Overall Equipment Effectiveness
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Overall Equipment Effectiveness (OEE) is a measure comparing how well manufacturing equipment is running to the ideal plant. OEE incorporates not only Availability but also Performance Rate and Quality Rate. In other words, OEE takes an holistic view of all losses that impact on equipment performance: not being available when needed; not running at the ideal rate and not producing first pass A1 quality output. Typical losses include:
Availability
- Planned downtime
- Set up time
- Unplanned recorded downtime or breakdowns
Performance Rate
- Reduced speed
- Minor unrecorded stoppages
Quality Rate
- Rejects
- Rework
- Yield and Start up losses
Many companies who recognise the important role equipment and process performance have on bottom-line results are using improvement programmes such as Total Productive Maintenance (Total Productive Manufacturing) and Lean Manufacturing to cost effectively maximise Overall Equipment Effectiveness through the elimination or minimisation of all losses.
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[edit] OEE Calculation
Various equations exist to help us measure OEE which is based on OEE = Availability x Performance Rate x Quality Rate, i.e OEE calculation is the product of the three key production parameters: availability, performance, and quality with time (e.g. planned shift time/s) being used as the baseline measurement.
OEE% = Availability% x Performance% x Quality%
Where:
Availability % = actual running time / planned cell production time
Performance% = pieces produced / the theoretical cell production rate
Quality % = good pieces / total pieces made
However many companies are finding the simple high level measurement of OEE created by reducing the equations where: OEE = Good Output Produced/(Required Production Time x Ideal Rate). Simplified this can be written as
OEE = Actual output / Theoretical maximum output
There are "golden rules" associated with OEE as defined by Laurence Richardson and generally available. An example would be no individual piece can exceed 100%.
[edit] Practical Suggestion Before Implementation
Using OEE is the goal but it can be a big jump for some companies to jump from no measures to OEE. Steve Borris, author of "Total Productive Maintenance" is an advocate of OEE, but recommends the introduction of standards first. Standards are written procedures that define how tasks and procedures should be carried out. Why? To achieve a uniform, high quality, everyone has to do the same task the same way. When people follow standards, irrespective of who carries out a task, the quality and the time taken to carry out tasks should be consistent. To check for consistency we need to measure.
Consider introducing QCD Measures. QCD stands for Quality, Cost and Delivery.
Quality should consider not only the standard of the product as it ships to the customer, but also the number of attempts it took to the get the parts correct. It should also consider the amount of scrap that is generated. Scrap and rework have to be paid for. One of the 7 QCD Measures is "Not right first time."
Cost includes rework and defects, over-purchase of stores items and productivity. If a production line is "capable" of making 100 units in an hour but makes only 50 units, this is the same as the tool being off half of the time. How could it possibly be so bad? It is easier than you think.
Lean Manufacturing recognises 7 wastes, one of which is waiting. This can be waiting for operators, parts, materials, repairs and, even, instructions or permission to proceed. Some tools have been "repaired" but run much slower than the tool is "capable" of. Steve Borris says a tool running slow is the same as the tool being off for part of the time.
Look at the list in the preceding paragraphs and see the possible cost consequences of just waiting and think, "How can I tell if that is happening to me?" Easy, measure it and graph it. The 7 QCD's includes includes a "units per hour" measure. Getting less than the 100 you expect? Then start investigating. No measures: no warning mechanism.
Delivery
Has anyone mentioned the customer yet?
He is the one who pays the wages. He might be a re-seller and have his own customers. We need to keep our customers happy. We can do this by making what he wants at a cost he will pay and to a (better) quality than he expects. We can also deliver on time. His customers might have been made promises too. QCD measures "On-Time Delivery". Measure it and graph it. It will let you know there could be other issues.
Why would delivery be late? This is a question with a similar impact to hitting a hornets nest with a pick-axe. Bad production planning; orders jumping the queue; rework making jobs take too long; bottlenecks; poor instructions; not ordering materials in time; unskilled labour or poor maintenance (equipment availability). The complete list is much larger. You will recognise some of the terms of OEE, though.
[edit] Reference
- Eli Goldratt. The Goal.
- Steve Borris. Total Productive Maintenance.
[edit] See also
- Downtime Management
- Total Productive Maintenance
[edit] External links
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