Finish Machining Post Hard Coat Type 3

[rgrin]

Hi all,

I have been tasked with figuring out a way to re-machine parts to .0002" flat post anodizing. We tried making the parts to .0002" flat pre anodize, but the plating process was too inconsistent and left a fairly rough surface on it. Normally we would grind them in the surface grinder, but the parts have bosses on the surface needing to be ground and it takes multiple setups to do it.  The powers that be are hoping we can set it up in CNC mill and grind them to spec as our grinding department has more work than they can handle.

Talking to our surface grinders, they use a silicon carbide wheel. So the most apparent solution would be to set up a silicon carbide cup wheel in a mill and go to town. Would have to figure out coolant filtration and wheel dressing in the machine, but I think it should be viable.

I would like to look for other options. I suggested using a diamond cutter of some sort.  My boss said they tried that 10 years ago and had little success as the coating wore the diamond down really fast. He couldn't remember if it was a PCD or MCD, so I wonder if that would make a difference. Talked to our anodize supplier and he had the same experience. My last two thoughts would be maybe a CBN cutter or maybe some sort of ceramic? 

 

Thoughts?

[Newbeeee™]

Plating will be rougher - for hard, you always need to machine at least twice as good surface finish pre plate, to what is required post plate.

Depending upon batch qty, general carbide cuts hard anodise okay in my experience.

With this flatness tolerance, how large is the area?

And you better not distort the part when clamping....

[Jobnt]

How thick is  the plating? Is it just build up or also penetrate? 

Like Newbub said you best not warp that part in your workholding. How big and of what shape is the part?

Tool wise, the bigger the tool the more the machine's tram will come in to play. Use as small of a tool as possible with as small of a stepover as possible so you're only cutting with a small area of the tool. Do not lift the tool up either. Once it's down, leave it down because it will be sketchy at best trying to get the Z to repeat.

Good luck, and as they say... "Better you than me!"

 

 

[rgrin]

I attached a dummy part that resembles the part I am making so we can all play along lol.  I highlighted the critical flatness areas in red. Basically a 17"x5" rectangle with some bosses to avoid and some islands to make co planar.

The plating is specced to be .001" penetration and .001" thick.  We have successfully made the parts .0001"-.0002" pre plate using Loctite 425 ( I believe) to secure the part to a flat plate with minimal distortion.  The long term issue is that we just got another order that takes our total part qty to ~150 over the next 3 or 4 months.  Using our glue process is just taking too long and the results we are seeing post plating are not reliable enough to continue down that road.

I found some CBN bottom grinding mandrels from a company called DI Coat. I'm thinking I can set the part on a vertical mill and basically cam block it in similar to how our grinders would do it and then just grind it in a mill in 1 set up taking multiple .0001" Z- step downs as required. 

Just looking for other options that wouldn't require a grinding wheel as I do not look forward to setting up a dressing cycle in the machine and getting grit everywhere. But it seems like our most likely option right now.

dummy.mcam

[Jobnt]

I can't open the file, I'm on 2020.

Is there an requirement for post-plating grinding on the drawing? Or is that a result of plating inconsistancy? Because anyone who designs that part with those tolerances and bosses has never made a part before. 

If the latter, Newbub is correct again in that you want a super-smooth surface before plating. But the penetrant will work against you to some degree. This can easily be done with the small tool / small stepover method I mentioned.

Is post-plate lapping an option?

Or maybe reconfigure so the bosses are an add-on after plating and grinding?

Also you might consider either bias ply tape instead of glue, or even making vacuum fixtures to hold the parts. 

 

[rgrin]

The .0002 flatness has to be in spec after plating. Just getting inconsistent results with plating. Some will come back fine, but the worse one was upto .0006 out of flat post plating.

The bosses being a bolt on solution post plate was asked but was denied.

Lapping could probably be an option but is outside of my wheelhouse. I know we lap some of the customers other parts. Not sure how would lap this one with the bosses being there.

[Newbeeee™]

13 hours ago, rgrin said:

The .0002 flatness has to be in spec after plating. Just getting inconsistent results with plating. Some will come back fine, but the worse one was upto .0006 out of flat post plating.

