Special Welding Processes 1 Submerged Arc arc buried

Special Welding Processes

1. ) Submerged Arc

arc buried in granular flux l single pass butt welds up to 3” thick l electrodes up to 1/2” in diameter l

l multiple electrodes

automated carriage that follows track

manual

hopper feeds granular flux to joint just ahead of the arc usually done in flat position l flux remaining over the completed weld acts as a heat insulator l unused slag can be reused l fast, no visible arc, no spatter, high quality welds, thick materials l

2. ) Electroslag

developed to weld very thick sections or joints

eliminates the need for multiple passes or grooves

Vertical joint - arc started between electrode & bottom

flux is added - forms a layer of molten slag - arc not needed l resistance to current flow thru the flux creates heat necessary to melt electrode and base metal

water cooled copper shoes contain molten metal in joint

adv: fast, no edge prep, thick plates can be welded

3. ) Electrogas - use shielding gas - flux cored wire fed in joint l arc maintained between electrode and weld

4. ) Narrow Gap less weld metal is required l used on thick sections l

similar to electrogas except weld joint has a narrow gap

Electrode guide tube used to feed electrode to joint bottom problem - getting the electrode to touch both sides of the joint l cure - bend electrode into wave form l

5. ) Stud l no drilling or punching holes in structure

stud placed in chuck on gun l ceramic ferrule placed on end of stud l contains molten metal

pull trigger stud pulled away from work l arc formed between stud and work l

Stud forced into molten metal and cools

ferrule is broken off

Aluminum can be welded using shielding gas

6. ) Plasma arc welding plasma means ionizing gas (a gas which has lost or gained electrons) l orifice gas becomes plasma as it passes through the arc toward the work piece l

Tungsten electrode surrounded by inert orifice gas l helium argon nitrogen

Separate shielding gas protects the welding or cutting process

square butt joint normally used

Transferred vs. Non Transferred Arc

fill metal is also added automatically

adv: l concentrated current flow l arc stability with large changes in arc length l low heat input l high speed (30 ipm) l best results when operated automatically

disadv: noisy

7. ) Underwater SMAW use well insulated electrode holder and special water proof covered electrodes l because of rapid cooling - use stringer beads not weaving l short arc length and DCEN l poor visibility - use #4 or #8 lens l communication system - person above starts and stops the current for the system l

Solid state welding processes do not use an arc l do not have a beam of energy l do not use a flame l do not use resistance to heat the metal l processes are done when the metal is cold, warm, or hot but temp does not exceed the melting point l no filler metal added l

1. ) Cold welding theory - pressure at the surface causes fusion only a few molecules deep l this fusion is sufficient to hold the material together and provide good strength l works best on soft ductile metals l

Cold Welding (Cont. ) no heat needed l enough pressure must be applied to reduce original thickness of metal by 1/4 of original thickness l oxides and contaminants must be completely removed l

Tool can be hand, pneumatic, or hydraulic l dies must be designed to impose proper pressure for different metals

2. ) Explosion welding metals placed at angle to each other l protective material is placed over the metal and the explosive material is placed around the metal l explosion forces the plates together at high velocity causing surface ripples in metal l ripples lock or weld the two metals together l

3. ) Friction welding

pieces to be welded are mounted in a chuck l one piece stationary - one revolves l brought together under pressure heating occurs l parts forced together under pressure allowed to cool l weld is produced in about 15 seconds l process is similar to upset or flash welding - but friction is used to generate the heat l

Adv. well suited for joining dissimilar metals to mild steel in production l no protective atmosphere is required saves time and materials l

4. ) Ultrasonic Welding welding equip contains transducer which convert high freq. Elect power into mechanical vibration at the same freq. (10 K to 75 K hertz) l metal clamped together under pressure and high frequency l

UT Welding (Cont. ) vibrations are introduced into metals through a welding tip l vibrations break up surface films causing metals to bond l max thickness is. 100" on al. and. 040" on harder materials l

UT spot welds

UT seam welds with lateral drive rollers

adv: fast l happens without heat or melting - no heat distortion l cleaning is not necessary l low clamping pressure which reduces deformation l no fluxes l no filler metals l

UT Adv (Cont. ) thin sections can be welded to thick sections l pressures less and welding times shorter than used in resistance welding l many types of metals can be joined to themselves or other metals l minimal training - semiskilled personnel l

High Density Welding Processes involves concentrating a lot of energy on a small spot l produces deep narrow welds l two processes include: » Electron beam » Laser beam l

1. ) Electron beam welding: uses a concentrated beam of high velocity electrons to melt welded metal l current passed through a tungsten filament which emits electrons l parts are placed very close together almost touching l edges must be very straight l part being welded is placed on a carriage that moves under the beam l

Electron Beam Welding (Cont. ) can make complete penetration weld in 10 inch steel plate l fast -. 25" plate welded at 200 ipm l

usually done in vacuum chamber no particles in air to interfere with beam l more vacuum, the narrower the beam is l can be done without a vacuum but the parts must be close to the beam source l

2. ) Laser beam welding Light Amplification by Stimulated Emission of Radiation l laser beam is just light l light beam has one wavelength l has one phase - [all the particles (waves) move together] l laser beam produced by CO 2 for welding l

Laser Beam Welding (Cont. ) beam is focused and aimed using lenses and mirrors l lasers are operated at atmospheric pressure l shielding gas is used to protect the metal from oxidation l parts to be welded must be close together with straight edges l travel speeds are fast l