×
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

Making tube with changing diameter along the length
8

Making tube with changing diameter along the length

Making tube with changing diameter along the length

(OP)
I have to make a tube with a variating diamtere from 45 to 60 mm. the thickness is 1mm. the length is 40 mm also and the diameter change happens like a 90 degree step in the middle of the length. The material is stainless steel

As far as I searched , there are two manufacturing methods, one is reducing the diameter from 60 to 45 mm (like tapering ) . the other is increasing the diameter from 45 to 60. My guess is the second one breaks and won't resist the deformation.

what suggestions do you have for evaluation and choosing between the methods ?

RE: Making tube with changing diameter along the length

I suggest you start with specifying design parameters: purpose of part, applied loads it must survive in service (tensile, compressive, bending, torsion), and the material (and any treatments) required for the application. Then investigate spin forming or flow forming processes.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com

RE: Making tube with changing diameter along the length

(OP)
Thank you for the points, the material is stainless steel, I edited my question as well. the diameters are both External.

there are no severe loads in the application, only the deformation of the part is concerned

RE: Making tube with changing diameter along the length

Quote:

what suggestions do you have for evaluation and choosing between the methods ?

I suggest that you choose the one that allows you to achieve your undefined requirements.

Alternately, you could think about 3 parts.

RE: Making tube with changing diameter along the length

Or 5 parts and one "tool" - 3 pieces of tube, two washers, and a Tig welder.

If you are forming tubing, stretching/expanding is easier in some ways than shrinking. Both should be done on annealed stock, and both processes will require multiple in-process anneals to keep from cracking the material. Shrinking requires that the material increase in thickness, or buckle/wrinkle. Usually the latter happens, and it is tough to control if/when it does.

RE: Making tube with changing diameter along the length

What equipment do you have?
You could layout the projection and then roll the piece and make a longitudinal weld.
Or you could just use a press and expand one end using form tool and lots of lube.
With this much stretch you will need an intermediate anneal.
If you wanted to do more work but less heat treat you could use 50mm starting stock and stretch one end and shrink the other (with a ring die).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Making tube with changing diameter along the length

Hey, nobody's mentioned it yet... You could just machine it out of a billet.

RE: Making tube with changing diameter along the length

(OP)
I want to thank all of you guys. sorry for the late reply. I can not talk about the application, but what I can say is that it should be one part , and maybe machining it out of a billet would be costly, in terms of material and time.

Thank you for the points on shrinking

RE: Making tube with changing diameter along the length

Not directly applicable perhaps, but you might research how traditional steel bicycle forks are manufactured.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Making tube with changing diameter along the length

Making it out of billet is cheap. It will 100% work, doesn't require any special setup. It's the sort of thing home-hobbyists can do.

RE: Making tube with changing diameter along the length

(OP)
@hemi : do you have any link or something about that ? I did not find any

@3DDave : Thank you Dave, well in industrial scale, the material discard rate should remain at 5% , I feel that's a lot of material to throw away if I start from a billet

RE: Making tube with changing diameter along the length

Where else have you seen parts made that look like this:


This is to scale proportion, to save others from spending 10 or 20 minutes seeing exactly what is required, based on the description so far.

Forming tech will make major changes to the wall thickness.

(Still have 15 out of 20 questions remaining.)

RE: Making tube with changing diameter along the length

Machine it out of pipe with the appropriate ID and OD - less waste than billet...

RE: Making tube with changing diameter along the length

Do you have to have the 90 degree transition? If you can live with a taper then swaging might work.

RE: Making tube with changing diameter along the length

When you say, "One part", if you mean that you only need qty 1 ever, then 100% machining from billet is the only thing that makes sense. All the time you will spend trying to figure out some other way to make it will cost way more than just making a drawing and sending it to a machine shop.

Now, if you mean that it has to be one piece, and it needs that shape, and you're going to make thousands of them, deep drawing should probably be on your list of things to investigate.

RE: Making tube with changing diameter along the length

Never mind,

Thanks to 3DDave, I now understand the geometry. No similarity to a bicycle fork.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Making tube with changing diameter along the length

3DDave has chosen the most horrible interpretation of the OP's desired geometry, probably deliberately. Here's one that my expert draftie knocked up that could be made much more reliably in any quantity.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Making tube with changing diameter along the length

I would find a tube of the same OD and of the same smaller ID of the shape shown by 3DDave and machine the inside to the same large diameter shown in the same drawing. to the desired depth.

