PPT3_Welding.ppt

1. COURSE: MANUFACTURING PROCESSS
CODE: AMEC11
VI Semester
Regulation: UG20
Institute of Aeronautical Engineering
(Autonomous)
Dundigal, Hyderabad- 500043
G.Praveen Kumar
Assistant Professor
Mechanical Engineering
Prepared by

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Heat Affected Zone
The heat affected zone (HAZ) is a non-melted area of metal that
has undergone changes in material properties as a result of
being exposed to high temperatures. These changes in material
property are usually as a result of welding or high-heat cutting.
The HAZ is the area between the weld or cut and the base
(unaffected), parent metal.
The HAZ area can vary in severity and size depending on the
properties of the materials, the concentration and intensity of
the heat, and the welding or cutting process used.

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Heat Affected Zone

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Heat Affected Zone
What are the Causes of Heat-Affected Zones?
1. The heating associated with welding and/or cutting generally
uses temperatures up to and often exceeding the
temperature of melting of the material in question,
depending on the welding process used.
2. However, the heating and cooling thermal cycle associated
with these processes is different to whatever processing has
occurred with the parent material previously. This leads to a
change in microstructure associated with the heating and
cooling process.

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Heat Affected Zone
3. The size of a heat affected zone is influenced by the level of
thermal diffusivity, which is dependent on the thermal
conductivity, density and specific heat of a substance as well
as the amount of heat going in to the material.
4. Those materials with a high level of thermal diffusivity are
able to transfer variations of heat faster, meaning they cool
quicker and, as a result, the HAZ width is reduced.
5. On the other hand, those materials with a lower coefficient
retain the heat, meaning that that the HAZ is wider.
6. Generally speaking, the extension of the HAZ is dependent on
the amount of heat applied, the duration of exposure to heat
and the properties of the material itself. When a material is
exposed to greater amounts of energy for longer periods the
HAZ is larger.

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Heat Affected Zone
7. With regard to welding procedures, those processes with low
heat input will cool faster, leading to a smaller HAZ, whereas
high heat input will have a slower rate of cooling, leading to a
larger HAZ in the same material.
8. In addition, the size of the HAZ also grows as the speed of the
welding process decreases. Weld geometry is another factor
that plays a role in the HAZ size, as it affects the heat sink, and a
larger heat sink generally leads to faster cooling.
9. High temperature cutting operations can also cause a HAZ and,
similarly to welding procedures, those processes that operate at
higher temperatures and slow speeds tend to create a larger
HAZ, while lower temperature or higher speed cutting processes
tend to reduce the HAZ size.

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Heat Affected Zone
10. Different cutting processes have differing effects on the HAZ,
regardless of the material being cut.
11. For example, shearing and water jet cutting do not create a HAZ,
as they do not heat the material, while laser cutting creates a
small HAZ due to the heat only being applied to a small area.
12. Meanwhile, plasma cutting leads to an intermediate HAZ, with
the higher currents allowing for an increased cutting speed and
thereby a narrower HAZ, while oxyacetylene cutting creates the
widest HAZ due to the high heat, slow speed and flame width.
13. Arc welding falls between the two extremes, with individual
processes varying in heat input.

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Welding Defects, Causes and Remedies
Defects are common in any type of manufacturing, welding
including. In the process, there can be deviations in the shape and
size of the metal structure. It can be caused by the use of the
incorrect welding process or wrong welding technique.
Weld Crack
The most serious type of welding defect is a weld crack and it’s not
accepted almost by all standards in the industry. It can appear on
the surface, in the weld metal or the area affected by the intense
heat.
There are different types of cracks, depending on the temperature at
which they occur:

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Welding Defects, Causes and Remedies
1. Hot cracks: These can occur during the welding process or
during the crystallization process of the weld joint.
2. Cold cracks: These cracks appear after the weld has been
completed and the temperature of the metal has gone down.
They can form hours or even days after welding. It mostly
happens when welding steel. The cause of this defect is usually
deformities in the structure of steel.
3. Crater cracks: These occur at the end of the welding process
before the operator finishes a pass on the weld joint. They
usually form near the end of the weld. When the weld pool
cools and solidifies, it needs to have enough volume to
overcome shrinkage of the weld metal. Otherwise, it will form
a crater crack.

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Welding Defects, Causes and Remedies
Causes of cracks:
1. Use of hydrogen when welding ferrous metals.
2. Residual stress caused by the solidification shrinkage.
3. Base metal contamination.
4. High welding speed but low current.
5. No preheat before starting welding.
6. Poor joint design.
7. A high content of sulfur and carbon in the metal.

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Welding Defects, Causes and Remedies
Remedies:
1. Preheat the metal as required.
2. Provide proper cooling of the weld area.
3. Use proper joint design.
4. Remove impurities.
5. Use appropriate metal.
6. Make sure to weld a sufficient sectional area.
7. Use proper welding speed and amperage current.
8. To prevent crater cracks make sure that the crater is properly
filled.

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Welding Defects, Causes and Remedies
Porosity
Porosity occurs as a result of weld metal contamination. The
trapped gases create a bubble-filled weld that becomes weak and
can with time collapse.

