X-ray Welding Machine

X-ray welding inspection and Ultrasonic inspection are the two most popular forms of weld inspection. Both are non-destructive testing which means that samples can still be used as final products if they pass the weld test. This reason explains why they are both popular.

While X-ray inspection is a radiographic form of weld test that works by emitting radioactive beams on test samples that are then absorbed by these objects, the rate of absorption of these X-rays is determined by the thickness of the test samples and the type of flaws detected.

However, Ultrasonic weld inspection relies on the velocity of sound travelling back after hitting the test samples. This method can also detect internal, external, and awkwardly shaped objects for flaws like the X-ray inspection method.

X-ray welding is the latest advance in welding technology. Similar to electron beam welding and laser beam welding, a high-powered focused X-ray beam is used to produce thermal heat. It will initiate the melting of the metal to form the weld once it gets cooled. Hence, it is very fast and stable. It is also possible to increase the accuracy of the weld due to this high-powered focused X-ray beam.

Still, there is a limitation. In case the X-ray beam is not adequate to penetrate the metal, it will then form a molten metal pool on the surface.

To overcome this limitation, a keyhole is created in the metal joint for heat penetration. This is where X-ray welding inspection is done to assess the quality of welds whether they are strong or not. It can also detect flaws during weld manufacturing as well.

 

There are varied aspects in detecting of lithium batteries:

• Checking the imperfection by measuring missing material, foreign material inclusions, and overhangs
• The performance of the battery can be enhanced by correlating it with the microstructure and design.
• Analysis of the failed battery cells through visual interpretation
• Usually, lithium sheets are rolled together to create a battery. Using CT (computed tomography) based X-ray machine, it is possible to determine any nick as well as check its length, twist, and fitting.
• Identify any sign of voids, holes, or the presence of any misalignment in the stacked parts.
• Detect insulation layer, faulty assemblies, fuses, welds, broken cables, etc.
• Measures the internal structure, linear distances, and alignments precisely
• Check if the lithium battery is fully functional
• Predicts if there is any chance of short circuit

 

Characteristics	X-ray welding inspection	Ultrasonic testing
Speed and cost	Comparatively slower and expensive	Comparatively faster and cheaper
Source	X-rays emitted by an X-ray tube	Sound waves emitted by laser at high frequency
Sample assessment	All material types	Only metals, plastics, ferrous as well as nonferrous substances
Principle	When X-rays are penetrated through the test weld sample, its internal structure is displayed in the film. There will be differences in energy absorption depending on both thickness and density. Hence, the region of the sample where the energy is not absorbed due to defects will be found darker in the film (Figure 18).	When ultrasonic energy is passed on the test sample, it diffuses with insignificant loss of energy. If there is any defect, these waves may reflect back to the point of origin that gets displayed on the monitor. By measuring the amplitude of the reflected pulse, UT can locate and examine the defects (Figure 19).
Geometry	Suitable to assess complex welds	Require special probes in varied geometries for weld assessment
Types of flaws detected	Surface and subsurface flaws, but not fine defects	Surface, subsurface, thicker section, deep finer planer or linear defects, lamination-like flaws, submerged-arc weld, control spot welding, and friction stir weld
Assessment	Can automatically assess the position and type of flaws from both sides	Can assess the accurate position, location, length, and type of the flaw as well as the thickness of the test sample from one side only
Result storage	Permanent	Temporary
Disadvantages	Poor resolution and wrong flaw size Easier to interpret a 2-D image of the discontinuity compared to a 3-D image. The film is so delicate to tolerate temperature, humidity, and pressure. Need access to both sections of the test sample.	The surface must be available for the transmission of ultrasound waves. You need a coupling medium to boost the diffusion of sound energy into the sample. You need reference standards for equipment calibration and flaw characterization. Tougher to evaluate cast iron and other coarse-grained metals because of an increase in noise signals with less sound transmission. It is also difficult to assess thin, rough, non-homogenous, and irregularly designed tiny samples. Need access to both ends or sections of the test sample.

Inspection of welded joints is a necessary activity to ascertain the quality of the welding job and to guarantee that it meets design specifications.

Quality assurance is fundamental in the manufacture of products. Since welding is used in the manufacture of most products, it follows that inspection of the welded portion of the product is critical to ensure that the product is quality.

Also, flaws like cracks, porosity, and spatters are common defects that accompany welding jobs and can significantly reduce the quality of the product. Only through quality inspection of these weld jobs can these defects be identified and corrected.

