Machining Titanium and Inconel Sheet for Weld Prep

cjarnutowski · May 27, 2020

Hi All,
I'm not a machinist by trade, so I'm hoping I can draw on someone's wisdom here.

I'm tasked with finding a way to prepare the sheared edges of titanium (CP, 6Al-4V, 15-3-3-3) and Inconel (718, 625) sheet metal tubing blanks to be welded (automated GTAW). We currently spend ~10,000 hours annually manually filing the edges of these blanks, with inconsistent results. The primary requirements are straightness and surface finish on the edge.

These sheets are .020-.080 thick, and the depth of cut we would require is on the order of .002-.004. Is it possible, with some combination of tool geometry, tool material/coating, speeds, feeds, etc. to achieve decent tool wear under these conditions? My understanding is that such lights cuts on nickel alloys will burn up cutters in no time.

Thanks for the help!
Chris

TeachMePlease · May 27, 2020

What are the length and width of these sheets?

Kingbob · May 27, 2020

Are you cutting a step or beveling the edges? If you just need a bevel it could be done with a water jet with a tilting head. If the sheets are small this could be done with a surface grinder. Be much more detailed and include pictures and we'll all be more than happy to armchair enjineer any number of solutions for your problem.

ChipSplitter · May 27, 2020

At 10,000 man hours you're talking a MAJOR pita.

That's 5 guys working full time...... :eek:

gbent · May 27, 2020

Tell us a little more about exactly what you are doing. Are you rolling sheet metal to make tubing? Are you shearing the sheet metal to size and the shear cut isn't straight?

cjarnutowski · May 27, 2020

TeachMePlease,
The sheets are just about any size that would fit in a 4'x10' envelope (big or small).

KingBob,
These sheets are never beveled, the purpose of this preparation is to remove the shear-tear and achieve a flat, straight, square edge which has a surface finish that allows us to thoroughly clean it.

gbent,
These are flat blanks that will be rolled or brakeformed into tubes and cones (later to be hydroformed). The preparation I'm talking about will be performed while the blanks are flat.

So to sum up, what we do is receive sheared/lasered/waterjet blanks and remove material from the edges to be welded to achieve a straight & square edge (removing all indications of shear-tear or laser HAZ). Then the parts are then rolled/bumped and welded.

Fixturing, motion control, etc don't seem to be a huge challenge. Straightness should be within about .004. Depth of cut should be .002-.005 or so. Squareness within, let say .5 deg (not as critical). I just want a straight line, and that's easy. Its the material removal method that I'm trying to nail down.

Milland · May 27, 2020

I think what you're calling "depth of cut", we would call width of cut. You're not making a step, you're machining the previously sawn/sheared/lasered/etc. edge for straightness and smoothness (for cleaning).

First off, you might consider increasing the amount left after roughing, to say at least .005"/surface. Too little left is false economy, as you'll compromise the milling and maybe not fully remove any HAZ or similar.

Next, use sharp cutters at low-ish SFM, so you minimize rubbing and burr formation. Adjust Z depth as you cut to use the full length of flute of the endmills and avoid notching the flute edges. Climb cut only.

Make SURE any coolant or oil used in the machine does not contain chlorine or other contaminants that could damage Ti sheets! Nickel is more resistant, but being aware of any chemicals used in process is important prior to welding. That includes purity of cleaning agents and weld shielding gases. Not to mention handling - clean gloves only, no bare hands. Obviously you have to balance that against safety, so perhaps the gloves only at final cleaning and weld setup.

Make sure your fixtures are cleaned properly so they can't contribute to contamination. A protocol should be established for when, how often, and how this is done.

Kingbob · May 27, 2020

I picture a large vacuum tabled cnc router. Something with a nice set of dowel pins to locate the sheets and a large dia shell mill to machine this small features. I say large shell mill so that you are spreading the work across lots of inserts so as to maximize time between indexing inserts.

Milland · May 27, 2020

Kingbob said:
I picture a large vacuum tabled cnc router. Something with a nice set of dowel pins to locate the sheets and a large dia shell mill to machine this small features. I say large shell mill so that you are spreading the work across lots of inserts so as to maximize time between indexing inserts.

If I understand the OP's needs (and I may not) then I would not use any insert cutters. Inserts are almost always edge-prepped to be duller than an endmill, and (again, if I understand the requirements) a sharp edge is needed to minimize burring after the cut.

Limy Sami · May 27, 2020

Have you looked at ''weld bevelling machines'' - like this ? weld bevelling machine - Google Search

ChipSplitter · May 27, 2020

For a few thou, why not use a CNC router with a small abrasive tool (CBN?).
A router won't be rigid enough for cutting superalloys with carbide (unless you go with a really high end one).

kustomizingkid · May 27, 2020

Ever seen a Burr Beaver?

Harig Bur-Beaver Deburring Chamfering Beveling Machine - 265-100 - Penn Tool Co., Inc

Milland · May 27, 2020

kustomizingkid said:
Ever seen a Burr Beaver?

