The Complete Guide to OEE

OEE measures how effectively TIME is used to produce a quality product. We have established the following definitions of TIME to be used to calculate OEE:

1. Scheduled Production Time or Planned Production Time
2. Planned Down Time: Scheduled down time events
3. Unplanned Down Time: Unscheduled down time events
4. NAT = Net Available Time (Scheduled Production Time – Planned Down Time)
5. NOT = Net Operating Time (Net Available Time – Unplanned Down Time)
6. IOT = Ideal Operating Time (Time to Produce All Parts at Rate)
7. LOT = Lost Operating Time Due to Production of Scrap or Non-Saleable Product.

Although we will provide examples of these calculations, the following formulas are used to calculate each of the OEE factors and overall OEE:

1. Availability % = NOT / NAT * 100
2. Performance % = IOT / NOT * 100
3. Quality = (IOT – LOT) / IOT * 100
4. OEE = Availability * Performance * Quality

You will notice that a quick way to check your OEE result is to calculate the time required to make good parts divided by the Net Available Time:

OEE = (IOT – LOT) / NAT

OEE = (IOT – LOT) / NAT

A word on Availability:

Availability is based on the actual “scheduled production time”. Assuming a production process is scheduled to run over an 8 hour shift or 480 minutes (60 * 8), the following definitions are applied for planned and unplanned downtime.

Planned Downtime:

1. Scheduled break times.
2. Scheduled clean up at the end of the shift.
3. Scheduled Preventive Maintenance.

Unplanned (Process/Equipment) Downtime:

1. Setup / Tool Changes
2. Material Changes
3. Material Handling
4. Quality Concerns
5. Process Downtime
6. Equipment Failures
7. Personnel Relief

While it could be argued that setup or tool changes are planned events, they are considered part of the overall production process. If tool change or set up events affect equipment or capacity utilization, then an effort to reduce these times will reflected by improved availability and an increase in available capacity. It also makes capacity utilization much easier to calculate. Again, knowing what is in the definition is important. The purpose of establishing OEE is to drive improvement in your organization. For example, Quick Die Change, or SMED, programs are specifically geared to improve the change over process. If a separate program is used to manage the change over process, then you may so choose to leave this activity as a separate entity.

A word of caution! OEE is a metric, not a program. Use existing systems and processes wherever possible to manage or support your OEE activities at launch. New initiatives often fail because they are introduced in isolation and are often accompanied by “new ways” of doing business and tend to disrupt other existing work flows. A true improvement or initiative that saves the company time and money will stand on its own merits. This same initiative can be acted upon regardless of whether an “OEE Improvement Plan” exists.

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 A real life example An 8 hour shift is scheduled to produce three parts as shown in the schedule below. The shift has two 10 minute breaks and a 5 minute clean up period

Production Schedule:

• M/C: A  Part #: A123, Cycle: 10 (seconds), Produced: 2240, SCRAP: 50, Unplanned Downtime: 32 minutes

Lets start by calculating our time factors for each machine:

Net Available Time: Since each machine is scheduled to run for the full 8 hour shift, the Net Available Time for each machine is calculated as follows:

1. Scheduled Time = 8 hours = 480 Minutes (8 * 60)
2. Planned Down Time = 2 breaks * 10 minutes + clean up 5 minutes = 25 minutes
3. Net Available Time (NAT) = 480 – 25 = 455 minutes

Machine A

1. Unplanned Downtime = 32 minutes
2. Net Operating Time (NOT) = Net Available Time – Unplanned Downtime
3. NOT = 455 – 32 = 423 minutes
4. Ideal Operating Time (IOT):  2240 total parts * 10 seconds = 22400 / 60 = 373.33 minutes
5. Lost Operating Time (LOT): 50 scrap parts * 10 seconds = 500 / 60 = 8.33 minutes

Machine A: OEE Factors are calculated as follows:

1. Availability: NOT / NAT = (423 / 455) * 100 = 92.97 %
2. Performance: IOT / NOT = (373.33 / 423 ) * 100 = 88.26%
3. Quality: (IOT – LOT) / IOT = (373.33 – 8.33) / 373.33 * 100 = 97.77%
4. OEE = A * P * Q = 92.97% * 88.26% * 97.77% = 80.22%

We could also have calculated OEE using the Quick Check as shown below:

Time to produce good parts ONLY: 373.33 – 8.33 = 365

OEE = (IOT – LOT) / NAT = (373.33 – 8.33) / 455 * 100 = 80.22%

i hope you now Understand What OEE is ....

thanks

Eng.islam Elhosiny