OEE is a KPI (Key Performance Indicator) indicating the overall operational performance of the machine. It takes into consideration the cumulative impact of three factors: the equipment’s availability (percent of scheduled production time in which units are actually produced, also called the Machine Operating Time), performance rate (percent of material produced compared to standard) and quality (percent of good material produced compared to all material produced during the Machine Operating Time).
OEE = % Availability x % Performance x % Quality
It is unlikely that any manufacturing process can run at 100% OEE. Many manufacturers benchmark their industry to set a challenging target, 85% is not uncommon.
Availability is a measure of the time a machine has been up and running without any downtime. This metric is dependent upon the time that the machine has been scheduled for production. Data from the machine is used to compute the downtime called the Availability Loss, as the amount of time that the machine has been running below its minimum threshold speed during the Plant Operating Time. Both the minimum speed and the Plant Operating Time are defined within the system by the customer. Availability Loss may be further sectioned into Planned and Unplanned Downtime.
Availability = MO / PO
- Scheduled Downtime (SD) – This is the time that the plant or machine is scheduled to not be in operation. Reasons for scheduling downtime include shutdowns, holidays, and other times. This schedule for a machine is entered to the remote monitoring system by the customer administrator. Any particular period of downtime measured on a machine can be assigned as Scheduled Downtime by a Downtime Tracking user or automatically by the system if set up to do so.
- Plant Operating Time (PO) – This is the time the plant is scheduled for operations, taking out time for shutdowns, holidays, vacations, and other times when the plant is not scheduled to operate. PO = Calendar Time – SD.
- Planned Downtime (PD) – This is the time during Plant Operating Time that the particular machine is scheduled to not be running. Reasons for planned downtime may include: no material to produce because of a line restraint, breaks, meetings, maintenance and others. Any particular period of downtime measured on a machine can be assigned as Planned Downtime by a Downtime Tracking user or automatically by the system if set up to do so.
- Planned Production Time (PR) – This is the portion of time that the particular machine is scheduled and planned to be available for production operation, sometimes referred to as Loading Time. It is Plant Operating Time (PO) minus all Planned Downtime (PD). PR = PO – PD
- Unplanned Downtime (UD) – This is the unplanned downtime of the machine. Reasons for unplanned downtime include technical or mechanical failures, material or operator issues and others. All downtime periods default to the Unplanned Downtime type unless they are assigned a different type, either automatically by PLC code or manually by a Downtime Tracking user.
- Machine Operating Time (MO) – This is the time that the particular machine was actually running production, after taking away all scheduled, planned and unplanned downtime. Also referred to as Uptime, it is the Planned Production Time (PR) minus all Unplanned Downtime whether assigned with a reason or not. MO = PR – UD
- Availability Loss – This is the amount of time that the machine was not running in production during the time it was scheduled to be available. It is the total of Planned and Unplanned Downtime. Availability Loss = PO – MO = UD + PD
Performance values in the OEE metric represents the average speed at which the machine runs during the Machine Operating Time (MO) of the calendar time period chosen, as a percentage of the designed theoretical maximum speed of the machine. It is a measure of the quantity of units actually produced as a percentage of the quantity of units that would have been produced in that same MO time period if the machine were running at maximum speed.
- Performance Loss – This is the difference between actual quantity of units produced and theoretical maximum quantity of units produced during the Machine Operating Time. It can be represented in units of time, material or speed. Performance Loss may be sectioned by Performance Downtime and Reduced Speed. Any particular period of downtime measured on a machine can be assigned as Performance Downtime by a Downtime Tracking user or automatically by the system if set up to do so. Reduced Speed is the remaining amount of time lost making the actual quantity of units produced because the average speed of the machine was less than its maximum speed. Reduced Speed = Performance Loss – Performance Downtime
Quality is represented by the quantity of Good Material produced as a percentage of the Total Material produced during the Machine Operating Time (MO) of the time period chosen. This is commonly referred to as First Pass Yield.
- Total Material – This is the number of total units of production as measured by the remote monitoring system. The Total Material value comes from the machines’ controller.
- Good Material – This is the total number of good units as measured by on-machine quality inspection systems. If there is not an on-machine quality inspection system in place, then the value comes from manually input data. Good Material = Total Material – Waste
- Quality Loss – This is the equivalent amount of time lost by the production of bad material, or Waste, during the running time (MO) of the machine. Waste is the total number of rejected units of production (for any reason, typically scrap or rework), as measured by on-machine quality inspection systems. If there is not an on-machine quality inspection system in place, then the value comes from manually input data.
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