Choosing a Process for 4,000 Feet of Fillet Weld
You must produce 4,000 linear feet of 1/4-in. fillet weld on A36. Theoretical deposited weight is 0.106 lb/ft; adding 10% for reinforcement and oversize, plan on 460 lb of deposited metal. Labor is $60/hr fully burdened, and either machine is already owned and idle, so there is no capital difference.
GMAW (0.035-in. solid): 3.5 lb/hr deposition, 40% operating factor, $1.60/lb filler at 98% efficiency, 25 cfh gas at $0.05/cf.
FCAW-G (0.045-in. E71T-1): 7.0 lb/hr deposition, 45% operating factor, $2.40/lb filler at 86% efficiency, 35 cfh gas at $0.05/cf.
1. Compute the cost per foot for each option and identify where the money actually goes.
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GMAW
- Arc hours: 460 / 3.5 = 131.4 h
- Paid hours: 131.4 / 0.40 = 328.6 h → labor $19,714
- Filler: (460 / 0.98) × $1.60 = $751
- Gas: 25 cfh × 131.4 h = 3,285 cf × $0.05 = $164
- Total ≈ $20,629 → $5.16/ft; labor is 95.6% of it
FCAW-G
- Arc hours: 460 / 7.0 = 65.7 h
- Paid hours: 65.7 / 0.45 = 146.0 h → labor $8,760
- Filler: (460 / 0.86) × $2.40 = $1,284
- Gas: 35 cfh × 65.7 h = 2,300 cf × $0.05 = $115
- Total ≈ $10,159 → $2.54/ft; labor is 86%
Difference: about $10,470, or 51%. The filler price gap ($586 more for FCAW) is noise against a $10,954 labor gap.
2. Filler prices are volatile and your engineer calls the 45% operating factor optimistic. How far can the FCAW case deteriorate before the choice flips?
Read the worked answer
Test both variables.
Filler price: at $3.60/lb instead of $2.40, FCAW filler rises to $1,926 and total to $10,801 - still about $9,800 ahead. Filler is the wrong thing to worry about.
Operating factor: set FCAW's labor plus filler plus gas equal to GMAW's total. 60 × (65.7 / f) + 1,284 + 115 = 20,629 → 3,942 / f = 19,230 → f = 0.205
FCAW would have to fall to a 20.5% operating factor - less than half the assumed value - before GMAW wins. The margin is large, but the operating factor is the number most likely to be wrong, because flux-cored welding adds deslag and cleaning time. On short, tack-heavy, repositioning-heavy work, re-measure it with a stopwatch before you commit.
3. What factors outside the arithmetic could still change the decision?
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Schedule and headcount. 146 paid hours is roughly 3.7 weeks for one welder; 329 hours is more than eight weeks on one man, so GMAW would need two arcs and two machines - that, not filler, is the real fixed cost.
Quality risk. Add expected rework to whichever process the shop has historically struggled with. At 5% of 146 hours, FCAW rework is about 7 hours (~$440) - immaterial, but it is only immaterial because the labor base is small.
Data credibility. The deposition rates came from a vendor sheet measured at 100% arc time. Verify them on your own floor with a stopwatch and a scale, using your wire and your positioner, before you quote $2.54/ft to a customer.