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Understanding Welding Current and Polarity.pptx

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Understanding Welding Current and Polarity.pptx

  1. 1. Understanding Welding Current and Polarity
  2. 2. Understanding Welding Current and Polarity • The welding current and polarities associated with them can often be confusing for beginners. At the same time some experienced welders also do not fully understand the electric current because there are many factors to consider. • This brief presentation will highlight what AC and DC currents are, there differences for welding and which one is better suited for certain applications.
  3. 3. What Is DC In Welding • DC stands for direct current where the electrical current flows in one direction. Since the electrical circuit must be continuous for the electricity to flow, we use a ground clamp and an electrode holder to complete the circuit. The arc jumps between the electrode and the metal with the ground clamp attached, thus completing the electrical circuit.
  4. 4. DCEP/Reverse Polarity • Direct Current Electrode Positive (DCEP). In this application the ground clamp is connected to the negative terminal while the electrode holder is connected to the positive terminal. The electrode will receive about 70% of the heat and the work piece about 30%. • The most common polarity for SMAW.
  5. 5. DCEN/Straight Polarity • Direct Current Electrode Negative (DCEN). In this application the ground clamp is connected to the positive terminal while the electrode holder is connected to the negative terminal. The electrode will receive about 30% of the heat and the work piece about 70%.
  6. 6. What Is AC In Welding • AC stands for alternating current where the current switches direction back and forth. Example is our standard home outlets will provide between 110-120V of AC power with a frequency of 60Hz. So your available power reverses polarity 50-60 times per second. The same is true when welding with an AC power source or AC polarity. • Though with increased technology some newer machines can allow the user to modify the output frequency, some machines can output up to 500Hz.
  7. 7. Differences Between AC & DC Welding • The obvious difference is that the AC output switches the polarity, and the current constantly flows back and forth. While the DC output keeps the polarity consistent, where the current flows in one direction. Typically AC polarity is limited to the SMAW & GTAW processes. • The first SMAW power sources were known as “buzz boxes” which were AC machines. The switching of the polarity caused the device to sound like a bumblebee.
  8. 8. AC Welding Advantages & Disadvantages • AC Advantages • AC does not experience a voltage drop when using long leads (ground clamp, electrode holder). • AC SMAW machines are inexpensive compared to DC machines. • AC output creates a more stable arc when welding metals prone to magnetic fields by preventing arc blow. • AC Disadvantages • AC creates more spatter and a less stable electric arc when welding mild steel and stainless steel. • Limited electrode selection. • Weld quality in general is lower compared to a DC machine.
  9. 9. DC Welding Advantages & Disadvantages • DC Advantages • DC output provides a more stable arc compared to AC. • Produces less spatter. • DCEP offers excellent penetration when using the SMAW process. • DCEN provides faster filler metal deposition rates, but penetration is reduced. DCEN recommended for thin sheet metal. • DC Disadvantages • Arc blow is possible when welding magnetized metal. • DC power sources cannot weld aluminum. • DC machines are generally more expensive than AC machines.
  10. 10. AC DC Weld Spatter More Less Arc Stability Worse Better Filler Metal Deposition Rates Moderate High Penetration Moderate High Voltage Drops Using Long Leads No Yes Arc Blow Occurs When Welding Magnetized Metal No Yes Weld Ferrous Metal Like Steel SMAW only All arc welding processes Welds Aluminum AC GTAW DC GMAW/FCAW GTAW Equipment Cost High Low SMAW Equipment Cost Low Medium to High

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