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Hi guys, I'm looking for a way to translate our AQL sampling plan to a manufacturer so he can integrate our requirements to his quality control plan.
Giving an example: I have the product ABC with General Inspection II, AQL 0.25, single sampling. I'm purchasing 5000 units. Therefore, I should inspect 200 units and start rejecting at 2 defect units. The product has 5 criteria to be inspected. Each criteria is done at a different stage during production.
From the point of view of the manufacturer, considering the principles of Total Defect Per Unit (TDPU), if I decide to adopt the same sampling size, saying 200 units for 5000 units produced, if I get one defect per inspection stage, I'll get a TDPU of 5. Knowing the customer can only accept 2 defect and there are 5 inspected criteria, it also means that during my entire production, I cannot have more than 2 defects. By experience, chances are rare to have only 2 defect on an entire production line from start to finished product.
So this is where I am stuck since a couple of months now. I'm trying to determine what would be the ideal sampling plan to produce this product and how to determine my sampling plan per inspection stage? More than that, how to do the reversed calculation from the customer's AQL needs back to the production line?
If I decide to work with the AQL methodology, then I would say that I can have only 2 defect on my entire line and I need to inspect 200 units per inspection stage. However, what if I had a stronger AQL and I could only allow 1 defect? It is impossible to say that in other words, I could have 1/5 defect per inspection stage.
I tried to see this as a DPMO too. Certified Six Sigma Green Belt, my teacher sent me on that path. But since AQL and PPM don't mix because of the LTPD curve, correct me if I am wrong, but we can't extrapolate in that direction and simply raise the quantity to inspect thinking it will raise my quantity of acceptable defect.
So there is something I'm missing here. In a ideal world, inspection would allow zero defect and production lines would be stopped until the variation has been found, but since this product involves a lot of made by hand steps using old machinery not even allowing real time SPC, we are stuck with a need to define the proper sampling plan and an accurate Gauge R&R system.
In resume, if anyone can help me, it would be very appreciated:
1-How to determine the sampling methodology and rejection level per inspection stage considering the AQL needs from the customer?
2-If AQL is different from an inspected criteria to another, is this a proper method to apply AQL? If it is, how should we deal with this and should we keep in mind TDPU? (that would generate a monster calculation model!)
3-Is there a light at the end of the tunnel?
Thanks
BTW, I'm also looking for a Quality Engineer to coach me on different quality control questions. Anyone interested, please beep me.
Giving an example: I have the product ABC with General Inspection II, AQL 0.25, single sampling. I'm purchasing 5000 units. Therefore, I should inspect 200 units and start rejecting at 2 defect units. The product has 5 criteria to be inspected. Each criteria is done at a different stage during production.
From the point of view of the manufacturer, considering the principles of Total Defect Per Unit (TDPU), if I decide to adopt the same sampling size, saying 200 units for 5000 units produced, if I get one defect per inspection stage, I'll get a TDPU of 5. Knowing the customer can only accept 2 defect and there are 5 inspected criteria, it also means that during my entire production, I cannot have more than 2 defects. By experience, chances are rare to have only 2 defect on an entire production line from start to finished product.
So this is where I am stuck since a couple of months now. I'm trying to determine what would be the ideal sampling plan to produce this product and how to determine my sampling plan per inspection stage? More than that, how to do the reversed calculation from the customer's AQL needs back to the production line?
If I decide to work with the AQL methodology, then I would say that I can have only 2 defect on my entire line and I need to inspect 200 units per inspection stage. However, what if I had a stronger AQL and I could only allow 1 defect? It is impossible to say that in other words, I could have 1/5 defect per inspection stage.
I tried to see this as a DPMO too. Certified Six Sigma Green Belt, my teacher sent me on that path. But since AQL and PPM don't mix because of the LTPD curve, correct me if I am wrong, but we can't extrapolate in that direction and simply raise the quantity to inspect thinking it will raise my quantity of acceptable defect.
So there is something I'm missing here. In a ideal world, inspection would allow zero defect and production lines would be stopped until the variation has been found, but since this product involves a lot of made by hand steps using old machinery not even allowing real time SPC, we are stuck with a need to define the proper sampling plan and an accurate Gauge R&R system.
In resume, if anyone can help me, it would be very appreciated:
1-How to determine the sampling methodology and rejection level per inspection stage considering the AQL needs from the customer?
2-If AQL is different from an inspected criteria to another, is this a proper method to apply AQL? If it is, how should we deal with this and should we keep in mind TDPU? (that would generate a monster calculation model!)
3-Is there a light at the end of the tunnel?
Thanks
BTW, I'm also looking for a Quality Engineer to coach me on different quality control questions. Anyone interested, please beep me.