 

If the component is uniform in shape, this is the component stress reliving....it has moved during the time it's been inspected>shipped>plated(temperature)>returned to Inspection for checking....

[crazy^millman]

This is where a lapping table would be the best solution.

For anyone that has never seen of heard of lapping tables here is a link to educate you on the process.

Lapmaster

Also learn what light band flatness means.

Light band Information

I have a sweep in plate for the Bridgeport I made 38 years ago that is 2 light bands flat.

[MrFish]

I have sized Hard anodized parts before with standard carbide cutters, when the anodizers forgot to mask said parts !!

[rgrin]

On 8/12/2023 at 6:39 AM, Newbeeee™ said:

If the component is uniform in shape, this is the component stress reliving....it has moved during the time it's been inspected>shipped>plated(temperature)>returned to Inspection for checking....

That could be, The process is we do a heat stress relieve prior to machining. Then we rough the parts and re-stress relieve prior to finish machining and then they go to plating. The material is 6061-T6 Kaiser Select, so it should be fairly stable at that point. But sometimes ya just never know. I believe the temperature we stress relieve to is around the temp of the hard anodize process. So we aren't removing any temper but we also kind of simulate the anodize process as far as the heat is concerned. 

[Jobnt]

1 hour ago, rgrin said:

The material is 6061-T6 Kaiser Select,

I take it using cast alum is out of the question? It's much more stable without all the intermitent heat treating. 

[Newbeeee™]

Or buy T6511 - that's artificially aged, then controlled stretched and straightened.

You shouldn't need any initial heat treat then (as it has zero stress), and depending upon your component shape and cutters/process, you shouldn't really need any other stress relieve. 

Aluminum can be a funny thing regarding heat and "stress relieving"....FYI hard anodise is a cold process - near freezing. 

[rgrin]

1 hour ago, Jobnt said:

I take it using cast alum is out of the question? It's much more stable without all the intermitent heat treating. 

Cast is probably out. The part has been approved for production since 2020 with 6061 being specced by the customer. They can be a pain to get changes through and most of the time asking fewer questions is just easier.

22 minutes ago, Newbeeee™ said:

Or buy T6511 - that's artificially aged, then controlled stretched and straightened.

You shouldn't need any initial heat treat then (as it has zero stress), and depending upon your component shape and cutters/process, you shouldn't really need any other stress relieve. 

Aluminum can be a funny thing regarding heat and "stress relieving"....FYI hard anodise is a cold process - near freezing. 

I looked at the print again and to my surprise they don't specify what temper of 6061 they want. So maybe we could look into that?

Also, thanks for telling me it's a cold process. I'm pretty new to this anodize stuff since I only deal with it pre-plating. Now that they got me going after it post plating I am trying to find as much info as I can.  I just recall (probably incorrectly) that when I first started here that someone told me we bake our parts since it helps stabilize them prior to anodize and that the temp we ran at was similar to the anodize process.  

[rgrin]

So I dug a bit deeper. Kaiser Select 6061 is in a T651 state which is almost the same as T6511. They get the same stress relieving, but T6511 gets a straightening operation.  Talking to our shop owner, his past experience is that the difference between the two has proven to be negligible once you get down to this extreme of tolerance.

So with that said, my current course of action is to design up fixturing that isn't reliant on super glue for flatness. That way I can start running them in our pallet changer and get our efficiency back up on the front end.  In the mean time, for the ones that have already been made and need Post Plate Processing, I found a CBN bottom grinding mandrel from a company called Di-Coat. $60 for a 1/2" diameter wheel seems like a no brainer easy way to at-least start testing grinding in one of our verticals that is currently idle.

 

Thanks for all the suggestions!

[crazy^millman]

Look at the Blue Photon Process. It seems expensive, but the good thing is no heat just ultra violet light to set the glue. Then a Steam nozzle to remove it.

Blue Photon

Blue Photon Catalog

[BSmith23]

I just looked at your dummy part file.  I didn't see any holes in it, but am curious if there are any that you can use expanding mandrels to locate and tighten with?  That would be an easy fixture to make if that's what you have.  You could also use a vacuum fixture if there are no holes in the part.  So there are a couple of other options as far as holding the part.

 

As far as the cutters are concerned, We use YG-1 X-Power end mills on our hardened steel parts, and usually get good results with tool life and flatness and finish.

