Sep 18 2015
“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.