4 An Application from a Defect—A Friction …
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Though the process was primarily developed to join aluminium alloys, the benefits
of FSW established its applicability to produce monolithic joints, such as Mg–Mg,
Cu–Cu, etc., and to join dissimilar alloys, including Al-steel and Mg-steel. Al-steel,
Mg-steel welded parts have considerable applications in the aerospace sector and
automobile industries.
The development of FSW has proven to be transformative in paving the way
for lightweight Al and Mg alloys in various industries. Replacing metals such as
steel with lightweight materials has significantly reduced the weight of different
machinery parts. For example, by substituting a conventional steel subframe of a
vehicle’s chassis with a lap welded Al-Steel subframe, Honda achieved a weight
reduction of 25% [3].
In this century, the FSW process has been extensively researched all over the
globe. This fact has resulted in the improvement of the technique and widespread
use in several new industries. The contemporary applications of FSW include aircraft
components, shipbuilding, rail carriages, bridge components, pressure vessels, etc.
NASA and SpaceX have broadly used FSW in various aerospace applications [4].
4.1.2 FSW Process
The FSW process is a solid-state welding process where the materials are welded well
below their melting point, eliminating numerous defects associated with a molten
state. FSW is performed with a non-consumable rotating tool with hardness and
strength higher than the materials to be joined. A shoulder and a pin are the essential
parts of the tool used during welding. The tool up to a certain depth of the shoulder
plunges into the part to be welded and traverses along the joint line. Frictional heat
generated because of the contact of the shoulder and pin with the workpiece surface is
primarily used to soften the material. The severe plastic deformation (SPD) induced
by the movement of the pin and the lower portion of the shoulder inside the material aids in supplementary heating and mixing of the material, providing successful
welding. Throughout the process, the plunging force on the softened material given
by the shoulder restrains its motion outwards, thus sealing the void created by the pin,
forming a macro defect-free joint. Being a type of friction welding, the workpieces
joined by FSW should be in close contact with each other, and specially designed
fixtures are used to accomplish this.
A vertical milling machine was conventionally used to conduct FSW by mounting
the FSW tool on the spindle. More recently, FSW machines with higher degrees of
freedom and simple human-machine interface (HMI) makes it an efficient adaptive
process for the industries. The introduction of robotic FSW machines will enhance
the productivity of the process to a higher level.
133
Though the process was primarily developed to join aluminium alloys, the benefits
of FSW established its applicability to produce monolithic joints, such as Mg–Mg,
Cu–Cu, etc., and to join dissimilar alloys, including Al-steel and Mg-steel. Al-steel,
Mg-steel welded parts have considerable applications in the aerospace sector and
automobile industries.
The development of FSW has proven to be transformative in paving the way
for lightweight Al and Mg alloys in various industries. Replacing metals such as
steel with lightweight materials has significantly reduced the weight of different
machinery parts. For example, by substituting a conventional steel subframe of a
vehicle’s chassis with a lap welded Al-Steel subframe, Honda achieved a weight
reduction of 25% [3].
In this century, the FSW process has been extensively researched all over the
globe. This fact has resulted in the improvement of the technique and widespread
use in several new industries. The contemporary applications of FSW include aircraft
components, shipbuilding, rail carriages, bridge components, pressure vessels, etc.
NASA and SpaceX have broadly used FSW in various aerospace applications [4].
4.1.2 FSW Process
The FSW process is a solid-state welding process where the materials are welded well
below their melting point, eliminating numerous defects associated with a molten
state. FSW is performed with a non-consumable rotating tool with hardness and
strength higher than the materials to be joined. A shoulder and a pin are the essential
parts of the tool used during welding. The tool up to a certain depth of the shoulder
plunges into the part to be welded and traverses along the joint line. Frictional heat
generated because of the contact of the shoulder and pin with the workpiece surface is
primarily used to soften the material. The severe plastic deformation (SPD) induced
by the movement of the pin and the lower portion of the shoulder inside the material aids in supplementary heating and mixing of the material, providing successful
welding. Throughout the process, the plunging force on the softened material given
by the shoulder restrains its motion outwards, thus sealing the void created by the pin,
forming a macro defect-free joint. Being a type of friction welding, the workpieces
joined by FSW should be in close contact with each other, and specially designed
fixtures are used to accomplish this.
A vertical milling machine was conventionally used to conduct FSW by mounting
the FSW tool on the spindle. More recently, FSW machines with higher degrees of
freedom and simple human-machine interface (HMI) makes it an efficient adaptive
process for the industries. The introduction of robotic FSW machines will enhance
the productivity of the process to a higher level.