[panther machine]

So I am new to this site and not sure if this would be the correct place for this post but I'll give it a try.

So there is a bearing block on the machine I manufacture, 1.3748+.0000-.0002. I recently sent a batch of 50pcs to our anodizer, the parts left in acceptable condition on the bore. Full inspection reports to go with. After receiving the parts back the bore is now measuring 1.376 to 1.377!?!

In 10 years I have never seen of, heard of, or in any other way known of any anodizing process that has made a bore shrink! And yes I mean shrink not grow as the bore should grow making it smaller.

Any ideas?

[keebler303]

The bore actually grew, it did NOT shrink. The metal may have shrunk, but the bore grew, thats why it is bigger.

I have never seen anything like that. Have you used the same anodizer in the past? Did the dimensions change then? The only thing I could see is if the guy maybe sandblasted the parts before anodizing to get a uniform finish. That would be real PITA!

Good Luck
Matt

[juergenwt]

A good example of this condition occurs during heat treating of steel. Low carbon steel like 1018 - case hardened - will grow in size. Bores will shrink. Lower grade tool steels like O-1 will shrink. Bores will grow. Keebler has it right.

[panther machine]

Thanks for the feedback. There is no sign of any media blasting on the parts. I have been using this same anodizer for years and have never had any issues.

Also, in terms of materials, and their inherent properties, the bore getting larger indicates shrinkage in the material, not growth. If the material grew, like in heat treating the bore diameter would decrease. Think about how true position with a most material condition affects location. It's the same theory of growth vs shrinkage.

We call for a MIL-A-8625 TYPE 3 class 2 anodize, .0010±.0002 thickness. This should, and always dose cause growth of the material surface. Example being a .500thk aluminum plate with the same anodize would, after anodize be .502 thick.

So if we take into account the bore being between 1.3748 and 1.3746 after machining, then with the anodizing the bore diameter should measure between 1.3728 and 1.3726 assuming a perfect .001thk coating. With an average diameter now being 1.3766, this indicates that even with the coating, the bore diameter increased to 1.3786.

Now a .004" increase in the diameter is far more then the acid etching could produce, and would be enough time in a blast cabinet to fully remove all machining marks from all surfaces of the part. This is simply not the case.

Again I appreciate the feed back and understand where you are coming from with the bore growing, but the fact is that the material underwent a shrinkage process when it should have grown.

[A1CNC]

Just a thought here, What material did you use?

Is it possible the manufacturer didn't age the material properly? I am not really familiar wih what happens during the aging process so this might be invalid.

[panther machine]

Kaiser 6061 T6511

[keebler303]

Have you talked to your anodizer?

[Delw]

more than likely when the etch material to anodize it. ( think they use Electro/acid etching of some sort) the bore got bigger, never seen it to this extreme but have seen it a few tenths.unless they left it in that tank too long. it happens but .001 is extreme.

or a likely problem was your gauging to check parts was wrong. dont know how your checking but I am assuming with a dial bore?

[panther machine]

Keebler, email went in to the anodizer as soon as I found the problem. No response as of yet but I will sum up what they have to say when they do respond.

Delw, I can't say i can accurately measure the amount of material removal from the etching but again, .004" just seems next to impossible. It may turn out to be the case, I just don't know. As for the inspection I use a Starrett hole mic to verify against the probe cycle I programmed to us my mill as a CMM. The tool is well calibrated and accurate and the Renishaw probe is calibrated once every 3 months, also very accurate.

I actually have 10pcs from my safety stock, cut in the same run in front of me as I type that all measure within tolerance and the anodized parts that are out. It makes absolutely no sense to me.

[txcncman]

i too am curious about your measurement tool used and metrology methods. cmm? dial bore gage? tri-mic? go no-go gage? how was it calibrated? tested? multiple inspectors?

also, what happened to other part dimensions? anodizing is an electrical process intended to build up the oxide layer on the surfaces. bores should always get smaller if any measurable change is present. if the current during the process were reversed to cause cathodic process, material would be removed. growth or shrinkage would be expected to be somewhat uniform on all surfaces, thus tool marks would appear almost identical before and after.

[panther machine]

Three sets of eyes for inspection, my mechanical engineer, my operator and me. That’s everyone who is ever involved internally with machining and QC. All equipment is regularly checked and certified by an external metrology company that I have worked with since trade school.

