×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Tube Crimping

Tube Crimping

Tube Crimping

(OP)
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: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

Are any other joining methods an option such as welding?

RE: Tube Crimping

(OP)
Welding or brazing would have been easy, but due to some energetic (explosive) material housed in the tube at the crimp stage, it is prohibited.

The connection must hold ~19kpsi internal pressure, which as described above, does the job.

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

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

we have used Rotary Swaging on products in the past.

Heckler   americanflag
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
      o
  _`\(,_
(_)/ (_)

This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.

RE: Tube Crimping

(OP)
Heckler, was rotary swaging done on a tube of similar size as above?  Do you recall having any torsional deformation?

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

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

I would use the equipment from one of the companies posted by CoreBlimeyLimey to achieve the crimp you require without any torsional problems. We used equipment by Airmo
to form ends on thin wall tube and it worked exceptionally well.
We also uses the hydraulic expansion technology to expand a CS into an Al component.

RE: Tube Crimping

Air cylinder manufacturers do it all the time.
Of course, they're using 316, not 17-4, and
the wall is thinner, and
the operating pressure is <250psi.

That's an ambitious design.

Mike Halloran
Pembroke Pines, FL, USA

RE: Tube Crimping

I've never used it.  What about eletromagnetic forming?

Ted

RE: Tube Crimping

hydtools' suggestion brought back memories form the recesses of my mind. We used this process in the late 70's to put a steel tube on an Al arbor. The only problems I recall was at the time we were pushing the capbilities of the machine and springback was a problem. The process was quite successful on other similar applications for components on high speed machinery.  

http://www.magneform.com/apps.html

RE: Tube Crimping

(OP)
Hydtools and Unclesyd, thanks for that.  I'll have to research and see if their EMF is a concern for our energetics.

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

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

(OP)
Well, I contacted Magneform and they can't use their process on 17-4 steel.  I'm waiting on a call from Airmo to see what they say.

If a commercial process isn't available, we are thinking about making our own tooling.  We are leaning towards a 3-jawed chuck that can be hydraulically clamped around the OD to from the crimp.  Can anyone offer any advice/experiences towards this method in regards to OD deformation?  If roll forming is a viable option, what deformation concerns should I consider?

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

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

Check out the crimping machines used for hydraulic hoses. Some sort of collet chuck is the favoured approach, presumably because the synchronisation of the jaws is much easier.


I worked on one that was used to squash aluminium rings, there were no hiccups that I can remember, but it was a much more compliant system than yours. Since yours is not using the swage for sealing then a collet chuck (which leaves slight witness marks) will be fine.


Cheers

Greg Locock

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

RE: Tube Crimping

I would machine a shoulder into the tube ID ( with corresponding increase in plug OD ) to easily hold the 0,005" position, and then roll over the tube end to close it. This process will leave a nice rounded end and not expand the OD. Shock absorber manufacturers often use this process to assemble.

RE: Tube Crimping

(OP)
Dgowans, that's an interesting item, but I couldn't use that.  There are bits of electronics that are housed in the "plug" of this assembly.

Gtracer2, we had considered this early on, but were worried about stress concentrations at the counterbored shoulder.  This v-crimp almost triples the amount of material in shear.

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

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

A former employer used swaging on cartridges.

Basically a shotgun shell (different filling) made of extruded aluminium with an aluminium end cap.

The cap was pushed in (up against an internal cardboard liner to make sure it didnt' go too far) and then the ends swaged.

It wasn't quite the same as your image though.  The end was reduced in diameter slightly.

KENAT, probably the least qualified checker you'll ever meet...

RE: Tube Crimping

Can you machine the critical dims after you crimp?

-b

RE: Tube Crimping

"Not sure whether this is suitable for your application, but you may want to check out:
http://www.avdel-global.com/avsealii.asp "

 Toward the bottom of the page it says
" Automotive low pressure applications  "

RE: Tube Crimping

(OP)
Tmoose, Dgowans posted that 2 days ago. morning

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: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

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...

RE: Tube Crimping

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."

RE: Tube Crimping

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.

RE: Tube Crimping

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

RE: Tube Crimping

(OP)
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: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

RE: Tube Crimping

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: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Tube Crimping

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

RE: Tube Crimping

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&amp;location_id=3494


These people make all types of crimping equipment.

http://www.customcrimp.com/

RE: Tube Crimping

(OP)
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: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources