Positioner Investment on a 2,800-Part Order
Precision Tube & Fab has won a blanket order for 2,800 pipe-to-flange assemblies per year: 6 in. Schedule 40 pipe to a 10 in. 150# slip-on flange, GMAW, one fillet pass each side. Today the work runs on two flat-position stations. Each part goes on a table, the operator welds one side, calls the overhead crane to flip it (about 6 min per flip, four flips per part), and welds again. Measured arc-on time is 4.0 min per part; total floor-to-floor is 32 min. Loaded labor is $46/hr, and the shop already runs Saturdays to keep up. Engineering proposes two weld positioners with powered rotation and foot control at $41,500 each installed, plus $7,000 for training and fixturing. Expected floor-to-floor is 14 min with no change in arc time. Allow a 12% learning-curve loss for the first three months, and maintenance of about $4,000/yr. The plant's capital hurdle is a 3-year simple payback.
1. Run the payback and state your recommendation with the arithmetic shown.
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The arithmetic passes, but the margin is thin enough that you should not buy both at once.
Savings per part = 32 - 14 = 18 min. Annual savings = 18 min x 2,800 parts = 50,400 min = 840 labor-hours. At $46/hr loaded = $38,640/yr. Less $4,000/yr maintenance = $34,640 net per year.
Investment = (2 x $41,500) + $7,000 = $90,000. Simple payback = 90,000 / 34,640 = 2.6 years - inside the 3-year hurdle.
The learning curve is not decisive: a first quarter at 88% of the savings costs roughly 25 hours, about $1,150.
What matters is fragility. The whole case rests on hitting 14 minutes. If fixturing problems leave it at 18 minutes: 14 min x 2,800 = 653 hr x $46 = $30,040, less $4,000 = $26,040, and payback stretches to 3.45 years - a fail.
Recommendation: approve one positioner as a 60-day pilot on the highest-volume configuration, measure floor-to-floor, arc-on ratio and repair rate, then release the second unit on data rather than on an estimate.
2. What does the payback calculation leave out that a supervisor should weigh?
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Several things the spreadsheet cannot see, and some cut both ways.
- Safety and ergonomics: four crane lifts per part x 2,800 parts is 11,200 crane lifts a year eliminated, plus far less manual handling of 60-80 lb assemblies at bench height. Fewer lifts also means less struck-by and pinch exposure in the bay.
- Quality: a positioner holds the joint flat and lets the welder keep a consistent travel speed and torch angle, which reduces the variation that drives repair. It also frees the crane for other work - a hidden capacity gain in a shop that is crane-bound.
- Capacity: 840 hours is roughly 21 weeks of one operator. That is the honest answer to the Saturday overtime, but only if labor is redeployed at the same time; otherwise the hours saved simply show up as idle time.
- Costs not in the estimate: fixture design for the slip-on flange, possible flange distortion if clamping is wrong, floor space, maintenance downtime on a single machine, and training time beyond the $7,000 allowance.
- Risk: concentrating both stations on positioners creates a single point of failure on a blanket order with a schedule commitment.
The payback answers "can we afford it." These factors answer "can we run it."
3. How would you structure the pilot so the decision on the second unit is evidence-based?
Read the worked answer
Set the measurement plan before the machine arrives, or the pilot becomes an opinion.
- Baseline first: time 30 parts on the current station and record floor-to-floor, arc-on time, crane wait, and repair rate. Without a baseline the 32-minute figure stays an assumption.
- Define pass criteria up front, tied to the hurdle: floor-to-floor at or below 16 minutes, arc-on ratio at or above the current 12.5%, repair rate no worse, and no new distortion rejects on the flange face.
- Run the pilot on the highest-volume part family so the sample is representative, and keep the second station unchanged as a control so week-to-week demand swings do not masquerade as improvement.
- Track the learning curve weekly for 60 days. If the trend line reaches 16 minutes and is still falling, the full payback case holds and the second unit is justified. If it plateaus at 18-20 minutes, revisit the fixture design before spending again.
- Report the result to the plant with the same arithmetic you used to request the capital, including anything that came in worse than estimated. Credibility on the next request depends on it.