Mother bobbin final inspection criteria

[ilkinsan]

Hello,

I am responsible to build a final inspection criteria for supplier of bobbin based paper. I am studying on ISO 3951 sampling procedures for inspection by variables. I hope you can guide me.

Here is a little bit of background;

1) At first, the batch is produced at supplier along web application.
Imagine a `mother reel' wrapped on a tube with 100cm width and 2000meter of web plastic in length.

2) Then, each mother reel is slit into 20 smaller bobbins which we receive into factory.
Each bobbin is now with 5cm width and 100meter length. In other words, 400bobbin per each mother reel.

3) We let supplier to release/ship the batch based on 5 different variables (numeric value, not attribute) with sampling plan AQL 2.5%, Normal Inspection, General Level II.

For 400 bobbin, we ask suppliers to take 30 bobbin (with k factor=1.471) and measure first 50cm from the end of the each bobbin. (I know the last part is a bit modified version of ISO).
Everything works well and there are also some incoming inspection process in place.
(By the way, please let me know if there is something can be improved).

However, nowadays some supplier suggest to perform the inspection of some variables on the mother reel itself, not necessarily on slitted bobbins - which make sense while considering the workload behind for them. This is also fine for me based on some experiments show that those variables are not affected by sliting/converting process.
Final width must be measured on slited smaller bobbins, but thickness can be also measured on mother reel. It is not affected by cutting process.

My question is how I should define the final inspection criteria at mother reel level. - for thickness for instance?

There are some limitations;
-It can't be inspected 100% of mother reel. Not only because of cost/time, also since winding/rewinding will most likely cause some problem(destructive).
-Unfortunately, not all supplier can measure the thickness via automated control, etc a sensor to measure web thickness continuously. (It would be perfect, then!)

Thank you for your time to read,

 

[toniriazor]

Hello

Have you audited your suppliers example the ones without automatic sensor to check their processes - how capable are they at producing the product you want, scrap rates and etc. For those without poke-yoke there should be strong process behind in my opinion. In fact a capable process is always better than inspection.
Ask your suppliers what alternatives equipment to automatic sensor can propose to measure this characteristic. This should be part of their MSA I think.
Is this inspection at your facility something extra you are doing or its mandatory ? I had some troubles understanding that.

 

[Steve Prevette]

For random sampling, we do desire to have any portion of the production be capable of being chosen to be sampled. There is a risk when only sampling the last (or is it first) 50 cm of the mother bobbin material. If the mother bobbin cannot be unwound and rewound without risk of damage, about the only way to do this is to sample the material as it is wound onto the mother bobbin. During the process of winding the bobbin, could the process be stopped at random time(s) in order to do a measurement? Or would that also cause damage?

I'll give credit to Dr. Deming for a similar situation unloading ore ships. They used to just pull a bucket of material when the hatch was opened, but that was not representative of the ore as the heavier (higher ore content) chunks settled to the bottom during transport. So they developed a random process for determining when to stop the unloading and go to a certain point on the conveyor belt and grab a bucket there.

 

[John Predmore]

I have not seen your equipment but is it possible to measure thickness of the paper as it passes over a roller with a digital test indicator? The ones I looked up are accurate to 0.00005", for less than $500. Maybe you have a clever engineer who can mount the test indicator in a way so the probe can be extended/retracted to the paper without stopping the machine, and moved cross-web to sample different points.