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PROCESS IMPROVEMENT


T


OEE Explained


he basic equation for OEE is: Availability x Performance x Quality, where Availability, Performance and Quality are metrics expressed as a number from 0 to 100%.


Availability represents the percentage of scheduled time that a particular workcenter is available to perform work.


Thus Availability = Up Time / Planned Production Time. For example, if there was 40 minutes of unscheduled down time out of 430 minutes of planned production time, the Availability would be 90.7%. Performance represents the actual speed that a particular workcenter runs as a percentage of its designed speed. Thus Performance = (Parts Produced x Ideal Cycle Time) / Up Time. For example, if a workcenter is designed to produce two parts per minute, the ideal number of parts produced would be 780 over the 390 minutes, but if only 759 parts were produced, Performance would be only 97.3%. Quality represents “Good Parts” versus “Rejected Parts” as a percentage of the total number of parts produced. Quality is a pure measure of process yield that excludes Availability and Performance. For example, if a total of 759 parts were produced, but 12 were defective, Quality would be 98.4%. Using these numbers, OEE = 90.7% Availability x 97.3% Performance x 98.4% Quality = 86.8% (Courtesy Wes Blankenship, Factory Systems)


employ variants of OEE, according to Blankenship. Managers at times use other metrics implicit to OEE computations that better suit the nature of their specifi c operations. “Factory Systems works with our clients to develop related metrics that provide the best feedback and diagnostic information to monitor and improve their processes,” he said. However, he had cautions. “While OEE seems simple, it can be diffi cult in a practical sense to implement,” said Blan-


kenship. For example, in calculating Availability for a CNC milling machine, the actual uptime could be affected by being starved for parts from an upstream process or unplanned maintenance due to broken tools or jamming. “This often times leads to debate in a plant as to how to defi ne [critical parameters] used in calculating OEE,” he said. Plants with older machines may fi nd it hard to get Availability data. “You may or may not be able to interface with older controllers or proprietary data formats.” Using the right data is critical.


Data Collection Karl Ritzinger, president of


Manufacturers often use statistics that include OEE and its companion, TEEP, such as these displays from Capstone Metrics.


72 AdvancedManufacturing.org | September 2016


Production Process (Londonderry, NH), said that his company both recognizes the data problem and provides devices to help collect that data. He has seen that it is diffi cult to calculate OEE by col- lecting data manually and using a spreadsheet, at least to any degree of accuracy. Their devices collect data for downtime tracking that connect to “dumb” machines (as Ritzinger describes them) that are not automated and usually are legacy machines. “Although we are slowly moving into the CNC


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