×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

In process statistics help

In process statistics help

In process statistics help

(OP)
We are a custom job shop with thousands of part numbers that rotate in and out over several years. Some products we might make 50 of in a year others we might make 1000s. I would like to implement some SPC to the floor to help reduce the amount of scrap that makes it to inspection.

I am trying to figure out how to approach this. I know what key dimensions should be checked but I dont know how often to develop good statistics within a run or from one run to the next.

We are a small company (little more 100 employees) so there is no budget for big statistical software like minitab either.

If you have some pointers or have implemented in process inspection in your facility please help me get off on the right foot.

Ryan

RE: In process statistics help

The issue is generally getting the data SOMEWHERE, rather than the program to process the data.  I think that Excel can do a pretty tolerable job of processing the data, once you've collected it.

Process control is about looking for trends and excessive variability.  Getting the data into a viewable form is more important than the program.  Much of the seminal work in SPC was done even before the availability of computers, much less SPC programs.

Don't forget that the key is NOT inspecting to weed out bad parts; it's to make sure that bad parts aren't made in the first place.  That's usually a discipline problem, not a measurement or analysis problem.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

RE: In process statistics help

Agree with IRstuff, in fact much of our production SPC is done in red wax pencil on plastic boards.

The key issue is to  understand the difference between the process potential, and what it is actually doing.

So typically we'd run 30 parts without touching the machine setup.

Plot the data on a histogram. Is it normal? hooray. Is it bimodal or uniform - ooer. Then plot the values in the order they were taken - is there a trend? Can you explain it?

Then set the machine up again and run some more parts. Do they fit in the original distribution? great. If not, you have a setup problem.

There is an enormous industry in SPC, but if you find a little book called "The Seven Tools of TQC" by McConnell or similar then you probably have enough to get you going, and is enough to run an 80 vehicle per hour production line.

Incidentally you should probably read The Goal by Goldratt.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: In process statistics help

(OP)
Thanks for your input. I have ordered the book Seven Tools of TQC for reference on this and future things. SPC will most likely be recorded on the fly on some paper form.

There is a large area of the plant where we plan on implementing this. I want to start in a small area to test the waters and see about getting the system in place to see what works and what doesnt work. I also have a few people that will be willing to work with me on the floor more so than others. So I'd rather start with some of them..

Does anyone have a recommendation on starting in an area where the process is pretty consistant (like punch and die) or not consistent (lathes and other manual)?  

RE: In process statistics help

You'll probably learn more initially from processes that are continuous. However in a sensible organisation they will already have been under the microscope and the scrap rates will be low anyway.

SPC on very short runs is not as useful (but there are many other things you can do).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: In process statistics help

Getting your feet wet is better with a stable process, since it will be more obvious that something has gone awry.  Inconsistent processes are, well, inconsistent, so trying to figure out the trend is much more hit and miss.  However, if you can tame such a process, that'll be a bigger feather in your cap compared with bringing something that was mostly stable back into stability.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close