hexagon logo

What Do I Inspect? - RANT

Hello Everyone,

For the most part, I've had unbelievable freedom when it came to creating a CMM inspection program. Number of points, which dimensions to inspect, which to leave out, what to name the features, number of probes needed, types to styli, etc... Managers and operators only asked my to to specific things that would help them with their jobs.

Example 1 is that I might get asked to check certain features first so they get quicker feedback for CNC offsets. That may be a slightly longer program or I might have to load a probe more than once but that's how they wanted it. Ok, I can do that.

Example 2 I'm checking a feature with a loose tolerance that is always out of tolerance but it doesn't affect the fit, form, or function of the part. Operators have to enter in non conformance reports which hold up the part from getting further processed and engineering has to get involved in the decision to accept or scrap to that part sits and waits which is a waste.

Example 3 is let say there is a reference dimension that the operators do by hand that is not on the drawing. No problem.

Example 4 is when non conformance reports on consistently entered to engineering and they finally tell me not to check that feature anymore because either its not important or production just can't hold it and therefore not important enough to check.

Example 5 is when the CMM inspection is longer than the CNC run time so now managers get involved, we have a meeting and review what is being checked and they ask me to remove what ever measurement that aren't needed to save time.

So about a year ago, our engineering department started using numbered bubbles on our drawings. We had a meeting and they said to only check what was bubbled and also to name the feature after the number inside the bubble for clarity and standardization. Great. That was so helpful to me. CMM programs and program creation got much faster.

Then we had a meeting a few months ago about only checking the numbered bubbles was NOT their intent. We need to check all the features at some point not just the numbered bubbles. Since there was some confusion, engineering decided to no longer use the numbered bubbles anymore ( I think they are just trying to save time on their part) so I'm back to square 1. Whiskey Tango Foxtrot.

So now that I've been programing for a few years, I understand that I don't want the CMM to be the bottleneck and give the operator as much dimensional information as they need to get their job done. Now I'm approving drawings and the new versions have no numbered bubbles and tolerances are changing and I'm at the point to where I'm asking myself, what do I inspect?

How do you all get your instructions for creating inspection programs? Does every inspection program need to be a meeting?
Parents
  • So I have an idea but it will come with a lot of work on my end. Our policy for our own parts is as follows: We are in inches. dimensions with +/-0.001" or less must be inspected every time. +/-0.005" and lower every 5 parts. +/-0.010" every ten parts. Then the cycle repeats to part 1.

    I could basically create 3 programs into 1 program per part. Using flow control to keep count, first part is checked 100% to the CMMs capabilities. 2 3 4 6 7 8 9 parts is the bare minimum inspection, and parts 5 and 10 have mid level inspection. We would save a lot on inspection time and we would be following our own inspection procedure as well.
Reply
  • So I have an idea but it will come with a lot of work on my end. Our policy for our own parts is as follows: We are in inches. dimensions with +/-0.001" or less must be inspected every time. +/-0.005" and lower every 5 parts. +/-0.010" every ten parts. Then the cycle repeats to part 1.

    I could basically create 3 programs into 1 program per part. Using flow control to keep count, first part is checked 100% to the CMMs capabilities. 2 3 4 6 7 8 9 parts is the bare minimum inspection, and parts 5 and 10 have mid level inspection. We would save a lot on inspection time and we would be following our own inspection procedure as well.
Children
  • This could work.

    I'd also look at how many dimensions are in the 100% program and the 20% (1 of 5) program.

    If the 100% program has 2 dimensions and the 20% has 4 but the 10% program has 100, maybe it makes more sense to move the 100% and 5% off the CMM and make a go/no-go jig or something.

    If you are pulling data from those CMM's into some statistics program for tool life, machine wear, environmental factor tracking purposes, a go/no-go jig will absolutely not work, but it might be a fit instead of parametric programming for three different AQL's.

    But it is a good idea.
  • I don't know your industry, but using statistics is important for determining lot samples.
    ANSI Z1.4 i believe is the statistical sampling Acceptance Quality Level (AQL) spec. There's little paper sliding scale thingees you can buy to quickly determine sample sizes, if the matrices are too confusing or time consuming.

    In lieu of just tossing numbers out like you did, you should speak with your quality manager about implementing AQL sampling. Implementing static 1pc 5pc and 10pc sample qty's (regardless of lot size) might get your organization in hot water during an audit otherwise.
  • how do you choose between RQL and AQL? is one preferred over the other or is each referred to a certain standard>?
  • KatmandudaMeow RQL as in Reject Quantity? Determining the number of rejected parts is highly dependent on your industry, the criticality of the dimensions or parts themselves, and the risks your company is willing or capable of taking.
  • per GOOGLE
    The AQL is the maximum defect rate that is ACCEPTABLE to ship to your Customer. The RQL is the minimum Defect rate that not acceptable to ship; in other words it is the rate that you want to detect and reject. A LTPD plan is an RQL based plan.
  • yah in some industries: if you sample 800 parts and all but 7 pass, the lot is still acceptable. if you ahve 8 rejected parts of the 800 sampled, lot needs to be rejected.
    AQL is 800, RQL would be 8.