TWI Frequently Asked Questions
by Chris Miller
The term duty cycle is used to describe the amount of time spent depositing weld metal (the arcing period) as a percentage of the total time taken to complete a weld. In the USA, the duty cycle is called the Operator Factor.
With the MMA process, frequent interruptions are required to allow for slag removal, inter-run dressing and changing the electrode. Consequently, the duty cycle can be quite low.
At the other extreme, a high duty cycle is possible from a programmed robot because it may be able to weld continuously for long periods with only short interruptions to allow for the work-piece to be manipulated.
While the duty cycle for each welding process will vary according to factors such as type of work, access to joints and the working practices of a particular organisation, it is possible to allocate some typical values such as those shown in the table below.
Some typical duty cycles for workshop welding
| Welding process | Duty cycle |
| Typical (%) | Range (%) |
| MMA (SMAW) | ~25% | 15 to 40% |
| MIG/MAG (GMAW) - semi-automatic | ~45% | 15 to 60% |
| MIG/MAG (GMAW) - automatic | ~90% | 50 to 100% |
| FCAW - semi-automatic | ~40% | 15 to 55% |
| SAW - mechanised | ~40% | 40 to 90% |
It is important to note that the term duty cycle is also used to rate welding power sources and refers to the maximum welding current that they can be used for a particular operating time.
