compared to manual arc welding process, and
it is difficult to join different plate thicknesses together.
1.4 Friction Stir Welding Tools
The tool plays an important part in the successful welding through FSW process. As
already mentioned, the tool consists of three main parts, viz. the shank, shoulder and
the pin. Broadly, the tool has a couple of functions: (a) heating in a localized area and
making the material soft and (b) flow of the softened material. Friction generated (at
shoulder and pin) due to the rotation of the tool provides local heating that leads to
material plasticization (softening) around the tool pin. Rotation of the tool together
with its translation (tool traverse) helps in the flow of the soft/plasticized material
from the leading side to the trailing side. This transfer of material helps in filling the
hole which is generated by the pin, thus forming the joint. The shoulder supplies the
majority of the frictional heat and also prevents the escaping of softened material
out of the weld zone. Thus, the quality of the weld depends a lot on the design
of the shoulder and that of the pin. However, the microstructure and mechanical
properties of the stir zone and HAZ zone of FSW also depend on the tool material
and its properties. For welding aluminum alloys and soft metals, these techniques
gained practical success. However, the design and selection of the tool became very
important while welding hard alloys, viz. steel, nickel alloys and titanium alloys, as
the life of the tool is shortened considerably and the cost increased. Thus, there has
been a concerted effort to develop cost-effective tools for the purpose which at the