There’s an old adage that you need to know the rules before you break the rules. That applies to everything from playing jazz to running a business.
I got to thinking about that idea after reading Industry Week’s cover story on OEE (Overall Equipment Effectiveness). The IW story discusses the benefits of OEE, and even gives a definition of OEE:
OEE tells users the percentage of time that equipment, when running or required for production, is producing good-quality products at an acceptable rate. It is the product of three ratios, or submetrics: machine availability rate, performance or run rate, and the quality rate. It is calculated by multiplying availability rate by production rate by first-pass quality rate.
This is a good textbook definition of OEE, but it leaves some gaps. This post and others in this series will fill some of those gaps. Once we fill in the gaps in the text book definition we’ll be in a better place to consider if we want to break any of the rules.
Mr. Sanders, my 5th grade teacher, was forever having us convert a story problem into an equation. Here is what that paragraph looks like as an equation:
OEE = Availability * Performance * Quality
Future posts will go into more detail on Performance and Quality. Today let’s look at Availability in more detail.
Availability
The formula for Availability is simple, but it relies on some operational definitions. Here are all the components for calculating Availability:
Availability = Actual Operating Time / Planned Production Time
Planned Production Time is the time any piece of equipment is scheduled for operation.
Actual Operating Time = Planned Production Time - Down Time.
Down Time is a measure of unscheduled production stops.
Down Time includes the time required for machine setup and changeover, or losses due to equipment breakdowns and material shortages.
We do not include planned shutdown time in this calculation. For example, If a machine is scheduled to run from 10am until 5pm on a specific day, then the Planned Production Time is 7 hours, or 420 minutes. (All of these times are usually measured in minutes or hours.) If a machine normally runs while an employee is at lunch, then the employee’s lunch time is included in the Planned Production Time. If the machine is scheduled to be shut down while the employee is taking a break, then the break is not included in Planned Production Time.
Down Time is usually measured in minutes. Consider establishing a policy for a threshold for what constitutes a trackable event. For example, you may wish to track stoppages of more than 5 minutes so that you don’t bother with every little hiccup in the system.
Availability, like the other components of OEE, is reported as a percentage, so after we calculate the ratio we just multiply it by 100. Here is a typical calculation:
| Total time in shift |
480 minutes (8 hours) |
| Machine setup |
95 minutes |
| Lunch break |
30 minutes |
| Other Down Time |
17 minutes |
Planned Production Time = 450 minutes (480 time in shift less 30 minutes for lunch break)
Actual Operating Time = 338 minutes (450 minutes - 95 minutes for machine setup and 17 minutes unscheduled down time.
Availability = Actual Operating Time / Planned Production Time
Availability = 338 / 450
Availability = 0.7511 (multiply by 100 to express as a percent = 75.1% )
This is the text book definition of Availability. How do you calculate it at your facility?
In the next post we’ll look at what goes into calculating Performance. In the meantime comment, schedule a conversation, or call us at 800-958-2709.