Harig Bur-Beaver Deburring Chamfering Beveling Machine - 265-100 - Penn Tool Co., Inc

Not suitable for what the OP wants - he needs to clean the entire edge while holding good geometric accuracy for weld line fitment.

gbent · May 27, 2020

10,000 hours of California-burden wages? That gives you lots of room for custom machinery. What about a special custom length belt sander? Do the whole part at one time.

turnworks · May 27, 2020

Have seen and used a custom made machine for something like this. Was a simple 6" wide belt sander mounted on some linear rails with a couple micrometer heads to adjust cut depth. The other side was a flat table with a simple bar spanning the width of the sheet.

Toss the sheet on the table with the belt sander in the middle of the sheet. Run the sheet until it hits the belt then pull it back slightly. Clamp down the sheet, fire up the sander then use the micro heads to get it to kiss the sheet edge, Run it back and forth then take another lite pass and call it good. very shallow last past so to not put a bur on the bottom edge.

Wasn't a pretty machine and took two people to do it right with the bigger sheets but it worked well. It wasn't idiot proof and the operators needed to keep their focus through out the day.

cjarnutowski · May 28, 2020

Thanks for all the feedback guys!

Milland,
You are correct. I was referring to what 'depth of cut' would be when side milling (amount of mat'l removed).
You also brought up something I failed to mention. This whole project would only be viable if it could be run dry - no coolant, no oil or lube. I am well aware of the contamination issues with titanium. 95% of all these welds will be x-ray inspected.

From a material yield standpoint, upsizing the blanks wouldn't be a problem. The real problem is that we are talking about 750+ unique items which would require planning changes, and the effectivity of each change would be staggered by the existing work in the pipeline. Its a mess that I could never sell to those I answer to.

Can anyone enlighten me about CBN abrasive tools? Do they wear much dimensionally speaking? Can they be used dry, and if so would they generate a lot of heat?

I've looked very closely at off the shelf edge beveling tools. I've yet to see something designed to deliver a square edge with the finish and straightness we require. A .005 gap at our weld joint is pushing it for many of our welds. The fitup of a scalloped finish, in our experience at the speeds we weld, promotes porosity in our titanium parts.

Milland · May 28, 2020

Sending you a private message.

BT Fabrication · May 28, 2020

cjarnutowski said:
Hi All,
I'm not a machinist by trade, so I'm hoping I can draw on someone's wisdom here.

I'm tasked with finding a way to prepare the sheared edges of titanium (CP, 6Al-4V, 15-3-3-3) and Inconel (718, 625) sheet metal tubing blanks to be welded (automated GTAW). We currently spend ~10,000 hours annually manually filing the edges of these blanks, with inconsistent results. The primary requirements are straightness and surface finish on the edge.

These sheets are .020-.080 thick, and the depth of cut we would require is on the order of .002-.004. Is it possible, with some combination of tool geometry, tool material/coating, speeds, feeds, etc. to achieve decent tool wear under these conditions? My understanding is that such lights cuts on nickel alloys will burn up cutters in no time.

Thanks for the help!
Chris

simple, find a router or linear rails if its straight. put in a flat face carbide burr and "cut" off that extra thin section with it to a straight clean face.
that or a small diamond wheel will work also.

BT Fabrication · May 28, 2020

cjarnutowski said:
Thanks for all the feedback guys!

Milland,
You are correct. I was referring to what 'depth of cut' would be when side milling (amount of mat'l removed).
You also brought up something I failed to mention. This whole project would only be viable if it could be run dry - no coolant, no oil or lube. I am well aware of the contamination issues with titanium. 95% of all these welds will be x-ray inspected.

From a material yield standpoint, upsizing the blanks wouldn't be a problem. The real problem is that we are talking about 750+ unique items which would require planning changes, and the effectivity of each change would be staggered by the existing work in the pipeline. Its a mess that I could never sell to those I answer to.

Can anyone enlighten me about CBN abrasive tools? Do they wear much dimensionally speaking? Can they be used dry, and if so would they generate a lot of heat?

I've looked very closely at off the shelf edge beveling tools. I've yet to see something designed to deliver a square edge with the finish and straightness we require. A .005 gap at our weld joint is pushing it for many of our welds. The fitup of a scalloped finish, in our experience at the speeds we weld, promotes porosity in our titanium parts.

Also if porosity is the problem, fitup isn't the issue, you need a back purge on it with a purge box to remove all oxygen. sounds like you are lacking weld gas coverage.

Milland · May 28, 2020

cjarnutowski said:
Can anyone enlighten me about CBN abrasive tools? Do they wear much dimensionally speaking? Can they be used dry, and if so would they generate a lot of heat?

CBN (and in my opinion, any abrasive finishing) would not be appropriate here. Unless dealing with very hard versions of Ni alloys, almost all Ti and Ni sheet would be too soft for a CBN abrasive, and you'd wind up with loading and burring of the edges.

Obviously just my opinion, but I think a machined edge using carbide endmills (perhaps followed with an inverted "V" cutter for final burr removal) would be the best approach for what I understand is needed.

Machining Titanium and Inconel Sheet for Weld Prep

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