Slitting saw nightmare.

HELP!?I have been trying for three days now to use a solid uncoated carbide slitting saw with zero success. Cutting .016 wide slits in 6AL-4V Ti bar. Saw has been 1.75 dia and 2.25 dia two different tries. The slits are going .2225 deep, 63 of them around a diameter of 1.720 tube end.
I have tried various chip loads, feeds and speeds. I have broken 7 saws....at nearly $100 a pop. At this point it would have been cheaper to write the customer a check and tell them have someone else do it. I have tried clpt in the millionths up to even .0005. I have tried cutting full depth of cut, two depth cuts...and even 4 depth cuts.I have been conventional cutting...that failed...even with zero more ideas attempt climb cutting( yes I know that is not the smartest thing with no keyway to lock the cutter in) But nothing has worked.The customer needs 3 of these parts right away...and it is aerospace...so as of now EDM or laser is not allowed. That would leave a casting on the part which they cannot have. Anyone out there that can possibly point me in a direction that will work for getting these parts out the door, your help would be very much appreciated.
In the morning I am to try cutting with a carbide cutter a partial depth of .040...then follow through with a HSS cutter 2.75 dia with a shop made
arbor that can support the majority of the flimsy blade at full depth. All i can think is super slow RPM and a chip load of maybe .0005 and try to chew through these three parts. Hopefully someone out there can give me a better faster and more successful direction to go.

So is this a tube, or a bar? If you are cutting the slits after turning that bar into a tube, my guess is that the tiny saw is not rigid enough to support itself as it begins to engage the "back side" of the tube. Is it possible to cut one side, index or move, then cut the other? Or better yet, put the slot in while the cut will be uninterrupted?

Also, FWIW, I almost always climb cut with carbide saws. Especially at that size; it's pretty hard to get them to spin without breaking first.

boosted said:

So is this a tube, or a bar? If you are cutting the slits after turning that bar into a tube, my guess is that the tiny saw is not rigid enough to support itself as it begins to engage the "back side" of the tube. Is it possible to cut one side, index or move, then cut the other? Or better yet, put the slot in while the cut will be uninterrupted?

Also, FWIW, I almost always climb cut with carbide saws. Especially at that size; it's pretty hard to get them to spin without breaking first.

Click to expand...

It is Ti bar we have turned into a tube. The slots do not go the full length of the tube. Only slotted for 1" The full cut depth is the thickness of the wall (.2225) and enough to break through the wall. I am cutting only one side of the tube at a time...then rotating with a 4th axis rotary "indexer" 5.625 degrees with only 30 minutes tolerance. On an ancient Haas VF1.
So I am cutting one slot at a time in succession. I thought the same about the climb cutting and it was relatively successful. It managed on death cut of .055 with an extreme low chip load...something like .00003 per tooth. (32 teeth). But on the second depth cut the cutter spun and broke teeth off in to the part.

put a cork in tube end before cutting.

Could you fill the tube with RotoMetal before cutting the slits and then melt out when done? Thinking this will dampen vibration and stiffen up the tube.

Is the tube collapsing on itself and pinching the saw? That's a surefire way to jam things up.

Mad_maxx said:

It is Ti bar we have turned into a tube. The slots do not go the full length of the tube. Only slotted for 1" The full cut depth is the thickness of the wall (.2225) and enough to break through the wall. I am cutting only one side of the tube at a time...then rotating with a 4th axis rotary "indexer" 5.625 degrees with only 30 minutes tolerance. On an ancient Haas VF1.
So I am cutting one slot at a time in succession. I thought the same about the climb cutting and it was relatively successful. It managed on death cut of .055 with an extreme low chip load...something like .00003 per tooth. (32 teeth). But on the second depth cut the cutter spun and broke teeth off in to the part.

Click to expand...

You could try using two saws, one to cut along the length of the tube wall to full depth (minus the very end, which will be the cutter radius), then use the expensive larger saw to square the ends of the tubes. This is tricky, as you have to match the saw heights exactly, which is why I think I'd use 1.25" OD carbide saws for the side cuts, then a large OD HSS blade at low RPM for cutting the ends. The HSS saw will be much more tolerant of the inevitable small height mismatch.

Also, what's your coolant setup, what SFM were you running the large carbide saws at, and how rigid is your setup? Put a tenths indicator on the end of the tube in its fixturing and push on it. If it moves substantially (over 3-5 tenths with moderate force) it may be too flexible to support the cut loads without moving, which will break your carbide saws.

