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.

1

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.

2

2.0 RESOURCE & FACILITIES

3

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.

4

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.

5

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.

6

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.

7

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.

8

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

9

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

10

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

12

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).

13