Blue Etch anodize inspection of Ti

[Bob W.]

We have a new aerospace customer that is requiring this inspection for qualification of some titanium casting machining.  Basically they etch the machined part, then inspect with some sort of blue dye.  I think the formal spec is RPS 675 Method B.  Is anyone familiar with this process and what sort of cutting conditions would produce a pass or fail?  Once this process is ironed out it will be a fixed process.  We are totally flying blind on this so any input will be a huge help.

Our customer will also be sectioning these parts and inspecting the sections of the machined regions under a microscope as well.  In any case, they haven't offered any insight on machining tooling, tool life, cutting conditions, etc...  that produces a pass or fail.

[Newbeeee™]

Bob, although they haven't "offered", have you specifically asked? And been a bit persistent - demanding even....?

On anything obscure like this, I'd be wanting to know all the ins and outs - there's no point trying to re-invent the wheel, and it SHOULD be your customers best interest to be as open as possible, because it's not in their interest to have failures, especially as the parts are castings (so increased lead-time and relevant knock on etc if scrap).

[Bob W.]

Just now, Newbeeee™ said:

Bob, although they haven't "offered", have you specifically asked? And been a bit persistent - demanding even....?

On anything obscure like this, I'd be wanting to know all the ins and outs - there's no point trying to re-invent the wheel, and it SHOULD be your customers best interest to be as open as possible, because it's not in their interest to have failures, especially as the parts are castings (so increased lead-time and relevant knock on etc if scrap).

Yep, we have asked and the answer we get is we are supposed to be the machining pros, LOL!  They are right but at some point everyone was at square one.  We are a pretty small operation for this customer, they are used to working with much larger shops so we feel fortunate to even have a crack at these.

[Newbeeee™]

12 minutes ago, Bob W. said:

Yep, we have asked and the answer we get is we are supposed to be the machining pros, LOL!  They are right but at some point everyone was at square one.  We are a pretty small operation for this customer, they are used to working with much larger shops so we feel fortunate to even have a crack at these.

Yes - I get you feeling optimistic and not doubting your skillset Bob for a second.

But as a long term supplier partnership aim (which they should be aiming at), all efforts for a smooth supply of product should be their focus - otherwise they're not doing their bit right. So genuinely, I'd be very cautious here. The last thing you want is to be set up for a fall - toolup and engineer a great product, for it all to fail their testing.

Then you get invoiced for the scrap castings....

Edit - I don't mean to come over as negative here. Just being cautious for you.

[crazy^millman]

Tread very very cautiously with them and make sure you terms and conditions allow for a way out should things go south. Make sure you put provisions in there to have an external company validate the results should they make the claim parts have failed. I seen one customer pull this and still use the parts, but tried to get out of paying for the work performed. Once we demanded the parts back to have tested at our expense in a different place we found out they were using them in flight. The still tried to refuse to pay for the parts until we threatened to go to government agencies about them using what they told us was failed parts for flight then using them for flight. Unless I can verify the results independently and have a procedure defined as to the correct method for machining the parts I would be extremely careful taking the job on. The biggest thing will be stress cracking the parts with the wrong process to cut the material. Getting under the skin on the casting is going to the trick without propagating the inherent stress into the material trying to remove it. What is the removable amount using the etching process? I know a lot of issues happen with EDM machining and removing the recast layers. Where I always had a defined amount of stock to leave defined by the customer for the acid etch needed to remove the recast layers when EDM was the only way to machine features in certain parts. 

Your company being successful doing this helps them be better so stonewalling about methods to machine the part correctly is a huge red flag. They are willing to work with you and let you do R&D and pay your company to come up with the process then great, but you need to make sure you have it all in writing and get progress payments for each milestone achieved. Put acceptance timelines in the milestones as well. Once a Milestone is reach for approval there is 10-20 days to but it off. If not bought off in that time frame all work stops payment is still expected. Hopefully it never comes to that, but trust me you stop all work because someone is dragging their feet that will come to halt very quickly. 

