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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 _ + + + + + + + + + + + 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