APPARATUS

RESULT & ANALYSIS

Reverse DC Current

AC Current

Forward DC Current

Lap joint

Underfill

Spatter

Poor penetration

Undercut

Incomplete fusion

DISCUSSION

In this experiment, we are going to understand and demonstrate some mostly used Shielded

Metal Arc Welding (SMAW) to complete lap joint. (SMAW) also known as manual metal arc

welding (MMAW), flux shielded arc welding or informally as stick welding, is a manual arc

welding process that uses a consumable electrode coated in flux to lay the weld. In this workshop,

our electrode series was E 6013 and it is primarily a rod used to stick weld thin surfaces. The

electrode size was 2.6 mm meanwhile the plate thickness was 4 mm. The allowable DC current in

this experiment was 50A to 90A. In order to complete the lap joint, we have tried three different

currents which were DC positive and negative and also AC current as presented in result above.

Between these three currents, we have to choose the most suitable one so that we are able to get

the best weld of lap joint. After tried all three currents, forward DC current was chosen to complete

lap joint due to comfortability when handle this current. But the defects still happened in lap joint as

shown in the result and analysis.

A welding defect is any flaw that compromises the usefulness of a weldment. This happened

due to lack familiarity with welding and misinterpret design intent for example applied stresses,

fabrication sequence and weld capabilities. The first defect that has been identified was undercut. It

is a groove cut at the toe of the weld and left unfilled. The possible causes are amperage too high

and arc length too long increasing the force of the arc so that it cuts into corners. The solution to

minimize this defect is clean the metal first before welding. Second defect was poor penetration

which happen when the metal does not extend to the required depth into the joint root. This defect

because of amperage too low and travel speeds too fast. In order to prevent this defect is correct

the contributing factors. Another defect was incomplete fusion where weld metal does not form a

cohesive bond with the base metal. The causes are low amperage, fast travel speed, short arc gap

and lack of preheat. Eliminate potential causes is a way to minimize this defect. Next defect was

underfill which is the weld surface is below the adjacent surfaces of the base metal. Improper

welding technique is one of the causes and how to prevent this defect is just apply proper welding

technique for the weld type and position. Lastly, spatter is one of the most common defect in

welding. Spatter is a small particles (droplet) of weld metal expelled from the welding operation

which adhere to the base metal surface. Long arc length, severe electrode angles and high

amperages are example of the causes.

The most important thing is we have to consider all the factors that led to get the best result

of welding. The factors are arc length, travelling speed and angle of electrode with the specimen.

The most suitable angle is 750 to 800. Another way is make sure the workpiece is clean as

possible before starting any welding project.

CONCLUSION

As a conclusion, welding is a practical skill that requires continual practice and careful

attention to the variables that the welder controls to improve. Even an experienced welder needs

continuing technical education to get the good weld. The old golden rule “practice makes perfect”

applies to welding in that the more you do, the better you become a welder. So, we can conclude

that the objective of this experiment have been completely achieved as required even there are still

defects and mistakes.

REFERENCES

http://en.wikipedia.org/wiki/Shielded_metal_arc_welding

http://www.slideshare.net/RonySimeon/9488085-weldingdefects

http://deltaschooloftrades.com/stick%20essentials.htm

http://www.thefabricator.com/article/arcwelding/how-to-improve-your-welds--helpful-

hints-for-gmaw