Download - Lab Report Welding (SMAW)-Fiza
TITLE: LW1: SHIELDED METAL ARC-WELDING (SMAW)
1.0 INTRODUCTION
1.1 THEORY
1.1.1 Definition
Shielded metal arc-welding (SMAW) is one of the oldest, simplest
and most versatile joining process.
Nearly half of all industrial and maintenance welding currently is
performed by this process.
The electric arc is generated by touching the tip of a coated
electrode against workpiece and withdrawing it quickly to a
distance sufficient to maintain the arc.
The heat generated melts a portion of the electrode tip, its coating
and the base metal in the immediate arc area.
The Stick welding power source provides constant current (CC)
and may be either alternating current (AC) or direct current (DC),
depending on the electrode being used. The best welding
characteristics are usually obtained using DC power sources.
The electrode coating deoxidizes the weld area provides a shielding
gas to protect it from oxygen in the environment.
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1.1.2 Advantages and Limitations
Advantages Limitations1. Ability to weld in all
position.1. High potential for weld contamination.
2. Easy in welding many different metals & alloys.
2. Frequent interruptions due to electrode length.
3. Ability to weld thin & very thick metals.
3. Need to remove spatter, smoke & Slag.
4. Very portable and good for field work.
4. Unsuitability for very thin material.
5. Good choice for repair work. 5. Poor choice for aluminum & bronze. 6. Low cost, low maintenance
equipment.6. Electrode requires special care to Prevent moisture pickup.
7. Good arc visibility.8. Fairly tolerant of different
environment.9. Good accessibility in
restricted areas.
1.2 OBJECTIVES
To perform on of the welding techniques that has learnt in Chapter 2.
To use the skill to do the welding, used the knowledge and understanding of
the theories, and also techniques discussed within the topics into the practical
application.
To analyze the outcome from the practical task that have been doing and
write the report.
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2.0 RESOURCE & FACILITIES
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POWER SUPPLY
Two types of supply: Alternating current (AC) welders. Direct current (DC) welder.
Wider variety of electrode available. Better for welding thin metals. DC straight polarity (DC-EP) has
electrode negative and workpiece positive. Produce high electrode melting rate.
o DC reverse polarity (DC-EP) has electrode
WORKTABLE
Place where all welding activity is completed. The workpiece will be placed on the table so
that welding process can be done.
ELECTRODE HOLDER
Grips the electrode.
Handles and clamp are insulated.
Grooves in the clamp enable changing the
position of electrode.
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PLIER
Hand tool used to hold objects firmly or for cutting and bending tough materials.
WORKPIECE CLAMP
Complete the electric circuit from power supply, through the electrode across the arc through the workpiece and back to the power supply.
Should be firmly attached to workpiece or worktable.
PROTECTIVE SHIELD
Provides full facial protection from: Sparks and flying metals. Intense light from arc. Ultra-violet light. Infrared red.
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WIRE BRUSH & HAMMER
Wire brush is used for cleaning rust and
removing paint.
It is also used to clean surfaces and to
create a better conductive area for
attaching electrical connections.
GLOVE
To protect hand from: Spark and flying metals. Hot metal during and after
welding.
3.0 METHODOLOGY
Firstly, make sure to wear protective clothing and
Then ground the workpiece by clamping to the table.
Suitable electrode was selected and inserted it in the electrode holder.
After that, the proper welding was setting that range from 90-130 AMP. For this task we
have to select three different type of amperage in order to compare the outcome. I have
selects 90A for low, 110A for ideal and 130A for high current.
After choosing the desire welding setting, then turn on the welder.
Be careful not to touch the electrode to the workpiece or worktable until ready to strike
an arc.
Then, strike an arc with long scratching motion of the electrode across the workpiece.
Finally of the weld, quickly lift the electrode away from the workpiece.
The electrode was dropped from the holder and put down the electrode holder.
Wearing clear shield on the welding helmet, chip away the slag on the weld bead.
After completed all the above process, make sure to tidy up your worktable.
