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Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 3:02 PM

Hi,

We get our suppliers produce a lot of machining parts for us from AL7075 T651 and AL 6082, AL 6061.

We frequently reject holes with diameters having tight tolerances like H7, H8, etc... The common comment coming from the machining suppliers is that these holes are drilled properly by them, but enlarged because of sulphiric acid during the anodizing process that is made by an other supplier.

What are your opinions?

Thanks.

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#1

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/15/2015 3:11 PM

What tolerances are you working with? How tight?

It is possible but I don't think it is happening unless they are letting the parts sit in the acid bath too long?

  • Get one (or more) of the parts from your supplier prior to anodizing.
  • Inspect the part(s).
  • Send the part(s) out for anodizing.
  • Inspect the part(s).
  • Compare your measurements!
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#9
In reply to #1

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/15/2015 6:54 PM

>>>>> ...

H7, H8 are the tolerances, used for axial size communication.

It could be useful to know the thickness of the Al material and the position of the holes.

In- hole anodizing requires special tricks to get it "fluxed". The aluminum we get is heavier anodized than non anodized. They add material in the process.

Ours is 15 micron / or 10 micron within 3%.

Have pics. evt

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#17
In reply to #9

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/16/2015 1:00 AM

Adding material would not enlarge the hole.

Talking about a hole and tolerances and anodizing I thought OP has a problem with too small some holes.

Maybe OP wants to clarify this.

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#2

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/15/2015 3:13 PM

If the machine shop takes care of the anodizing (either internally or through an external shop) then the answer is pretty simple. Your drawing should show hole size and tolerance for the final part. Call out drilled hole size as a reference dimension. If their subordinate processes alter the hole size then they are responsible for making the adjustments.

Your drawing should state acceptance criteria for the final part. The machine shop is responsible for their own intermediate manufacturing steps.

Note that you must do this before putting the drawing out for bid/quote.

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#3

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/15/2015 3:26 PM

In your specification for bid, you must specify acceptance criteria after the parts are anodized. You should not have to be concerned what happens outside your realm. The sub has to be responsible for all inspection as you have no contact with their sub (the anodizer).

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#4

Re: Does Anodizing enlarge hole dia. on 7075 T561 aluminum?

06/15/2015 3:51 PM

I'm with the others.

The part drawing/spec must be for the finished part, after all processing has been performed.

Anodizing MAY remove material, causing an enlarged hole diameter of smaller outside feature dimension.

Specify the finished product.

Where's your engineering department, and why aren't they working with your purchasing department?

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#5

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 4:19 PM

Sulfuric Acid Anodizing can deposit a surface film .0001 to .001 of an inch. Hard Anodizing with Sulfuric Acid even more a couple thousands of an inch. As other have mention tolerances need to be spec out. Especially where fits fall with in the range of these deposits.

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#8
In reply to #5

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 6:43 PM

GA. That's been my experience in the aerospace industry, that anodizing aluminum adds to the dimension, not remove.

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#10
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 6:57 PM

Likely true, but why would one specify an intermediate dimension for a part with subsequent process steps which could change that dimension?

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#11
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 7:00 PM

All our drawings with anodizing always specify the post-treatment size. The machinist has to figure out what size to machine to allow for the increase if it is a critical dimension. I guess the problem is that the OP is using two different houses to produce the part. (Fingers pointed at each other)

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#12
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 7:11 PM

Looks like the OP has abdicated his responsibility to communicate and coordinate with multiple suppliers to be sure the final product met HIS needs.

We called that having everybody on the same page back in my day.

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#13
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 7:42 PM

Here is some info on Type III coatings from MIL-A-8625.

So in general, the increase in dimension will be one-half of the coating thickness except in those cases where the radius of the hole is less than the radius of curvature as specified in Table III on page 17 of the spec.

For those interested, you can go to DLA QuickSearch Assist website and download the mil-spec.

http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=7074

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#16
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 12:45 AM

I think you need to be more careful how you word that!

In my limited experience, (also mostly in aerospace) I agree that anodizing adds material to the surface, but that means that exterior dimensions increase, while interior dimensions decrease. That means that holes get smaller ID after anodizing, not larger.

If in fact the holes are larger after anodizing, then some other process is causing the enlargement. Too much time in the acid bath sounds like a reasonable culprit.

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#25
In reply to #16

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 5:12 PM

OK, adds to the material.

I was hoping I wouldn't have to explain inside dimensions versus outside dimensions. Why won't my Cavalier start?

