A larger lot can reduce setup’s arithmetic contribution per piece while leaving the physical setup duration unchanged. Keep those meanings separate.
Retain fixed and repeated work
Production-route definitions distinguish setup time from run time, with quantity-dependent run work calculated separately. In a simplified lot model with one fixed setup S, N pieces and repeated service t per piece, total assigned time is S + Nt. Dividing by N gives S/N + t per piece. Primary reference: Microsoft production routes: separate setup and quantity-dependent run time.
State whether preparation occurs once per lot or for every piece. Fixed lot work belongs outside quantity-multiplied service. Repeated loading is not one-time setup merely because it prepares an item.
Compare fictional lot sizes
Suppose a hypothetical lot needs a 20-minute setup and 1 minute of repeated service per piece. For 10 pieces, total assigned time is 20 + 10 = 30 minutes, or 3 minutes per piece. For 40 pieces, total is 20 + 40 = 60 minutes, or 1.5 minutes per piece.
The setup remains 20 minutes in both cases. Only its allocated contribution changes from 2 to 0.5 minute per piece. The example excludes waiting, transfers, interruption and extra setup within the lot; introducing any of those would require additional terms.
Review the proposal’s scope
Prepare a trial breakdown showing setup occurrence, lot quantity, repeated service and excluded intervals. When comparing lot sizes, retain the same fixed and repeated inputs if the intention is to isolate amortization. A changed process or different tooling would make it a broader comparison.
A lower allocated time per piece does not establish the preferable lot size: release timing, inventory, due dates and other constraints may matter. These numbers are not HM changeover or production times. The guide checks the arithmetic meaning of spreading fixed setup across a defined quantity.
Customer Questions
Does a larger lot shorten the stated setup?
No. It spreads the same setup across more pieces in this model.
What is assigned time per piece for forty pieces?
One and a half minutes, using the fictional 20-minute setup and one-minute repeated service.
Does this determine the best lot size?
No. It isolates setup amortization and omits other decision constraints.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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