What is Arc Welding?An electric arcbetween the andelectrode and thework piece generatesheat. Sufficient heatis generated to meltthe work piecestogether.ARCELECTRODEWORK PIECES
ElectricityThe range of welding current usedcan be from 5 to 500 amps. Thevoltage ranges from 20 to 30 volts,AC or DC. Both are determined bythe material thickness.A 60 watt light bulb draws .5 amps.
Four Common Types of Welding•Stick SMAW (shielded metal arc welding)•Mig GMAW (Gas Metal Arc Welding)•Flux-Core FCAW (Flux-core Arc Welding)•Tig GTAW (Gas Tungsten Arc Welding)
CharacteristicsEach welding process has unique traits thatmake it more suited for particular processes
Some TermsElectrodeThis is where the current passes from thewelder to the work piece.There are two types:1) Contact/consumable2) Non Contact
More TermsAtmospheric protectionThere are 2 types:1) Shielding Gas2) Flux
Stick Welding• Uses a consumable electrode (rod), with a fluxcoating.• Stick welding requires a moderate to high skilllevel.• Advantages:PortableCan be used in all environmentsNot as dependent on surface preparation
Mig Welding• The electrode is a wire, fed from a spool to the end ofthe “gun”.• A shielding gas is used to give atmospheric protection.• This process requires a low to moderate skill level.Advantages:1) Very fast process2) Easy to learnDisadvantages:1) Weld area must be protected from air movements
Flux Core• This process is a hybrid between Mig and Stickwelding.• It is the same process as Mig welding, exceptinstead of a shielding gas, there is flux in weldingwire.Advantages:1) Can be done in all environmentsDisadvantages:1) Requires additional clean up to remove flux
Tig Welding• There is a Tungsten electrode through which thecurrent is passed. (Melting pt. = 3700 degrees K)• Argon is used as a shielding gas.• Requires the highest skill level.Advantages:1) Nearly all metals can be welded using this process.2) Very preciseDisadvantages:1) Slow process
TIG welding a Nascar chassis together.Filler RodArc
A semi-truck is parked along side I-80 with abroken air brake mount on it’s trailer. The mountis made out of standard steel. The truck can notbe moved until the repair is made. Which weldingprocess, (MIG, TIG, Stick, Flux Core) could beused to make the repair? Discuss what factorswere involved in your selection process.Answer on page 4 of handoutPROBLEM 1
There are two process that could be used to makethe needed repair. Those two processes are fluxcore, and stick welding. Because the repair hadto take place in the field, a process must be usedthat did not require an external shielding gas.Both of the processes are equally suited to makethe repair. Stick welding requires a higher skilllevel than flux core, so the operator skill level is afactor.ANSWER TO PROBLEM 1
Automatic/ Robotic Welding• Can be done using the MIG or TIGprocesses• Used when there are long, reproducibleweld joints• It can be used where the environment ishazardous to humans• Saves time and money
This robotic TIG welder is sealing nuclear waste storage containers.Weld Head
An automatic Multi-Head Mig welder joins sections of pipe together.WELD HEAD
Radiography• A non-destructive process to test weldsusing X-Rays
Flaw (porosity)Welds with internal flaws can lead to failures
Radiograph of a steel pipeOutside pipewallInside pipe wall UndercutPorosity
This will show Mig welding and willshow some common joint typesAnd now for a short movie
Things to consider in weld design• Material selection is critical for success• Some factors that influence selections are:StrengthWeightCostService environmentLocation where the welding is going tooccur
Other things to ponder• Welding apparatuseshave physical size andthat can limit welddesign45 deg.
Design ConsiderationsPlanning must be done to allow joints to be weldedBecause of poor design this weld isdifficult to complete successfully.
Weld Strength• A “good” weld is stronger than the parentmaterial• Welding creates stresses at the weldboundaries• The stresses will always lead to a failure atthe weld edges, not in the weld itself
Effects of weldments on fatigue strength1 million cycles = 25800 psi2 million cycles = 22800 psi1 million cycles = 25400 psi2 million cycles = 18900 psi1 million cycles = 22900 psi2 million cycles = 13100 psiAvoid abrupt changes in stiffness43% reduction in fatiguestrength
Welding Safety• Arc rays can injure eyes causing scar tissueand even blindness with prolonged exposure• Arc rays emit UV light and have been foundto cause skin cancerSPF 1000 sun block is recommended• High levels of current can causeelectrocution• Extreme heat can cause severe burns
Welding SafetyWelding fumes are hazardous to your health!• Short term effects include:Nausea, dizziness, irritation of the nose,throat and eyes.• Long term effects include:Iron deposits in the lungs, centralnervous system effects, Bronchitis andCancer
PROBLEM 2Assume that you are an Engineer whohas designed a device, and you mustnow specify a particular weld process.Discuss some of factors that could affectthe decision.
ANSWER TO PROBLEM 2Material to be welded:-Some materials require special processes that takemore time and skill than others.Number of welds, or length of weld:-Some welding processes are faster than others.-MIG/Flux core are fastest, then Stick, then TIGWeld bead size:-Tig welding produces a smaller weld than mig or stick.If space is critical, then a small weld bead is desirable.Answers included on page 5 of the handouts
PROBLEM 2 CONTINUEDWeld bead size:-Tig welding produces a smaller weld than mig or stick.If space is critical, then a small weld bead is desirable.Location where welding is to occur:-See question one.Operator skill level:-The four welding processes require different skilllevels. TIG highest, MIG/Flux core lowest.
Albert Einstein once said:“Education is what remains when one has forgotteneverything he learned in school”