2DefinitionGas Tungsten Arc Welding (GTAW) is an arc welding process that uses a non consumable tungsten electrode to establish the arc and gas from a cylinder to provide shielding. The filler metal is supplied by a manual rod.Also called Tungsten Inert Gas (TIG) welding.2
3Machine Functions Store and provide shielding gas at the correct rate Provide desired welding currentVariable current controlStore and circulate water through the torch (watered cooled)Semiautomatic control
4Machine Nomenclature Torch Power switch AC balance control Mode switch Digital Amp meterOutput (Amp) controlCylinderFlow meterRoto meterFlow control valveRegulatorPost flow timerPulse frequency controlPolarity switchOutput connectorRemote pedalGround clampRemote receptacleExplain the function(s) of each one of these controls/parts.
5Torch Nomenclature Cap Collet Torch body Collet body Gas orifice Cup ElectrodeWhat is the function of each part?How are GTAW torches cooled?
6IntroductionHow does the GTAW process meet the three requirements of arc welding?HeatShieldingFiller metalGTAWHeat = electric arcShielding = gas from cylinderFiller metal = manual rod
7Hazards Associated with GTAW Hot metal Harmful rays Fumes High frequency RF Flying objects Loud NoiseWhat is the best management practices for these hazards?Hot metal Gloves, pliersHarmful rays Correct shade of lens, not exposed skinFumes VentilationHigh frequency Warning signsFlying objects Safety glassesLoud noise Appropriate hearing protection
8HeatThe heat produced by an electric arc between the nonconsumable tungsten and the metal is sufficient to melt the base metal and the filler rod.What determines the amount of heat produced by the electric arc?Amount of currentamperageFor the TIG welding process, is the current adjusted by changing the amperage or the voltage?
9Heat – Currents Three common currents: DC- DC+ AC--HF Note: many power supplies have the option of pulsed current for better puddle control.Non contact starting.Why is HF (high frequency) used with AC?
10Heat – Current - Polarity For the best welds, and ease of welding, the correct current must be used for the metal being welded.
11Heat - TungstenThe tungsten electrode is nonconsumable and is used to form the arc between the torch and the metal.Different alloys of tungsten are available.ID% AlloyColorCharacteristicEWP100 % TungstenGreenGood arc stability with ACEWTh-22 % ThoriumRedBetter Arc with DCEWZr-11 % ZirconiumBrownAC when high weld quality is requiredEWCe-22 % CeriumOrangeBetter starting, higher current2% lanthanum/blackEWLa-22 % LanthanumBlack50% greater current capacity with ACWhich alloy/color should be used when welding thicker aluminum with AC?
12Heat – Tungsten - Preparation The shape of the tungsten electrode end must be appropriate for the current being used.ACHemispheric or balled end no more than 1.5 times the electrode diameter. Grinder lines parallel with electrode.DC-Needle point for very thin metal, blunt point for thicker metal. Taper = 2 to 2-1/2 times the diameter.What does it mean if the end of the electrode appears dull?What does it mean if the end of the electrode is blue or blackened?Excessive current was usedInsufficient postflow shieldingone second per 10 amps of welding currentHow long should the the shielding gas flow after the welding has stopped?
14Shielding How is the flow of the shielding gas controlled? In the GTAW process shielding is supplied from a cylinder.How is the flow of the shielding gas controlled?For best results the shielding gas must be appropriate for the type and thickness of metal.Flow meter112 ft3How much gas (ft3) will each gallon of liquid argon produce?
15Filler Metal What are three important characteristics of GTAW rods? A welding rod is used to fill in the joint. Most common type is 36 inch rods that are fed into the weld pool by hand.What are three important characteristics of GTAW rods?Material must be compatible with welding metalDiameter must be appropriate for thickness of metalMust be clean and free from oxidation
18Preparation for Welding Three (3) steps in preparing to weld:Safety checkMetal preparationSet up machine
19Preparation - SafetyCheck the machine, cables, torch and ground clamp.Insure the helmet is in good condition and the correct shade of lens.Cover all exposed skin.
20Preparation – Metal – Aluminum Contamination is the biggest problem when welding aluminum with the GTAW process.The metal must be cleaned with a stainless steel wire brush.The brush can only be used to clean aluminum.Must clean the adjoining faces and the back edgeInsure the filler rod is clean also.
21Preparation - Machine Attach the GTAW torch to the output connector. Attach the remote control pedal to the remote receptacle.Position the polarity switch on AC.Turn on the machine.Insure the torch is not groundedSet the mode switch to TIGSet the amperage.150 amp maximum for air cooled torch.Set the AC balance control.Set the pulse control.Set the postflow timer.
22Preparation – Machine - Torch If the torch has been used to weld carbon steel or stainless steel then the cup and electrode must be replaced.The tungsten electrode must be clean and the correct shape.The torch cup must be cleanThe electrode must be set with the correct stickout.
24Aluminum Amperage ACHF Setting AmperageAluminum is a good conductor of heat. Aluminum melts at a lower temperature that steel.Aluminum Amperage ACHFThicknessJointTungsten electrode diameterFiller rod diameterAmperageGasTypeCFH1/8 inButt3/32 – 1/8 in3/32 inArgon20LapCornerFillet3/16 in1/8 – 5/32 in190 – 2401/4 in5/32 – 3/16 in25250 – 320
25Troubleshooting GTAWTroubleshooting is the process of determining the cause of a problem.Assumes the welder is in proper working order.Requires gathering information and a logical thought process.
26Troubleshooting - 1 Problem Cause Excessive electrode consumption Inadequate gas flowDCEP electrodeExcessive current densityTungsten oxidation during coolingWhat would you do to remedy these causes?
27Troubleshooting - 2 Problem Cause Aluminum contamination of electrode Electrode contacting filler rodElectrode contacting metalWhat would you do to remedy these causes?
28Troubleshooting - 3 Problem Cause Weld porosity and dark color Condensation in systemAtmospheric contaminationContaminated filler metalWhat should be done to remedy these causes?Contaminated base metal
29Troubleshooting - 4 Problem Cause Yellow powder or smoke on cup Insufficient gas flowAtmospheric contaminationInadequate post flowWhat should be done to remedy these causes?Incorrect shielding gasIncorrect tungsten size or cup size