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Arc-on time and operating factor calculator
Enter a joint length, the travel speed being run, the number of passes and the time the arc spends off, and read the three numbers a production plan is built on: arc-on time per joint, joints per hour, and the operating factor that connects them.
Then run it the other way. Type the output the plan demands and the tool returns the operating factor that target requires, and how many minutes of handling per joint it leaves you.
Two times, one ratio, and the same identity run backwards
Arc-on time per joint tarc = n · L / v
Non-arc time per joint toff = Tweld + n · Tpass
Cycle time tcyc = tarc + toff
Operating factor OF = tarc / tcyc
Joints per hour N = 60 / tcyc
Backwards, from a target N OFrequired = tarc · N / 60, and the non-arc time it leaves is 60 / N − tarc
n = passes · L = joint length in mm · v = travel speed in mm/min · times in minutes
The first line is the travel-speed relation and is arithmetic. The fourth is the definition of the production operating factor, sometimes called the production duty cycle: arc-on time over elapsed time. Nothing here is taken from a standard, because nothing here is a limit — the two time inputs are measurements from your own shop, and the tool reports the ratio they produce.
One distinction is worth stating before the number is quoted anywhere. The duty cycle printed on a welding power source is a thermal rating of the machine, defined by the IEC 60974-1 family against a fixed reference period. The operating factor computed here is about how the cell is scheduled and has no relationship to that limit. The duty cycle glossary entry puts the two senses side by side.
How to calculate arc-on time and operating factor
From a joint on a drawing to the hourly output of the station that welds it — and back again from a target.
- Enter the joint and the arc. Joint length, the travel speed actually being run, and the number of passes. Arc-on time per joint is the passes multiplied by the length divided by the speed, and nothing else enters it.
- Measure the time the arc is off, in two buckets. Once per weld for fit-up, tacking, clamping, positioning and unloading; once per pass for deslagging, brushing, restarting and any interpass check. A six-pass joint pays the per-pass bucket six times, which is why pass count moves the cycle harder than it moves the arc.
- Read the operating factor. Arc time divided by cycle time. The joints per hour and the metres of finished joint per hour follow from the same cycle, and a shift length turns them into a per-shift ceiling.
- Compare the two levers the badge reports. The tool computes what a 10 % faster arc saves per joint and what 10 % less handling saves, both from your own numbers. Which one wins depends on the operating factor you are starting from, so it is worth reading before a rate increase is proposed.
- Run it backwards from the target. Type the output the plan demands as joints per hour or as metres of finished joint per hour. The tool returns the operating factor that target requires and the non-arc time it leaves per joint — or reports that the arc itself is too slow to reach it whatever the handling does.
- The operating factor is the share of the cycle a faster arc can touch. That is the whole argument in one sentence. Raising deposition rate or travel speed compresses only tarc; everything else in the cycle is untouched by it. At a low operating factor a 10 % faster arc is a rounding error against 10 % less handling, and the tool computes both from your inputs so the comparison is yours rather than somebody else's average.
- Pass count is the multiplier nobody costs. It multiplies the arc time and the per-pass handling together, so a preparation that needs two extra fill passes costs the per-pass bucket twice more on every joint of the batch. The joint volume calculator shows how the preparation drives the metal that has to go in, which is what sets the pass count in the first place.
- The productivity lever and the metallurgical one are the same lever. Travel speed sets the arc time here and the heat input there. Before a target output turns into a faster procedure, check what that speed does with the heat input calculator: a cycle time that hits the plan and misses the qualified heat input window has not solved anything.
- Deposition rate and operating factor answer different questions. One says how fast metal goes down while the arc burns, the other says how much of the hour the arc burns for. The deposition rate calculator takes an arc-on time as an input for exactly that reason; this page is where that input comes from.
- An estimate is not a measurement. A stopwatch held for one morning measures the morning somebody was watching. Arc-on time recorded from the current trace on every pass measures the shift — see welding parameter monitoring for how that record gets made, and WeldTrace for the acquisition behind it.
For where the time and the money actually go in an automated cell, read the robotic arc welding monitoring ROI guide.
Questions engineers ask about this calculation
What is the operating factor of a welding station?
It is the share of elapsed time during which the arc is actually burning: arc-on time divided by the total time the same work occupied, usually quoted as a percentage. Take one joint as the unit and it is the arc minutes divided by the whole cycle, handling included. It is a scheduling and organisation measure, so it belongs to the cell and the shop around it rather than to the welding machine, and two stations running the same procedure at the same current can differ by a factor of several in it without any parameter being different.