For cheaper carbide saws, check out Maritool (Solid Carbide Slitting Saw 1.25 X .50 X .0156 Thick 32 teeth MariTool) or one of the other vendors here. Double-check your SFM and FPT values, I'd try .0002/tooth to start with the 1.25" OD saws I linked to. Make a stout arbor that runs true with a .500 pilot and .7" OD in the clamp zone (you can make it larger in the shank with enough length to clear the stock).

True running will save your cutters, and try cutting only .06" deep a pass to start, so four passes for each slot. Watch engagement at the end of each pass, you want to have the cut lengths taper down as you go deeper so you don't bury the tool in the radius. And don't forget the basics, you want to flush, flush, flush the cut zone with plenty of coolant to make sure the cutter stays free of chip buildup.

Most of my slitting saw woes over the years have been due to lousy arbors in one way or another. Life got a lot better when I switched to integrated slitting saw holders rather than an arbor held in a collet chuck.

What are you holding them in?

I have not done any slitting of Ti, but I have done a fair amount of titanium parts in a Haas, and I would start by saying that any VF machine is not really rigid enough to cut titanium effectively. Ti likes a super rigid setup, and Haas machines are more like wet noodles. The first thing I would do is support the workpiece as much as possible, with at least a tailstock, and get the shortest, most robust arbor you can. Second, as mentioned before, you need to make sure your slitting saw is running true and concentric to the arbor. Thirdly, 6al4v likes to work harden if I recall correctly, and it likes to flex and grab around tight tooling. Make sure your slitting saws have some offset, or at least are relieved to some extent for a cut that deep. I would probable try to run a coolant line through the tube for better flushing, Ti does not transfer heat so you need to make sure there is plenty of coolant in there. And I wouldn't reduce the feed too much, if you feed too slowly, you are just rubbing and hardening the material. And I also like to arc into my cuts in Ti to try to give it a little smoother transition, carbide tooling doesn't like sudden changes in load.

What about using a titanium nitride coated HSS saw? I use titanium nitride coated HSS drills in some titanium parts I used to make and seemed to get decent tool life. It is obvious the carbide can't take the shock or vibration.

Have you tried to plunge cut instead of profile cutting? That is not great on a carbides saw that thin but it will give the blade more support. I would also prefer a HSS blade but that thin, I dont know that will really work but please let us know how it works out.

Charles

You need almost Zero axial and radial run-out on a saw that flimsy. Titanium is shrinking down on your saw just like it does on a reamer.

Wish I had better ideas... good luck

You might load/fill it with a low temp filler, then slit it with using coolant, held in a solid /ridged fixture, with saw side wobble <.0005, with a ball screw machine so to have no slack to climb on.
(With a non ball screw machine down feed and travel into the feed screw so no slack to climb/draw on.)
Low-Temperature Solder by Indium Corporation

If you have time I can quote a custom saw for you. Something like 1.5 or 1.75 dia X .016 thick but with only 24 teeth. Solid carbide with a Tialn or Altin coating. Also I would make it staggered tooth. Normally you dont want to take off more than 3x width in a single pass. So roughly .05 depth per pass. For sure use flood coolant and 120 sfpm with .0007 ipt.

Also I can have a saw made with a thicker hub 1/2 smaller than cutting diameter. Something like 1/8" or 3/16 thick. That will really improve its rigidity.

Yes saw must be dead true. Especially on something so thin. Good luck.

My approach may be really dumb but when one gets desperate... rough the slots with edm then clean up with slitting saw. Not very efficient but you've put a lot of time and money into this. I hope something works out.

Just to add to what others have said. Filling the inside of the tube will help a bunch. I would turn a tight fitting brass slug in the end of the tube. You could also add a center in that slug and use a tail stock. And if you are worried about getting the brass slug out drill and tap a hole in it for a slide hammer.
The slug will also help a lot when it comes time to debur,that will save you a ton of time. Turn a new slug per piece.

I have also built supports that cradled a part in a 4th axis. Somewhat along the lines of a cylindrical grinding steady rest. My approach to thin waled parts was it to make them think they are solid.

The Ti is collapsing into the saw. Fill the tube with expanding casting alloy. Saw run-out is critical.

Well, the OP has probably already figured this out or not, but it struck me 32 tooth saw,1. 75 or 2.25 diameter .17 and .22 tooth pitch. Kinda coarse for .22 wall.

gustafson said:

Well, the OP has probably already figured this out or not, but it struck me 32 tooth saw,1. 75 or 2.25 diameter .17 and .22 tooth pitch. Kinda coarse for .22 wall.

Click to expand...

On a modern cnc with ball screws and precise feed rate control this does not matter as much as a manual mill.

yeah, but if I was having this problem, I think might go with a finer saw