Job Shop Machine Shop Quality System

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    I work in a company that has around 300 customers.  Each customer orders between 1 and up to 100 assemblies.  These assemblies all require parts that are customer specifice.  A customer may order their finished assembly a few hundred times a year or once a year.  Around 80% of the parts begin in our machine shop.  Of those 80%, around 80% of these parts go on a turret punch and then are processed through a press brake operation.  The other 20% may go on a CNC router table and may or may not go to the press brake.  Currently, my company has no inspection/quality system other than looking at the finished shipable part.  So if a part is made wrong in our machine shop, it is a headache.  The assembly departments had to bang and cut to make parts fit.  I am undertaking the project of setting up a quality system in our machine shop.  I would like a very visual system to the employees so they can see how well their department is performing on creating parts that match drawings.  Any suggestions on where I should start?


    Michael Mead

    This is a complex question with a few hidden issues. Can I assume that you don’t want to add an inspector, just continue with self inspection?
    One way to begin reporting is to capture all the failures that occur internally and develop a running control chart, posted in a conspicuous place. Then, using this data, create a Pareto chart to see what types of defects are being made. From here, you can start to address the problems.
    Another idea is to just perform random checks. It seems your defects are from an operator-dominated process, which relies on craftsmanship rather than machine variation.You can sample a few characteristics (maybe 4 to 6) about 4 times a day at each machine, and make control charts for each operator or machine. For an example of this, see Donald Wheeler’s Statistical Process Control book. I think Chapter 11 deals with a socks factory. 
    Good luck.



    Wow, from nothing to lots of control charts! That is advice that is
    bound to fail.Original poster – go read something about the visual factory or visual
    workplace. You get over 400,000 hits on Google. Go to for
    books on the subject – there are many good ones. On the broader
    subject you should really be interested in go read what you can from
    Shingo and/or Ohno.


    Mike Carnell

    I agree with Stan. The solution to your problem or at least the beginning of it is not in control charts. With short runs on machines you are much better off controling the setup. Watch you setups and see where people are turning machines on for production. Frequently when setup guys get things just inside a spec limit they will turn it loose for production. You can use Pre-Control to kkep them from doing that. If you are willing to slow things way down instead of taking the whole spec width and dividing it into 4 sections cut it in half and then divide the half spec width into 4 sections. That will force then to setup in the green but the green will only make up 25% of the total spec width rather than the normal 50%.
    When you are in machining operations it is fairly common to see parts produced where they creep up on a spec limit and then take small cuts to get the parts just inside the spec limits. This protects them for rework. If they hang a chip or something like that it leaves them enough material to rework without scraping a part. The parblem that leaves is that if you were turning a shaft it would tend to be at a max material condition so it would large. If it has to fit into a hole that was drilled so that it left room for rework that hole would be to the small side. Any variation or measurement system issues will leave you forcing parts together if they fit at all.
    You don’t need control charts to figure all this stuff out and sure don’t need inspectors. Just spend some time on the floor talking to people about how they do their jobs.
    Just my opinion.

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