 

Whichever way you go, let us know how it turns out.

[rgrin]

We actually have blue photon at our other facility that we use for the tricky to hold aerospace prototype parts.  I'm keeping that one in my back pocket as last resort. I would prefer a method that uses mechanical means to work hold. For instance with the super glue process I am running right now on a different part, I have 5 ops that utilize it.  It takes me about an hour to get all ops glued up and then cure for another hour.  On the smaller batches I am running right now, that's fine. But this new project that I am being put in charge of, I need to yield start to finish 10 parts a week for the next 3 months. If I have to wait/setup 15 - 30 minutes for my workholding, it will kill me and my deadline. 

2 minutes ago, BSmith23 said:

I just looked at your dummy part file.  I didn't see any holes in it, but am curious if there are any that you can use expanding mandrels to locate and tighten with?  That would be an easy fixture to make if that's what you have.  You could also use a vacuum fixture if there are no holes in the part.  So there are a couple of other options as far as holding the part.

 

As far as the cutters are concerned, We use YG-1 X-Power end mills on our hardened steel parts, and usually get good results with tool life and flatness and finish.

 

Whichever way you go, let us know how it turns out.

There are holes in it and I intend to use them with expanding mandrels. My first op will be to rough/finish a bunch of lightening pockets on the backside and drill all the non critical holes. Then my 2nd op I will use expanding pins to secure/float it with hopefully minimal twist and remachine the periphery. Then it gets stress relieved and I remachine the flat surfaces again on both sides. The goal is to get .0005" flatness Pre plate and then remachine the plating to .0002" in a vertical mill with the grinding wheel I mentioned.  The concern with going above .0005" flat is that you will see discoloration since the anodized gets dyed black and it starts to look bad as you machine the unevenness out of it

[Jake L]

1 hour ago, rgrin said:

the super glue process I am running right now on a different part

If you don't mind me asking, how do you get that stuff off? 

[rgrin]

34 minutes ago, Jake L said:

If you don't mind me asking, how do you get that stuff off? 

I am using Loctite 425. The best way I have found is when you are done machining, you pop the part off the fixture and let it sit in open air for a day and it just flakes right off. My cycle time is such that it runs for about 8 hours and then before I leave I pop all the parts off and blow the coolant off and set them on the table. Then I scrape it all off with a plastic piece I cut up.

 

If you need a faster turn around, acetone works but it can leave a gummy residue. So, it requires a once over after the initial cleaning. They also sell a solvent but I haven't used any and I can't recall what it's called.

 

All in all, I do not recommend glue as a production process. It is quite cumbersome and is prone to failure if left in the machine/exposed to coolant for too long.

[MrFish]

Anyone tried the wax from MiteeBite for this style of application ?

[Jake L]

14 hours ago, MrFish said:

Anyone tried the wax from MiteeBite for this style of application ?

We had this demo'ed at our shop. The stuff seems good for the most part, we didn't end up buying it. Our biggest complaint was how hot it needed to be to melt/form. Then you have to wait for the whole setup to cool to room temperature before machining. 

[rgrin]

Figured I would come back to this with an update in case it helps anyone in the future. Finishing up running the last 2 parts tonight out of my order of 60. Successfully made all of them to the flatness spec, but ended up not needing a grind op at all. The process we settled on was to bake the stock, rough both sides, cryo treat it, and then finish both sides.  I was able to machine to better than .0002" flat over 98% of the part and the other 2% crept close to .0003"-.0004" but fortunately it was in a spot that customer was ok with that.  The cryo treatment takes the parts to -200F for 3 hours and then throws them in an oil bath at 200F for 3 hours.  This seems to have solved our warping issue as previously my parts were coming back at .0005"-.0007" flat from plating and now with the cryo, we are maintaining .0002" flat over 98% of the surface.

I never got the chance to try and grind the anodize since we were able to use a manual process to straighten the more warped ones back into spec.

The finishing fixture supported the part on 3 pads and clamped on 2 pads on the longest dimension of it. I used 2 pitbull clamps torqued to 5 in/lb to force the part to sit on 2 of the pads.

Attached is file with the fixture I used and mock part.

Flatness Fixture.mcam