5_231127_Eargle_VT-5 ISO5817_Fundamentals of GMAW.pptx

Click to insert Picture Fundamentals of Gas Metal Arc Welding (GMAW)     Sidney Eargle CWI KION NA - Summerville, SC DEC 04, 2023 © 2021 Holdren Engineering Fundamentals of GMAW Gas Metal Arc Welding (GMAW) 2 © 2021 Holdren Engineering Fundamentals of GMAW GMAW Schematic 3 © 2021 Ho...

Click to insert Picture Fundamentals of Gas Metal Arc Welding (GMAW)     Sidney Eargle CWI KION NA - Summerville, SC DEC 04, 2023 © 2021 Holdren Engineering Fundamentals of GMAW Gas Metal Arc Welding (GMAW) 2 © 2021 Holdren Engineering Fundamentals of GMAW GMAW Schematic 3 © 2021 Holdren Engineering Fundamentals of GMAW GMAW electrode designation • Silicon • Aluminum • Titanium 4 Deoxidizers removes impurities as the silicon bead that is the little blob/ bubble on the weld © 2021 Holdren Engineering Fundamentals of GMAW Typical GMAW electrodes ER10S-6C / ER70S-6M • 70,000 psi minimum tensile strength • Solid wire • C = 100% CO2 shielding gas [EN ISO 14341-A G46 3 C4Si1] • M = Ar/CO2 or Ar/O2shielding gas [EN ISO 14341-A G46 5 M21 4Si1] E70C-6C / E10C-6M • 70,000 psi minimum tensile strength • Metal core - metal sheath surrounding powdered metal alloy material • C = 100% CO2 shielding gas • M = Ar/CO2 or Ar/O2 shielding gas 5 © 2021 Holdren Engineering Fundamentals of GMAW GMAW equipment • Volt = shape • Amp = heat ~> wire feed speed 6 © 2021 Holdren Engineering Fundamentals of GMAW GMAW equipment — wire feeder 7 © 2021 Holdren Engineering Fundamentals of GMAW GMAW equipment - welding gun Should be changed periodically as could become brittle. If loose O2 will be sucked into mixture leads to porosity 8 © 2021 Holdren Engineering Fundamentals of GMAW GMAW equipment - gas supply • Cylinder • Pressure regulator • Flowmeter − WPSs require flow rate of 28- 50 cfh • Gas hose 9 © 2021 Holdren Engineering Fundamentals of GMAW Metal transfer modes • Metal transfer mode. The manner in which molten metal travels from the end of a consumable electrode across the welding arc to the workpiece. • Dependent on: − Power IeveI − Shielding gas type − Power source controls and output 10 © 2021 Holdren Engineering Fundamentals of GMAW Metal transfer modes • Four basic types • Spray • Globular − Short circuiting − Pulsed • Contact with work • Sheet metal 11 © 2021 Holdren Engineering Fundamentals of GMAW • High current • Pulsing power supply Metal transfer modes • Spray − High power, high deposition − Requires 80% argon, minimum − Flat position only − Root bead welding only with backing • Globular − Same as spray, except argon shielding not required 12 © 2021 Holdren Engineering Fundamentals of GMAW Transition current • Transition current. That current level, above which spray transfer can be attained. 13 © 2021 Holdren Engineering Fundamentals of GMAW Metal transfer modes • Short circuiting − Lowest power level − Excellent for sheet metal, open root, and out-of-position welding − Could result in incomplete fusion in thick sections 14 © 2021 Holdren Engineering Fundamentals of GMAW Metal transfer modes • Pulsed (GMAW-P) • Requires power source capable of varying electrical characteristics of arc − Essentially, intermittent spray transfer • Requires 80% argon, minimum • Essentially an intermittent spray transfer, with one droplet per pulse • Can be used for same applications as SC, plus thick sections 15 © 2021 Holdren Engineering Fundamentals of GMAW GMAW Nomenclature 16 © 2021 Holdren Engineering Fundamentals of GMAW Effect of electrode extension • Electrode extension (distance from contact tip to arc) a very critical variable − When increased Electrode preheated Higher deposition − If too great, too much of the available energy used to melt the electrode, resulting in potential for incomplete fusion − Excessive electrode extension also reduces effectiveness of shielding and may result in excessive porosity − A worn contact tip can cause this same effect, even though it doesn't appear to the welder that the visible electrode extension is excessive 17 © 2021 Holdren Engineering Fundamentals of GMAW Effect of electrode extension on bead shape 18 © 2021 Holdren Engineering Fundamentals of GMAW Technique variables Travel angel 19 © 2021 Holdren Engineering Work angel Fundamentals of GMAW GMAW Advantages • Semiautomatic process • High productivity • No slag to remove • Clean process • Continuous filler metal feed • Welds most alloys 20 © 2021 Holdren Engineering Fundamentals of GMAW GMAW Limitations • Unsuitable for windy conditions • Little tolerance for contamination • Usually limited to shop welding • Equipment is more complex • Consumables - liners, contact tips 21 © 2021 Holdren Engineering Fundamentals of GMAW Potential discontinuities Porosity • Insufficient shielding − Gas flow rate too low − Gas flow rate too high − Gas nozzle plugged with spatter − Contact tip-to-work distance too great − Excessive wind or drafts in weld area − Contaminated electrode and/or base metal 22 © 2021 Holdren Engineering Fundamentals of GMAW Potential discontinuities Incomplete fusion • Especially with short-circuiting transfer • Other causes − Insufficient voltage and/or amperage − Incorrect travel speed − Base metal contamination − Incorrect weave motion − Improper joint geometry 23 © 2021 Holdren Engineering Fundamentals of GMAW Potential discontinuities • Incomplete joint penetration − Incorrect welding parameters (voltage, amperage and travel speed) − Incorrect joint geometry − Insufficient root opening • Undercut − Travel speed too fast − Voltage too high − Amperage too high − Incorrect work angle (too steep) − Insufficient dwell time at edges of a weave bead 24 © 2021 Holdren Engineering Fundamentals of GMAW Potential discontinuities • Cracking − Insufficient filling of weld crater  crater crack − Vertical-down welding resulting in concave weld bead  centerline cracking − Stress concentration at sharp corners of slots − Potential for underbead cracking with armor material; however, use of GMAW (low hydrogen process) prevents occurrence 25 © 2021 Holdren Engineering Fundamentals of GMAW GMAW Summary • GMAW an effective and efficient process for welding steel armor • Use of metal core electrodes has resulted in improved overall weld quality due to the potential for desirable weld profiles and absence of spatter  acceptable welds with little or no cleanup required • Must be operated within acceptable WPS limits 26 © 2021 Holdren Engineering Fundamentals of GMAW Visibility and contrast • Visibility and contrast enhances by choosing colors of particles that are easy to see against the color of the surface of the test object • Visibility and contrast can also be enhanced by coating the test object with a contrasting color, such as penetrant developer, which can be used in conjunction with dark particles • Use of fluorescent dyed particles will improve sensitivity because human eye can more readily detect fluorescent indication 27 © 2021 Holdren Engineering Fundamentals of GMAW