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4.0 RESULTS
The figure above is my result after I finished my work on performing SMA welding. There are
three different types of amperage is used. As a result, what I can conclude on my work is that:
By using high current, the electrode melt faster and molten puddle will be excessively
large and irregular. It will also leave a groove in the base metal along both sides of the
weld and therefore undercut will occur.
Effects of high current:
Spatter occurs in large drops alongside the weld.
Bead is too wide, too thin and undercut at edges.
Flux melts too rapidly, runs off the top of the weld.
If the current is too low, there is not enough heat to melt the base metal and the molten
pool will be too small.
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Low amperage: 90AIdeal amperage:
110A
High amperage: 130A
Figure 1: Result of my workpiece
Effects of low current during weld:
Inadequate penetration (weak weld).
Difficulty in striking arc.
Arc goes out often and difficulty in maintaining the arc.
From my welding techniques is that the speed that I used is too fast. As a result, the
molten pool will be thin and irregular. This will also lead to lack of penetration where
shallow fusions happen between weld metal and base metal.
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5.0 DISCUSSION
As a result, a welded joint may develop various discontinuities. Welding discontinuities also
can be cause by an inadequate or careless application of proper welding or by poor operator
training. The major discontinuities that affect weld quality are described here.
1) Porosity
Porosity in welds may be caused by:
Gases released during melting of the weld area, but trapped during solidification.
Chemical reactions during welding.
Contaminants.
Porosity can be reduced by:
Proper selection of electrodes and filler metals.
Improved welding techniques, such as preheating the weld area or increasing the
rate of heat input.
Proper cleaning and the prevention of contaminants from entering the weld zone.
Reduced welding speed allow time for gas to escape.
2) Slag Inclusions
Slag inclusions are compounds such as oxides, fluxes and electrode coating materials that
are trapped in the weld zone.
Welding conditions are important as well as with the control of welding process
parameters, the molten slag will float to the surface of the molten weld metal and thus
will not become entrapped.
Slag inclusions can be prevented by the following practices:
Cleaning the weld-bead surface by means of wire brush (hand or power) or a
chipper before the next layer is deposited.
Providing sufficient shielding gas.
3) Incomplete Fusion and Penetration
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Incomplete fusion produces poor weld beads. A better weld can be obtained by the use of
the following practices:
Raising the temperature of the based metal.
Cleaning the weld area before welding.
Changing the type of electrode used.
Providing sufficient shielding gas.
Incomplete penetration occurs when the depth of the welded is insufficient. Penetration
can be improved by:
Increasing the heat input.
Reducing the travel speed during welding.
Modifying the design.
Ensuring that the surfaces to be fit each other properly.
4) Weld profile
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Figure 2: Examples of various discontinuities in fusion welds
Its effects on the strength and appearance of the weld, but also because it can indicate
incomplete fusion or the presence of slag inclusions in multiple-layer welds.
Underfilling results when the joint is not filled with the proper amount of weld
metal. (Figure 30.20a).
Undercutting results from the melting away of the based metal and consequent
generation of a groove in the shape recess or notch. (Figure b)
Overlap is a surface discontinuity (Figure b) usually caused by poor welding or
by the selection of improper materials. A good weld is shown in figure c.
5) High amperage11
Figure 3: Examples of various defects in fusion welds
The electrode will melt faster and molten puddle will be excessively large and irregular.
Excessive spatter will occur due to high amperage. It’s a scattering of molten metal
particles that cool to solid from near weld bead.
6) Low amperage
Not enough heat to melt the base metal and molten pool will be too small.
Lead to incomplete fusion as both metals are not completely joined by the weld.
The correction for this problem would be to increase heat, slow travel speed and
increase arc length.
6.0 CONCLUSION
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Figure 4: Comparison of chart weld over the current and speed travel
As conclusion, the objective can achievable to do the practical welding. The student must
have skill to do the welding, used the knowledge and understanding of the theories, and also
welding techniques are applied in the practical welding. The practical task have been complete
and the report will accomplished to prove the student can be do the practical task of Shielded
metal arc-welding (SMAW).
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