If you have not heard this term before, do not be surprised. It is one that is used within the industry to describe the number of minutes within a 10-minute period of time that a welder is able to safely produce a particular welding current.
For example, you may come across a duty cycle that has a 150-amp current. The duty cycle for this weld may be 30%. That means that in a given 10-minute period of time, you could only continuously weld for three minutes. This means that seven minutes of this time would have to be in a “resting” state.
The Higher the Duty Cycle the Better
For contractors, businesses, and industries where time is money, having a low duty cycle is extremely costly. If you were to use the previous example, where the duty cycle was 30%, that would mean in a one hour period of time the welder would be able to perform the operation for only 18 out of a total of 60 minutes.
That is a significant amount of waste in terms of time. As much as 42 minutes of the welder’s time would be spent doing nothing or working on something outside the scope of this particular project. Many welders are making a significant amount of money, so to have them working 30% of the time on a project is a complete waste of any company or business’ resources.
Ideally, the higher the duty cycle the greater the amount of value that the contractor or business is receiving. Most companies are looking for a duty cycle of 100%, as any value less than that is a waste of money.
It’s in the Math
It is important to understand that there is a significant difference between using a welder 100% of the time and him or her being available for that duration. It is clear that no welder is going to be able to continuously work on a project for eight straight hours. Even if the duty cycle is at 100%, they are going to need brakes to ensure that they are maintaining their skills and integrity during the well.
In addition, there are both state and federal laws which demand a certain amount of rest or a certain number of breaks for those working in these types of industries. They understand that employees need maybe as much as 15 minutes every hour or other hour to give them an opportunity to relax and unwind.
In this case, it is clear that some portion of their work time is being lost. However, this makes sense. You want employees who are at their best, and working for three or four straight hours without a break can lead to a weld that has lost its integrity. This is understood by virtually everyone within the industry.
However, when a welder is unable to perform their task because the machinery does not allow them to do so or limits their ability to do the work, this is when a waste can occur.
Consider that on many projects there may be two or more welders working in the same area. One welder could be performing additional tasks related to the weld while the other is actually performing the weld itself. After 30 minutes, they could switch roles, but this would not be possible if the duty cycle was less than 100%. They would have to give the equipment a break, and their schedule would surround the availability of the equipment.
Effects on Duty Cycle
While the welder is looking for the highest possible duty cycle, it is important to understand that the output current has a direct impact on this value. The higher the output current, the greater the decrease in this duty cycle. For example. Welders would be able to attain a 100% duty cycle on output currents of 370 A, but that value will decrease to 60% when the amperage reaches 500 A.
The reason behind this is that when large amperages of current are produced, it can lead to extensive overheating of the welding tools. As this begins to warm, a breakdown can occur and this is why it becomes necessary to give time off for cooling to occur.
You Can Estimate Duty Cycle
While you may be provided the duty cycle percentage, sometimes this is not true. There are instances where you will have to figure this out on your own, and this is not very difficult for you to do. The formula for this is:
Dn = (I/ln)2 x D
Dn is the required duty cycle in percent.
I is the rated current at the required duty cycle, provided in amps.
ln is the maximum current at the required duty cycle, again provided in amps.
D is the rated duty cycle.
So, for example if you are using a welding device that has a power source rated at 200 A the duty cycle may be rated at 60%. However, if the power source increases to 250 A, then this will change the overall required duty cycle.
In this case, the formula would provide
Dn = (200/250)2 x 60
Which equals 38.4%
Just a small increase in amperage nearly cuts the duty cycle in half.
This is an important factor to consider whenever you are performing welds. If possible, if you are intending to use your welding device for an extended period of time and you can decrease the power source output, then you should do so. This allows you to use the tool for a longer period of time, keeping your welder working, thus greatly reducing the amount of wasted time.
This should hopefully give you a clear picture of what the duty cycle is. Now you know the mathematical formula to determine it should the power source amperage change.