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N. Bhardwaj et al.
direction. On the retreating side (RS), the traverse velocity and tangential velocity
are in opposite directions. As the relative velocity between the tool and workpiece is
higher on the advancing side, it shows higher temperature [20, 49, 71]. This results
in microstructural differences and difference in physical properties [54]. Thus, the
thermal cycle and stresses in various parts of the weld are important aspects, and
modeling can help in predicting the quality of weld produced.
3.2.2 Parameters Affecting FSW Process
The important parameters that affect the weld quality in FSW are traverse speed,
rotational speed, tool tilt angle, plunge depth and tool offset. Modeling of the FSW
process can be helpful in determining the optimum combination of these process
parameters for producing quality welds with minimum defects. Rotational speed
determines the amount of heat input into the weld and also affects the plasticization
of the workpiece material. Traverse speed of the tool determines the peak temperature
produced in the weld. Greater the traverse speed, less is the time for heat to dissipate
into the workpiece. Plunge depth is an important parameter controlling the depth of
the stir zone as well as the forging force on the joint. The forging force is also affected
by the tool tilt angle. On the other hand, tool offset determines the heat distribution
in the joint, especially in case of dissimilar material welding.
3.2.3 Defects in Welding
The formation of defect-free welds depends on the amount of heat input during FSW.
Improper process parameters cause upward movement of material from the lower
sheet into the upper sheet, especially in welding of dissimilar materials. This is known
as hook defect formed mainly at the thermo-mechanically affected zone (TMAZ).
Deficient material consolidation due to low heat input results in tunneling defect left
behind the pin as the tool moves forward. Low heat input resulting in ineffective
plastic deformation also causes kissing bond defect, where there is no metallurgical
bond between interfaces. Kissing bonds mainly appear in the stirring zone (SZ). On
the other hand, incomplete root penetration is caused due to insufficient tool plunge
depth, inappropriate tool design or inadequate length of pin. The understanding of
the thermal cycle, stresses and material flow using modeling can greatly help in
minimizing these defects.
N. Bhardwaj et al.
direction. On the retreating side (RS), the traverse velocity and tangential velocity
are in opposite directions. As the relative velocity between the tool and workpiece is
higher on the advancing side, it shows higher temperature [20, 49, 71]. This results
in microstructural differences and difference in physical properties [54]. Thus, the
thermal cycle and stresses in various parts of the weld are important aspects, and
modeling can help in predicting the quality of weld produced.
3.2.2 Parameters Affecting FSW Process
The important parameters that affect the weld quality in FSW are traverse speed,
rotational speed, tool tilt angle, plunge depth and tool offset. Modeling of the FSW
process can be helpful in determining the optimum combination of these process
parameters for producing quality welds with minimum defects. Rotational speed
determines the amount of heat input into the weld and also affects the plasticization
of the workpiece material. Traverse speed of the tool determines the peak temperature
produced in the weld. Greater the traverse speed, less is the time for heat to dissipate
into the workpiece. Plunge depth is an important parameter controlling the depth of
the stir zone as well as the forging force on the joint. The forging force is also affected
by the tool tilt angle. On the other hand, tool offset determines the heat distribution
in the joint, especially in case of dissimilar material welding.
3.2.3 Defects in Welding
The formation of defect-free welds depends on the amount of heat input during FSW.
Improper process parameters cause upward movement of material from the lower
sheet into the upper sheet, especially in welding of dissimilar materials. This is known
as hook defect formed mainly at the thermo-mechanically affected zone (TMAZ).
Deficient material consolidation due to low heat input results in tunneling defect left
behind the pin as the tool moves forward. Low heat input resulting in ineffective
plastic deformation also causes kissing bond defect, where there is no metallurgical
bond between interfaces. Kissing bonds mainly appear in the stirring zone (SZ). On
the other hand, incomplete root penetration is caused due to insufficient tool plunge
depth, inappropriate tool design or inadequate length of pin. The understanding of
the thermal cycle, stresses and material flow using modeling can greatly help in
minimizing these defects.