Team Work

1. Roya Ginting

2. Lukmanul Hakim

3. Eko Priyanto

4. Theodorus Oxario

5. Yodi Prasetyawan

1. Gas Tungsten- Arc Welding

2. Gas Metal- Arc Welding

This is a welding process where coalescence isachieved by heating with an electric arcproduced by a virtually non- consumabletungsten electrode.

During the welding cycle a shield of inert gasexpels the air from the welding area andprevents oxidation of the electrode, weldpuddle, and surrounding heat affected zone.

For joints where additional weld metal isneeded a filler rod is fed into the puddle in amanner simlar to the oxyacetylene process

The gas tungsten- arc process especiallyadaptable for welding light gage materialswhere the utmost in weld quality or finish isrequired.

Later gas tungsten- atc process fuond to bevery suitble for welding aluminum, stainlesssteel, carbon steel, copper and nickel.

1. Power Supply

The choice of an AC or DC elder depends orcertain distinct weld characteristics that may berequired. Some metals are joined more easily withAC current while with othes better results areobtained when DC current is used.

2. Direct Current Reverse Polarity (DCRP)

When the machine I set for straight polarity theflow f electrons from the electrode to the plateexert considerable heat on the plate. But in reversepolarity the of electrons is from the plate to theelectrode thus causing a greater concentration ofheat at the electrodde.

3. Direct Current Straight Polarity (DCSP)

DCSP is used for welding most metals becausebetter welds are achieved. With the heatconcentrated at the plate the welding process ismore rapid, there is less distortion of the basemetals and the weld puddle is deeper andnarrower than with DCRP.

4. Alternating Current (AC)

AC welding is actually a combination of DCSP andDCRP. During a welding operation the completestoppaga of current flow (rectifecation) wouldcause the arc to be unstable and sometimes evengo out. To prevent such rectification AC weldingmachenes incorporate a high frequency currentflow unit. The high frequency current is able tojump the gap between the electrode and the workpiece piercing the oxie film and forming a path forthe welding current to follow.

5. Thorches

These torches are either air or water cooled. Aircooled torches are desidned for welding light gagematerials whre low current values are used. Watercooled torches are recommended when thewelding requires amperages over 200. Sometorches are equipped with a “gas lens” to eliminateturbulence of the gas stream which tends to pull inair and cause weld contamination.

6. Types of Electrodes

Basic diameters of non consumable electrodes are1/16”,3/32”,1/8”. The diameter of the electrodeselected for a wwelding peration is governed bythe welding current to be used. Larger diametertungsten electrodes are required with reversedpolarity than with straight polarity.

7. Gas Regulators

Gas flow is regulated by a single or dual stagepressure redducing regulator and flow meter. Thefloe meter s calibrated in cubic feet per hour (cfh)or liter per minute (lpm).

Shielding gas for tungsten arc welding can beargon, helium, or a mixture of argon and helium.

Advantages from argon:a) More extensively because it is less expensive than helium

b) Argon is 1.4 times as hevy as air so it provides a betterblanket over the weld

c) Argon normally produces a better cleaning actionespecially in welding alumunium and magnesium withalternating current.

d) With argon there is a smoother and quieter arc action

Higheer welding speeds are possiblewithhelium because higher arc voltage can beobtained at the same current.

A mixture of argon and helium s often used inwelding metals thas require a higher heat input

A weld is made by applying the arc heat on theabutting eddges of the workpiece. Before thearc is generated the electrode must be adjustedso that it extends about 1/8” to 3/16” beyondthe end of the gas cup for butt welding andappximately ¼” to 3/8’ for fillet welding.

The are may be struck in two ways:

a) With a DC machine the electrode is briughtdownard to touch the plate

b) On a AC mavhine the electrode dosen’t have totouch the metal to start the arc

• Once the arc is initiated the torch is positioned at anangel of about 75 degree to the surface of the weldmetal.

• The starting point of the weld is preheated bymoving the torch in small circles

• As soon as the puddle becomes bright and fluid, thetorch is moved slowly and steadly along the joint.

During the welding process there may beoccasions when the arc has a tendency towander. This may be due to low electrodecurrent density, contamination of theelectrodes, magnetic effects and air drafts.

Automatic or machine weldig does involve agreater investment of equipment and requirescloser control of joint tolerances. On the otherlabor cost are reducedd since ewer operatorsare needed and welding speeds increased.

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