OEE calculation – how to manipulate it, and the end results
OEE calculation can cooked up in various ways to make the OEE number look good. Here are some recipes, and what each dish tastes like.
Make the part change time a part of the cycle time, because “How can you consider this a downtime ? You have to unload the completed part and load a new part, right ? So it’s actually part of the cycle”. The taste: Maybe you can reduce the part change time by using a pallet changer, or with better and faster clamps on the fixture, a better and faster crane, or a robot. You’ll never do this, because you have hidden this manufacturing downtime waste forever and will never know that it exists.
Do not consider setup change times as downtime, because “How can you consider this a downtime ? After one batch of parts is done, you have to do a setup change and it takes time, right ? So it’s actually part of the cycle”. The taste: Maybe you can reduce a 2 hour setup time to 15 minutes by the use of quick change tooling, or by using a tool presetter, or by work and tool offset probes. You’ll never do this, because you have hidden this downtime waste forever and will never know that it exists.
Do not consider chip cleaning, insert changing and part inspection times as downtime, because “All these are part of the process. They are not downtimes.” The taste: Maybe you can eliminate the chip cleaning time by using better chip breaker geometry and cutting parameters, reduce the frequency of insert changes by using an insert with a better life. Maybe you can speed up the inspection or reduce its frequency. You’ll never do this, again because you have hidden these downtime wastes in manufacturing forever and will never know that they exist.
As you can see, the taste in all these recipes is uniformly bad. These are only some examples of bad practices in OEE calculation. There really is no point in hiding downtimes to inflate OEE numbers. This comes from an obsession with the absolute value of the OEE. Instead, use it as a measure of productivity that needs to be improved. Set a target for periodic improvement, not an absolute value. Just let ALL the downtimes be visible, out there, so that you will keep reducing them and never forget them.
This is the key tenet of going LEAN – be honest about your wastes. Do not hide them.
An amazing pickle
Speaking of recipes reminds me of one of my favourite pickles, Raiwala Marcha, Gujarati green chilly pickle. Rai means mustard, and Marcha means chilly. It is made of a special type of chilli called the Bhavnagari chilli (named after the city of Bhavnagar in Gujarat). It takes very little effort to make, has just a handful of ingredients (chilli, yellow mustard seeds, turmeric, salt, hing and oil), and is ready to eat in a mere 1 hour.
The pickle’s bark is way worse than its bite. It looks deceptively spicy, but is actually zero (and I mean ZERO) spice. It merely smells strongly of the chilli, and the dominant taste is of the mustard. You can eat it with anything at all. The Bhavnagari chilli is actually very spicy, but the pickle only uses the outer skin. The spice in any chilli (caused by a chemical called capsaicin) is actually in the central white rib, and in some of the seeds in contact with the rib. On every trip to Rajkot, I pay a visit to my favourite source of this pickle, a shop called Kakkad Brothers. It is a grocery store with a huge variety of pickles and other interesting food, located in Thosa Galli in the Old vegetable market.
Here’s a trick that I learnt from the web: If you’ve eaten something particularly hot and want to put off the fire in your mouth, there’s no use drinking water. Capsaicin dissolves in fats and oils, not in water. So just drink some milk, curds or any oil. The capsaicin dissolves in the fat and gets washed off your mouth surface, and you can then swallow it or spit it out.