I know you very organized and anal about your documentation and that is good in a situation like this, but kick it up a notch. Detail and define everything. Step over, Depths of cut, Sped and feeds and work holding pressures along with anything else you can think of. The more information the better on the whole process. Need to account for this in the quote as well. You want to have check offs for each step of the process and have your people understand unless they are willing to foot the bill for any mistake that scraps a part they will follow every step and process to the letter. If there are 12 steps to locate and clamp the part and each one takes 2-3 minutes to complete then it is what it is. Tools are replaced after every 6 hole tapped holes or endmill is replace after every part then each one of the steps is not open to change to pushing your luck.

Do what you say and document that process and then audit it regularly to make sure everyone is following them. It will get mundane and boring really quick so you want women involved in this if the work takes off. Women handle this better than men do. Not sure why, but they do.

Best of luck and you have my number if you want to talk about it.

[Bob W.]

Without going into too much detail, there are three parties.  There is the casting supplier and the OEM.  We are working for the casting supplier but we need to be approved by the OEMs quality department.  We have no exposure (within reasonable limits) on the casting liability but at the end of the day we do want to be approved for the OEM and win the contract.  We have worked with this casting supplier for some time and have other contracts but none of the work has been done for this OEM.

[Bob W.]

The main things I am curious on are boring precise holes with end mills or ream with carbide reamers?  What sort of tool life to expect?  Speeds/ feeds?  The tolerances aren't very tight with the tightest being +/-.002".  True positions are pretty tight though at .005" on a part that is ~30" long and fairly thin and flimsy.  We have produced one part that met all tolerances but didn't meet the surface finish requirement on a surface machined feature (32 finish req is at 40 in places.)  This could be fixed by hand but there are tight limitations on that, needs to be done in an automated process...  That is just a tooling issue though and we are working on it.  It wasn't easy by any means to hit the tolerances but it is a good process and will repeat.  It will be a real bummer if it fails the blue dye inspection however.  The biggest risk is going through all of the qualification parts, which we will be paid for, and not end up winning the work. 

[Colin Gilchrist]

https://iftworldwide.com/services/non-destructive-coating/

I'd see if these guys can help answer your questions. The dye inspection stuff I've done was on parts where certain processes were forbidden. Like EDM or Roller Burnishing on Titanium. Part of the inspection was looking for cracks which can develop from machining or fixturing stresses. 

[Newbeeee™]

Bob - does the drawing show mandatory location points for the casting (initial seating points)?

As it's 30" long with a 5thou TP, you certainly need to be sat on the exact same location points, that Inspection sit on when checking.

[crazy^millman]

10 hours ago, Bob W. said:

The main things I am curious on are boring precise holes with end mills or ream with carbide reamers?  What sort of tool life to expect?  Speeds/ feeds?  The tolerances aren't very tight with the tightest being +/-.002".  True positions are pretty tight though at .005" on a part that is ~30" long and fairly thin and flimsy.  We have produced one part that met all tolerances but didn't meet the surface finish requirement on a surface machined feature (32 finish req is at 40 in places.)  This could be fixed by hand but there are tight limitations on that, needs to be done in an automated process...  That is just a tooling issue though and we are working on it.  It wasn't easy by any means to hit the tolerances but it is a good process and will repeat.  It will be a real bummer if it fails the blue dye inspection however.  The biggest risk is going through all of the qualification parts, which we will be paid for, and not end up winning the work. 

Wiper endmills will take care of the 32 finish issue problem solved there. Boring bars for all the tight tolerance holes no endmills or reamers. I have used the Carr-Lane Torque Limiting screws on this Ti parts and once designed an internal fold able spider for a customer to support a Ti part to help it's stability during machining.

Link

You can use air rests at the different areas to help stabilize the part and limit how much force is put onto the part to support it. With the right tools, speed and feeds you will not need much to hold the part is supported and fixtured in such as away to capture what you're machining.

If you're making money on the R&D to make the parts then win-win. We never win all the projects, but trust me the the experience learned and gained through it will better prepare you for the next big challenge headed your way. They are becoming more and more difficult everyday thanks for the lack of experience most engineers have coming out of college today. The better prepared you are now for more work like this you will win in the future.

[Bob W.]

5 hours ago, Newbeeee™ said:

Bob - does the drawing show mandatory location points for the casting (initial seating points)?

As it's 30" long with a 5thou TP, you certainly need to be sat on the exact same location points, that Inspection sit on when checking.

