30
S. K. Das et al.
1.7.1 Rotational Speed of Tool/Spindle
It is seen that a variety of parameters affect the FSW joint parameters. Thus, their
interrelationship makes the situation quite complex and difficult to understand.
According to the inventor of FSW Wayne Thomas, the three most important welding
parameters are [64] tool rotational speed (along with the direction, i.e., CW or CCW),
traverse speed of tool and tilt angle of tool. The rotation of the tool has several implications. Firstly, frictional heating from the rubbing of the shoulder surface to the
workpiece is affected. Secondly, the tool rotation also affects the mixing of the softened material. Higher tool rotation results in greater generation of heat and more
material softening. The spread of the HAZ is also quite an extent affected by the tool
rotation. The spindle speed depends on the material type as well as thickness of the
workpiece being used.
1.7.2 Traverse Speed
Tool traverse speed also impacts the weld characteristics. Material is transferred from
the leading edge to the trailing edge due to the translation of the tool. Traverse speed
along with tool rotational speed decides whether enough heat input is being supplied
to the processed material which is favorable for development of desired metallurgical
and mechanical properties. Lower welding speed generates excessive heat and makes
the welding slow. At high speed, heat generation is low which may not be desirable
as it puts higher loads on the front side of the advancing tool (material is not softened
enough). Thus, an optimum traverse speed needs to be selected based on a particular
case of FSW depending on the type of material and thickness of the workpiece being
used. A smooth material flow around the tool pin is always desired. In fact the choice
of feed rate along with rotational speed decide the heat generation and ensure the
material flow which also leads to reduced forces acting on the tool. Stevenson et al.
[61] identify the high cost and low lifespan of FSW tools as well as low welding
speed as the major problems resisting commercialization of FSW for steel.
1.7.3 Tilt Angle of Tool
Tool tilt angle is another important FSW process parameter which influences the
weld characteristics. The angle of inclination of spindle w.r.t. the workpiece surface
in case of linear welding is known as the title of the tool. The tool is normally given
a backward tilt (refer Fig. 1.2b) which gives more open space in front of the tool
while forging of the workpiece material is done by the back of the shoulder behind
the pin. This is particularly true for featureless shoulders, which because of the tilt,
can effectively contain the stirred material. Transfer of material from leading to the
S. K. Das et al.
1.7.1 Rotational Speed of Tool/Spindle
It is seen that a variety of parameters affect the FSW joint parameters. Thus, their
interrelationship makes the situation quite complex and difficult to understand.
According to the inventor of FSW Wayne Thomas, the three most important welding
parameters are [64] tool rotational speed (along with the direction, i.e., CW or CCW),
traverse speed of tool and tilt angle of tool. The rotation of the tool has several implications. Firstly, frictional heating from the rubbing of the shoulder surface to the
workpiece is affected. Secondly, the tool rotation also affects the mixing of the softened material. Higher tool rotation results in greater generation of heat and more
material softening. The spread of the HAZ is also quite an extent affected by the tool
rotation. The spindle speed depends on the material type as well as thickness of the
workpiece being used.
1.7.2 Traverse Speed
Tool traverse speed also impacts the weld characteristics. Material is transferred from
the leading edge to the trailing edge due to the translation of the tool. Traverse speed
along with tool rotational speed decides whether enough heat input is being supplied
to the processed material which is favorable for development of desired metallurgical
and mechanical properties. Lower welding speed generates excessive heat and makes
the welding slow. At high speed, heat generation is low which may not be desirable
as it puts higher loads on the front side of the advancing tool (material is not softened
enough). Thus, an optimum traverse speed needs to be selected based on a particular
case of FSW depending on the type of material and thickness of the workpiece being
used. A smooth material flow around the tool pin is always desired. In fact the choice
of feed rate along with rotational speed decide the heat generation and ensure the
material flow which also leads to reduced forces acting on the tool. Stevenson et al.
[61] identify the high cost and low lifespan of FSW tools as well as low welding
speed as the major problems resisting commercialization of FSW for steel.
1.7.3 Tilt Angle of Tool
Tool tilt angle is another important FSW process parameter which influences the
weld characteristics. The angle of inclination of spindle w.r.t. the workpiece surface
in case of linear welding is known as the title of the tool. The tool is normally given
a backward tilt (refer Fig. 1.2b) which gives more open space in front of the tool
while forging of the workpiece material is done by the back of the shoulder behind
the pin. This is particularly true for featureless shoulders, which because of the tilt,
can effectively contain the stirred material. Transfer of material from leading to the