Plant floor glossary: maintenance and production terms

Plants use shorthand that varies from site to site, so check how your own plant defines a term before comparing numbers with anyone else. Where a formula applies, it is given. The OEE guide uses many of these terms in a worked example.

Andon

A signal, often a light or a display board, that tells the line something needs attention. Operators can use it to call for help or to stop the line.

Availability

The share of planned production time that a machine was actually running. Run time divided by planned production time.

Bottleneck

The step in a process with the lowest capacity. It sets the pace for everything downstream, so an hour lost there is an hour lost for the plant.

Breakdown

An unplanned stop caused by equipment failure that has to be repaired before the machine can restart.

Changeover

Switching a machine from one product to another, measured from the last good part of the old run to the first good part of the new one.

CMMS

Computerized maintenance management system. Software that holds equipment records, schedules preventive tasks and tracks work orders.

Corrective maintenance

Repair work done after something has failed or has been found out of tolerance.

Cycle time

The time one part takes to go through a step or a machine.

Downtime

Time when planned production is not running. Most plants split it into planned and unplanned downtime.

First pass yield

The share of units that pass inspection the first time, without rework or repair. Units that pass first time divided by units started.

Good count

The number of parts in a period that meet specification. It is the numerator of the quality factor in OEE.

Ideal cycle time

The fastest time per part a machine can sustain while making good parts. It usually comes from the rated speed or the best demonstrated run, and it is what performance is measured against.

Kanban

A card, bin or electronic signal that tells the previous step to make or send more. It pulls work through the plant instead of pushing it.

Lead time

The time from an order being placed, or released to the floor, until the product is finished or delivered. Say which start point you mean.

Lockout/tagout

The procedure of isolating and locking a machine’s energy sources, and tagging them, before servicing so it cannot start unexpectedly. In the United States, OSHA 1910.147 governs it.

MES

Manufacturing execution system. Software that tracks work on the floor as it happens, such as orders, counts and machine status.

Micro-stop

A short stop that an operator clears without a repair, such as a jam. Many plants set a time threshold and count anything shorter as a performance loss instead of downtime. Pick a threshold and apply it consistently.

MTBF

Mean time between failures. Operating time divided by the number of failures.

MTTR

Mean time to repair. Total repair time divided by the number of repairs.

Nonconformance

A part, material or process that does not meet a specified requirement.

OEE

Overall equipment effectiveness. Availability times performance times quality.

Performance

The share of ideal speed a machine achieved while running. Ideal cycle time times total count, divided by run time.

Planned downtime

Scheduled time when the machine is not producing, such as planned maintenance. Plants differ on whether it counts against OEE, so decide and write the rule down.

Predictive maintenance

Scheduling work from the measured condition of equipment, such as vibration, temperature or oil analysis, instead of a fixed calendar.

Preventive maintenance

Scheduled work done at fixed time or usage intervals to reduce the chance of failure.

Quality factor

In OEE, good count divided by total count.

Rework

Reprocessing a nonconforming part so that it meets specification.

Root cause analysis

A structured effort to find the underlying cause of a problem instead of fixing its symptom. The 5 Whys method asks “why” repeatedly until it reaches a cause you can act on.

Scrap

Material or parts that cannot be reworked and are discarded.

Setup time

The time to prepare a machine for a run: tooling, material, adjustments and first-part approval. It often overlaps with changeover.

Takt time

Available production time divided by customer demand for that time. It is the pace at which a unit must be finished to meet demand.

Throughput

The number of good units produced in a given time.

TPM

Total productive maintenance. An approach in which operators take on routine care of their own machines alongside the maintenance staff, aimed at removing losses.

Unplanned downtime

Stops that nobody scheduled, such as breakdowns, material shortages and waiting for people.

Work in process

Items that have been started but are not yet finished. Often shortened to WIP.

Work order

A request or record for a maintenance task: what, where, who, when, which parts and how long it took.