FPY – Where to Count Rework
This topic contains 3 replies, has 2 voices, and was last updated by Chris 4 months, 2 weeks ago.
- July 26, 2018 at 3:52 am #56051
My company recently started calculating FPY and RTY statistics for individual cells last year however we have half the plant split on how to handle rework with FPY.
The first thought
When a part reaches an process but was incorrect per a previous process. Rework is calculated at the station it was found.
The second thought
When a part reaches an process that was incorrect per a previous process. The part is given back to the process in error and it is counted as rework at the process in error, not where found.
I coach to follow the first thought but I hear arguments on both sides. I am looking for the standard six sigma way of calculating FPY and perhaps some coaching tips when teaching teams how to run to this standard. Thank you.July 27, 2018 at 6:56 am #202859
Good question, I would also consider a 3rd options to count as failures / missed opportunity / rework at both stations? The key question for me is do we lose time at the 2nd station?
If the answer is no, then the 2nd station is acting as a QC / inspection step and I would lean towards counting as rework for station 1 only.
If the answer is yes, i.e. it either takes time to spot the defect at station 2 or we have already started to process the item through station 2 before we spot the defect, then in these cases I would be tempted to count this as a double fail (fail at station 1 and station 2) and I’d then be likely to count as a double rework at both stations also.
The upshot of that, and I think closer to reality, is that reducing defects at station 1 will boost the FPY of both stations.July 30, 2018 at 9:47 am #202872
Chris There is no standard Six Sigma way. This is my opinion. If I want to know yield (not rework – I actually don’t understand what you mean by that) then I track where it was found. It has nothing to do with where the defect was created. People need to understand when you track yield people finding it have nothing to do with creating it, assuming you are using inspectors.
If I am tracking defects then I track by where the defect was created.
Tracking yield is more of a management number, maybe good for planning. tracking defects is about process improvementJuly 31, 2018 at 8:14 am #202878
To shed more light, every station should verify the previous stations work before adding more value. For Liam’s example, yes it would explain either a loss in production that hour or a loss in swip levels that could potentially cause a loss in production if not addressed. I would count as rework for the purposes of FPY at station two to highlight that they are being negatively affected by quality be that their own or a previous station.
Going further I will track FPY (rework and scrap) where found and track defects via a cell improvement board, process control board or other means.
Thank you for both of your insights.
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