Is it really possible to compare OEE’s of your machines? Or is it like comparing apples with oranges?
To answer this question, I give you an example. Country A has a mobility rate of 18% and Country B 13.5%. You’ll probably conclude that country A does better. Or do they?
The data shows that in country A 40% of the time their cars are running. The average top-speed of their cars is 230 Km/h and on average they are cruising 130 km/h. 80% of the trips go without any problem. So their mobility rate is 40% x 56% x 80% = 18%.
In country B only 15% of the time the cars are running. They have a well-functioning public transportation system. All cars are limited at 100 km/h and on average they are cruising 90 km/h. 99,99% of the trips go without any problems. Their mobility rate is 15% x 90% x 99,99% = 13,5%.
Now… which country is doing better?
This comparison is totally ridiculous of course? And yet, this is what you ask for when you start comparing factories based on OEE… I will show you why you can’t even compare the OEE’s from one machine running the same product in two shifts:
Both the early- and the noon shift runs 46% OEE. Is there a best shift?
- Shift A runs 60% of the time on 80% of the max speed, with 95% quality: 46% OEE
- Shift B runs 80% of the time on 95% speed producing 60% Quality: 46% OEE
So… this comparison is about one and the same machine. What happens when machines are different, and you think about the complexity of the product, the product mix, the lot-sizes…?
OEE as a number cannot be used to compare factories, machines or even shifts.
You will not give up, right? So you ask me what happens if you build in some weighting factors. Well, back to country A and B. In Country A there are 4,8 times more cars than in country B, so what would the weighting factor be? What would be the criteria to define such factor?
Let’s assume we have a factor and as a result country A becomes 17,2% and B 19,3%. What will the management do to improve the results?? And what will be the real effects? It is this kind of ‘management by excel’ that often leads to catastrophic decisions. Before running into a huge pitfall, think:
- What do you really want to achieve?
- How can you really visualize where you are and where you are heading?
- How can you help factories to move in this direction?
My advice when a company starts comparing OEE’s: sell shares!