What to put on a drawing that guarantees that your part is vapor polished? How to inspect?

[dennisbernal91z]

I am a product engineer that makes drawings for parts that need to be vapor polished. In the past I have received parts that were spec’ed to be vapor polished, yet showed up not polished. The parts were buffed slightly so it was a bit hard to tell if they have been polished or not, this was the first time I had ordered the part, so it was hard to tell if it was polished or not. (Very small part, about the diameter of a BIC pen and a thickness of 0.053"). I used the parts thinking they were polished. Later to learn from the vendor they were not. This problem got sorted out, but in the future inspection will not be done by me, it will be done by a non-technical QA employee. How do I make sure they know what a polished part looks like? Give them a polished and a non-polished piece and allow them to do a visual comparison? My company is very small (I am 1 of 2 engineers) so we don't have a lot of cash for inspection equipment.

Thanks for any insight.

 

[ShaggyPE]

Perhaps you can rely on your supplier more heavily. Can they provide a QA certification or statement on their end that the part has been vapor polished? Then your QA employee will simply verify the receipt of the cert.

-Dustin
Professional Engineer
Pretty good with SolidWorks

 

[dennisbernal91z]

Thats what I wanted to do, but the engineer I work with brought up the point that the vendor already lied about polishing the part the first time, what makes us 100% sure they won't, or any other vendor won't in the future?

I hate working with vendors that make me have to think like this, but it is simply the truth. Maybe it is becuase we are small fish, so we need to use small fish vendors that are not as stellar as other companies that we simply can't afford.

 

[dhengr]

Dennisbernal91z:
Include in your PO and contract paperwork an item which allows you to pick a testing lab of your choice, X number of random selected parts, you pick them, for verification and certification, at a fixed price to the supplier. Non-conformance has a significant penalty cost to the supplier. And, you have already arranged this inspection and testing, and its cost with the local lab of your choice.

 

[rb1957]

how do your inspectors verify that a part made in house has been polished ? hopefully not asking the guy if he did it !?

how critical to the performance of the part is the polishing ? how critical is the function of the part ? (if it fails, can it kill people?)

if you can't trust your vendors, get different vendors! if you have to work with them ('cause their your boss' buddies) get them to pay for 3rd party inspection. (how will the 3rd party inspection comfirm the polishing?)

Quando Omni Flunkus Moritati

 

[IRstuff]

You say this guy "already lied about polishing the part," but that's only the lie you caught him in. Did they pay reparations? Why would you go back at all to someone who has already been proven to be dishonest? What assurances do you have that they won't or haven't lied about something else, like material composition or anneal?

TTFN
faq731-376

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[MintJulep]

Vapor polishing is generally done for optical reasons, so it would seem that the inspection would be optical in nature.

 

[rb1957]

is there a difference between something at is polished and something that looks polished ?

how do you know if a surface is 128, 64, or 256 (surface roughness)?

Quando Omni Flunkus Moritati

 

[dennisbernal91z]

OK, a lot of questions here... I will try to answer you all in a nut shell so I do not drag on.

My origional question was about how to spec out vapor polish and that the person inspecting parts is not an engineer. That question still stands. First are there people here that spec out polish of some kind and need to inspect their parts? If so how is this inspected?

I know I can use outside vendors to verify things, I will tell you right now that is 100% out of the question for how things are run here. Simply put, never ever going to happen. Cost and time is far to great. No parts have any potential to hurt anyone, ever. We always strive to look for new competent vendors, but what about if you have been using a vendor for 10 years with no issue and all of a sudden they make a mistake? You walk away? If that is how you work you will spend all you time looking for vendors, and not designing products. As for the company that messed up, no, they did not pay anything. That is not part of my job though, I do not deal with what happens after the failure, I just try and guarantee that they don't happen as best I can (practically for free). It is a whole differnt mind set when working for a fast moving small company, there is little time to do inspections and things like that. For example, when I make a drawing for a stainless steel probe that must be 316 to avoid rusting how do I verify that it is 316? I use a COC (Certificate of Compliance). That is all I can rely on, I do not have time of $ to send the parts out for verification.

Does no one else have these issues? All your companies have the capital to get evey part analyzed before use to ensure that it is truly the material you speced out? Same goes for plastics, how to confirm that White ABS is not actually White PVC. They look extreamly similar.

I guess that is my main point, how do others verify or feel confident about things that can not be checked???

 

[rb1957]

i quite agree that a CoC doc (even one from China) is supposed to show that the part conforms to the drwg. in your case it sounds like a vendor whom you have a long and positive relationship with screwed up once; not sure if it is nice or foolish that they admitted it to you.

i understand narrow margins and no time to check.

the person doing the inspection doesn't need to be an engineer, these days they only need to be able to read ! (CoC, tick; more along)

a lot of things look alike (different steel tempers and alloys, plastics, etc) ... there are no doubt tests for comfirming this type of plastic or that, etc; but you don't have time for that. you trust the CoC and that's the end of it.

remember everyone, and i mean Everyone, was caught out some years back with "bogus bolts" ... H11 bolts that didn't meet spec.

Quando Omni Flunkus Moritati

 

[MikeHalloran]

I don't understand why anyone would want vapor polishing (partial dissolution) rather than mechanical polishing, or, infinitely better, polishing the mold and eliminating the secondary operation altogether.



Mike Halloran
Pembroke Pines, FL, USA

 

[dennisbernal91z]

rb1957: Thank you for understanding where I am coming from.

