Downtime
Downtime is any period when a machine or process is not producing although it is scheduled to. It is the primary driver of availability losses in OEE.
Downtime divides into two categories: Planned downtime (scheduled maintenance, breaks, changeovers) and unplanned downtime (breakdowns, material shortages, quality holds). Unplanned downtime is pure waste and the primary target for improvement.
Every minute of unplanned downtime has a cascading cost: Lost output, missed delivery dates, overtime to catch up, idle operators, and disrupted schedules downstream. In high-throughput environments, one hour of downtime can cost tens of thousands in lost revenue.
Tracking downtime by cause is essential: Most plants find that a small number of failure modes account for the majority of lost time (Pareto principle). Addressing the top 3 causes often eliminates 60-70% of unplanned stops.
Effective downtime reduction combines reactive and proactive strategies: Quick response (Andon) to minimize the duration of each event, root cause analysis (5-Why, Ishikawa) to prevent recurrence, and preventive maintenance to anticipate failures before they occur.
Formula
Availability = (Planned Production Time - Downtime) / Planned Production Time x 100%
Practical Example
A CNC cell is scheduled for 960 minutes per day (two shifts). Actual downtime log: 45 min breakdowns, 30 min material waiting, 60 min changeovers, 15 min minor stops. Total downtime: 150 minutes. Availability: (960 - 150) / 960 = 84.4%. Eliminating material waiting alone would raise availability to 87.5%.
How Lean Shift Helps
You enter the disruption rate in LeanShift's target state calculator. If you link a recording, LeanShift pre-fills it with an estimate from the gap between the average and the fastest cycle. You note the cause of a stop in the Muda analysis by marking the affected step, for example with “Waiting”, and adding a note.
Frequently Asked Questions
What counts as downtime?
Any time the machine or process is scheduled to produce but is not. This includes breakdowns, changeovers, material shortages, quality holds, and minor stops. Planned breaks and maintenance may or may not be included depending on your OEE definition.
How do you reduce unplanned downtime?
Three pillars: Preventive maintenance (avoid failures), quick response systems like Andon (minimize event duration), and root cause analysis (prevent recurrence). Data-driven prioritization using Pareto analysis focuses effort on the biggest losses.
What is the difference between downtime and idle time?
Downtime means the equipment cannot run (breakdown, no material). Idle time means the equipment could run but has no demand (no orders). Both reduce output, but the causes and countermeasures are different.