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OEE - The Six Major Losses And How They Affect Equipment Effectiveness
In a World Class Manufacturing one of the metrics of high impact is the OEE and it is the main metric to improve at TPM deployment and obviously all the actions must start at Genba with the Teamwork effort.
OEE is essentially the ratio of Fully Productive Time to Planned Production Time. In practice, OEE is calculated as the product of its 3 contributing factors
OEE = Availability x Performance x Quality
This type of calculation makes OEE a severe test. For example, when all 3 factors are at 90%, OEE would be 72.9%. The following table shows generally accepted World Class goals for each factor.
Worldwide studies show that the average OEE rate in manufacturing plants is 60%
OEE analysis starts with Plant Operating Time; the amount of time your facility is open and available for equipment operation.
From Plant Operating Time, you subtract a category of time called
Planned Shut Down, which includes all events that should be excluded from efficiency analysis because there was no intention of running production (e.g. breaks, lunch, scheduled maintenance, or periods where there is nothing to produce). The remaining available time is your Planned
OEE begins with Planned Production Time and scrutinizes efficiency and productivity losses that occur, with the goal of reducing or eliminating these losses. There are three general categories of loss to consider - Down Time Loss, Speed Loss and Quality Loss.
Availability takes into account Down Time Loss, which includes any events that stop planned production for an appreciable length of time(usually several minutes - long enough to log as a trackable Event).
Examples include equipment failures, material shortages, and changeover time. Changeover time is included in OEE analysis, since it is a form of down time. While it may not be possible to eliminate changeover time, in most cases it can be reduced. The remaining available time is called Operating Time.
Performance takes into account Speed Loss, which includes any factors that cause the process to operate at less than the maximum possible speed, when running. Examples include machine wear,substandard materials, misfeeds, and operator inefficiency. The
remaining available time is called Net Operating Time.
Quality takes into account Quality Loss, which accounts for produced pieces that do not meet quality standards, including pieces that require rework. The remaining time is called Fully Productive Time. Our goal is to maximize Fully Productive Time.
The right approach to have a good results on OEE is basically focus the Kaizen events on reduce the 6 big losses.The main metrics for the team will be expressed on how capable they are on eliminate or reduce the 6 big losses.
As we can see , the OEE is a result , of Availability , Performance , and Quality however those 3 are result of 6 Big Losses.
Addressing the Six Big Losses
Now that we know what the Six Big Losses are and some of the events that contribute to these losses, we can focus on ways to monitor and correct them. Categorizing data makes loss analysis much easier, and a key goal should be fast and efficient data collection, with data put to use throughout the day and in real-time.
Eliminating unplanned Down Time is critical to improving OEE.
Other OEE be addressed if the process is down. It is not only important to know how much Down Time your process is experiencing (and when) but also to be able to attribute the lost time to the specific source or reason for the loss (tabulated through Reason Codes). With Down Time and Reason Code data tabulated, Root Cause Analysis is applied starting with the most severe loss categories.
Setup and Adjustments
Setup and Adjustment time is generally measured as the time between the last good part produced before Setup to the first consistent good parts produced after Setup. This often includes substantial adjustment and/or warm-up time in order to consistently produce parts that meet quality standards.
Tracking Setup Time is critical to reducing this loss, together with an active program to reduce this time (SMES or OTED program).
Many companies use creative methods of reducing Setup Time including assembling changeover carts with all tools and supplies necessary for the changeover in one place, pinned or marked settings so that coarse adjustments are no longer necessary, and use of prefabricated setup gauges.
Small Stops and Reduced Speed
Small Stops and Reduced Speed are the most difficult of the Six Big Losses to monitor and record. Cycle Time Analysis should be utilized to pinpoint these loss types. In most processes recording data for Cycle Time Analysis needs to be automated since cycles are quick and repetitive events that do not leave adequate time for manual data-logging.
By comparing all completed cycles to the Ideal Cycle Time and filtering the data through a Small Stop Threshold and Reduce Speed the errant cycles can be automatically categorized for analysis. The reason for analyzing Small Stops separately from Reduced Speed is that the root causes are typically very different, as can be seen from the Event Examples in the previous table.
Startup Rejects and Production Rejects
Startup Rejects and Production Rejects are differentiated, since often the root causes are different between startup and steady-state production. Parts that require rework of any kind should be considered rejects. Tracking when rejects occur during a shift and/or job run can help pinpoint potential causes, and in many cases patterns will be discovered.
Team in action: