2 Fundamentals of Friction Stir Welding, Its Application, and Advancements
81
2.8.4.3 Micro Friction Stir Welding
When welding is performed for the material with a thickness less than a millimeter
than it is called micro-FSW. This process can be performed for different materials
having a sufficiently lower thickness for similar and dissimilar configuration [177].
Micro-FSW is used for joining micro-mechanical components, electronic components, and micro-electrical components. Optimization of input welding factors i.e.
tool rotation speed, welding speed, axial force, and tool tilt angle is also significant to deliver a good and efficient joint [178]. Huang et al. [179, 180] investigated
μFSW of 0.5 mm thick Al-6061 at a plunge depth of 0.05 mm. Higher or lower
plunging depth leads to various welding defects i.e. unfilled groove, flashes, and
reduction in thickness. An increase in rotational speed from 1500 to 2000 resulted
in enhanced surface properties and eliminated kissing bond defects within the workpiece. Maximum weld efficiency of 90% was obtained. They also investigated a tool
with a concave shoulder and triflat pin for similar configuration. A lower plunge
depth of 0.02 mm resulted in a lack of root penetration. This defect starts appearing
at the bottom of the joint. The possible reason could be unsatisfactory frictional heat
resulting in lowering the thermo-mechanical behavior of the joint. Further increase
in plunging depth to 0.08 mm led to flash formation as a result of higher frictional
heat.
Papaefthymiou et al. [181] welded ZnTiCu sheets of 700μm by micro-Friction Stir
Welding (μFSW). The process temperature reached up to 320ºC which equivalent to
the 0.75T m . Process parameter of 1000 rpm and 318 mm/min provided the refined
grain structure at nugget consisting of equiaxed small grains of (0.17 μm) due to
dynamic recrystallization as compared to 2 μm of base metal. It differs from columnar
large grains formed during the fusion welding. The TiZn 15 β-phase particles are
disintegrated during the μFSW procedure and it shows a reduction in size in the stir
zone. Regardless of the effective μFSW joints, three main defects associated with
input parameters were reported and they are root opening at the bottom, thinning of
the workpiece, and kissing bond.
2.8.4.4 Friction Stir Additive Manufacturing (FSAM)
FSAM process is a non-fusion additive manufacturing process and is a remarkably simple technique. It involves a rotating non-consumable tool designed with
shoulder and pin. The tool is plunged into stacked sheet/plates to be joined and consequently navigated lengthwise the weld line. The multi-layered shape is obtained by
successively stacking layers one onto the other. Therefore, FSAM is a method of
manufacturing parts by the sequential joining of sheet layers to build up an object.
Also, the mechanical property associated with this process is better as the FSAM
occurs in solid-state. Due to this, it has numerous advantages over the other additive
manufacturing process [182].
Palanivel et al. [183] manufactured a multi-layered stack of Mg-based WE43 alloy
using FSAM. This multi-layered stack consists of four sheets each having 1.7 mm
81
2.8.4.3 Micro Friction Stir Welding
When welding is performed for the material with a thickness less than a millimeter
than it is called micro-FSW. This process can be performed for different materials
having a sufficiently lower thickness for similar and dissimilar configuration [177].
Micro-FSW is used for joining micro-mechanical components, electronic components, and micro-electrical components. Optimization of input welding factors i.e.
tool rotation speed, welding speed, axial force, and tool tilt angle is also significant to deliver a good and efficient joint [178]. Huang et al. [179, 180] investigated
μFSW of 0.5 mm thick Al-6061 at a plunge depth of 0.05 mm. Higher or lower
plunging depth leads to various welding defects i.e. unfilled groove, flashes, and
reduction in thickness. An increase in rotational speed from 1500 to 2000 resulted
in enhanced surface properties and eliminated kissing bond defects within the workpiece. Maximum weld efficiency of 90% was obtained. They also investigated a tool
with a concave shoulder and triflat pin for similar configuration. A lower plunge
depth of 0.02 mm resulted in a lack of root penetration. This defect starts appearing
at the bottom of the joint. The possible reason could be unsatisfactory frictional heat
resulting in lowering the thermo-mechanical behavior of the joint. Further increase
in plunging depth to 0.08 mm led to flash formation as a result of higher frictional
heat.
Papaefthymiou et al. [181] welded ZnTiCu sheets of 700μm by micro-Friction Stir
Welding (μFSW). The process temperature reached up to 320ºC which equivalent to
the 0.75T m . Process parameter of 1000 rpm and 318 mm/min provided the refined
grain structure at nugget consisting of equiaxed small grains of (0.17 μm) due to
dynamic recrystallization as compared to 2 μm of base metal. It differs from columnar
large grains formed during the fusion welding. The TiZn 15 β-phase particles are
disintegrated during the μFSW procedure and it shows a reduction in size in the stir
zone. Regardless of the effective μFSW joints, three main defects associated with
input parameters were reported and they are root opening at the bottom, thinning of
the workpiece, and kissing bond.
2.8.4.4 Friction Stir Additive Manufacturing (FSAM)
FSAM process is a non-fusion additive manufacturing process and is a remarkably simple technique. It involves a rotating non-consumable tool designed with
shoulder and pin. The tool is plunged into stacked sheet/plates to be joined and consequently navigated lengthwise the weld line. The multi-layered shape is obtained by
successively stacking layers one onto the other. Therefore, FSAM is a method of
manufacturing parts by the sequential joining of sheet layers to build up an object.
Also, the mechanical property associated with this process is better as the FSAM
occurs in solid-state. Due to this, it has numerous advantages over the other additive
manufacturing process [182].
Palanivel et al. [183] manufactured a multi-layered stack of Mg-based WE43 alloy
using FSAM. This multi-layered stack consists of four sheets each having 1.7 mm