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D. Mishra et al.
obtained from these instruments are accurate and usually depend upon the precision
of the machine. However, they are usually destructive in nature, time-consuming
and are carried out offline. As such, they do not help in getting inferences about the
quality of the weld in real time.
8.3.1.1 Non-Destructive Techniques
An alternative to the above is the use of non-destructive testing (NDT) techniques,
such as visual sensing, dye penetrant, magnetic particle testing, radiography, ultrasonic testing, which are being employed for quality monitoring of the welded samples
[21]. The visual sensing makes use of instruments such as magnifying glasses, endoscopes, profilers to measure the surface conditions, such as weld dimensions, surface
defect and alignment. Penetrant testing and magnetic particle testing are two other
techniques used for identifying the surface anomalies in welded samples, which are
invisible to bare eyes. The penetrant testing makes use of the capillary properties
of liquid where the liquid with low surface tension infiltrates into clean and dry
surface. A series of steps are applied in this technique which involves: pre-cleaning
of the job, application of penetrant and developer, and post-cleaning of the job. The
magnetic particle testing is applicable for ferromagnetic materials only. Here, the
weld surface is magnetized by using a specialized powder, usually iron powder, and
the observation is to identify the area where the powder gathers itself. This indicates
possibility of defects being present in the sample. This is because of flux leakage at
the spot of crack present in the welded sample, which makes the powder gather over
that spot, in the presence of magnetic field. A major drawback of these techniques
is their inability to detect the discontinuities inside the welded area. Though they
are non-destructive in nature, they work offline, and thus, cannot fulfil the aim of
Industry 4.0.
The challenge of identifying discontinuities within a material has been resolved
by radiography technique. The X-ray radioactivity system has been one of the widely
adopted techniques for the identification of the welding defects because of the ability
of the X-rays or gamma rays in penetrating into the weldments. The entire weld
surface is covered with a film, and the X-rays or gamma rays from a suitable radioactive source are allowed to pass through the welded sample. With the presence of
cavity, hole or void in the welded sample, the radiation being received over the film
varies, and this film is then processed and viewed under a special light emitting
device to identify the degrees of variations. The major limitation of this method
includes the execution of this activity in controlled conditions, i.e. because of the
harmful radiations to humans, it is required to seal a major part of the area where
the test would be carried out. Another limitation is that their inability to be applied
in real-time application. Computed tomography is another such method which also
utilizes the X-rays for detection of the welding defects.
An article reports the use of NDT techniques such as visual testing, penetrant
testing and ultrasonic testing in the arc welding technique for monitoring of the
welded samples, and ultrasonic testing was found to be more suitable because of its
D. Mishra et al.
obtained from these instruments are accurate and usually depend upon the precision
of the machine. However, they are usually destructive in nature, time-consuming
and are carried out offline. As such, they do not help in getting inferences about the
quality of the weld in real time.
8.3.1.1 Non-Destructive Techniques
An alternative to the above is the use of non-destructive testing (NDT) techniques,
such as visual sensing, dye penetrant, magnetic particle testing, radiography, ultrasonic testing, which are being employed for quality monitoring of the welded samples
[21]. The visual sensing makes use of instruments such as magnifying glasses, endoscopes, profilers to measure the surface conditions, such as weld dimensions, surface
defect and alignment. Penetrant testing and magnetic particle testing are two other
techniques used for identifying the surface anomalies in welded samples, which are
invisible to bare eyes. The penetrant testing makes use of the capillary properties
of liquid where the liquid with low surface tension infiltrates into clean and dry
surface. A series of steps are applied in this technique which involves: pre-cleaning
of the job, application of penetrant and developer, and post-cleaning of the job. The
magnetic particle testing is applicable for ferromagnetic materials only. Here, the
weld surface is magnetized by using a specialized powder, usually iron powder, and
the observation is to identify the area where the powder gathers itself. This indicates
possibility of defects being present in the sample. This is because of flux leakage at
the spot of crack present in the welded sample, which makes the powder gather over
that spot, in the presence of magnetic field. A major drawback of these techniques
is their inability to detect the discontinuities inside the welded area. Though they
are non-destructive in nature, they work offline, and thus, cannot fulfil the aim of
Industry 4.0.
The challenge of identifying discontinuities within a material has been resolved
by radiography technique. The X-ray radioactivity system has been one of the widely
adopted techniques for the identification of the welding defects because of the ability
of the X-rays or gamma rays in penetrating into the weldments. The entire weld
surface is covered with a film, and the X-rays or gamma rays from a suitable radioactive source are allowed to pass through the welded sample. With the presence of
cavity, hole or void in the welded sample, the radiation being received over the film
varies, and this film is then processed and viewed under a special light emitting
device to identify the degrees of variations. The major limitation of this method
includes the execution of this activity in controlled conditions, i.e. because of the
harmful radiations to humans, it is required to seal a major part of the area where
the test would be carried out. Another limitation is that their inability to be applied
in real-time application. Computed tomography is another such method which also
utilizes the X-rays for detection of the welding defects.
An article reports the use of NDT techniques such as visual testing, penetrant
testing and ultrasonic testing in the arc welding technique for monitoring of the
welded samples, and ultrasonic testing was found to be more suitable because of its