Production & Cost Control
This domain tests whether the supervisor can turn welding variables into time and money. Questions cover deposition rate, operating factor, duty cycle, labor and consumable cost, rework, and the trade-offs between process selection and total cost per foot. The exam rewards supervisors who compare total installed cost, not just the price on the electrode box.
Core formulas and definitions
- Deposition rate (lb/hr): weight of filler actually deposited per arc hour. It rises with current, wire-feed speed, and process efficiency.
- Operating factor: arc time divided by total paid time. SMAW often runs 20-30%; FCAW and GMAW can reach 40-60% because there is less stopping to change electrodes and clean.
- Labor hours per foot: (deposited weight per foot ÷ deposition rate) ÷ operating factor.
- Cost per foot: labor + filler + shielding gas + power + overhead + rework and scrap.
- Duty cycle: the percentage of a 10-minute period a power source can run at a rated current. It falls as current rises; exceeding it causes thermal shutdown.
Worked example
A joint needs 1.2 lb of deposited metal per foot. SMAW deposits 3 lb/hr at a 25% operating factor; FCAW deposits 8 lb/hr at 50%. Labor is $60/hr.
SMAW: arc time = 1.2 ÷ 3 = 0.4 hr. Paid time = 0.4 ÷ 0.25 = 1.6 hr. Labor = $96.00. Filler at $4/lb = $4.80, plus stub loss.
FCAW: arc time = 1.2 ÷ 8 = 0.15 hr. Paid time = 0.15 ÷ 0.50 = 0.30 hr. Labor = $18.00. Filler at $2.50/lb = $3.00; add gas and nozzle/liner cost.
FCAW is far cheaper per foot even if its wire costs more per pound, because labor dominates. The supervisor should present the comparison as total cost per foot.
Traps that cost marks
- Using deposition rate as if it were production rate; forgetting the operating factor inflates output estimates.
- Comparing filler price per pound without accounting for stub loss, spatter, and rework.
- Ignoring fit-up, cleaning, and repositioning time when estimating labor.
- Choosing a process on purchase price alone rather than cost per acceptable foot.
- Overlooking duty cycle when assigning a machine to high-current production.