Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Manufacturing Processes Lab I, MET 1321 Gas...

Manufacturing Processes Lab 1 (MET 1321)Prof S. Nasseri

Manufacturing Processes Lab I, MET 1321Gas Tungsten Arc Welding (TIG)

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Welding Processes

ARC Welding(AW)

1. Shielded Metal Arc Welding (Stick welding)2. Gas Metal Arc Welding (MIG)3. Gas Tungsten Arc Welding (TIG)4. Flux Cored Arc Welding5. Submerged Arc Welding6. Plasma Arc Welding

Oxyfuel WeldingOFW Oxyacetylene Welding (OAW)

Resistance WeldingRW



Gas Tungsten Arc Welding (GTAW)Tungsten Inert Gas (TIG)

GTAW or TIG is an arc welding process in which a shielding gas protects the arc between a non consumable tungsten electrod and the weld area. Gas is fed through the torch to shield the electrode and molten weld pool. If filler wire is used, it is added to the weld pool separately.

Usage: Joining thin-wall tubing and depositing the root pass in pipe joints.

GTAW Produces high quality weldment.



TIG equipmentEquipment consists of the welding torch plus additional

apparatus to supply electrical power, shielding gas, and a water inlet and outlet.

Personal protective equipment should be worn to protect the operator from the arc rays during welding operations.



TIG equipment

TIG welding torch

(1) Cap. Prevents the escape of gas from the top of the torch and locks the electrode in place. (2) Collet. Made of copper; the electrode fits inside and when the cap is tightened, it squeezes against the electrode and leeks it in place. (3) Gas orifice nut. Allows the gas to escape.

Argon regulator with flowmeter



Shielding GasIn general, the shielding gas is Argon or its mixture

with other gases. The gas is regulated by a flowmeter.

Summary of all gases used: Argon Argon + Hydrogen Argon + Helium

Helium is generally added to increase heat input (increase welding speed or weld penetration).

Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.



AdvantagesTIG welding benefits:

It can weld more types of metal and metal alloys than any other welding process.

Superior quality welds Welds can be made with or without filler metal Precise control of welding variables (heat) Free of slag and spatter Low distortion



CurrentThe welding machine used for TIG can provide either AC or DC current.

The choice of using AC or DC current depends on the metal to be welded.

TIG requires precise current control, especially in the low range (to maintain a stable arc), particularly for welding light-gauge metals.

Aluminum, Magnesium, Thin stainless steel AC

MOST FERRUS METALS (Steel, Thick Stainless Steel, Cast Iron), Silver, Brass, Copper

DC (DCEN)



DeratingA welding machine originally designed for use with SMAW

(stick welding) must be de-rated to protect it from the effect of internal heating that occurs during GTAW.

Derating is a lowering of the current output level (or the duty cycle or both) of an AC welding machine.

Duty cycle is a welding equipment specification which defines the number of minutes, within a 10 minute period, during which a given welder can safely produce a particular welding current.

For example, a 150 amp. welder with a 30% duty cycle must be "rested" for at least 7 minutes after 3 minutes of continuous welding.



How to weld

Before starting to weld, ensure that the Tungsten electrode has the proper stickout beyond the end of the gas nozzle.

Joint Stickout

T-joint 1/4” to 3/8”

Butt-joint 1/8” to 3/16”

Corner joint 1/8”

The diameter of the electrode selected for a welding operation is determined by the required welding current.



How to weld

The type and amount of shielding gas used is determined by current, type of weld, base metal and welding conditions.

Gas nozzles that are too small for the welding task may overheat, crack, or deteriorate rapidly.

A water-cooled torch is recommended when using currents over 200A. Ensure cooling water is flowing before welding.



How to weldWhen welding light-gauging metals, a copper backing

bar is usually required.

Filler metal containing deoxidizers should be used when welding with GTAW to prevent porosity in the weld.

Medium and high-carbon steels require preheat and postheating to avoid loss of toughness and ductility.

Ensure that there is good ventilation when welding copper or copper alloys. Fumes of these metals are highly toxic.



Striking an arcSet the welding current and hold the torch in a horizontal

position about 2” above the workpiece.

When using DC current, lower the torch until the electrode touches the workpiece. Once the arc is started, withdraw the electrode so it is about 1/8” above the workpiece.

When using AC (ACHF or Alternating current high frequency), the electrode should not touch the workpiece to start the arc. Keep it 1/8” above the workpiece. Use this method for the DC welding machine with a high-frequency start up.

To stop the arc during welding, swing the electrode back to the horizontal position without touching the welding area.



Striking an arc Establish an arc. Create a weld puddle. Add filler metal "dip" into the puddle while pushing the

weld puddle along the weld joint. End the arc and leave the torch over the weld puddle to

protect it until the puddle cools. Clean

Cleaning both the weld joint area and the filler metal is an important preparation. Remove all oil, grease, dirt, paint, etc. The presence of these contaminants may result in arc instability or contaminated welds.

ClampClamping may be required if the work piece cannot be supported during welding.

Tack weldMake short 1/4 in. tack welds along the work pieces to hold them together.



How do I position my TIG torch for different types of joints?

Butt welds: When welding a butt joint, center the weld pool on the adjoining edges. When finishing, decrease the heat (amperage) to aid in filling the crater.

Lap joint: For a lap weld, form the weld pool so that the edge of the overlapping piece and the flat surface of the second piece flow together. Since the edge will melt faster, dip the filler rod next to the edge and make sure you are using enough filler metal to complete the joint.

Work angle Push angle



How do I position my TIG torch for different types of joints?

T-joint: When welding a T-joint, the edge and the flat surface are to be joined together, and the edge will melt faster. Angle the torch to direct more heat to the flat surface and extend the electrode beyond the cup to hold a shorter arc. Deposit the filler rod where the edge is melting.

Corner joint: For a corner joint, both edges of the adjoining pieces should be melted and the weld pool should be kept on the joint centerline. A convex bead is necessary for this joint, so a sufficient amount of filler metal is needed.

Work angle Push angle



Test yourself!GTAW or TIG is an arc welding process in which a shielding gas protects

the arc between a consumable tungsten electrod and the weld area. TrueFalse

In TIG welding, the main shielding gas is Argon.TrueFalse

The TIG current used for welding the most ferrous metals (Steel, Thick Stainless Steel, Cast Iron), is AC.

TrueFalse

non-consumable

DC (DCEN)



Test yourself

Derating (lowering of the current output level or the duty cycle of an AC welding machine) is done – to increase the minutes during which a given

welder can safely produce a particular welding current.

– to protect the machine from the effect of internal heating that occurs during GTAW.

– to have a high-frequency start up in welding.



Test yourself

Filler metal containing deoxidizers should be used when welding with GTAW to prevent …… in the weld.

– contaminations– porosity– instability


Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Manufacturing Processes Lab I, MET 1321 Gas...

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