Tube I.D. Machining

[skybird]

Hello everyone, this is my first post on engineering tips.com. What I have is mult length tubing (~ 20 ft long). The tubing has an O.D. of 1.220" (31 mm) and an I.D. of 0.709" (18 mm). I am using this product in trying to develop a tubular part that will be used in a torsional fatigue application. The tubing I have is 4140 seamless product. I machined (peeled) the O.D. to remove any surface defects and then manufactured my parts and tested them. Unfortunately, the fatigue fractures are initiating from the I.D. of the tubing. When I investigated further, I found that this tubing was hot rolled after it was made into a tube and, as a result, it has small surface I.D. fissures that go down to about 0.005" in depth. Therefore, what I would like to do is to find a company (and process) that can machine this I.D. in order to take the I.D. from an 18 mm to ~18.5 mm or something close to fit whatever tooling someone would have available. I have heard of a process called skiving but can't find a company that can do it in the sizes I need. If a company cannot do this operation in the 20 ft mult lengths I have, then I can machine the O.D. surface first and cut it into lengths that are close to 4 ft long. Thank you for the reply.

 

[Wrenchbender]

Something like an automotive cylinder hone (e.g. for brake cylinders), driven by a long flexible cable, might be able to smooth out your .005 deep fissures, although 5-mils over 20-ft sounds like a fair amount of material. Dimensional tolerances should be pretty good. Google ‘hone’ to see who makes the equipment and try starting there.

 

[ornerynorsk]

0.005 is a lot of material to remove with a hobby-type hone. You will want your material to be done by a professional tube honing shop.

 

[Compositepro]

You should talk to tube suppliers to get an appropriate tube to begin with. There are many manufacturing processes. Are you using DOM (Drawn on Mandrel) tubing?

Another option could could be electropolishing.

 

[EdDanzer]

One problem you will encounter with tubing is wall thickness variation if you use seamless tube. DOM is a welded product that probably won’t work.

You may have to gun drill, straighten and hone the ID then finish the OD.

Induction hardening the OD can provide a longer life product. We have made a torsion bar subjected to high loads, reverse twisting and high speed full rotation actuation. The material is 4340 Q&T to 30-32 RC Induction hardened with the case drawn at a specific temperature for maximum life.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[TVP]

All tubes, whether they are initially created by welding or by a seamless process, can be cold drawn (drawn over mandrel) to improve the surface roughness, reduce the thickness, improve mechanical properties, etc. The tubes that skybird describes are seamless not welded, and it seems as though they were hot finished (terminology used in ASTM A 519) and not cold finished (mandrel drawn). Cold drawing the original hot-finished seamless tube should be able to smooth out the ID defect, provided that a sufficient reduction ratio is used.

 

[racookpe1978]

It would appear that cold-drawing over that length would produced a more uniform surface than honing, particularly since he would get scratches and vibration and "wiggles" in the hone from the drive link twisting the hone.

 

[pirko]

Dear
Try deep drilling

http://www.deepdrill.nl/Products+and+Services/Deep+Drill+Tubulars+BV/Drill+pipe+_+collars

Best Regards

 

[skybird]

The seamless tube we used was hot pierced to make a tube 1.900 x 0.375" (O.D. x Wall), annealed, cold worked (over mandrel) to 1.500 x 0.313, annealed, & cold worked (over mandrel) to finish size of 1.220 x 0.256". So it was cold drawn a couple different times but the surface fissures still remain. That is why I am looking to "clean" up the surface. I am going to send some out for gun drilling but was asking the question to find out if there was a better way / process for cleaning up the I.D. I had heard of a process called skiving and was wondering if anyone out there knew of it and if it was used to clean up the I.D. surface of metal tubing (in the sizes I have).
I have used welded tubing that was hot stretch reduced, and Drawn Over Mandrel (DOM) but it also has small surface I.D. fissures. I have also used as-welded tubing and this does have a good I.D. surface quality except for the region where the weld flash is scarfed off. However, I can't get welded tubing in carbon levels over 0.30%. Hence the reason for going to seamless.

 

[MikeHalloran]

At the 4-ish ft length, you could broach the ID, and finish hone if need be. You might need to support the OD a little.



Mike Halloran
Pembroke Pines, FL, USA

 

[TVP]

skybird,

Thanks for the additional information about the tube manufacturing process. Tubes that have been drawn twice should not still have a defect. Having said that, yes, skiving is a method for improving the ID surface of the tubes, especially when combined in 1 tool with roller burnishing. Ecoroll makes such a device. Use the following link for more information:

http://www.ecoroll.de/downloads/kat/ecoroll_catalog_en_web.pdf

http://www.ecoroll.de/produkte/Produktauswahl/33.5.04.html

 

[unclesyd]

There are several companies that have this type machine to accomplish your finish requirements. You should be able to find a toll shop to polish your tubes.

http://www.tubefinishing.com/ID pipe polishing.html

 

[Neubaten]

I have experience in tubular suspension parts subject to torsional fatigue, and I have came across the exact same problem as you. We had to discard cold mandreled tubes because of too many defects and surface roughness at the ID that originated internal cracks.

Finally, we successfully decided to use precision welded tubes, as per DIN 2393. They have a more than necessary ID surface finish. Obviously, it is a more expensive material, but it is far cheaper than doing an ID finish, which is an overkill operation for the part, money wise.

Using this kind of tubes we never had again a failed test because of internally originated fatigue fractures.

Also I did some benchmarking, and all european automotive manufacturers used welded tubes for that application with no further ID finish. Some of the top-notch car manufacturers (for top performance, very expensive models) performed shot peening internally, but also on welded tubes.