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Anodising Help

Gavin Perkins

Plastic
Joined
Jan 16, 2018
Hi,

I'm trying to anodise colour match a component for a customer and I'm getting decentish results but the sample part the customer has given the finish is quite satin/matt I am hoping to get some advice on the next step.

I know there is probably more information that you will need to help ask away and I'll hopefully be able to answer you.

The sample parts are the two components on the right of the picture

IMG_2294.jpg

I have tried getting these parts anodised by a subcontractor and because they are small, finicky and need colour matching they don't seem to want to touch it with a 6ft barge pole.
 
It's hard to tell from the picture, but are the parts media blasted? Media used will affect reflectance of the final result, with something like glass bead giving a brighter/more reflective finish and aluminum oxide giving a more matte finish.

In my experience, the variables affecting finish the most are media, etch, alloy, usually in that order.
 
I don't know how much experience / knowledge you have about the anodizing process, so please do not think I am speaking down to you. Cause buddy I sure don't know it all either.
Anodizing certain colors is not possible due to the size of the molecules of the dye. Ever see white anodization, nope the molecule is big to fit in into the Al pores. And that is really what the electrolytic passivation process we call anodization is, replacing the natural oxidation that occurs on bare Al. So color matching is probably quite hit and miss. I would think this would be the reason for your local plater is reticent to do it, again what I just proposed is what I learn more than a few years ago in school. So if any other members can explain further I would like know some more of the technical minutia, please chime in.
 
Ah sorry the picture is abit naff hopefully this is a better one.

IMG_2273.jpg

From what I know they previously had them laser cut from sheet and just anodised no media blasting then sent to a jeweler to get dyed, so I know I'm having to go down a very deep rabbit hole.
 
No not at all I know buggar all apart from the basics, I'm just trying to expand my skillset and help out a potential customer as the test piece fits great is just getting the colour right.

I understand what your saying it does explain why several places said no, I was expecting it to be quite alot of trial and error, I'm close but no cigar.
 
2nd picture you posted:
the left part indeed looks laser cut (tabs are a give away), the right part seems to have mill finish

if you want to match the original part, I suggest you copy their process and laser cut it from a sheet, no milling, if you need to machine it, you need to get the surface finish as close to what a rolled sheet looks like before you send it out to be anodized, if you need to sand it - use non silicon containing abrasives, they'll contaminate the surface and you'll end up with either a matte surface or dirty looking (like the G3 part in the attached picture), aluminum oxide sand paper is fine, use WD40 when sanding - WD40 works really well for this, water or water soluble oils do not, they may, but WD40 will work for sure

if you decide to go the laser cutting way, I'd suggest keeping them nested in the sheet and don't break them out, send the whole sheet to the anodizer and brake out your parts when they are done, size the tabs so they have 1mm cross section minimum - they'll need to carry the current to the part - racking a sheet like that can be much easier for the anozier than handling individual thin parts with tiny features, but you need to make sure there is no dross around the cuts, some lasers will leave black oxides on the cut edge - you'll have to clear those before you send it to anodizer

comments regarding the 1st pic, I understand that the parts I marked G0 and B0 are originals you want to match your parts to:
G1 - mill finish, tool marks visible, you may ask the anodizer to etch it longer to remove those, but results may vary depending on the alloy and the composition of their etching tank, I don't recommend relying on the etching approach to match the surface finish - not reliable, a lot can depend on the batch of the alloy (including temper), it is not uncommon for extruders to screw things up with may ruing your work
G2 - difficult to tell from that picture, may be etched too long, too thick oxide, too long in the gold dye, reduce etching time to avoid the matte surface finish, less time in the dye will make it lighter, so will reducing the anodizing time (thickness), 15 micron is enough to reach good blue and gold dye saturation, it may be easier to control the dye uptake with a thinner oxide than the other way around, thicker oxide tends to absorb the dye quicker which may lead to oversaturation
G3 - dirty part, not enough degreasing and/or etching to remove the contamination, may not be the same gold dye used for the other parts, different aluminum alloy also possible, not all alloys anodize the same, which has an affect on the dye uptake and resulting hue

B1 - difficult to tell, seems ok, might be slightly glossier than the B0, hence the slight difference in hue, too thick oxide may also make it look a bit "bluer" than the B0 sample
B2 - may suffer from similar issues as the G3 (same batch?)

another note - racking, holding on to, thin parts with tiny features is very difficult without purpose made rack, they are prone to loosing contact, which may lead to lighter parts (low oxide thickness), as I said before - I'd consider keeping then nested in the sheet VERY seriously

edit: forgot to attach the picture:
IMG_2294.jpg
 
Wow thank you for a very detailed response.

Yeah the previous parts were laser cut but the customer was having to "glue" on the lugs so I was hoping to machine them on saving them some labour.

so I was milling the face of the part but this was making it too shiny so at the minute I have left it with the stock finish and that seems to be better.

I have taken on your advice to keep the anodising thickness to 15 microns and added more degreasing and rinsing steps.

I have also made sure the anodising tank is at more of an appropriate temperature as it was around 15 degrees Celcius it is now between 22-25 and the dye tank is as per the dye manufacturer's sheet of 55-60.

I am looking into a nickel acetate sealing solution and possibly a double stage one perhaps whats your thoughts on that? whereas now I'm using boiling DI water.

the blue dye seems to need a longer time in the anodising tank than the gold/orange.

The material is all the same grade of aluminium and a known spec whereas before they had the finest chineseium so hopefully, batch to batch it will be more consistent.

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IMG_2363.jpgIMG_2363.jpg
 








 
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