Spare Parts Inventory
Spare parts inventory is the systematic stock of critical components, materials, consumables, and specialty tools maintained to support equipment reliability, minimize downtime, and ensure rapid response to failures or planned maintenance activities.
In shop floor maintenance, spare parts inventory is integrated into CMMS like ServiceGrid to link parts directly to assets, work orders, and schedules, enabling real-time tracking of quantities, locations, reorder points, and usage history. Stock levels are optimized using reliability engineering: preventive maintenance spares are calculated via failure rates (λ × PM interval), while corrective maintenance spares use Poisson distribution for target availability (e.g., 99%). Criticality-based stocking (VED: Vital, Essential, Desirable) determines minimum/maximum quantities, with vital items often holding 1 unit. Safety stock is derived from 3-year consumption patterns, using Poisson if variance ≤10% of mean, or bootstrapping if >10%, for lead-time service-level modeling.
How is the optimal number of corrective maintenance spares calculated for 99% availability?
Compute mean CM spares as λ × PM interval, then use Excel’s POISSON.DIST(x, mean, TRUE) to find x where cumulative probability ≥ 0.99, matching with MATCH and rounding up via CEILING.
When to use Poisson vs. bootstrapping for safety stock?
Use Poisson if daily variance ≤10% of daily mean; use bootstrapping if variance >10% to model consumption frequency/probability during lead time.
What reliability metric defines spare part inventory success?
Stock reliability—the probability that a spare request is not rejected due to lack of stock—is a core optimization criterion alongside cost minimization and equipment availability maximization.