OEE Integration Part IX – Where do we measure OEE?
Our recent posts have included numerous examples to calculate OEE correctly. We also discussed integration of OEE as an effective metric for managing your processes and ultimately how to analyze and use the data to improve your profitability. We spent little time discussing where this measurement should occur. OEE can be measured for both manual and automated lines as well as any stand alone operation.
The OEE factors (Performance, Availability, and Quality) are process output results. The expectation, of course, is to manage the inputs to the process to assure the optimal result is achieved. Availability, Performance, and Quality can be measured in real-time during production. However, the results should be subject to a due diligence review when production is complete.
At a minimum, it makes sense to measure OEE at the end (output) of the line or process but this is not always ideal. The complexity of OEE measurement occurs when single or multiple sub-cells are constrained by an upstream or downstream operation or bottleneck operation. The flow, rate, or pace of a process is always restricted or limited by a sequence / process constraint or bottleneck operation. Just as a chain is only as strong as its weakest link, so too is the line speed limited by the bottleneck operation.
We contend that the “Control-Response” loop for any process must enable immediate and effective corrective action based on the measured data and observations. Measuring OEE in real-time at the bottleneck process makes it an ideal “Trigger Point” metric or “Control-Response” metric for managing the overall process even in “isolation” at the bottleneck operation. Any variations at the bottleneck correlate directly to upstream and downstream process performance.
A disruption to production flow may occur due to a stock-out condition or when a customer or supplier operation is down. While these situations affect or impact the OEE Availability factor, external factors are beyond the scope of the immediate process.
Real-time OEE requires that these events and others, such as product disposition, are reported in real-time as well. External events are more difficult to capture in real-time and by automated systems in particular. Operator interfaces must accommodate reporting of these events as they occur.
Reporting PITFALL – After-the-Fact events
If a quality defect is discovered several days after reporting production and all parts are placed on hold for sorting or rework, the QUALITY Factor for that run should be changed to ZERO. In turn, the net OEE for that run will also be ZERO. If the system is not changed, the integrity of the data is lost. This also exemplifies that real-time data can be deceiving if proper controls are not in place.
“Where do we measure?” is followed by “When do we measure?” The short list of examples provided here are likely events that are far and few between. If this is a daily occurrence, consider adopting the banking policy of, “adjustments to your account will be reflected on the following business day”. Your process / system is in need of a rapid fix.
OEE is one of the few vital signs or key performance metrics for your manufacturing operation. As such, measure where you will reap the greatest benefit and focus your attention on the process or operation accordingly. OEE is as much a diagnostic tool as it is a monitoring tool.
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