Consistancy in fabrication of multiple units
Consistancy in fabrication of multiple units
(OP)
Today the shop manager approached me and stated there was too much variation between each heat exchange unit being built. These composites are layed up by hand from an outside source, and are fabricated using faceplating by three different technicians. Any advice or ideas on how to have three different technicians be able to cut and build the fabricated parts with no variation so as one technician's part is EXACTLY the same as the next technician's part? It seems like an impossible task to me with just the mere fact that it is what it is: a fabricated part. Although the units are all within tolerance they are not happy with the variation. Please, does anybody have any experience and advice to lend on how to take a completely hand built part, built by multiple technicians and have the units turn out exactly the same???





RE: Consistancy in fabrication of multiple units
[ At my very first job ever, I made simple architectural drawings for a consulting engineer. His stuff looked gorgeous, mostly because all the (freehand) lettering on every drawing appeared exactly the same, as if the same person had done every drawing in a set. That was, of course, not true. It was just a 'house rule' that everyone in the shop had to letter exactly like the chief draftsman. And we did. Only the shop crew could tell who had done a particular drawing without looking at the title block. There were individual differences, but they were subtle. ]
You can get your crew to buy into the idea of making the parts consistent, not by making it a 'quality' issue, but by making it a 'pride' issue.
"Those clowns downstream think we're amateurs because of the cutting and layup variations they can see. Let's make it impossible for them to tell who did a particular layup, by developing a consistent style, and making every part appear to be exactly the same. Please agree among yourselves how you're going to do that, and make a record of it, with sketches, drawings, photographs, whatever it takes." Then give them time to do it. Make it an official project to the extent that you can. In other words, give them some attention, and take advantage of the Hawthorne Effect.
"At the same time, I'd like to be able to tell at a glance whose work I'm looking at, so at the same time, please work out individual 'signatures' that you can work in without outside detection. They have to be distinct from each other, but subtle enough that you need to be looking for them to find them."
Again, ask them to work together, and to fully document their efforts, and treat them as if their participation is valuable... because it truly is.
Mike Halloran
Pembroke Pines, FL, USA
RE: Consistancy in fabrication of multiple units
Then the tolerances are wrong.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Consistancy in fabrication of multiple units
what sort of "variation" are you talking about ... obviously nothing too physical, maybe just appearence ?
personally i don't think you're going to get the tech's to agree on one way to do the job, they each have their own experience and preferrence for doing things a particular way (for both rational and irrational reasons), but none of them are wrong.
i gues you could ask the shop manager what the specific problem (variation) is, and talk to the guys about it ?
RE: Consistancy in fabrication of multiple units
This could get you much closer to the uniform part. Keep in mind that you will never get a 100% identical part in an out of autoclave hand layup. But you can get pretty darned close.
Obviously this statement makes a lot of assumptions, but if you post what the variation is maybe we can help some more.
Wes C.
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RE: Consistancy in fabrication of multiple units
We'll need more details to make more detailed suggestions, and perhaps you need more information as well. Here are a few things to consider:
Greg noted
" Although the units are all within tolerance they are not happy with the variation. "
Then the tolerances are wrong.
And that very well may be true. But consider this. Is it the shop manager's responsibility to define the tolerances or performance requirements for the heat exchanger? Is the shop having a SPECIFIC problem that they believe is caused by part-to-part variation?
You seem gung-ho to go out an make the vendor make changes to his process. You don't know what changes to ask for. You don't know what the PROBLEM is.
This approach will add lots of cost to the part, very likely without adding any value.
Step one in solving any problem is understand the problem.
RE: Consistancy in fabrication of multiple units
RE: Consistancy in fabrication of multiple units
A thou? Sanding? Yikes! You won't get that even in a jig.
Mike Halloran
Pembroke Pines, FL, USA
RE: Consistancy in fabrication of multiple units
If the customer wants a machined appearance then you need to use a female mould in that area. I suggest you get the customer in, and see what exactly it is that they want. Then give them the options. If you need to retool to meet their new requirements then that will cost them. If you can work out some acceptable compromise with your current process, great.
As usual most engineering problems are to do with cmmunication, not maths.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Consistancy in fabrication of multiple units
What does that mean? Horizontal and vertical points of what? Off with respect to, or from what? You stated earlier that everything fell within the allowed tolerance. Yes or no?
So it's an appearance issue only? How about a nice pretty piece of glue-on trim?
Otherwise, get the client to write down exactly what he wants you to change, and exactly where in the specification or contract it states that his request is a defined requirement.
If he can't do that, offer to price a change order.
RE: Consistancy in fabrication of multiple units
Some of the tolerances might be close to, or actually, impossible. The one that comes to mind is a pump-skid production project (mild steel fabrication, square tubing and plate stock), where the skids are 46 feet long, 18 feet wide, and 18" high. TIR spec from end to end (along the 46' length) is 1/16 of an inch (~ 0.060"), as fabricated. Is this a reasonable spec?
BK
RE: Consistancy in fabrication of multiple units
However, the above just means that contractually the client probably can't reject the parts.
If in the future though you've decided you need to try and please the customer then you'll want to update your product documentation to reflect this requirement.
Is possible to tigten the tols to achieve what your client wants? If you tighten the tolerance to meet the customers visual requirement are they still manufacturable with the same process/cost?
Create a detailed spec or work instruction like Mike H describes. Make sure and get input from the techs involved etc. Reference this on the drawing/MBD that the part shall comply with or be made in accordance with that spec.
If at present each techs parts are acceptably similar, it's just the variation between techs that's the problem, then this may be adequate (when backed up with QA).
One of our sister sites has 'cosmetic parts' where they have a number of requirements for the parts to basically look pretty. Cosmetic parts are identified on the drawing with a reference to the spec that gives the requirements. Can't recall the details, sorry.
KENAT, probably the least qualified checker you'll ever meet...