OEE & Six Loss Model
This article has been written to better explain how speed loss should be calculated for a piece of equipment or line. The calculation of speed loss can be slightly confusing and to ensure that it is done correctly consider the following example:
In a 480 minute shift :
On a machine rated at 100 products output per minute
Maximum output = 480 mins x 100 units = 48000 units
Output (Good Production) = 32000 units
Speed = 98 units per minute
Planned downtime = 82 mins
Bottleneck loss due to B/down = 30 mins
Bottleneck loss due to minor stops = 28.66 mins
Rejects (in process) = 1255 in 8 hr shift
In reality only 32000 good units were produced compared to a maximum of 48000 which equates to a total loss of (48000-32000)/48000 = 33.3%.
The relevant Losses can be calculated as follows:
Breakdown = 30/480 = 6.25%
Planned downtime = 82/480 = 17.08%
Minor Stops = 28.66/480 = 5.97%
Rejects = (1255/98)/480 = 2.67%
It seems quite logical to assume that the Speed Loss can be calculated as (100-98)/100 = 2%.
This would then equate to a total loss of 6.25+17.08+5.97+2.67+2.00 = 33.97%. This is incorrect as the total loss should equate to 33.3%. By calculating speed loss in this way it is assumed that the machine is running all the time and since we know that it is not, it is double allocating the loss. Speed Loss is only relevant when the machine is actually running and producing good product. Therefore to ensure that the losses are not double allocated, the following equation should be used to calculate speed loss:
(Good Output / Ave speedxTotal production time) – (Good Output / Rated speedxTotal production time).
In this example the actual speed loss is (32000/47040) – (32000/48000) = 1.36%.
If all the losses are now added together the total is 6.25+17.08+5.97+2.67+1.36 = 33.3%. This is equal to the total loss calculated above.
Therefore in Summary:
- Speed loss is only relevant when the machine is running and producing good product.
- Speed loss should be calculated using the formula: (Good Output / Ave speedxTotal production time) – (Good Output / Rated speedxTotal production time. This ensures that the loss is not double allocated.
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The Quiz varies for each of the topics (e.g. OEE & Six Loss; Data Gathering & Visualisation).
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What does OEE stand for?Correct
What are the 3 elements of OEE?Correct
What are the 2 Availability losses?Correct
What are common reasons for Minor Stops?Correct
Which method is recommended for reducing Planned Downtime/Changeovers?Correct
The answer we were looking for is SMED (Single Minute Exchange of Dies)