OEE Integration – Where do We Measure OEE? – Part I

OEE Integration Part IX – Where do we measure OEE?

Our recent posts have included numerous examples to calculate OEE correctly, we have discussed integration of OEE as an effective metric for managing your processes, and ultimately we reviewed analyzing and using the data to improve your profitability.  We have spent little time discussing where this measurement should occur.    Note that 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 may be calculated during the run, performance can only be measured after the machine cycle has been completed, and Quality can only be determined after the part is produced.

At a minimum then, 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 arises where 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  to be taken 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. 

If a customer operation is down, production is disrupted – no product demand.  If a supplier operation is down, product is disrupted – product in demand.  A customer down situation may be outside the scope of the operation or external to the organization and the same may be true for an external supplier.  Both situations will have an impact on the OEE Availability factor.

It is also important to note that real time OEE requires that these events and others, such as product disposition, are reported in real time as well.  External events may be 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 production was reported and all parts have been 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 may be deceiving if proper controls are not in place.

It would appear that the question, “Where do we measure?”, is accompanied by the question, “When do we measure?”  The short list of examples provided here should be events that are far and few between.  If this is a daily occurrence, you may consider adopting the banking policy of, “adjustments to your account will be reflected on the following business day”.  We would suggest that a system is in need of a rapid fix.

OEE should be one of the few vital signs or metrics for your manufacturing operation.  As such, measure it where you will reap the greatest benefit.  Focus your attention on the process or operation that will provide the greatest benefit.  OEE is as much a diagnostic tool as it is a monitoring tool.

Until Next Time – STAY lean!