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Welding Defects, Causes and Remedies
Causes of porosity:
1. Inadequate electrode deoxidant.
2. Using a longer arc.
3. The presence of moisture.
4. Improper gas shield.
5. Incorrect surface treatment.
6. Use of too high gas flow.
7. Contaminated surface.
8. Presence of rust, paint, grease or oil

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Welding Defects, Causes and Remedies
Remedies:
1. Clean the materials before you begin welding.
2. Use dry electrodes and materials.
3. Use correct arc distance.
4. Check the gas flow meter and make sure that it’s optimized as
required with proper with pressure and flow settings.
5. Reduce arc travel speed, which will allow the gases to escape.
6. Use the right electrodes.
7. Use a proper weld technique

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Welding Defects, Causes and Remedies
Undercut
This welding imperfection is the groove formation at the weld toe,
reducing the cross-sectional thickness of the base metal. The
result is the weakened weld and workpiece.

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Welding Defects, Causes and Remedies
Causes:
1. Too high weld current.
2. Too fast weld speed.
3. The use of an incorrect angle, which will direct more heat to
free edges.
4. The electrode is too large.
5. Incorrect usage of gas shielding.
6. Incorrect filler metal.
7. Poor weld technique.

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Welding Defects, Causes and Remedies
Remedies:
1. Use proper electrode angle.
2. Reduce the arc length.
3. Reduce the electrode’s travel speed, but it also shouldn’t be
too slow.
4. Choose shielding gas with the correct composition for the
material type you’ll be welding.
5. Use of proper electrode angle, with more heat directed
towards thicker components.
6. Use of proper current, reducing it when approaching thinner
areas and free edges.
7. Choose a correct welding technique that doesn’t involve
excessive weaving.
8. Use the multipass technique

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Welding Defects, Causes and Remedies
Incomplete Fusion
This type of welding defect occurs when there’s a lack of proper
fusion between the base metal and the weld metal. It can also
appear between adjoining weld beads. This creates a gap in the
joint that is not filled with molten metal.

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Welding Defects, Causes and Remedies
Causes:
1. Low heat input.
2. Surface contamination.
3. Electrode angle is incorrect.
4. The electrode diameter is incorrect for the material thickness
you’re welding.
5. Travel speed is too fast.
6. The weld pool is too large and it runs ahead of the arc.

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Welding Defects, Causes and Remedies
Remedies:
1. Use a sufficiently high welding current with the appropriate arc
voltage.
2. Before you begin welding, clean the metal.
3. Avoid molten pool from flooding the arc.
4. Use correct electrode diameter and angle.
5. Reduce deposition rate.

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Welding Defects, Causes and Remedies
Incomplete Penetration
Incomplete penetration occurs when the groove of the metal is
not filled completely, meaning the weld metal doesn’t fully extend
through the joint thickness.

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Welding Defects, Causes and Remedies
Causes:
1. There was too much space between the metal you’re welding
together.
2. You’re moving the bead too quickly, which doesn’t allow
enough metal to be deposited in the joint.
3. You’re using a too low amperage setting, which results in the
current not being strong enough to properly melt the metal.
4. Large electrode diameter.
5. Misalignment.
6. Improper joint.

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Welding Defects, Causes and Remedies
Remedies:
1. Use proper joint geometry.
2. Use a properly sized electrode.
3. Reduce arc travel speed.
4. Choose proper welding current.
5. Check for proper alignment.

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Welding Defects, Causes and Remedies
Slag Inclusion
Slag inclusion is one of the welding defects that are usually easily
visible in the weld. Slag is a vitreous material that occurs as a
byproduct of stick welding, flux-cored arc welding and submerged
arc welding. It can occur when the flux, which is the solid shielding
material used when welding, melts in the weld or on the surface of
the weld zone.

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Welding Defects, Causes and Remedies
Causes:
1. Improper cleaning.
2. The weld speed is too fast.
3. Not cleaning the weld pass before starting a new one.
4. Incorrect welding angle.
5. The weld pool cools down too fast.
6. Welding current is too low.

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Welding Defects, Causes and Remedies
Remedies:
1. Increase current density.
2. Reduce rapid cooling.
3. Adjust the electrode angle.
4. Remove any slag from the previous bead.
5. Adjust the welding speed.

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Welding Defects, Causes and Remedies
Spatter
Spatter occurs when small particles from the weld attach
themselves to the surrounding surface. It’s an especially common
occurrence in gas metal arc welding. No matter how hard you try,
it can’t be completely eliminated. However, there are a few ways
you can keep it to a minimum.

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Welding Defects, Causes and Remedies
Causes:
1. The running amperage is too high.
2. Voltage setting is too low.
3. The work angle of the electrode is too steep.
4. The surface is contaminated.
5. The arc is too long.
6. Incorrect polarity.
7. Erratic wire feeding.

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Welding Defects, Causes and Remedies
Remedies:
1. Clean surfaces prior to welding.
2. Reduce the arc length.
3. Adjust the weld current.
4. Increase the electrode angle.
5. Use proper polarity.
6. Make sure you don’t have any feeding issues.

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Destructive and Non-destructive Testing of Welds
The tests described below have been developed to check the skill
of the welding operator as well as the quality of the weld metal
and the strength of the welded joint for each type of metal used in
ordnance material.
Many tests detect defects not visible to the naked eye.

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Destructive and Non-destructive Testing of Welds
Destructive Tests
Some of these tests, such as tensile and bending tests, are
destructive, in that the test Specimens are loaded until they fail, so
the desired information can be gained.
Destructive Tests are in two categories:
1. Workshop based tests
2. Laboratory tests (corrosive, chemical, microscopic,
macroscopic/magnifying glass)

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Destructive and Non-destructive Testing of Welds
Non-destructive Tests (NDT)
Other testing methods, such as the X-ray and hydrostatic tests, are
not destructive (NDT).
This type of testing is also referred to as NDE or nondestructive
examination and NDI or nondestructive inspection.
The goal of these methods is to exam the welds without causing
any damage.

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