Gas Shielded Welding Processes - . Plasma Arc Welding (PAW) Lecture 5 p1 PAW: Process Fundamentals ( • In PAW the heat source is an arc maintained between a non-consumable­ electrode and the workpiece • The arc is constricted by a cooled orifice that surrounds the electrode • Inert gas is supplied separately to the orifice and to a surrounding low-velocity shielding flow 5 p2 PAW: Comparison with GTAW SHIELDING ELECTRODE GAS SHIELDING t GAS . GTAW PAW Lecture 5 p3 PAW: Effect of Arc Constriction ( GTAW PAW Arc Temperatur~s • >24000K • 18 000 - 24 000 " • 14000 - 18 000 " • 10 000 - 14000 " 200 A, 15 V 5 p4 PAW Modes CONSTRICTING NOZZLE ORIFICE GAS SHIELDING GAS TRANSFERRED ARC NON-TRANSFERRED ARC Lecture 5 p5. PAW: Keyhole technique ( KEYHOLE WELD BEAD p6 PAW: Welding Procedures Keyhole welding of stainless steel sheet T = Matenal Thickness -4 E 20 B= Upper Clamp Spacing E . C =Back-up Bar Spacing ......... 3 15 A = Weld Current () B - 2 III B 10 -j C 1 7-- ~I 1 ~~ L:--_--L.__---'-__----:-I.::-...J 'ViC .5 1.0 1.5 T(mm) Lecture 5 p7 PAW: Backing for Keyhole Welding ( TORCH- ~ \!~Il. PlASMA JIT . BACKINGGA BACKING BAR p8 PAW Welding Equipment START/STOP SWITCH .-----.-1 COOLANT o 01--------, ,.-----1CIRCULATOR '--'-~IFICEGAS -rL--.!-Jl IELD GAS -----I TORCH WER & COOLANT IN CONTROLLER 1-- --, WER & COOLANT OUT -.....----r----' WORK WELDING GAS POWER SOURCE REMOTE CURRENT CONTROL Lecture 5 p£ PAW Welding Torch ( COOLANT OUTLET ORIFICE GAS INLET -----.,POWER CONDUCTORS COOLANT INLET HIELDING GAS INLET 14+--f+----'TUNGSTEN ELECTRODE ORIFICE BODY .,OUTER SHIELD CUP ~5 p10 PAW Applications • Very thin sheet (down to 0.1 mm), wire and mesh sections in microplasma mode • Full penetration welding of sheet and prate up to about 5mm thick in single pass keyhole mode. • Keyhole mode usually in flat position, rarely for tube and pipe welding • Melt-in mode applications similar to GTAW Lecture 5 P 11. PAW Capabilities & Limitations ( + Higher intensity heat - Little tolerance for joint source than GTAW misalignment _ - higher welding speeds - Torch orifice must be . - reduced heat input and well maintained for distortion consistent weld quality + Insensitive to torch - PAW torches are more stand-off distance bulkier and more + Applicable to almost all difficult to manipulate metals manually than GTAW + Adaptable to precision mechanized applications ·5 p12 Electron Beam _. & Laser Welding Lecture 5 p13 EBW, LBW Fundamentals ( , • Heat source is radiant energy from focused beam of electrons or photons (light) • Shielding from atmospheric contamination by welding in vacuum chamber (EBW), inert gas shield (LBW) e5 p14 LBW, EBW Capabilities and Limitations + Very high energy density - Little tolerance for joint heat sources misalignment _ + Very deep penetration in - EBW requirement for "keyhole" mode vacuum chamber + Narrow welds and HAl limits maximum size + High welding speed that can be welded + Reduced heat input and - Equipment is complex distortion and costly. + Adaptable to precision mechanized applications Lecture 5 P 15.