By visual inspection, a strong weld will have no sign of overheating but with adequate weld penetration into all openings. 

Also, the welds cover the welded points in uniform width without necessarily being straight. Furthermore, inclusion, gas pockets, and porosity are the most common defects in welding jobs in a strong weld.

However, assessment of the internal consistencies on the weld is also essential, and this can only be carried out using a non-destructive inspection like X-ray welding inspection.

An X-ray welding machine with a source for emitting radiation energy is used to detect weld faults using X-rays. This machine releases X-ray energy that penetrates the welded joints, including the internal parts of the welds.

An image forms on the screen after the X-ray energy penetrates the object, and the residual radiation passes on to the screen to form the image. 

The areas with the highest energy absorption appear white on the screen, while those with low absorption appear dark. Hence, a consistent welded joint will appear white while welding errors like porosity occur as dark spots.

X-ray equipment determines the size and of the presence of flaws in the given sample weld during its manufacture. The more the weld size, the more it can tolerate stress. 

Here is the list of varied weld defects:

1. Cold lap/ cold shuts/ lack of fusion – Here, the weld filler metal inappropriately merges with the base metal. 

► Causes: 

• Poor welding technique
• Presence of a very wide weld joint
• Too low welding voltage
• Very low travel speed
• Attempt to make a large weld in a single pass

 

 

2. Porosity – Occurrence of dark round or irregular spots singularly, in rows, or in groups on a radiograph.  

► Causes:

• Gas entrapment in the solidifying metal
• Failure to clean the base metal
• Failure to shield the weld from atmospheric contamination
• Striking with a long arc

 

 

3. Cluster porosity – It is similar to the porosity issue. But the spots will group together very closely.

► Cause: Vaporized constituents are entrapped in the molten weld during solidification

 

 

4. Slag inclusions – Occurrence of dark, jagged asymmetrical shapes on a radiograph.

► Causes:

• Entrapment of non-metallic solid material in weld metal or between base metal and weld
• Use of an improper welding angle with low current
• Letting the quick cooling of the weld pool
• Use of an extreme high weld speed
• Improper base metal cleaning before welding begins

 

 

5. Incomplete penetration/lack of penetration – It is one of the most offensive flaws where the weld does not penetrate the joint and leads to the appearance of cracks.

► Causes:

• Use of improper welding techniques like arc misdirect
• Failure of thick metal preheating
• Insufficient current for weld penetration
• Poorly designed joint

 

 

6. Incomplete fusion – Here, the weld filler inappropriately fuses with the base metal. 

► Causes:

• Use of a wrong electrode angle
• Following wrong welding process
• Failure of slag removal on joint surfaces
• Failure of oxide layer break up on base metals

 

 

7. Internal concavity or suck back – Here, the weld metal contracts as it cools and draws up into the weld’s root of the weld.

 

 

8. Internal or root undercut – Here, the base metal damage occurs next to the weld’s root.

 

 

9. External or crown undercut – Here, the base metal damage occurs next to the weld’s crown.

 

 

10. External undercut

► Causes

• Failure to clean rust from the metal
• Use of a damp electrode in small angle
• Excess current use
• Following poor welding techniques
• Use of an incorrect filler

 

11. Offset or mismatch – It occurs on the surface due to the improper alignment of two pieces while welding together.

 

 

12. Inadequate weld reinforcement – Here, the weld metal’s thickness is less than base material’s thickness.

 

 

13. Excess weld reinforcement – Here, weld metal is added more in the weld area.

 

 

14. Cracks – It looks as jagged with very faint irregular lines.

► Causes:

• Base metal contamination
• Poor joint design
• Use of hydrogen during ferrous metal welding
• High welding speed and low current
• Failure of metal preheating before welding begins
• Shrinkage in solidification leading to a residual stress formation

 

 

15. Tungsten inclusion – Here, tungsten traps in the weld if welding is done improperly. It looks lighter with a distinct outline radiographically.

► Cause: Molten weld or filler in contact with tungsten electrode’s tip

 

 

16. Oxide inclusion – Oxides are seen on the surface of the material being welded. It appears dark and irregular radiographically.

 

 

17. Burn-Through – It occurs when surplus heat causes weld metal to enter the weld zone. These lumps of metal sag create a thick glob (icicles) on the backside of the weld. 

 

 

18. Whiskers – These are short weld electrode wires found within the weld or on its top or bottom surface.