How do you calculate arc-on time for a multi-pass joint?
One pass takes the joint length divided by the travel speed, and a multi-pass joint takes that multiplied by the number of passes, provided every pass runs the full length at the same speed. A 600 mm joint at 300 mm/min is 2 minutes of arc per pass, so three passes are 6 minutes of arc. Where the root runs slower than the fill, or the cap only covers part of the length, calculate each pass separately and add them: the tool assumes one speed for all passes and says so, because that assumption is the one that quietly breaks on real procedures.
Why does the operating factor move welding cost more than the deposition rate does on manual work?
Because deposition rate can only compress the part of the cycle the arc occupies, and on manual work that part is the minority. Take a 600 mm joint welded in three passes at 300 mm/min, with 8 minutes of handling per weld and 1.5 minutes per pass: 6 minutes of arc inside an 18.5 minute cycle, an operating factor of about 32 %. Welding 10 % faster removes about 0.55 minutes from the cycle. Removing 10 % of the handling — 12.5 minutes of it — removes 1.25 minutes, better than twice as much, and it does it without touching the current, the heat input or anything a welding procedure controls. The tool computes both of those sensitivities from your own numbers rather than from a published figure, because the answer flips once the operating factor gets high enough, which is exactly what happens on a well-fixtured automated cell.
What counts as non-arc time on a welding station?
Anything the joint costs while the arc is off. Split it into two buckets, because they scale differently: time attached to the weld happens once per joint — fit-up, tacking, clamping, positioning the work or the welder, unloading — while time attached to the pass repeats on every run, which is deslagging, wire brushing, restarting, and an interpass temperature check where the procedure calls for one. A joint welded in six passes pays the per-pass bucket six times, which is why pass count moves the cycle far more than it moves the arc time alone.
How do I work out the operating factor a production target requires?
Invert the identity. A target of N joints per hour fixes the cycle at 60/N minutes, the arc time per joint is already fixed by the travel speed and the pass count, so the required operating factor is the arc time divided by that cycle. In that same 600 mm three-pass example, 5 joints per hour means a 12 minute cycle against 6 minutes of arc, so the target demands 50 % and leaves 6 minutes of handling per joint against the 12.5 minutes the station spends today. That is a concrete brief for the shop floor: six and a half minutes of handling per joint has to go, and the calculation says nothing about how.
What happens when the target output cannot be reached at all?
When the required cycle is shorter than the arc time itself, no amount of handling improvement reaches it, because the arc alone already overruns the cycle. Twelve joints per hour on that same example asks for a 5 minute cycle against 6 minutes of arc, so no operating factor reaches it: the tool leaves the required-operating-factor tile empty rather than printing a figure above 100 % as if it were a target, and says so in the badge. The lever then has to be the arc: a faster travel speed, fewer passes, or a different process. The tool gives the travel speed that would close the gap at zero non-arc time, which is a lower bound and not a recommendation — whether that speed is allowed is a question for the welding procedure and its heat input window.
Is the operating factor the same as the duty cycle printed on a power source?
No, and conflating them is the usual way this number gets misread. The rating on a machine is an equipment duty cycle: a thermal limit, defined by the IEC 60974-1 family against a fixed reference period, that says how much of that period the source may deliver its rated current before it has to cool. The operating factor on this page is a production figure about how the cell is scheduled, and it has no relationship to that limit — a station can sit at 20 % operating factor while its power source is rated for far more, simply because most of the shift is spent not welding. The glossary entry on duty cycle sets the two senses side by side.
Why does the joints-per-shift figure not include breaks and downtime?
Because the non-arc time on this page is the time attached to a joint, and shift-level losses are not. Breaks, the shift briefing, waiting on an upstream station, a breakdown, consumable changes and the setup at the start of the shift all sit outside the per-joint cycle, so multiplying the hourly rate by the shift length gives a ceiling that assumes cycles run back to back for the whole shift. Treat the difference between that ceiling and what the shift actually produced as a second, separate measurement: it is usually where the largest and least visible part of the loss lives, and it is a different problem from the handling inside the cycle.
An operating factor written on a spreadsheet is an estimate. An arc that was recorded is not.
WeldTrace records current, voltage and wire feed speed at 25 kHz on every pass, so arc-on time per joint, per shift and per cell comes from when the arc was actually burning rather than from a stopwatch somebody held for one morning.
