“There are many different ways to measure manufacturing speeds. Depending if you need the losses included or not, if you want parts per time or its inverse or only a time, single processes or entire systems, actual or current values, you may have a completely different number. This post will help you to sort out what is what…”
Sourced through Scoop.it from: www.allaboutlean.com
Michel Baudin‘s comments:
The main conclusion from this post is that, when discussing production speed, you should define your terms if you want to avoid confusion.
It is a useful and well researched article, but there are a few points I would make differently:
- OEE is a ratio, not a difference.
- “Time” can mean duration or timestamp. I would use both terms to avoid ambiguity..
- I would discuss the practical implications of using time per part versus parts per unit time. When you say you produce 1 part every minute, it usually means that one part is completed every 60 seconds exactly. When you say you make 60 units/hour, on the other hand, you make no difference between completing one every minute and having a batch of 60 coming out every hour.
- Averages are additive; medians or maxima are not. The average of a sum is the sum of the averages, but this is not true of the other statistics. This is of vital importance when adding up operation times in a process, and a key reason why ERP systems plan based on absurdly long lead times.
- I prefer to define a parameters by its intended meaning, and the formula then becomes the way you estimate it. The intent of the takt time of a line is to be the interval between the completion timestamps of two consecutive units. The formula then shows how you estimate it.
- Little’s Law applies to steady-state averages, and it needs to be said. It does not apply, for example, during ramp-up.