Welding math
Deposition Rate
Deposition rate measures how fast a process puts metal in the joint while the arc is actually burning, which is only half the productivity picture and often the less important half.
The formula
DR = W_deposited / t_arc, or DR = melt-off rate x efficiencyDeposition rate in pounds per hour is the weight of metal deposited divided by the arc-on hours it took, or equivalently the rate at which electrode is consumed multiplied by the deposition efficiency.
Work it out
Weigh what went in the joint and time the arc. Arc hours, not clock hours.
- Deposition rate
- 6.00 lb/hr
- Per minute of arc time
- 0.1000 lb/min
The same arithmetic as the worked examples above, on your own numbers. It reports geometry and physics, never an acceptance limit: what a joint is allowed to be comes from the job's own code and contract documents.
What each symbol means
| Symbol | Meaning | Units |
|---|---|---|
| DR | Deposition rate, weld metal laid down per hour of arc time | lb/hr |
| W | Weight of weld metal actually deposited in the joint | lb |
| t_arc | Arc-on time, not clock time | hours |
| MR | Melt-off rate, the rate the electrode itself is consumed | lb/hr |
| e | Deposition efficiency, deposited weight per pound of electrode consumed | fraction |
Why it works
The definition is deliberately narrow. Deposition rate counts only arc-on time, so a process that lays down twenty pounds an hour while burning does exactly that regardless of how long the welder spends fitting, chipping, or waiting. Keeping the definition narrow is what makes the number comparable between processes; combining it with operating factor is what makes it comparable between shops.
There are two ways to arrive at it. Weighing a test coupon before and after and dividing by the timed arc period is the direct measurement, and it is the one that settles arguments. The indirect route multiplies the melt-off rate by deposition efficiency, which is useful because melt-off is easy to compute from wire feed speed and wire diameter, and because it makes the efficiency loss explicit.
Deposition rate rises with current, which is why processes and positions that tolerate high current are the productive ones. A flat-position submerged arc weld runs currents no overhead stick welder could hold. That relationship also sets a limit: pushing current for deposition raises heat input at the same time, so on a heat-input-limited procedure the productive setting and the permissible setting can be different numbers.
Worked examples
What you are given, what you do with it, and what the answer actually tells you. Cover the steps and try it before you read them.
Example 1: Weighing a timed test coupon
Given
- Weld metal deposited
- 6.4 lb
- Arc-on time
- 48 minutes
Working
- Convert arc time to hours: 48 / 60 = 0.8 hours.
- Divide deposited weight by arc hours: 6.4 / 0.8.
Result
8 lb/hr
Eight pounds an hour of arc time is a respectable semi-automatic figure. What it does not say is how many of the shift's hours were arc-on, which is where most of the real difference between shops lives.
Example 2: Deriving it from melt-off and efficiency
Given
- Electrode melt-off rate
- 12 lb/hr
- Deposition efficiency
- 0.85
Working
- Recognise that only the efficient fraction of consumed electrode stays in the joint.
- Multiply: 12 x 0.85.
Result
10.2 lb/hr
Nearly two pounds an hour of electrode never becomes weld metal, leaving instead as slag, spatter, and fume. That gap is what separates the consumable purchase from the deposit.
In practice
- Arc-on time is not shift time. A deposition rate quoted against clock hours is roughly three times too low and describes something else entirely.
- Melt-off rate can be computed from wire feed speed and wire cross-section without weighing anything, which makes the indirect route practical for wire processes.
- Position dominates deposition rate on manual work. The same welder, consumable, and machine will deposit far less overhead than flat, because the puddle sets the ceiling on current.
- Chasing deposition rate on a heat-input-limited joint is self-defeating; the limit will bind before the process runs out of capability.