Semiconductor Fab Equipment Manufacturing worked example

Service Spare Buffer with spare parts consumed per day of 3,000 units / day: a worked example

What does the result look like when spare parts consumed per day reaches 3,000 units / day? The full calculation is worked below with real intermediate numbers. Use it when service spare buffer in semiconductor fab equipment manufacturing is being sized for a buffer or safety stock review.

The inputs for this scenario

  • Spare parts consumed per day: 3,000 units / day (raised for this scenario; the documented default is 1,200)
  • Supplier replenishment lead time: 85 days (unchanged)
  • Safety stock held above cycle stock: 1.1 units (unchanged)

Working through the calculation

  • Applying the documented formula (Service spare buffer cycle stock = service spare buffer daily usage × service spare buffer lead time) to the inputs above produces each figure below.
  • At this operating point the engine returns 32.09 days for protected days of supply, the number this scenario is built around.
  • At this operating point the engine returns 35.29 days for unprotected days.
  • At this operating point the engine returns 3,000 pieces for inventory.
  • At this operating point the engine returns 85 pieces / day for daily usage.

How this compares with the baseline

  • Against the tool's baseline example, where spare parts consumed per day sits at 1,200 units / day and the headline result is 12.83 days, this scenario comes in 150% above the baseline at 32.09 days.
  • A figure at this level is achievable when spare parts consumed per day is genuinely sustained, not just peaked for a shift. It assumes steady daily usage; spike demand from a fleet-wide PM campaign or a systemic failure mode can drain the buffer far faster than the average implies.

Results at a glance

  • Protected days of supply: 32.09 days (headline result)
  • Unprotected days: 35.29 days
  • Inventory: 3,000 pieces
  • Daily usage: 85 pieces / day

Run it with your numbers

  • Every input above is editable in the live Service Spare Buffer calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.