Yes, we are given a raw casting along with a text file with a number of point coordinates to reference for machining.  We use these points to establish the datums and when done we need to reinspect these points back to the datums and they ALL need to be within .005 TP along with the other features called out on the drawing.  It has been a fun project but a pretty good source of stress because you just don't knw how it is going to go.  When the first part came off the machine with a max TP of .0015 it was a huge relief to say the least.  The process works and after centering and tuning we should be able to get all TP under .001" because that is how we roll   There were a number of custom macro probing routines we developed for this and when all is said and done we should be able to ship these in under two days from receipt.  Typically we are turning around castings same day.  They are really interesting and present a whole different set of challenges.  A really good inspection department is a must.

The blue etch inspection is a whole different animal though, totally in the dark there...

[Bob W.]

1 hour ago, crazy^millman said:

Wiper endmills will take care of the 32 finish issue problem solved there. Boring bars for all the tight tolerance holes no endmills or reamers. I have used the Carr-Lane Torque Limiting screws on this Ti parts and once designed an internal fold able spider for a customer to support a Ti part to help it's stability during machining.

The 32 finish is on a curved surface that is surface machined.  It has some really tight features requiring a .031" ball mill with a 1" reach.  We are using clearance cutters from Harvey tool (tapered shank with stubby ball mill at the end) but they aren't very rigid.  On the next part we plan to have a look at the die/mold cutters from RobbJack which appear to be a lot stiffer.  Great idea on the boring heads!  The holes are pretty small (.25") but nothing a boring head wouldn't do with ease.  We'd just need two of them for this part so that isn't bad either.

[Bob W.]

1 hour ago, crazy^millman said:

Boring bars for all the tight tolerance holes no endmills or reamers.

How would you bore these?  Feed in/ feed out, or feed in, stop spindle and rapid out?  I usually feed in and out but in this case I'm not sure how the insert rubbing on the way out would go.  Do people write custom macros for these that stop and orient the spindle, offset in X or Y by a few thou, then rapid out?  It seems like that would be the best method.

[crazy^millman]

52 minutes ago, Bob W. said:

How would you bore these?  Feed in/ feed out, or feed in, stop spindle and rapid out?  I usually feed in and out but in this case I'm not sure how the insert rubbing on the way out would go.  Do people write custom macros for these that stop and orient the spindle, offset in X or Y by a few thou, then rapid out?  It seems like that would be the best method.

Feed in and out on Ti always has been my method. Yes can get very small with the boring systems today.

Taper or Barrel Form Tools might be the other choice. Fraisa make an 8 Flute for Aluminum, but with the right speeds and feed will work on Ti. Emuge now offers them in 6 flutes and just did a end block with a 1mm step over using one and the finish was about a 12. Part had 1.5mm fillet radius for the crank clearance and used a small on there with the 20 deg taper form finish was about 20-24.

[Newbeeee™]

Bob - any good?

It's P&W's spec https://cdn.ymaws.com/titanium.org/resource/resmgr/ZZ-WCTP1973-VOL1/1973_Vol.1-5-Non-Destructive.pdf

[cncappsjames]

9 hours ago, Bob W. said:

How would you bore these?  ....Do people write custom macros for these that stop and orient the spindle, offset in X or Y by a few thou, then rapid out?

That's a specific canned cycle that does that. The retract direction is set by parameter and the shift amount is set by the Q argument on the canned cycle line. 

Feed in to depth. Spindle stop. Spindle orient. Shift. Retract. Spindle restart. etc...

[Bob W.]

21 hours ago, Newbeeee™ said:

Bob - any good?

It's P&W's spec https://cdn.ymaws.com/titanium.org/resource/resmgr/ZZ-WCTP1973-VOL1/1973_Vol.1-5-Non-Destructive.pdf

Yes, this is great!  Thanks!

[Colin Gilchrist]

2 hours ago, Bob W. said:

Yes, this is great!  Thanks!

 

On 12/16/2021 at 4:03 PM, Newbeeee™ said:

Bob - any good?

It's P&W's spec https://cdn.ymaws.com/titanium.org/resource/resmgr/ZZ-WCTP1973-VOL1/1973_Vol.1-5-Non-Destructive.pdf

 

So good, it even tells you how to "do it yourself", if you're interested in setting up the correct processing equipment!

I think it might be time for a new building/company Bob!!!