Friction Stir Additive Manufacturing—A Review
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Ultrasonic seam welding was the first process to be deliberated for additive manufacturing which piloted the development of a direct metal manufacturing process,
“ultrasonic consolidation” in 2001 [33]. Researchers at Boeing have manufactured
large complex structures from simple building blocks through linear friction welding
at Boeing [34]. Airbus [35] and Boeing [36] claimed that the technology is capable
of addressing two of the specified challenges, (a) achieving high throughput leading
to faster production rates and (b) less material wastage [37].
The friction stir-based techniques show great potential in the field of additive
manufacturing among other solid-state techniques. As they use mechanical energy
to bond the material together, they tend to be more energy efficient. Further, they
are not limited by the size of material and have a vast number of different processes
which can be customized according to the need of the operation and the type of
material. Moreover, they show the highest synergy with conventional techniques and
are very suitable for the development of hybrid processes.
2.2 Friction Stir-Based Welding Joining Techniques
All friction stir-based technologies can be classified into two major categories on
the basis of their application, welding and processing. The various techniques are
classified according to their applications under welding and processing categories and
are shown in Fig. 2. The welding techniques are fundamentally employed for material
fusing and joining, while processing techniques are undertaken for applications that
are intended at improving the quality of the material in terms of its mechanical,
chemical and physical properties [38–40].
The friction stir equipment constitutes of a rotating tool also called the shoulder
and has a protruding pin in most of the technologies listed in Fig. 2. The tool is used
to generate frictional heat required for the plastic deformation of the material. The
tool rotates and translates relative to the substrate with a substantial axial pressure
that generates significant heat due to friction at the interface. As the heat is generated
through friction produced by stirring of the tool, this family of operations is widely
known as friction stir technology. The frictional heat ensures the development of a
regional zone that is distinct from the tool as well as the workpiece which is known
as the ‘third body region’ [42]. This plastically deformed region is characterized by
solid state displaying (1) three-dimensional fluidity, (2) relatively high viscosity and
(3) low flow stress [41]. These characteristics are specific only to the local third body
region and allow the material to flow and mix with other material in this region. These
local regions develop at temperatures ranging from the recrystallization temperature
and melting point of the material that is deformed. Figure 3a, b show the welding
positions and location of the third body regions in the friction stir operations using
non-consumable and consumable tools, respectively.
The third body region is produced either on the workpiece when the tool is nonconsumable or on the tool when the tool is consumable during the operation. The tool
is the chief part of the process because it generates the required frictional heat. Further,
17
Ultrasonic seam welding was the first process to be deliberated for additive manufacturing which piloted the development of a direct metal manufacturing process,
“ultrasonic consolidation” in 2001 [33]. Researchers at Boeing have manufactured
large complex structures from simple building blocks through linear friction welding
at Boeing [34]. Airbus [35] and Boeing [36] claimed that the technology is capable
of addressing two of the specified challenges, (a) achieving high throughput leading
to faster production rates and (b) less material wastage [37].
The friction stir-based techniques show great potential in the field of additive
manufacturing among other solid-state techniques. As they use mechanical energy
to bond the material together, they tend to be more energy efficient. Further, they
are not limited by the size of material and have a vast number of different processes
which can be customized according to the need of the operation and the type of
material. Moreover, they show the highest synergy with conventional techniques and
are very suitable for the development of hybrid processes.
2.2 Friction Stir-Based Welding Joining Techniques
All friction stir-based technologies can be classified into two major categories on
the basis of their application, welding and processing. The various techniques are
classified according to their applications under welding and processing categories and
are shown in Fig. 2. The welding techniques are fundamentally employed for material
fusing and joining, while processing techniques are undertaken for applications that
are intended at improving the quality of the material in terms of its mechanical,
chemical and physical properties [38–40].
The friction stir equipment constitutes of a rotating tool also called the shoulder
and has a protruding pin in most of the technologies listed in Fig. 2. The tool is used
to generate frictional heat required for the plastic deformation of the material. The
tool rotates and translates relative to the substrate with a substantial axial pressure
that generates significant heat due to friction at the interface. As the heat is generated
through friction produced by stirring of the tool, this family of operations is widely
known as friction stir technology. The frictional heat ensures the development of a
regional zone that is distinct from the tool as well as the workpiece which is known
as the ‘third body region’ [42]. This plastically deformed region is characterized by
solid state displaying (1) three-dimensional fluidity, (2) relatively high viscosity and
(3) low flow stress [41]. These characteristics are specific only to the local third body
region and allow the material to flow and mix with other material in this region. These
local regions develop at temperatures ranging from the recrystallization temperature
and melting point of the material that is deformed. Figure 3a, b show the welding
positions and location of the third body regions in the friction stir operations using
non-consumable and consumable tools, respectively.
The third body region is produced either on the workpiece when the tool is nonconsumable or on the tool when the tool is consumable during the operation. The tool
is the chief part of the process because it generates the required frictional heat. Further,