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Remanufacturing and Advanced Machining
• Structural steels, alloy steels, non-ferrous metals, and even gas-sensitive
special metals can be successfully welded.
Since vacuum limitation is usually mentioned among the main drawbacks of electron beam welding, it should be noted that processes without vacuum are now available and gaining new industrial applications (Middeldorf and von Hofe, 2008).
Laser welding has gained great popularity as a promising joining technology with
high quality, high precision, high performance, high speed, good flexibility, and low
deformation or distortion, and the number of its applications is increasing due to
ease of use with robots, reduced man-power, full automation, systematization, production lines, etc. (Katayama, 2018). Its main advantage is high energy density and
hence the ability to melt the area close to joint edges without affecting a large area
of the workpiece. Other benefits are high welding speed, achievability of a narrow
and deep weld, good mechanical properties, and low structural distortion (Xiao and
Zhang, 2014).
There are also advantages of laser compared to conventional welding in respect
of joining of dissimilar materials (Martinsen et al., 2015). Laser welding is able to
fuse dissimilar metals and alloys and overcome the problems with large differences
in thermal conductivity. The small size and accuracy of the beam provide control
of the microstructure, and a small heat-affected zone results in rapid solidification
and less grain growth. Using through-transmission laser welding (TTLW), where
the upper part is transparent for the laser beam and the lower part absorbs the laser
energy, thermoplastic polymers can be welded, as well as dissimilar polymers, and
even polymer–metal bonds are possible.
Friction stir welding (FSW) is a solid-state process where a rotating stirring tool
softens a material with frictional heat and welded materials are mechanically stirred
and bonded (Martinsen et al., 2015). The process minimizes brittle intermetallic
phases, metallurgical incompatibility, differences in melting points, and thermal
mismatch. The friction stir process family includes friction stir processing, friction stir casting, friction stir micro forming, friction stir powder processing, friction
stir channeling, and friction stir spot welding. Among the advantages of FSW are
its environmental friendliness, application of non-consumable tool, requirement of
little or no post-processing, removal of residual stresses, corrosion resistance; the
process doesn’t require the addition of a filler material or oxide removal, cost effectiveness, and the possibility to create dissimilar material joints. Middeldorf and von
Hofe (2008) emphasize that due to low temperatures, significantly below the melting
point, only minor metallurgical alterations take place in joint materials. However,
large forces applied to joint details require additional strong equipment, which may
be considered a disadvantage of FSW.
Structural adhesive bonding is a joining technology with many advantages, especially in aerospace applications in the context of structural repair, a major challenge with advanced composites because of their inherent complex damage behavior
(Katnam et al., 2013). In their review, Martinsen et al. (2015) listed several theoretical mechanisms of adhesion:
Remanufacturing and Advanced Machining
• Structural steels, alloy steels, non-ferrous metals, and even gas-sensitive
special metals can be successfully welded.
Since vacuum limitation is usually mentioned among the main drawbacks of electron beam welding, it should be noted that processes without vacuum are now available and gaining new industrial applications (Middeldorf and von Hofe, 2008).
Laser welding has gained great popularity as a promising joining technology with
high quality, high precision, high performance, high speed, good flexibility, and low
deformation or distortion, and the number of its applications is increasing due to
ease of use with robots, reduced man-power, full automation, systematization, production lines, etc. (Katayama, 2018). Its main advantage is high energy density and
hence the ability to melt the area close to joint edges without affecting a large area
of the workpiece. Other benefits are high welding speed, achievability of a narrow
and deep weld, good mechanical properties, and low structural distortion (Xiao and
Zhang, 2014).
There are also advantages of laser compared to conventional welding in respect
of joining of dissimilar materials (Martinsen et al., 2015). Laser welding is able to
fuse dissimilar metals and alloys and overcome the problems with large differences
in thermal conductivity. The small size and accuracy of the beam provide control
of the microstructure, and a small heat-affected zone results in rapid solidification
and less grain growth. Using through-transmission laser welding (TTLW), where
the upper part is transparent for the laser beam and the lower part absorbs the laser
energy, thermoplastic polymers can be welded, as well as dissimilar polymers, and
even polymer–metal bonds are possible.
Friction stir welding (FSW) is a solid-state process where a rotating stirring tool
softens a material with frictional heat and welded materials are mechanically stirred
and bonded (Martinsen et al., 2015). The process minimizes brittle intermetallic
phases, metallurgical incompatibility, differences in melting points, and thermal
mismatch. The friction stir process family includes friction stir processing, friction stir casting, friction stir micro forming, friction stir powder processing, friction
stir channeling, and friction stir spot welding. Among the advantages of FSW are
its environmental friendliness, application of non-consumable tool, requirement of
little or no post-processing, removal of residual stresses, corrosion resistance; the
process doesn’t require the addition of a filler material or oxide removal, cost effectiveness, and the possibility to create dissimilar material joints. Middeldorf and von
Hofe (2008) emphasize that due to low temperatures, significantly below the melting
point, only minor metallurgical alterations take place in joint materials. However,
large forces applied to joint details require additional strong equipment, which may
be considered a disadvantage of FSW.
Structural adhesive bonding is a joining technology with many advantages, especially in aerospace applications in the context of structural repair, a major challenge with advanced composites because of their inherent complex damage behavior
(Katnam et al., 2013). In their review, Martinsen et al. (2015) listed several theoretical mechanisms of adhesion: