Cadmium Plating

[Sparweb]

Below are a pair of AISI 4130 steel pins 0.37" diameter that were sent out for cadmium plating. They returned looking like this:

That's a color photo. The white finish can be removed with a fingernail. The processor says this is the "normal appearance". I would call BS but I don't know enough about the process to say exactly what the real problem is.

The parts are AISI 4130 steel, not heat-treated. The drawing called for "Cad plating per QQ-P-416 type I, class 2". Should this have been "Type II" OR "III"?
If I had done the drawing I would have specified Nickel plating, but I did check this drawing, and didn't catch the "Type I" so the egg's on face no matter what.

From the spec QQ-P-416:

Types.
I - As plated
II - With supplementary chromate treatment
III - With supplementary phosphate treatment

Is this what TYPE I cad plating looks like?

STF

 

[swall]

Type I is as-plated,no supplemental treatment. Your parts are not heat treated, so a 375F bake which would tend to discolor the parts was not required. Given the absence of a supplemental treatment and the absence of a post plating bake, I find the appearance of your parts to be normal.

 

[tbuelna]

You can read the visual appearance requirements in section 3.5.2 of your (superseded) QQ-P-416 plating specification. From looking at the photo provided it appears the plated finish meets the specification workmanship requirements. Section 3.2.7 also states a dull luster surface is acceptable.

Cadmium is a soft (white) metal, so it would not seem unusual that the coating surface is easily abraded.

Since your engineering drawing specified a controlled process for applying the cad plating (QQ-P-416), I would assume the work was contracted to an approved vendor. All US vendors approved for performing this type of controlled aerospace process are now AS9100 and/or NADCAP certified. So if the job was sent to an approved vendor I'm sure the work was performed correctly. If you still have any doubts, contact the vendor and pay for a copy of their processing records and a C of C (Certificate of Compliance).

Hope that helps.

 

[Sparweb]

Thank you,
I didn't find the wording of QQ-P-416 as clear as you do. In fact, subsequent descriptions of failure of the corrosion test made me wonder if these articles were subjected to that test when they are actual production articles. I do follow your reasoning, though. Given what I said before about checking the drawing but not carefully considering the plating spec details, I believe it was just an oversight on my part not noticing that the wrong type of plating was chosen, by a designer that knew even less about the process than me. That designer's left the company now, so I'll be steering this back on the right path.

Any comments on the following:
a) removal of current plating and re-plating CAD plate type II,
b) removal of current plating and re-plating Nickel.


STF

 

[BrianE22]

Somewhat related, we used to cad plate and yellow chromate some steel shafts. We didn't have a problem with the plating being easy to scratch off. Does the chromate make is harder?

 

[JohnRBaker]

I was lucky... When I was working as a machine designer, the industry for which our equipment was going to be used, food production (baking to be specific), Cadmium was verboten. If you were to plate anything it had to be something like Nickel or Zinc. We also used a lot of Stainless and Aluminum, and when we did have to paint welded steel structures, we had to use special aluminum-based, food-grade paint. Our biggest issue was that we had to use either Stainless or more commonly, Zinc-plated, fasteners, which could be significantly more expensive than your normal Home-Depot quality 'nuts & bolts', which are almost always Cadmium-plated. Which meant that when we shipped a large piece of machinery, which had to be field-erected, that we had to include sufficient extra fasteners so as to make sure that someone didn't accidentally or inadvertently use fasteners which were not approved for use in food-production facilities.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[tbuelna]

SparWeb,

Before making any changes to your engineering documentation and/or issuing rework instructions for your pins, give your plating vendor a call. One thing any vendor with an AS9100 or NADCAP certification is very sensitive to is any action by a customer that might adversely affect their QA record. Your vendor will be quite happy to provide guidance on exactly what needs to be done to resolve this issue to everyone's satisfaction.

The first thing you should do is obtain a current version of your cad plating spec, which is AMS-QQ-P-416 rev E, and review it. The first page of the spec lists the minimum information your PO should include. You will also need to provide the vendor written instructions for removing the existing plating. Unless your application requires the lot QA testing described in the spec, for a small batch of parts it is probably not worth the significant added cost to have your vendor perform them. And if so, your PO should clearly state which of these QA tests are not required. Lastly, it is well worth paying a couple extra bucks for a copy of the vendor's processing records.

 

[Sparweb]

Yes indeed we are speaking with them. They're just busy guys and didn't get back to my questions quickly. I am glad that it allowed me a chance to run this by you to calibrate my expectations. They were selected specifically for their capability, and they've been a go-to vendor for many plating/finishing processes for that reason for many years. I may have portrayed a casual attitude in my OP, that was meant to express my concern about what different plating types look like, but doesn't reflect the relationship we have with our vendors. They just don't like being pestered by inquisitive engineers like me!

I notice that there are no takers on my previous questions about re-plating the parts. In a way, that confirms my expectation that there is no way to re-plate the parts and they need to be made again. I'm also going backward through the same designer's drawings looking for other parts that called for this same Type I plating...

STF