1 Friction Stir Welding
11
with a sintered TiC tool. Also, cooling arrangement was provided so that the excess
heat could be extracted from tool to prevent its damage. Molybdenum-based alloy
tools are employed to weld titanium and steel workpieces. Tool wear is found to be
greater in case of metal matrix composites than soft alloys as the former consisted
of hard abrasive particles. The tool rotational speed as well as its traverse speed can
affect the life of the tool. Tool life is found to be optimum when lower rotational
speed is used with a relatively higher traverse speed.
1.4.2 Geometry of FSW Tool
Heat generation rate, transverse force, torque and the thermo-mechanical aspect of
the experiments depend on the tool geometry. Geometry of the tool also affects the
material (plasticized) flow of the workpiece. The shoulder diameter, shoulder surface,
shape, size, the nature of the tool surface and the pin geometry are the factors which
influence the weld quality. Selection of appropriate shoulder with pin geometry is
again complicated by the following factors [38]:
• Dimension of workpiece which determines its capacity to acts as heat sink.
• Efficiency of the joint required.
• The forces expected on the tool so that the tool can survive mechanical failures.
1.4.2.1 Shoulder Diameter and Surface Features
The diameter of the FSW tool shoulder is particularly an important parameter as
it decides the amount of friction heat produced due to the rubbing of the shoulder
surface with the workpiece surface. The thickness of the workpiece decides the
shoulder diameter of the tool. This is because for good welding, the material should
be softened adequately. Now, as the thickness of the workpiece increases, it requires
more heat for softening. This can only be generated by a larger shoulder diameter.
Moreover, if the size of the workpiece increases, it acts as larger heat sink, thus
requiring more supply of heat for plasticizing of the material. However, it is worth
noting here that higher heat generation is also possible by increasing the rotational
speed of tool as well as decreasing the feed rate. A suitable shoulder diameter results
in splendid joint properties.
Features of the shoulder surface also affect the characteristics of the weld. Traditionally, the shoulder surface can be flat, concave or convex (Fig. 1.6). Among these,
the flat face shoulder is the most simple to manufacture. But the flat shoulder fails to
contain the plasticized material within the weld zone leading to excessive material
flash. Thus, tools with flat shoulder surface are normally operated with a tilt angle.
To solve this issue, the concave shoulder was conceptualized which is found to be
quite effective and is the most commonly used tool nowadays. The third variety can
be tool with convex shoulder which however causes material displacement away
from the pin. The benefit of using tool with convex shoulder is that it can handle
11
with a sintered TiC tool. Also, cooling arrangement was provided so that the excess
heat could be extracted from tool to prevent its damage. Molybdenum-based alloy
tools are employed to weld titanium and steel workpieces. Tool wear is found to be
greater in case of metal matrix composites than soft alloys as the former consisted
of hard abrasive particles. The tool rotational speed as well as its traverse speed can
affect the life of the tool. Tool life is found to be optimum when lower rotational
speed is used with a relatively higher traverse speed.
1.4.2 Geometry of FSW Tool
Heat generation rate, transverse force, torque and the thermo-mechanical aspect of
the experiments depend on the tool geometry. Geometry of the tool also affects the
material (plasticized) flow of the workpiece. The shoulder diameter, shoulder surface,
shape, size, the nature of the tool surface and the pin geometry are the factors which
influence the weld quality. Selection of appropriate shoulder with pin geometry is
again complicated by the following factors [38]:
• Dimension of workpiece which determines its capacity to acts as heat sink.
• Efficiency of the joint required.
• The forces expected on the tool so that the tool can survive mechanical failures.
1.4.2.1 Shoulder Diameter and Surface Features
The diameter of the FSW tool shoulder is particularly an important parameter as
it decides the amount of friction heat produced due to the rubbing of the shoulder
surface with the workpiece surface. The thickness of the workpiece decides the
shoulder diameter of the tool. This is because for good welding, the material should
be softened adequately. Now, as the thickness of the workpiece increases, it requires
more heat for softening. This can only be generated by a larger shoulder diameter.
Moreover, if the size of the workpiece increases, it acts as larger heat sink, thus
requiring more supply of heat for plasticizing of the material. However, it is worth
noting here that higher heat generation is also possible by increasing the rotational
speed of tool as well as decreasing the feed rate. A suitable shoulder diameter results
in splendid joint properties.
Features of the shoulder surface also affect the characteristics of the weld. Traditionally, the shoulder surface can be flat, concave or convex (Fig. 1.6). Among these,
the flat face shoulder is the most simple to manufacture. But the flat shoulder fails to
contain the plasticized material within the weld zone leading to excessive material
flash. Thus, tools with flat shoulder surface are normally operated with a tilt angle.
To solve this issue, the concave shoulder was conceptualized which is found to be
quite effective and is the most commonly used tool nowadays. The third variety can
be tool with convex shoulder which however causes material displacement away
from the pin. The benefit of using tool with convex shoulder is that it can handle