9.6 Total Productive Maintenance and Visual Controls
Key Takeaways
- TPM aims for zero breakdowns, zero defects, and zero accidents through operator ownership of routine equipment care.
- Autonomous maintenance transfers cleaning, inspection, lubrication, and tightening to operators, freeing technicians for planned and predictive work.
- The eight TPM pillars sit on a foundation of 5S, and OEE is TPM's primary measure.
- Visual controls make the standard condition and any deviation from it apparent within seconds, without training or interpretation.
- Andon systems signal abnormality and call help immediately, converting a hidden problem into a visible one.
Total productive maintenance
TPM is a company-wide approach to equipment care aimed at zero breakdowns, zero defects, and zero accidents. Its distinguishing feature is that equipment care is not solely the maintenance department's job: operators take ownership of routine care for the equipment they run.
Why it belongs in the Control phase
A Six Sigma project that stabilizes a process and hands over a control plan can be undone entirely by equipment deterioration. Tool wear, contamination, loosening fasteners, and degraded seals all reintroduce variation gradually and invisibly. TPM is the control mechanism for that failure mode, and it is the reason the Body of Knowledge lists it under maintaining and sustaining improvements.
Maintenance strategies
| Strategy | Trigger | Cost profile | When appropriate |
|---|---|---|---|
| Reactive (run to failure) | Failure | Low planned, very high unplanned | Non-critical, cheap, redundant equipment |
| Preventive | Elapsed time or usage | Moderate, predictable | Known wear-out mechanisms, Weibull shape above 1 |
| Predictive (condition-based) | Measured condition: vibration, thermography, oil analysis | Higher setup, lowest total | Critical equipment with detectable degradation |
| Autonomous | Operator's daily routine | Very low | All equipment, as the foundation |
| Maintenance prevention | Design stage | Design effort | New equipment specification |
Note the connection to reliability distributions: preventive replacement only helps when the failure rate is increasing (Weibull shape parameter above 1). For a constant failure rate, scheduled replacement provides no benefit, and for a decreasing rate it actively increases failures.
The eight pillars
TPM is conventionally drawn as eight pillars on a 5S foundation:
- Autonomous maintenance -- operators clean, inspect, lubricate, and tighten.
- Planned maintenance -- scheduled work based on failure history and condition data.
- Quality maintenance -- maintain equipment to the condition required for zero defects, not merely for running.
- Focused improvement -- kaizen on the six big losses.
- Early equipment management -- feed maintenance and operability lessons into new equipment design.
- Training and education -- build operator and technician capability.
- Safety, health, and environment -- zero accidents.
- TPM in administration -- apply the same thinking to office processes.
Autonomous maintenance
The most distinctive pillar. Operators take on CILT: cleaning, inspecting, lubricating, and tightening. The insight is that cleaning is inspection -- an operator wiping down a machine finds the leak, the loose bolt, and the abnormal wear far earlier than a monthly inspection would.
Practical implementation elements: a one-page visual standard at the machine, shadow boards for tools, transparent guards so conditions can be seen without disassembly, lubrication points colour-coded and brought to accessible positions, and an abnormality tag system so operators can flag what they cannot fix themselves.
Measuring TPM
OEE is TPM's primary measure, decomposing loss into availability, performance, and quality against the six big losses. Supporting measures: mean time between failures (MTBF), mean time to repair (MTTR), the ratio of planned to unplanned maintenance hours, and schedule compliance for planned work.
Visual controls
A visual control makes the standard condition and any deviation from it apparent at a glance, without training, measurement, or interpretation. The test is simple: could someone unfamiliar with the area identify an abnormal condition within a few seconds?
Levels of visual management
| Level | Function | Examples |
|---|---|---|
| 1. Visual indicator | Shares information | Signs, labels, notice boards |
| 2. Visual signal | Attracts attention to a condition | Andon lights, alarms, coloured flags |
| 3. Visual control | Constrains behaviour toward the standard | Marked floor locations with capacity limits, kanban squares, min-max lines |
| 4. Visual guarantee | Physically prevents the error | Poka-yoke fixtures, shaped connectors that only fit one way |
Each level is stronger than the one above it. A sign asking people not to exceed a quantity is weaker than a marked square that physically holds only that quantity, which is weaker than a fixture that cannot accept an extra unit.
Common visual controls
| Control | What it makes visible |
|---|---|
| Shadow boards and tool outlines | A missing tool, instantly |
| Floor marking and address labels | Whether material is in the right place, and how much |
| Min-max level lines on bins and tanks | Whether replenishment is due |
| Green-band gauge markings | Whether a reading is normal, without reading the number |
| Colour-coded lubrication points and matching containers | The correct lubricant, without a manual |
| Match marks on fasteners and flanges | Whether a bolt has loosened |
| Kanban cards and squares | Whether production is authorized |
| Andon lights and boards | Abnormality and the call for help |
| Production status boards, hour-by-hour | Whether the line is on plan right now |
Andon
An andon is a signalling system, typically a light column or overhead board, that an operator activates when an abnormality occurs. Conventional colours: green normal, yellow help needed or minor issue, red line stopped or serious problem, blue quality issue.
Andon works only if two conditions hold: the operator has the authority to pull it without permission, and someone responds within a defined time. An andon system where pulls are discouraged by output targets, or where nobody comes, converts into a system that teaches operators to hide problems.
Visual controls in the control plan
Visual controls are the most durable control mechanism available, because they do not depend on memory, vigilance, or a chart being read. When designing the Control phase, prefer them in this order:
- Eliminate the possibility of the error by design (poka-yoke, level 4).
- Make deviation impossible to miss (visual control, level 3).
- Signal deviation immediately (andon, level 2).
- Monitor statistically (control chart with an OCAP).
- Audit and inspect (weakest; detection only, and after the fact).
Most control plans are written starting at level 4 or 5 because those are familiar. A Black Belt who moves controls up the hierarchy produces a gain that survives the departure of everyone who ran the project.
What is the central idea of autonomous maintenance in TPM?
A team must choose a control for an assembly error. Which option is strongest under the hierarchy of visual management?
A pump's failure data fits a Weibull distribution with a shape parameter of 1.0. What maintenance strategy does TPM's logic recommend?