Download Basic Production GTAW

Intro to Production Welding
Review Questions 1 – Arc Fundamentals
1. Define the following terms:
Current flow of electrons in a conductor
Voltage Force of current
Resistance Opposition to current
2. What does it mean if a welding machine’s duty cycle is 60%?
The machine can run 6 out of 10 minutes
3. Illustrate the welding circuit and label its parts.
Power source, Work piece, electrode lead, work (ground) lead
4. What creates the heat in a welding circuit?
Resistance to current - arc gap
5. What is arc length?
The distance between the end of the electrode and the weld puddle
6. Where is the majority of heat in the DCEN (DCSP, DC-) arc? What are the basic
characteristics of
this type of arc?
In arc welding processes, the majority of arc heat is always at the positive terminal
In DCEN, 70% of the arc heat is in the work piece.
See polarity reference for uses with various arc processes
7. Where is the majority of heat in the DCEP (DCRP, DC+) arc? What are its basic
characteristics?
In arc welding processes, the majority of arc heat is always at the positive terminal
In DCEP, 70% of the arc heat is at the electrode.
See polarity reference for uses with various arc processes
8. What is arc blow?
In DC welding, a magnetic field is built up in the weld deposit. Arc blow is the
deflection of the arc from its path by these forces.
9. Explain or illustrate alternating current.
In alternating current, electron flow reverses direction at regular intervals . . . 60Hz = 60
full cycles/second = 120 reversals . When using AC, the electrode will be positive in half
the cycle and negative in half the cycle
See polarity reference for uses with various arc processes
10. Why do arc welding processes need a means of shielding the molten puddle?
Molten metal absorbs oxygen & nitrogen, which cause weakness & porosity in the
solidified weld metal
Intro to Production Welding
Review Questions 2 – SMAW
1. What does SMAW stand for?
Shielded Metal Arc Welding
2. What are the functions of the stick electrode coating?
Shield the molten puddle from the atmosphere
Slow cooling rate of the deposited weld metal
Alter composition of weld deposit (iron powder, abrasion resistence, etc.)
3. What factors will affect your choice of electrode for a particular application?
Function of part (load bearing or not)
Type of machine (AC only, AC/DC)
Position of Welding
Joint geometry (open root, wide groove, etc.)
4. What does 6010 mean?
60
tensile strength of weld deposit
1
position 1=all, 2=flat & horizontal only
0
type of coating 0,1 – cellulose coating
5. How do you decide whether to use AC, DCEN (DCSP), or DCEP (DCRP) with a particular
electrode?
Coating determines appropriate current choices. . . . .DCEP for best penetration, AC to
eliminate arc blow
6. What 4 skills must you master for successful “stick” welding?
Arc Length, Travel Speed, Travel Angle and Work Angle, Amperage
7. What happens to your weld when your arc length is too long?
How long should it be?
Voltage gets too high, bead too flat , amperage decreases - 1/8” optimum
8. What happens to your weld when your travel speed is too fast?
Too narrow, insufficient penetration
Intro to Production Welding
Review Questions 3 – GMAW/FCAW
1. What are some advantages of the GMAW and FCAW processes?
Continuous feed electrode - high depositon, high travel speed
All position welding
2.
What does GMAW stand for?
Gas Metal Arc Welding
3. What shields the molten puddle from the atmosphere in the GMAW and FCAW processes?
Argon & CO2
4. How does your Wire Feed Speed (WFS) setting affect the amperage?
WFS determines amperage, amperage determines penetration
5. What type of current is used for GMAW and FCAW?
DCEP
6. What happens to your weld when your stickout is too long? What happens when it is too
short?
Stickout acts as resistance to current, so longer stickout, less amperage
7. What gasses are used for shielding on plain carbon steel?
Argon & CO2
Short circuit – 75% Ar/25% CO2 or 100% CO2
Spray transfer – 90% Ar/10% CO2
8.
Illustrate or explain short circuit transfer. What is it good for?
Low heat input with fast cooling
Mild penetration, great for vertical & overhead work
Not for major structural work
9.
Illustrate or explain spray transfer. What is it good for?
