Tube Crimping

[MadMango]

Not sure where to post this.

I am looking for manufacturing advice for crimping a tube with an internal end cap. The OD cannot dimensionally change more than +/-.002, and forming the crimp must not move the internal end cap more than +/-.005.

Tube: .450"OD with .030" wall thickness, 17-4 steel
Crimp: ~.090" wide with .414"OD

I was told that roll crimping this feature may impart a twist on the OD of the tube, so I am looking to form this some other way. My concerns are that any method will deform the OD which is very critical. Internally we discussed that the tube could be crimped with a 2-part clamp about 50%, then rotated 90deg and then fully crimped to reduce deformation.

Looking for any advice or suggestions.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[MadMango]

Tmoose, Dgowans posted that 2 days ago.

Bvanhiel, we are worried about post-assembly machining because there may be a risk of ignition since this assembly contains explosives. We've designed a 3-jaw crimping tool, we should have a working tool late next week. We'll see how that goes.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[btrueblood]

Mango,

It's the .002 deformation requirement that's a bugger. If the 3-jaw chuck idea gives warping/wrinkling of the o.d. beyond the .002 limit, you may need to try making a 2-stage crimp (first bump goes halfway, and you bump the part multiple times around the o.d., 2nd bump is basically the full crimp jaws you already have).

I like the idea of roll forming better, but with the ability to adjust and slowly advance the rolls until the crimp is fully formed. That should minimize the torque on the tube, especially if it's gripped correctly, and the speed of advance of the rolls should allow forming the part with minimal distortion/buckling of the tube walls.
Course, that's much more expensive too...

 

[Tmoose]

Madmango said "Tmoose, Dgowans posted that 2 days ago. "

I put Dgowan's comment and the link in quotes.

My addition was the low pressure rating as described on the website.

I reckoned your 19kpsi requirement is a bit above " a low pressure automotive application."

 

[dgowans]

Tmoose,

I don't want to start a nit-picking contest, but the section of the website that contains the line you quoted lists both thin wall and high pressure applications as possible applications.

 

[MikeHalloran]

A set of custom jaws in a hydraulic crimper should work nicely. Beware of jaw designs with delicate parts, e.g. small springs that are intended to push the jaws apart when the pressure is released.





Mike Halloran
Pembroke Pines, FL, USA

 

[MadMango]

Actually we found a hydraulic push cylinder with an internal spring for the "pull" return. That was an early concern. And we will probably double-kiss the crimp as btrueblood mentioned. I'll keep everyone updated.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[GregLocock]

On aluminium dia 50mm rings, crushed by one or two mm (can't remember) we got a 0.3 mm witness line from a 3 jaw crimper.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tlee123]

Look into how the gas spring manufacturers do it. Suspa, Stabilus, IGS. They're dealing with high (>2kpsi) pressures.

I've heard (from a manager, not an engineer) that they crimp right on the end of the tube for some important reason that I can't remember.

Tom

 

[unclesyd]

After further thought and playing with some samples of 17/4, If possible I would use an intermittent type crimp like staking the cylinder in three places or using something like a hydraulic hose crimping device to produce the locking force you require. The hydraulic die could be modified to crimp at any number of spaces.

This site shows one pattern for a crimp.

http://www.gates.com/brochure.cfm?brochure=2398&location_id=3494

These people make all types of crimping equipment.

http://www.customcrimp.com/

 

[MadMango]

Unclesyd, I'm going to follow-up with your 2nd contact. Thank you.

It's been a few weeks, I still do not have all of the parts received for our custom crimper, but I am informed it should be no more than 8 working days. If the crimp holds during testing, then we'll need a production crimper, and I think that CustomCrimp may be the ticket.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?