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#27
In reply to #25

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 5:40 PM

Re: the Cavalier:

It looks like you have fuel, air, and spark. It should fire right up!

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#28
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 5:48 PM

Well done. GA.

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#30
In reply to #25

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 9:23 PM

WOW! You have a really "hot" car!

The burnout is awesome!

Is it nitro powered with a turdbo-charger?

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#6

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 5:03 PM

the process of anodizing makes the natural Al2O3 lay that forms on all aluminium in air as soon as it sees the O2.

Aluminium never exists in nature as the element.

The process of anodizing passes a current through the layer that deepens the oxide layer. There are limits to how deep it can be and how quickly it can be formed and manipulation of these allows foreign ions to enter the anodized layer to give it various colors.

So I would say it will be thicker. A few test runs to quantify the process should help the maker predrill and anodize measure. An insert can be used to block the hole to prevent sidewall build-up. It can be removed later by dissolving it or melting or subliming it

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#7

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/15/2015 6:21 PM

Well there is going to be some variance in coating thickness by the nature of the process...Anodizing is generally 50/50, in that half of the anodizing layer will penetrate the aluminum and half will be additive to the surface, but this is not an exact science with typical methodology...I would expect a variance of several thousandths of an inch...You could install a quality control person on site(anodizer), who could check incoming and outgoing specs and make a determination on what action could be taken with out of spec pieces, whether to scrap the piece or send it back for rework ... sort of catch the problem upstream to make a determination...

http://www.thomasnet.com/articles/custom-manufacturing-fabricating/anodizing-versus-ceramic

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#14

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 12:33 AM

If the hole are too large, drill them a little smaller before picking/plating/anodizing them. If the holes are too small, drill them a little larger, either before or after. If you can't figure that out, take up astrology or religion or some other pseudo-discipline that does not operate on sensible principles.

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#15
In reply to #14

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 12:42 AM

Before, not after.

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#18
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Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 1:13 AM

Some dumbstick voter obviously knows nothing, but that doesn't prevent poor voting.

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#19

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 1:23 AM

Our friend is, devoid of common knowledge.

"I need the tolerances and allowances table for the inch system."

Tolerance and Allowance for the Inch System

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#29
In reply to #19

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 8:32 PM

Lynn,

We don't know how old the OP is.

Inches, Feet and many other units saw "a" light because the English traveler had nothing to measure with.

Nothing other than: here we go

In Payless Shoe, they store shoes from size 7 up to 14 and that is all refering to 1 foot.

Inch in French is pouce, in dutch duim (thumb)

It is just like penises, they come in all sizes too.

So tolerance and allowance, whatever it may stand for?

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#20

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 6:35 AM

Anodizing grows an AL oxide coating on the metal. typically if you are losing material this will occur in the surface preparation steps, mainly in the etch.

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#21

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 8:09 AM

Review the process, the holes should be drilled undersize then reamed to the correct size. Anodizing will not enlarge a hole dia.

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#22

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 9:25 AM

Any time we purchase plating services on parts made in-house the machine shop normally undersize all holes/openings then specify drilling or machining them to specifications after plating is complete unless the coating is also required to be on the inside surface(s) of the openings.

If the coating is required on the inside of the openings, the machinist enlarges the openings enough to stay within tolerance of the specified thickness of plating material that is going to be applied to the part

It is critical to the process that the specifications spell out exactly what is being done and who is responsible if the part does not meet specifications.

If your agreement with the supplier is correctly detailed and the supplier is not meeting your specifications, it is the supplier's responsibility.

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#23

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 2:09 PM

How many holes get enlaged in the part you describe? (or... do all the holes in your part get enlarged? how many are they? what is the thickness of it?)

If itĀ“s just a couple of holes (which may be the 100% your part has) take into account that the anodizing process requires the part to be hung into the bath by means of conductive wires.... and that thse holes may be used for such a purpose.

The anodyzer has to balance the current for the process calculating the size and shape of the parts to be treated. (ideally he should make it in batches with all parts are more or less of the same size).

If he puts a large part (requiring higher currents) close to yours (smaller = less current) you may have an electrolytic process on yours and ... eventually observe the enlargement of a hole / s, spotted / defective color of the surface, etc.

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#24

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 2:22 PM

Just a reminder:

OP says, "drilled properly by them, but enlarged because of sulphiric acid during the anodizing process".

To me that means material has been removed.

That says over-etching.

I know this has already been said.

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#26

Re: Does Anodizing Enlarge Hole Dia. on 7075 T561 Aluminum?

06/16/2015 5:17 PM

<Unsubscribing from this farce>

Good luck.

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