Determing Machine Capability in a High Mix, Low Volume Sheet Metal Shop

B

Bruckim

#1
#1
I've been assigned to turn around a sheet metal forming shop. Most the the equipment is rather old (+25 years in service) and a lot of the work is performed by tribal knowledge.

We have many pieces of equipment (Shears, back presses amd turrets) that are know trying to cut and form sheet metal blanks and assemblies to a +/- 0.015 inch tolerance.

What I need to do is quickly determin if the equipment at hand is capable to repeatability produce product at the specification needed.

My problem it is very very difficult to break into the production and run 30-50 test panels to perform capability tests.

My question, since we are running extensive components with the +/- 0.015 requirements, can I just measure the deviation from nominal to everything thats being produced and use the deviation from nominal to perform the capability studies?

One issue, is the data is not normal in distribution. Second, I would have both positive and negative numbers to workd with in respect fro niminal.

Looking for advice, comments, suggestions and a general opinion if this is statistically valid approach.

Please help, I am under a tight deadline and I will be very greatful for any and all constructive advice.:thanx:
 
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Stijloor

Stijloor

Leader
Super Moderator
#2
#2
Re: Determing machine capability in a high mix, low volume environment (Sheet Metal S

A Quick Bump!

Can someone help?

Thank you very much!
 
M

MikeSeymourAtl

#3
#3
Re: Determing machine capability in a high mix, low volume environment (Sheet Metal S

Bruckim,

I think I've been in that shop! If not, then one very much like it. We ran metal fabrication in sets of several hundred, using machines of similar vintage. Work instructions that said things like "See Bobby". With a team effort, we did find our way.
I feel like I can speak to the shear question. For the most part, a sheared blank is a sheared blank. So, I would be inclined to look at the machine capability across several jobs. However - be mindful of factors. Group the jobs by "type". For instance, light gage, medium gage, heavy gage. Large blanks, medium blanks, small blanks. Also, look at how the setups are done. The setup person might use one type of setup for a certain set of jobs, and another methodology for another set.

Also, think of Paereto. If the shear is currently producing blanks that are good enough, and the next process down the line is happy with what they are getting from the shear, let that one be lesser priority. What I'm suggesting is that perhaps the shear experts are getting it done, and if they aren't going anywhere tomorrow, let them keep going for now. Focus your efforts on the areas of greatest need.
Good luck Fireman!
 
C

Curtis317

#4
#4
Re: Determing machine capability in a high mix, low volume environment (Sheet Metal S

Mike S makes some good points. Most of what I have to say is what I learned during a short run SPC class I took some time ago. Yes perform your capability based on the tolerance not the part. Identify a characteristic that is the same across all parts with the same tolerance. then establish your capability around how that machine meets that tolerance. Whether or not the data is "normal" is another discussion. As long as it does not deviate from normal ie. skewed significantly it should not be a problem.

Good Luck
 
Miner

Miner

Forum Moderator
Leader
Admin
#5
#5
In addition to the prior comments regarding your proposal, plot the standard deviation versus actual size. In some situations, the standard deviation may increase with size.
 
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