Where it becomes a problem is when the operator can not immediately detect the rejects. If scrap parts are not noticed bij the operator, such parts will go on to next step (or even to the customer).
This might show a too high First Time Right but would lower the FTR at the next step (assuming it causes a reject there).
A clear feedback loop should be established to make sure the problem is being solved where it arises.
Where to calculate First Time Right?
FTR should be calculated at the machine where the specification of the intende conversion has not been met.
So what when it was noticed in the next step?
One approach could be to send all scrap found in the next step back to the previous step, where then
- it would need to be registered in retrospect and bring the FTR to the correct level.
- a root cause analysis should be startet to prevent this from ever happening again.
We see people resist this approach; it takes an effort, it needs to be registered etc.
A quality defect always has to be noticed in the quality part of the OEE: this is the most expensive part of the loss-cascade.
When a machine loses time because of incoming scrap, this has to be registered as an availability loss.
After the actual scrap is sent back to the place where it was made, there it has to be registered as a quality loss.
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