SMAW Versus FCAW on 1,800 Feet of 1/4 in. Fillet Welds
Your shop must complete 1,800 linear feet of 1/4 in. fillet welds on A36 channel frames. The current plan uses SMAW with 1/8 in. E7018 at 2.0 lb/hr deposition, 60 percent deposition efficiency, and 40 percent operating factor. Alternatively, you can switch to FCAW with 0.045 in. E71T-1 at 8.0 lb/hr, 85 percent efficiency, and 50 percent operating factor. The weld metal required is 0.106 lb per foot before waste; add 10 percent for spatter, stubs, and scrap. FCAW consumables cost $1.60/lb versus $2.20/lb for E7018. Fully burdened labor is $55/hr. Changeover, gas, and a new WPS qualification cost $4,500. FCAW needs 16 hours of training for four welders, paid at $55/hr, before production. The customer accepts either process if qualified. Your superintendent wants the decision by tomorrow.
1. Calculate the labor and consumable cost for each process, including the FCAW fixed costs. Which process do you recommend?
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Use weld metal, not wire purchased, as the base. Required weld metal = 1,800 ft x 0.106 lb/ft = 190.8 lb; add 10 percent = 209.9 lb. SMAW: wire consumed = 209.9 / 0.60 = 349.8 lb; arc time = 349.8 / 2.0 = 174.9 hr; work hours = 174.9 / 0.40 = 437.3 hr; labor = 437.3 x $55 = $24,052; consumables = 349.8 x $2.20 = $770; total = $24,822. FCAW: consumed = 209.9 / 0.85 = 246.9 lb; arc time = 246.9 / 8.0 = 30.9 hr; work hours = 30.9 / 0.50 = 61.7 hr; labor = 61.7 x $55 = $3,394; consumables = 246.9 x $1.60 = $395; changeover and WPS = $4,500; training = 4 x 16 x $55 = $3,520; total = $11,809. FCAW saves about $13,000, roughly 52 percent, so I recommend FCAW if the WPS is qualified and the quality assumptions hold.
2. What non-cost factors could reverse your recommendation?
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FCAW is cheaper only if the procedure is qualified for the positions, thickness, and joint details in production. Check whether the project code accepts FCAW as prequalified or requires a new procedure qualification; the $4,500 estimate may be low if impact testing or multiple positions are needed. FCAW produces more visible fume and spatter, so ventilation and cleaning time may rise. The 50 percent operating factor is an assumption; if the shop's actual factor is 30 percent, the labor advantage shrinks. The four welders may need more than 16 hours to become consistent, and poor starting technique can create lack of fusion. Confirm machine duty cycle and wire-feed capacity. If rework rises above about 4 percent, the savings can disappear. Also consider distortion and fit-up: higher deposition means more heat input unless parameters are controlled.
3. If only 600 feet remain on the contract, does your recommendation change? Show the reasoning.
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Yes. The fixed costs dominate at low volume. Weld metal = 600 x 0.106 = 63.6 lb; add 10 percent = 70.0 lb. SMAW: consumed = 70.0 / 0.60 = 116.7 lb; arc time = 58.3 hr; work hours = 145.8 hr; labor = 145.8 x $55 = $8,019; consumables = 116.7 x $2.20 = $257; total = $8,276. FCAW: consumed = 70.0 / 0.85 = 82.4 lb; arc time = 10.3 hr; work hours = 20.6 hr; labor = 20.6 x $55 = $1,133; consumables = 82.4 x $1.60 = $132; fixed costs = $4,500 + $3,520 = $8,020; total = $9,285. SMAW is cheaper by about $1,000. Keep SMAW unless the FCAW changeover and training are already sunk for other work or the schedule requires the higher deposition rate.