Six Big Losses

The six big losses are the most useful piece of structure in TPM and the thing that turns an OEE number from a scoreboard into an action list. The framework was developed in Japanese maintenance literature as a way to categorize every loss that erodes equipment capacity, in a way that connects directly to the OEE calculation. A shop that knows which of the six is the biggest drag knows which improvement work to do first.

"OEE tells you the score. The six big losses tell you the play."

How the six big losses work

The six categories cover every way a machine loses capacity, and each maps to one of the three OEE factors:

Availability losses 1. Equipment failure. Unplanned breakdowns that stop the machine for a meaningful period. Driven by reliability issues, addressed through preventive and predictive maintenance. 2. Setup and adjustment. Time spent on changeovers and any adjustment needed before the first good part. Driven by changeover complexity, addressed through quick changeover work.

Performance losses 3. Idling and minor stops. Stops shorter than a defined threshold (often five or ten minutes) that are usually not logged as breakdowns. Jams, sensor false alarms, brief operator interventions. Often the largest hidden loss in a small shop. 4. Reduced speed. Running below the machine's ideal cycle time for any reason: conservative feeds, worn tooling, inconsistent material, operator caution.

Quality losses 5. Process defects. Parts produced during a normal run that fail inspection. Includes scrap and parts that require rework. 6. Reduced yield at startup. Parts scrapped or reworked during ramp up after a stop or changeover, before the process is fully back in spec.

Each category has its own diagnostic approach. Equipment failure pulls toward mean time between failures work. Setup pulls toward single minute exchange of die. Process defects pull toward quality maintenance. The framework's value is that it forces the conversation to move from "OEE is low" to "this specific loss is the biggest contributor, here is how we attack it."

Where the six big losses fit on the shop floor

Picture a 25 person plastics injection shop with OEE on its lead press hovering at 62 percent. The owner has been trying to improve it generically. A six big losses categorization over three weeks reveals:

• Equipment failure: 4 percent of planned time
• Setup and adjustment: 12 percent
• Idling and minor stops: 6 percent
• Reduced speed: 8 percent
• Process defects: 4 percent
• Startup yield: 4 percent

The biggest single loss is setup at 12 percent. The investigation finds that changeovers between similar molds were averaging 90 minutes when they could be 30 with better external preparation. A quick changeover effort cuts setup loss to 6 percent. The second biggest is reduced speed at 8 percent, traced to one part program written conservatively years ago that the tooling has long outgrown. A program revision cuts reduced speed to 3 percent. OEE moves from 62 percent to 74 percent over a quarter, on the back of two specific changes the loss data pointed to.

Common mistakes with the six big losses

• Stopping at the high level category. "Equipment failure" is not actionable. The specific failure mode is. Pull each category down one level for real targets.
• Ignoring minor stops. Stops under five minutes often add up to the largest single loss and are the easiest to overlook.
• Using the framework only on the bottleneck. Other machines have loss patterns too, and the framework can reveal which deserve attention.
• Treating the framework as a final answer. The categories are starting points. The fixes still require root cause work on each loss.
• Skipping the connection back to OEE. The whole point of the framework is that each loss is mapped to an OEE factor. Without that connection, the categorization is just a sorting exercise.

Six big losses and related Lean tools

The six big losses are the diagnostic framework behind overall equipment effectiveness, with each loss mapped to availability, performance rate, or quality rate. Total minutes of loss feed downtime tracking, which in turn becomes the input to availability.