The OEE measure
OEE - The Basics
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Many companies measure the Utilisation, Throughput and Quality of a process, but fail to consider the combined effect of these on overall performance.
Overall Equipment Effectiveness is:
- A measure which embraces all losses to 'good' output that can occur on any machine or process
- The standard machine performance measure adopted by World Class companies
The OEE measure is based on the premise that all production losses on machines and processes can be quantified.
For example, poor maintenance will lead to more breakdowns, which in turn can be measured in terms of lost time.
All equipment production losses can be grouped into 3 categories...
Down Time Losses - Availability - A
Speed losses - Performance - P
Reject/Re-work losses - Quality - Q
Availability (A) losses might include:
- Breakdown losses
- Tea and lunch breaks
- Change-over and set-up of tooling - lost tooling
- 'Unplanned' maintenance
- Waiting for support
- Waiting for supervisor
- Waiting for maintenance
- No operator
- Waiting for paperwork
- Shift hand-over
- Waiting for 1st off inspection
These equipment losses are all grouped under the heading of Availability losses. Note - they are sometimes referred to as 'downtime' or 'outages'.
Performance Rate (P)
When a machine is running slower than its design speed or experiencing small stoppages, the Performance Rate is reduced.
Performance Rate losses might include:
- Reduced speed
- Minor stoppages
- Idling losses
- Material feed problems
- Equipment failures that cause production to slow
Quality Rate (Q)
All time losses due to the generation of out-of-specification material arising from normal production or start-up at the beginning of shift or after changeover are classed as quality losses, and lead to a reduction in the Quality Rate.
- Quality rejects
- Reworks
How do we translate these losses into a measure?
Firstly, we need to understand the basic ingredients of machine performance
The level of good output is determined by:
- How many hours the machine runs in a day, a week, or a year
- When the machine does run, how quickly it runs (units/minute or tons/year etc.)
- How much of what is made was scrap or rework?
How many hours a machine runs (operating time) compared to how many it was planned to run (i.e. its loading time)
= Availability
How quickly it runs compared to its design speed
= Performance Rate
How much good quality product (i.e. not scrap/rework) compared to the total output
= Quality Rate
In general A, P and Q can all be expressed as the following percentages (%):
Operating Time / |
= Availability % |
|---|---|
| Total Parts Produced x Design Cycle Time / Operating Time |
= Performance Rate % |
| Good Parts Produced / Total Parts Produced |
= Quality Rate % |
To establish the overall performance of the equipment, these three % figures are multiplied together:
% Availability x % Performance Rate x % Quality rate = % OEE
Key implications...
- It's not enough to know the individual scores of Availability, Performance Rate and Quality Rate.
- It's only when you multiply all 3 elements together that you see the compound effect...
- ...and this often highlights a surprisingly aggressive erosion to OEE!
- Two percentages multiplied together will always result in a smaller percentage!
Using the OEE Measure to identify and prioritise improvement activity
The losses can also be split further to give more detail e.g. if Availability is 80% - the 20% loss will be due to a number of factors -breakdown, changeovers etc. - and each of these elements can be quantified in % terms and the largest of them potentially tackled first.
For a more detailed description of the OEE measure, and for an insight into how it can be used to improve performance across the life-cycle of assets, enter the oee Improvement library and click on 'briefings'.
OEE Across the Project Lifecyle
Philip Godfrey explains how ROI and cash flow can be improved by using the Overall Equipment Effectiveness measure throughout the asset lifecycle in the attached article.
A PDF version of this document is also availble
here
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topMoney and Machines?
Money & Machines is a suite of educational software targeted at manufacturers who want to make more money from their existing assets as well as realising the benefit from any new investments.
It utilises the Overall Equipment Effectiveness (OEE) measure to show how equipment performance losses can be identified and eliminated without recourse to excessive capital expenditure.
Our free introductory Money & Machines presentation gives a quick, user friendly insight in to the 'boring but important' issue of effective asset performance, and the major impact this has on profit, capital expenditure and business performance.
Please navigate through Money and Machines using the links below.
