 OEE Calculations |   |
|
OEE Calculations | |
Overview
Overall Equipment Effectiveness (OEE) is a hierarchy of metrics developed used to evaluate how effectively a manufacturing operation is utilized. An OEE score of 100% represents perfect production which is manufacturing only good parts, as fast as possible, with no unplanned down time. It is best used to identify scope for process performance improvement, and how to get the improvement. If for example the cycle time is reduced, the OEE will increase i.e., more product is produced with less resources.
OEE in DataXchange
The first step to using OEE in DataXchange is to setup up the overall rules for a few of the variables used in the OEE calculations.
The Manage tab à Metrics à Metric Definitions page can be used to set these rules.
Use Defined Shifts as Total Time can be set to True automatically adjusting the Total Time to the amount of active shift time. For example, if there are two ten hour shifts per day and the report is being run for a calendar day the Total Time will be 20 hours with this option set to True. The Total Time will be 24 hours with this option set to False.
Limit Performance to 100% will cap the Performance metric at 100% if the resulting calculation exceeds 100%. 100% can be exceeded if the ideal cycle times are set too high.
DataXchange has an option allowing the Ideal Cycle Times to be calculated from previously collected data. The calculation is an average of cycle time while the part number is active divided by total part counts. The type of cycle time along with the number of parts that should be used for the calculation can be specified as well. Values will be calculated based on the settings on the Metrics form, which sets a minimum number of parts that must run before the average is used on the selected equipment. The value for the ideal time will be recalculated when the current part number changes providing an updated value for the next run.
Default Values
Default Ideal Cycle values and default quality percent can be set on a part number basis as explained in the Manage Part Defaults section. Default quality values are used solely for reporting purposes.
If a default quality number exists for the part number and zero scrap parts have been recorded for the selected timeframe for the report then rather than using the quality calculation which would result in 100%, the default quality number assigned to the part number will be used. As soon as a scrap part has been entered then the default will no longer be used and the quality calculation will be used.
If this behavior is not desired then the Default Quality Percent should be left blank.
The reason a default is used is to assume a certain failure rate. In certain scenarios the scrap information may not be entered until the end of the shift and the desire is to have numbers as realistic as possible on the Real Time Dashboard.
Order of Precedence for Ideal Times
Values set explicitly on a part number and equipment will take precedent. If a value is not explicitly set, then the calculated value will be used if it has been set to do so, and meets the minimum part number requirement. If a calculated value is not available, then a default that was explicitly set on the part number will be used. If a default was explicitly assigned to the part number, a default inherited from a level higher in the part number hierarchy will be used.
OEE Calculations
Below are the details on how the OEE calculations are broken down within DataXchange.
Availability =
(Total Time – Planned Downtime – Unplanned Downtime) / (Total Time – Planned Downtime)
Performance =
(Total Parts * Ideal Cycle Time) / (Total Time – Planned Downtime – Unplanned Downtime)
Quality =
Good Parts / Total Parts
OEE = Availability x Performance x Quality
OEE Calculation Notes
OEE Calculations for Multiple Part Numbers and Pieces of Equipment
If OEE or any of the OEE components are calculated for more than one piece of equipment or more than one part, we need to do a weighted average based on Planned Time.
Weighted Availability = ∑ (Equipment Availability * (Equipment Planned Time / ∑ Planned Time) )
Weighted Performance = ∑ (Equipment Performance * (Equipment Planned Time / ∑ Planned Time) )
Weighted Quality = ∑ (Equipment Quality * (Equipment Planned Time / ∑ Planned Time) )
Weighted OEE = ∑ (Equipment OEE * (Equipment Planned Time / ∑ Planned Time) )
For example, let us say there are two machines. Machine 1 has an OEE of 90% and machine 2 has an OEE of 40%. Machine 1 was planned to run for 4 hours and machine 2 was planned to run for 12 hours. Total planned time is 16 hours.
The OEE calculation would be as follows:
(.9 * (4/16)) + (.4 * (12/16)) = .525