OEE is the product of equipment availability times performance times product quality. Changeover, the total process of converting a line from one product to another, negatively impacts all three.
Availability is the amount of time the line is available to run production. There are a number of reasons a line may unavailable. Few plants these days have the luxury of dedicated lines. Unless they do, changeover, including cleaning, paperwork, material movement, as well as actual machine set-up, will probably be the biggest single cause of unavailability.
Much of the time spent on changeover is wasted. It is usually possible to reduce changeover times by 50% in six months if a serious program is implemented. One way is to use the ESEE technique. That is, Eliminate unnecessary tasks, Simplify as much as possible, Externalize tasks that can be done while the line is running and perform the changeover Exactly.
Performance is the ratio of the actual to the theoretical production rate. Performance is usually particularly poor immediately after the line is restarted and performance glitches can occur through the entire production run. One cause of poor performance is variability in materials or product. More often, the cause of poor performance is that the line set-up was not performed Exactly. The more exactly the set-up can be performed, the more perfectly the line will run. Yes, “exactly” and “perfectly” don’t exist in the real world. That does not make them any less worth striving for.
To perform an exact set-up, two tools are needed:
Detailed, written set-up procedures are a must to avoid missed steps and misunderstandings. They must include all set-points and adjustments in quantitative terms. Not “Set the chuck as close as possible to the cap without touching.” Rather “Set the chuck 1/16-inch above the cap.” The first is subject to interpretation. The second is not.
That’s only half the story. In addition to specifying the distance, a means must be provided to measure it. This can be a gauge or other indicator. If not provided, the mechanic is back to guessing. This will cause variability and degraded performance.
Quality in OEE is defined as the number of products rejected for defects. This ties directly to the performance metric. When machines jam, they damage products. When they are not properly adjusted, they will not produce quality product. Some of this may be product that is out of specification, caught and rejected. Some may be product that is marginally within specification but not quite as good as the consumer expects. Worst of all is a product that is out of specification, is not caught and is sent to the consumer.
Today’s plant has no choice but to improve OEE. Doing this requires continuous improvement through attention to detail. Changeover frequently offers a tree full of low hanging fruit. To improve OEE, improve changeover. F&BP