I have had vendors polish things that were not supposed to be polished too, simply because they, and I quote "polish and anneal all acrylic parts". Just strange. Of course we can stop using them someday, but that is not my question, my question is how do you stop them during inspection the first time, not leave them after the damage is done.

Maybe there is no way, without spending $ and time. Just wanted to gauge the rest of you guys to see if there was perhaps something I was not thinking of.

 

[dennisbernal91z]

Parts are machined, not molded. The internal structure is critical for the visual appearance of the part for customers and for ease of final assembly.

 

[MintJulep]

How to spec vapor polish on the drawing: "Finish: Vapor Polish" Hopefully there is a specification or process that can be added to the note.

How to inspect that something has been made correctly: You specify vapor polish for a reason, right? There is something quantifiable that works correctly when the part is vapor polished and doesn't work correctly when the part is not vapor polished. So you perform an inspection to measure that quantifiable thing. You need to identify what that quantifiable thing is, then perhaps someone can suggest you to inspect for it.

Inspector is not an engineer: Then you write an inspection procedure at a level of detail appropriate for their level of education and train them on how to perform the procedure.

How to perform an inspection for free: Don't do an inspection.

 

[MintJulep]

I guess that is my main point, how do others verify or feel confident about things that can not be checked???

This is not the right question to ask.

Anything can be checked. Some things more easily than others.

What you want to ask is "How can I feel confident that things are made correctly so that I don't have to check each and every one?"

 

[3DDave]

It all costs time and therefore money. If you are really worried, call up their QA and Manufacturing Engineers and have them send copies of the process they will follow in making parts for you. If they are a good supplier, they probably will, presuming the cost of doing so still lets them make money making the part.


"how do others verify or feel confident about things that can not be checked???"

You don't, particularly if your supplier is not cooperative. It also doesn't matter how long you've used them. If they make a mistake, that's one thing. If they actually lie about it, you can elevate the problem through their management, but if there is no resolution, run away. There are enough good suppliers that can and will do a job as quoted, per drawing, for the same or less cost than one that ships unuseable items.

 

[drawoh]

dennisbernal91z,

This is one of the reasons you specify the results, not the process.

Specify how shiny and transparent your part must be. You do not care how they do it. Now, the thing is checkable.

--
JHG

 

[dennisbernal91z]

Ok let me touch on a few points here from different people. A lot of stuff is being said and it is a bit hard to sort out since in the end no one knows exaclty what I am talking about and I have not described it all perfectly.

So let me start at the top and give a little more detail since everything everyone has stated is quite obviouse to everyone else in here, as well as me.

Here we go:

The part is made from clear cast acrylic, is about 0.240" is diameter x 0.053" thick. It has some small features to it like ultrasonic energy directors, flash traps and a thru hole of 0.080". Looks a lot like the smallest pieces LEGO makes. During my prototype phase of my project I speced out Vapor Polish in my "Finish" box of my drawing. This is what I always do. I got the parts from a very trusted supplier that does good work. The got me the parts and I could not tell if they were polished or not seeing as how they were so small and I figured maybe it is hard to polish such a small part well. I used them and they worked. Later on after buying the parts again, this time my purchasing department used a vendor with a shorter lead time, the part parts showed up looking VERY clear. This was the first time I thought to myself. "Maybe the first lot I got was not polished". The polishing ended up making my parts weld slightly worse. The parts that were NOT made to the drawing actually worked better! So of course I changed my drawing, but that is not why I started this thread. What I wanted to know is that for something that is clearly subjective, like clarity in this instance, how do people spec things out? Of course there are ways to spec anything in the world, but I can't make this thing cost more than $2, and I only need to buy a couple hundred at a time. The part is small, and my company is not going to send the parts out for testing, we are also not going to buy expensive equipment to test for clarity. Those ideas are literally on another planet in terms of something a company like this would ever spend its money on. Also it not so critical that someone could ever get hurt or anything like that. It is litterally like making a LEGO that needs to be clear, (or actually not clear, due to the welding), not to any specific spec, just clear. We can't test this and I can't expect the QA person to know what the correct level of clear is. Can I? I have thought of setting up a part catalouge that shows how polished parts should look. This would give a gold standard, and if a part comes in not looking like the standard the lot can be failed, or engineering can be called to confirm the failure?

Anyways, I have gone on long enough. I have so much more to ask but feel like this example is maybe a bit too convoluted to get thru here. General consesuse seems to be test or find a new vendor, or to add a clarity spec. Something I can't even measure. Maybe the gold standard and training of the QA inspector is the way to go... or only way to go given the constraints I have...

 

[rb1957]

do you want the part to be clear (there's got to be a mil-spec for that) or weldable? is it important for the final product's function that the part is clear, or is it an appearance thing? often parts are prototyped so the best way to do things is developed over time (as you've discovered, unpolished makes for better welding).

i think it's a problem with out-sourcing ... it's hard to have the discussions about how a part is going to be used, what's better for the ultimate product ? with out-sourcing, the vendor gets the drwg and makes it; sure sometimes the vendor works with the prime to develop the part (but that often breaks down into squabbles over SoW and cost).

Quando Omni Flunkus Moritati

 

[1gibson]

Give them a laser pointer and do some sort of light diffusion test where they shine through to a white backdrop. Keep reference samples. Make a fixture so position of part and laser is constant. Take pictures (or video, why not?) of pass/fail and keep it handy.