High amperage, high voltage pinches off droplets of filler in steady stream into puddle
Very fluid puddle, high deposition, good penetration, only good for flat & horizontal
welding
10. If your arc length is too short, how can you fix it?
Increase voltage
11. What does the flux in flux-cored wire do for the weld?
Shields puddle, slows cooling rate of puddle
Intro to Production Welding
Review Questions 4 – GTAW
1. Why doesn’t the electrode melt in GTAW?
The tungsten electrode is non-consumable – filler is added separately
2. How is the molten puddle shielded from the atmosphere in GTAW?
Inert shielding gas - Argon
3. What does GTAW stand for?
Gas Tungsten Arc Welding
4. What is the purpose of the high frequency control on a GTAW machine?
The HF allows for arc starting without touching the electrode to the work. . . . the high
frequency current can jump the arc gap - the 60Hz welding current can not.
HF current also stabilizes the AC arc (aluminum welding) by ionizing the arc path, so
that current reversal can occur
5. Why isn’t DCRP used for GTAW?
DCRP = DCEP . . . 70% of arc heat on electrode. . . electrode will melt
6. How should you prep tungsten electrodes for welding with DC current and for AC current?
DC – tapered end (length - 2 ½ times diameter )
AC – balled up end
7. What kind of electrode should you use for DC welding? How about AC welding?
DC – thoriated - red (or lanthanated – gold)
AC – pure – green
8. What shielding gasses are used for the GTAW process?
Argon
Helium (not very common)
9. What is the purpose of the postflow function on a GTAW machine?
Allows gas flow after arc extinguished – cleaning at end of weld
10. What factors determine the electrode diameter you choose for GTAW?
Thickness of base metal
Position of welding
Type of electrode
Joint Geometery
11. How long should your arc length be for GTAW?
What happens if you stick the tip of your electrode into your molten puddle?
About 1/16”
It gets schmutzed up, stuff sticks to it, and the arc wanders around
Intro to Production Welding
Review Questions 5 – Cutting Processes
1. In oxyfuel cutting, what factors determine the appropriate tip size for a cut?
Thickness of metal
2. What happens to an oxyfuel cut when too much fuel gas is used?
Excessive preheat – top edge gets rounded over. . . .too much slag on back side
3. What happens to an oxyfuel cut when the oxygen pressure is too low?
Cut can be lost, gouges
4. About how far should the torch be held from the work in oxyfuel cutting? Why?
Preheat flames 1/8” from surface of metal . . . . .
If you hold the torch too close, too much heat is forced back up into the tip, causing
backfires & possible flashback
5. What happens to an oxyfuel cut when the travel speed is too fast?
Cut may be lost due to insufficient preheat, gouging
6. What is plasma?
4th state of matter . . . ionized gas
Arc plasma – a gas that has been heated by an arc to an ionized condition, enabling it to
conduct electric current
Comparison of Currents & Polarities for Arc Welding
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+
+
+
+
+
+
+
+
+
+
+
DCEP (DC+)
DC Electrode Positive
Reverse Polarity
75% of Arc Heat @ Electrode
DCEN (DC-)
DC Electrode Negative
Straight Polarity
75% of Arc Heat @ Workpiece
+
AC
Alternating Current
50% of Arc Heat @ Electrode,
50% of Arc Heat @ Workpiece
SMAW
DCEP (electrode positive)
DCEN (electrode negative)
AC
Digging Arc
“Soft” Arc
Moderate Arc
Deep Penetration
Light Penetration
Moderate Penetration
Light Buildup
Good buildup
Moderate Buildup
E6010, E7018
E7014, E7024, E6013
E7014, E7024, E6013
The arc characteristics listed for the currents and polarities above will also depend on
electrode type and operator-controlled variables.
GMAW/FCAW
All Metals
Rarely Used
Not Used
Good Penetration due to
Sometimes used for surfacing and
majority of arc heat on electrode
with self-shielded FCAW wires
GTAW
Rarely used
Steels
Aluminum
Excessive electrode consumption Good Penetration due to majority
Penetration - EN half cycle
due to heat on electrode
of arc heat in base plate
Cleaning Action – EP half cycle
Sometimes used with large
electrode on thin sheet metal