Just how good is your process?

Check your O.E.E. and find out

By Richard Clark

There is no better statistical tool to use when evaluating the all-around efficiency of a production process than Overall Equipment Effectiveness. O.E.E. is a simple series of formulas that be can used with any calculator and some basic data that are most likely currently at your disposal. There are 3 factors within the production process that are evaluated using O.E.E.

• Availability: The actual uptime of the process divided by the scheduled available runtime. Example: The scheduled runtime was 7.2 hours (432 minutes). A broken parts feeder stopped production for 45 minutes. The uptime for the shift was 387 minutes. 387/432 = 0.89583 or 89.6 percent.
Bottom line– Availability represents machine breakdowns.

• Performance efficiency (P.E.): During the actual uptime, how efficient was the process when compared the designed optimum cycle time. Example: The optimum cycle time for the process is 15 seconds per part or 4 parts per minute. For 387 minutes of uptime, the process would produce 1548 parts if it never stopped once. During our shift, we produced 1357 parts. 1357/1548 = 0.87661 or 87.7 percent.
Bottom line- Performance efficiency represents short stoppages of the process.

• Rate of quality product (R.O.Q.P): Of the total number of parts produced during the uptime, what percentage was conforming. Example: During our 387 minutes in which we produced 1357 parts, 14 were defective and 12 need re-worked. 1331 conforming parts were made. 1331/1357 = 0.9808 or 98.1 percent.
Bottom line- Lower your in-process scrap and rework.

The Overall Equipment Effectiveness is computed by the formula – Availability x P.E. x R.O.Q.P.

0.896 x 0.877 x 0.981 equals 77.1 percent, which is our O.E.E. for this process.

A "World Class" process would produce a consistent 85 percent O.E.E. (or an average of 95 percent in each category).

There are some simple items to look at for an O.E.E. improvement. Availability deals with scheduled uptime. Be sure routine items such as machine changeovers, preventive maintenance, and department meetings are scheduled through the production controller (however titled) at your facility.

Improving P.E. means correcting a short stoppage before the cycle time is lost. Never lose sight of the parts counter at the end of the process. Some processes are made up of smaller stations with their own unique cycle times. The stations form a chain and the optimum cycle time of the process will be the cycle time of the slowest station. This is beneficial because it can be determined which stations are capable of "catching up" after a stoppage. If more than one stoppage occurs at the same time, it may be best to correct them from the closest to the end of the process and then work backwards towards the beginning.

This goes against conventional thinking. If a stoppage occurs down toward the end of the process and at the same time a machine jams up right in front of you (while you're at the front of the process), it may be better to walk down to clear the other stoppage first. The reason behind this is if the stoppage down the line is not fixed first, it is possible the last process will run out of parts. Each and every 15 seconds is lost forever. By fixing the stoppages toward the end of the line first, you have a better chance of parts "catching up" and there will be no cycle time lost at the last process.

In some situations any stoppage will shut the entire process down. In that case I would suggest placing re-settable trip counters at various intervals. When a stoppage occurs, the operator can trip the counter. After a week of production, the counters will tell you where the most stoppages are occurring and further evaluation can be planned.

R.O.Q.P. is too product-specific to be discussed in the article. If your facility doesn't have an organized quality system, I suggest developing one.

Remember that no system will be any better than the operators who use it. Machines make parts, but people make products. Keep an open mind and always, always, always be creative.

Richard Clark is a consultant from Portland, IN. For more information about statistical process control, contact him by e-mail at rcmetrology@ yahoo.com