Year2, Mod3, Welding

  1. When was GMAW first introduced?
    1920s, commercially available 1948. Developed to eliminate use of fluxes when welding aluminum and magnesium alloys.
  2. What polarity does GMAW generally use?
    DCEP (reverse polarity)

    direct current, electrode positive
  3. How are electrode holders rated?
    by their current carrying capacity
  4. Describe the regulator.
    responsible for reducing the gas source pressure to a constant working pressure
  5. Desrcibe flow meter.
    control the rate of flow of a sheilding gas to the nozzle.Calibrated in L/min or CFH.
  6. What are the three basic modes of metal transfer?
    • - short-circuiting transfer
    • - globular transfer
    • - spray transfer
  7. Desrcribe Short Circuiting Metal Transfer
    lower current settings and specific voltage range (19-20V)

    only occurs when filler wire is in direct contact with the base metal

    Can be used in all positions
  8. Describe Spray Transfer.
    • - shielding gas >85%
    • - weld current above critical value (transition current). 26-35 V
    • - generally used for flat and horizontal positions
  9. Name the welding positions.
    • 1- flat
    • 2- horizontal
    • 3- vertical
    • 4- overhead
  10. What are the amperes range for machines?
    100 to 500
  11. Does the DC Constant Current (CC) machine work well for GMAW?
    NO. Good for SMAW and GTAW.
  12. What controls the amperage?
    wire speed
  13. What are the preffered wire drive rollers for solid wires?
    V-groove and U-groove
  14. What is voltage? In relation to GMAW?
    • - force that overcome resistance to allow amperage flow
    • - high voltage = wider, flatter weld bead w/ shallower penetration
  15. What is amperage? In relation to GMAW?
    amount of current flow. Controls penetration and burn-off rate of electrode.
  16. What is DCEN known as?
    straight polarity
  17. What is the distribution of arc energy when welding with DC current?
    2/3= arc energy associated with the negative side of the welding circuit.
  18. What is stickout?
    distance between electrode contact tip and the end of the unmelted electrode.
  19. List the basic components of a GMAW set-up.
    • 1. power source
    • 2. wire feeder
    • 3. gun and cable assembly
    • 4. spooled filler wire
    • 5. shielding gas and gas control equipment
  20. What is a major advantage of pulsed spray transfer?
    all-position welding on thinner materials
  21. Constant Arc Voltage machines produce:
    a relatively flat volt-amp curve
  22. What type of volt-amp curve does a constant current machine produce?
  23. What is the recommended stickout for short circuiting metal transfer?
  24. What may occur when too much slope is set on a CP machine?
    bending and stubbing of the wire
  25. Slope and inductance are use to ...
    reduce spatter and improve arc stability
  26. the power sources used for pulsed spray transfer are:
    DC synergic, micro-processor controlled
  27. A pull type welding gun is designed to be used with...
    soft wires.
  28. What type of wire-drive system allows greater machine-to-work distances?
    push-pull system
  29. What is the purpose of the curved neck on a gmaw welding gun?
    to ensure proper electrical transfer to the wire electrode.
  30. What is the max distance for a push wire system?
    15 feet
  31. What is the main purpose of the contact tube?
    to transfer the welding current to the filler wire
  32. Is carbon dioxide an inert gas?
  33. Which shielding gases are recommended for Al?
    • Argon
    • Helium
  34. When short-circuiting, number of short circuits varies from...
    20-200 tiimes/second
  35. Welding power sources are construced to ______ standards.
  36. OCV is defined as.
    Open Circuit Voltage
  37. Another name for wire-hangups is.
    bird nesting
  38. What is slope?

    What is it's main purpose?
    reduction in output voltage with increasing amperage

    reduce spatter,
  39. Define Helix.
    cork screw effect exhibited by a ring of electrode filler wire. If very large can cause wire to wander and produce poor welds
  40. Define Cast.
    the permanent set wire takes when wound on a spool
  41. Classification of GMAW Wire


    E- electrode
    R- Rod
    49 - min. tensile strength
    S - solid wire
    X- chemical analysis of wire
  42. list some basic properties of shielding gases.
    • - specific gravity
    • - ionization potential
    • - thermal conductivity
    • - oxidation potential
  43. Describe some characteristics of Helium as a shielding gas.
    • - flow rate is 2-3 times that of argon
    • - high thermal conductivity
    • - produces arc-plasma for uniformly distrubuted energy
  44. What is the benefit of O as a shielding gas?
    up to 10% concentration increases puddle fluidity thus reducing undercut
  45. What is C25 characterize by?
    • - stable arc
    • - good puddle control
    • - little spatter
    • - can be used on lower voltage and current settings
  46. What polarity is generally used for GMAW?
    Direct Current Eletrode Positive
  47. How is the work positioned for a 1F Tee joint?
    90' and 0' to the horizontal plane
  48. What would be the normal electrode angle when doing single-pass 1F welds?
    45' to the joint angle
  49. In what positions can you do surface welding with GMAW using short-circuit metal transfer?
    all positions
  50. What is the most likely weld progression for the first pass on 3F weld on 3/8" material?
  51. What type of bead is usually used for the cover pass on a 3F weld on 3/8" material?
    weave bead
  52. What is the recommended gun angle for the first pass of a 2F weld on 3/8" material with three stringer bead passes?
    45' to the horizontal and vertical planes
  53. What amount of argon is needed to achieve spray transfer?
  54. What GMAW mode of metal transfer is best suited for all-position welding?
    pulsed spray arc transfer
  55. The power source best suited for short-circuit mode of metal transfer is:
    constant voltage power source
  56. When using teh short circuiting mode of metal transfer, inductance controls the:
    rate of rise and fall of amperage
  57. The purpose of a flowmeter is to:
    maintain a constant flow of gas
  58. What would be a cause of excessive root pentration?
    to slow of a travel speed
  59. Welds having longitudinal cracks are the result of:
    the travel speed being too fast
  60. How will penetration be affected when stickout is increased?
    will decrease pentration
  61. What can excessive spatter on the gun nozzle cause?
    inadequate gas coverage
  62. When arc hunting occurs, the problem is likely in the:
    contact tip or the conduit liner
  63. Stubbing is caused by:
    excessive wire feed speed.
  64. What is the major cause of cold lap when using GMAW short-circuit metal transfer?
    slow travel with a large bead
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Year2, Mod3, Welding