1. Hello and Welcome to The Quality Forum Online...Continuing in the spirit of People Helping People !
    Dismiss Notice
Dismiss Notice
You must be a registered member in order to post messages and view/download attached files in this forum.
Click here to register.

Initial capability studies

Discussion in 'IATF 16949:2016 - Automotive Quality Systems' started by bkirch, Oct 1, 2018.

  1. bkirch

    bkirch Member

    Joined:
    Jun 24, 2016
    Messages:
    20
    Likes Received:
    0
    Trophy Points:
    1
    In the AIAG Production Part Approval Process Fourth Edition blue book, for initial process studies it states that for initial process studies, you should use 25 subgroups of at least 100 from a significant production run. It defines a significant production run as a minimum of 300 consecutive parts. If I have multiple cavities or multiple fixtures, would a significant production run be interpreted as 300 from each cavity or fixture, or would it be a minimum 300 total as long as each cavity or fixture was part of the production run?
     
  2. Golfman25

    Golfman25 Well-Known Member

    Joined:
    Nov 6, 2015
    Messages:
    472
    Likes Received:
    150
    Trophy Points:
    42
    My guess is your customer may want capability on every cavity (it may even be in the AIAG book somewhere). So in that case, 300 cycles.
     
  3. tony s

    tony s Well-Known Member

    Joined:
    Sep 10, 2015
    Messages:
    670
    Likes Received:
    429
    Trophy Points:
    62
    Location:
    Laguna Philippines
    As per the Section 2 of PPAP Process Requirements:

    upload_2018-10-9_9-59-0.png
     
  4. ncwalker

    ncwalker Well-Known Member

    Joined:
    Sep 21, 2015
    Messages:
    248
    Likes Received:
    148
    Trophy Points:
    42
    Location:
    North Carolina
    Here we go :)

    So the problem is, if you have a multiple cavity tool or multiple parallel processes, this becomes A LOT of parts. And it's not just good quality practices, there's significant COST involved. If the studies were dirt cheap to do, we'd just do them, right? Add to this, with the accelerated launch timelines we are all seeing, there's now significant risk that if you do this PPAP run as 300 cycles of a multi-cavity tool, you run the risk of having to eat a LOT of orphaned parts. You do this once and your financial folks are going to be pretty upset. With that said, here's some food for thought:

    1) If your customer SQ wants capability on 300 pieces of a 12 cavity tool, that's 3,600 pieces. How many PPAP parts did they order? You can push back and tell them you will run as many as they order. Because if they get orphaned by a revision change or plain just don't work in validation, then that's THEIR problem.

    2) Once you give them a bit of pause with this request, you can propose an alternate study.
    a) Let's say you have a 4 copies of a machine making parts. You can do the study on only one of them, prove out the cell design is capable. It's on you to make sure the copies are tracking the original once the first one comes into play. If they want evidence, you can certainly show this with an SPC chart. It doesn't HAVE to be a capability study. Remember - it's a prediction, and a sketchy one at that. It's not a control metric.
    b) Let's say you have a mutliple cavity tool, and you have to make 16 per cycle. You can do a study and get a feel for things with 5 or 6 cycles. You're looking for how alike the different cavities behave, easily done by looking at delta mean vs tolerance. And you're looking for consistency. Harder to do when you're cycling a few times. Do you have a similar process in production? You can use THAT data to show that the PROCESS is stable. Also, right after PPAP you should be going into Early Containment or GP-12. You can use that period to demonstrate stability as well.

    If you're lucky, you will have an SQ who can think. If you have a "check the box" SQ, push hard on the "they have to order the PPAP parts" angle.

    The goal is to gain confidence in the repeatability and stability of the process so that everyone is comfortable with opening the flood gates. There's options to do this OTHER than capability studies.
     
    tony s and Atul Khandekar like this.
  5. S1D3K1CK

    S1D3K1CK New Member

    Joined:
    Nov 5, 2018
    Messages:
    1
    Likes Received:
    0
    Trophy Points:
    1
    Hello, so I have never done a capability study because my company doesn't use Six Sigma practices. Although I would like to implement Six Sigma and Lean Manufacturing. So I am now required to do a 30 part capability study and a PPAP on a certain part. From what I have read I understand somewhat what to do but I am stumped on exactly how many measuring points to check and what's required to get the capability study completed! Can you help with some advise or give some direction to where I can research this information?
     
  6. ncwalker

    ncwalker Well-Known Member

    Joined:
    Sep 21, 2015
    Messages:
    248
    Likes Received:
    148
    Trophy Points:
    42
    Location:
    North Carolina
    Your best bet is to google it. But to do a capability study briefly:

    0) We ASSUME you are using a gage that works, satisfying criteria of Gage R&R

    1) You need to make what is defined as a "significant production run" which is usually called 300 pieces as a starting point. This is negotiable with your customer.

    2) During this production run, you are going to grab you subgroups at random points during the run. Most people grab 5 pieces in a row, and do this 6 times during the run totaling 30 pieces. Customers are now asking for 100 pieces in the study (in truth, 30 is a bit light, 35 or 40 being better). Again, what is your customers requirement for number of pieces?

    KEY POINT: You MUST keep the parts IN ORDER. For the math for Cp/Cpk to work, they MUST be in order. (Pp/Ppk are not affected by order).

    3) Once you have your samples, measure them for the features you are interested in getting capability for.

    4) Plug your results into software such as Minitab or Statistica OR you can grab something online. (Or build your own in Excel).

    And that's about it.
     
    Andy Nichols likes this.

Share This Page