Reduced Inspection & SPC

[lee01]

Okay here goes. . . .

Lets say we have a production run or 1 item per month (perhaps), we 100% digitally inspect (CMM) every that part every time. We need to start to reduce the inspection time allocated. How do we do this? There are several options:

1, Inspect 10 off to determine capability etc and then start to reduce inspection to inspect 1 miss 1, inspect 1 miss 2, inspect 1 miss 3 etc. Therefore reducing the inspection required whilst still inspecting the part as it comes through.

2, Once we have a proven stable process (inspect 10 @ 100%) start to reduce the number of measurement points inspected. Therefore previously you measured 500 points on a surface, you now only measure 250 points. The problem with this is that you will have the set up time and CMM tie up remaining.

Is there any advice or suggestion out their so we can apply this? Remember, we do not have any constant production runs so the usual sampling plans do not seem to apply.

Lee01

[Al Dyer]

Lee01,

What is your production rate?

1/day
1/week etc.......

Al...

[Bob_M]

Ignoring Statistics and sampling plans for a moment...
Why are you 100% inspecting these parts?
Customer requirement?
Internal Requirment?
Unstable Process and/or high rejects?

IF you are not required to 100% inspect, (correct me if I'm wrong) its up to you and your capabilities to determine the necessary inspection rate for you needs.

BTW - I'm sure there are plenty of people here who can recommend reduces rates if you provide more details and production run quantities.

[lee01]

We are making approx. 1 item per month (Aerospace). We are inspecting 100 % on every feature because the inspectors will not stamp off the documentation without inspecting the item.

HELP REQUIRED

[Bob_M]

Originally posted by lee01
We are making approx. 1 item per month (Aerospace). We are inspecting 100 % on every feature because the inspectors will not stamp off the documentation without inspecting the item.

HELP REQUIRED

(Don't quote me I'm far from an expert but...)

On the surface if you are literally only making ONE part part per month (for areospace none the less) 100% inspection sounds like a good idea.

If your customer does not require this 100% inspection WHY are you doing it that way?

If you have not proven stability to YOURSELVES YET how can you justify reducing inspections?

If you have proven stablity to YOURSELVES then change the control plan and inspection requirements. Then the inspector will HAVE to approve the documents and parts based on the DOCUMENTED requirements.

(Have I over simplified this? I've never worked for/in areospace so I may be missing alot here.)

[David Hartman]

lee01,

With some experience in Aerospace (1 complete assembly every 18 months), I have to pose the question: How stable is your design? The reason I ask, is that in my experience our design was in constant flux. Although we were contracted to assemble 8 "identical" units, customer requirements had a tendency to vary with each unit, supplier's (and their processes varied) - some of the materials procured were of such substantial size that we could not stock them, and had to have them made to order, and personnel performing the assembly processes varied. As a result 100% inspection was the best we could do.

Just a caution to ensure product and process stability prior to giving consideration to turning to sampling.