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Arc-Welding

Operation Tips

Arc welding requires an operator and a power source. Both the operator and the equipment have roles to play in making the welding process more energy efficient.

Some Important Definitions

Arc-on time: When the welder holds an arc between the electrode and the work piece

Idling time: When welding equipment is ready for use but is not generating an arc

Operating factor: The ratio of arc-on time to the total time worked, often expressed as a percentage:

operating factor

Work time: Convention is to assume total annual work time of 4000 hours (two shifts).

Power Efficiency

Welding power sources draw power when idling. Efficiency is greater when idling is reduced and the operating factor is close to 100 percent. The higher the operating factor, the more efficient the process. The following are ways to improve efficiency:

  • Use the most efficient welding process. Use gas metal arc welding (GMAW) instead of shielded metal arc welding (SMAW). Typically, operating factors for SMAW fall between 10 to 30 percent; operating factors for GMAW fall between 30 to 50 percent.
  • Use multi-process inverter power sources. Modern inverter power sources can be used for several welding processes and save time and effort when switching processes. For example, the Miller XTM 304 can be used for GMAW, FCAW, SMAW and GTAW.
  • Automate when possible. Manage repetitive operations by applying advances in automation and computer programming.
  • Reduce idling time. Cut the time spent on pre-welding tasks such as assembly, positioning, tacking and cleaning, and on follow-up operations, such as slag removal and defect repair.
  • Position the work to allow down-hand welding. Experience has shown that down-hand (vertical high to low) welding is faster, easier on the operator and more error-free than other techniques.
  • Train the welder. Well-trained welders work better and faster and are usually conscious of energy savings opportunities.

Power Source Performance

Certain characteristics determine the energy efficiency of power sources:

  • Power factor: Power factor is the ratio of “real” electrical power made available by the welding power source for producing a welding arc (the power you can use) to the "apparent" electrical power supplied by the utility (the power you pay for). The older technology of transformer-rectifier power sources can have power factors in the order of 75 percent; modern inverter power sources have power factors close to 100 percent.
  • Arc-on power and idling power: Transformer-rectifier power sources use more power in arc-on and idling modes than modern inverter power sources do with the same output.

The following table shows that the average annual electrical energy required by a typical transformer-rectifier source is five to nine times the energy required by an inverter power source for the same job. In other words, the inverter source uses only 10 to 20 percent of the power needed by a transformer-rectifier source.

Power Source Process Apparent Arc-On Power (kW) Apparent Idling Power (kW) Operating Factor (OF) Annual Energy Required (kWh)
Transformer – rectifier SMAW
(stick)
10.26
10.26
4.86
4.86
10%
30%
18 600
25 920
Inverter SMAW
(stick)
   3.91
   3.91
0.12
0.12
10%
30%
   1 996
   5 028

To compare the performance of power sources use the following formula:

energy conversion efficiency

The kVA input and output values for power sources at rated outputs can be found in manufacturers' equipment data sheets.

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