Thin Ti Wall Pulling Inward

[McLaren]

Anyone have thoughts on how to prevent this from happening? Finished wall thickness is .080", and depth to center solid is about 1.5". I tried the 8:1 rule and ended up with even worse bend in the part, as well as multiple blend issues. This last attempt was roughing it to .130", at which point there was no bend. Then I ran 2 passes, one at .010" stock to leave, one at finish dimension. Running it with spring passes also made the bend worse. Material is 6Al4V

 

[nickbe10]

Can't open / see pics......

[McLaren]

 

[Charlie Pierson]

Is that wall bent ? or bent and tapered ??

 

btw,  I like your straightedge.

[Leon82]

Rough it out first. Mill it parallel, Then make your finish cuts and support both faces

[McLaren]

12 minutes ago, Charlie Pierson said:

Is that wall bent ? or bent and tapered ??

 

btw,  I like your straightedge.

 Wall is bent, not tapered. Measures .090"-.095" in the corners where the inward deflection is.

 

http://www.starrett.com/metrology/product-detail/C305R-6

[McLaren]

8 minutes ago, Leon82 said:

Rough it out first. Mill it parallel, Then make your finish cuts and support both faces

I'm roughing it out to .130" wall thickness before I run my finish passes. Shows no bend at that point.

[crazy^millman]

I cannot see the Pics, but can you add bondo to the inside of the part using tape to prevent sticking on the part to stabilize it? Can you window frame it? Can you make a male stabilize to supports the part form the ID to machine the OD and then same for doing the ID where you help stabilize things? Biggest thing thinking about how you machine a bell. To machine a Bell you must stabilize it. Without Stabilization you cannot machine it very well. Again without seeing it I am thinking the same principal needs to be applied here.

[Matthew Hajicek - Singularity]

What cutter are you finishing it with?

[McLaren]

Will try attaching the images instead.

[McLaren]

2 minutes ago, Matthew Hajicek™ - Conventus said:

What cutter are you finishing it with?

 Originally I was using a 1/2" 6 flute .030"R SGS T-Carb necked with 5/8" LOC. Now I am using a 1/2" 6fl. 2"LOC .060"R.

[mkd]

tough nut to crack.

I'd say finish the "pockets" with MUCH more stock on the outside face that is bending (picture with scale on it)..

you will have many more option for removing material from the outside in a way that hopefully doesn't collapse the pockets.

[Leon82]

Rough the wall and leave thickness oversized then remove false bottom. 

Flycut flat and parallel.

Then in a fixture of soft jaws clamp light and finish the pocket. 

[crazy^millman]

Surface machine it and don't side cut it. Seen parts do the same thing and no matter how much they tried to side mill it the parts was moving. When we surface machined the same part in the same holding a lot those issue when away. Proper Support was the key and good fixtures. Don't go making them out of aluminum if production. 15-5 in a 1025 condition would be my 1st choice.

PDF about 15-5

[nickbe10]

OK see it now. Titanium , like Aluminum is a heat resistant metal. Usually the culprits in situations like this are:

1   Insufficient chip load. Because the material does not conduct heat very well a thick chip at the highest temp point (just behind the cutting edge where the chip is riding up cutter face) means the heat can get into the chip and then is ejected from the part. Too thin a chip and the heat bleeds into the part and causes thermal distortion.

2   Number of cutter impacts. This is usually more apparent with insert cutters and usually only starts rearing its ugly head above 9" part size.

The overhang here is probably trapping the heat and making the heat dissipation via the chips more problematic as they cannot eject cleanly. Try using a toolpath with fewer passes and more chip load. Maybe a smaller diameter cutter than you might at first think suitable might give you cleaner chip ejection. Work in steps / layers and rough AND finish as you go. That will stop additional tool rubbing (and hence heat generation) as you start the next roughing pass by giving some relief . Working in layers / steps will also help with stability issues as pointed out by Ron above.

Try a three flute Helical HST (with LBS to keep rubbing contact to a minimum) for maximum chip clearance while roughing

Your finish looks good so my money is on the roughing.....

[mkd]

10 minutes ago, C^Millman said:

Surface machine it and don't side cut it. Seen parts do the same thing and no matter how much they tried to side mill it the parts was moving. When we surface machined the same part in the same holding a lot those issue when away. Proper Support was the key and good fixtures. Don't go making them out of aluminum if production. 15-5 in a 1025 condition would be my 1st choice.

PDF about 15-5

Very useful experience.

 wonder if something similar could be replicated with super short flutes/ relieved cutters without going 5-axis?

--keeping long flutes and cutter shanks from rubbing should help, no?