Q: My machine cuts different material at different speeds. Some material is thicker and denser than the other. What NPC do you set?
Arno Koch • There is only ONE Name Plate Capacity (NPC). The NPC nevertheless is usually not equal to the theoretical maximum speed of the machine. If the supplier reports the machine can run at maximum 100 strokes, it is not unusual to discover it can run at 110 or more. Obviously suppliers take a certain margin, maybe for reasons of liability or covering deviations between machines. Do not be afraid to adjust your NPC to this higher lever, even if you are not going to run the machine at this speed. In this way you prevent the performance rate ever to go over 100% and you make visible there is a hidden potential in this machine which later might be approached as a chronic loss.
The ideal product for a machine, from perspective of effectiveness, would be a product running at this maximum speed.
Imagine a machine that has a NPC of 60 strokes per minute. A thin product A can be cut in one stroke. The standard (maximum speed) for this product A on this machine would be 60 products per minute.
The thicker product B be can be cut in two strokes. This means the standard for product B on this machine is 30 products per minute.
So running 60 product A per minute means a performance rate of 100 % while running 30 products B also results in 100 % performance.
This is where the OEE Top value comes in. OEE Top calculates the performance rate ALWAYS based upon the NPC. In this example the performance of product B would drop to 50%, indicating you might want to move this product to a heavier cutter that can cut this product in one stroke. This also works in the opposite direction. Imagine there is a product C, half the thickness of product A. What would be the standard?
I would say it has a standard of 120 because the cutter could cut two of these pieces in one stroke.
In a technical sense, determining the NPC and the standard for each product on a machine is probably the most difficult part of defining your OEE settings. Always make sure you look for the theoretical maximum because the goal of OEE is to make losses, and specially those hidden losses, visible. Making them visible is the first step on overcoming the losses! Hiding them away between excuses like ‘this is not realistic’ closes the road for improvement…