Other part dimensions, length, width, thickness are all also under sized. None by as much as the bore, but still under the documented inspection records.

[fizzissist]

Could someone have the polarity reversed???
Check OTHER dimensions to see if the whole part has mysteriously shrunk..

The boss caught it, the switched it back, and anodized your parts...and everything looks ok...

[Delw]

Could someone have the polarity reversed???
Check OTHER dimensions to see if the whole part has mysteriously shrunk..

The boss caught it, the switched it back, and anodized your parts...and everything looks ok...

yup or the etching went on way too long,
since everything is now wrong on the part undersized and oversized( on bores) thats the only thing that could have happened.

if you have threads, I am betting they are way sloppy, like 3-4times smaller than the part shrunk

[Geof]

...Also, in terms of materials, and their inherent properties, the bore getting larger indicates shrinkage in the material, not growth.....

Not so. If you have a hole through a piece of material which expands in all three dimensions, such as by heating, the hole will get larger.

If the hole is larger either material has been etched away or the material has expanded.

[panther machine]

I acknowledge that I miss-stated what I was trying to say in my earlier post. For the purpose of this discussion, and my question, I should have said that the parts underwent some unknown material removal process. Knowing that anodizing is an electrochemical process, not a thermal process I guess I made the assumption that it would be understood what I was trying to convey.

Thank you to those of you who actually put in a theory about what could have happened.

[hub]

So I am new to this site and not sure if this would be the correct place for this post but I'll give it a try.

So there is a bearing block on the machine I manufacture, 1.3748+.0000-.0002. I recently sent a batch of 50pcs to our anodizer, the parts left in acceptable condition on the bore. Full inspection reports to go with. After receiving the parts back the bore is now measuring 1.376 to 1.377!?!

In 10 years I have never seen of, heard of, or in any other way known of any anodizing process that has made a bore shrink! And yes I mean shrink not grow as the bore should grow making it smaller.

Any ideas?

I had to read that a few times until I got it.. It's a confusing way of saying the diameter got larger after anodizing
I'm no expert at it, but I think some acids are used in the process. Maybe too high of an acid concentration or too long in the acid might have corroded the part too much before the anodizing coat..?

[RomanLini]

Sounds like he left it in the preprocess (caustic cleaning) tank for too long before doing the anodising. That's very bad for a professional anodiser.

I once had a bad experience with an a-hole chrome plater, After he finished "stripping the chrome" off a valuable antique motorcycle part, the threads on the steel neck were totally gone! He even argued with me... "There were no threads on that bit!"

Of course I had carefully inspected the threads (they were perfect) when I first got the part, to analyse whether it was worth the cost of re-chroming.

[mactec54]

panther machine

In normal anodizing the hole would of gone .0005 smaller in most cases,More for hard coat, I think the problem is when it was machined, you built more stress into the parts & when it was heated to 210/240deg it relieved the stress in the part & opened up the hole, 6061 has a lot of stress in it to start with

Stress free machining practice is needed for high tolerance parts

Etching can take material off the part, but would take a long time to remove that much material

Reversing the polarity won't do this, I use reverse polarity in the cleaning process sometimes

I do my own anodizing, so I have found out most things that can go wrong with the process

[hub]

panther machine

In normal anodizing the hole would of gone .0005 smaller in most cases,More for hard coat, I think the problem is when it was machined, you built more stress into the parts & when it was heated to 210/240deg it relieved the stress in the part & opened up the hole, 6061 has a lot of stress in it to start with

Stress free machining practice is needed for high tolerance parts

Etching can take material off the part, but would take a long time to remove that much material

Reversing the polarity won't do this, I use reverse polarity in the cleaning process sometimes

I do my own anodizing, so I have found out most things that can go wrong with the process

How would you do stress free machining practice? Heat up the stock to stress relieve before machining? Sorry if this is a stupid question.. (it probably is)

[panther machine]

If this were the first time I had made the part in question I may see stress being a factor. I have been making roughly 200-250 of this particular part per year, for three years with the same program and the same machine. It has never happened before.

As for the answer from the anodizer they believe it was the etching process, and now after receiving my last batch of work from them it in no way surprises me that they have some problems with the etching process. One of the parts I sent to them came back with a section roughly ½ inch by ¼ inch completely dissolved out of the part.

Needles to say, they have lost all of my business. I would attach a picture of the part but the URL link to a photo just wont work out for me.