RE: Making tube with changing diameter along the length

Overspecifying the requirements for a part makes it expensive, and it might make it impossible. Underspecifying your actual requirements means we can't answer the question for you.

"Stainless steel" is a vague description. There are countless types. Some can be formed readily, some cannot.
How accurate do the specified dimensions need to be
How accurate do UNspecified dimensions need to be (e.g. how much variation in thickness can you accept)
Does the step in the middle need to have sharp corners
How good does the surface finish need to be (A) along the diameters (B) at the corners (C) in the diameter-step
Does the step in the middle need to be "flat" (90 degrees as shown in diagram above) or can it be a conical transition from one diameter to the next and if so, over how much length?

Go back to the end use functional requirements for the part and establish how much wiggle room you have for altering the design slightly in the interest of making it easier to manufacture. Do you REALLY need an abrupt diameter step with sharp corners? Does the end-use function demand that? Understand that this geometry will be costing you money.

If you have to make one and you need that step transition, machine it from billet and get on with life.
If you have to make one and you can have a tapered transition with rounded corners and the surface need not have absolute uniformity, go to an exhaust system shop and get them to make you one from exhaust system pipe, and get on with life.
If you have to make lots of them and you cannot wiggle on the thickness, sharpness of corners, the step has to be 90 degrees etc., there is still something to be said for making this thing out of 2 pieces of tube and a washer, welded together. An automated fixture could weld this thing in a hurry.

RE: Making tube with changing diameter along the length

(OP)
Thank you all again for your attention and responses , I wish I had all these clarifications before :

- yes the part absolutely has fillets as Greg pointed out. like around 2 or 3 mm radii

- since the strain is 37% , then definitely the most deformable types of stainless steel ought to be used.

- the precision is not super high. therefore around 0.5mm tolerance should be acceptable

- the 90° is required, it can not be conical

RE: Making tube with changing diameter along the length

2
I see only two straightforward options:
1. Buy hollow bar or solid billet and machine it.
2. Fabricate it from 3 pieces, two tubes and a plate. Weld and final anneal.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Making tube with changing diameter along the length

Oh yeah, Ed? What the heck would you know about tubing anyway?

upsidedownlol

RE: Making tube with changing diameter along the length

The part may be able to be hydroformed starting with a smaller tube but you would probably need to give a little on the 90 degrees. They may need a degree or two to in the tool.

RE: Making tube with changing diameter along the length

The requirement for the 90 degree step-change in diameter is the killer specification here. I'm with EdStainless at this point: machine from solid, or weld together from 3 pieces.

RE: Making tube with changing diameter along the length

26 posts after OP. 21 posts after OP that are not OP's replies.
The 22nd post, which was by OP, should have been his first because it had some significant content to further his cause.
I tried to give OP a star for that informative post because it (finally) was informative, but it (the star) did not seem to stick.

RE: Making tube with changing diameter along the length

(OP)
Tmoost

Thank you very much, I just tried to edit my question but it sounds that it's a little bit late now. Thank you all for all the great hints indeed !

also, yet many of the first 22 posts, had great points in them, and I appreciate them as well

RE: Making tube with changing diameter along the length

Still no clear info about quantity required.

Quote (sftvbr )

...well in industrial scale...

Implies large quantity?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Making tube with changing diameter along the length

(OP)
Yes, but not in hundreds of thousand. the order is a bit lower, like a few thousand

RE: Making tube with changing diameter along the length

At my first real job, we made step-tapered mild steel tubes to serve as the outer ends of a car axle housing.
Basically, a straight piece of 3.25" od X .25" WT tubing maybe 30" long was squeezed axially by a pair of carbide-lined dies in a hydraulic press.
... during which process the tubes' overall length grew by >.25".
One end was shrunk by ~.25" dia to fit into a bored hole in the center section casting.
The other end was shrunk in two steps, quite a long length to the spring seat diameter, and the tip to axle tube diameter over the roller bearing.
Then the l/r halves had all the brackets welded on, were torque tested by deadweights, both ends were chamfered, and the bearing bores bored and reamed.
Finally, the finished axles tubes were pressed into the center section and plug welded.
At a rate of something like 5,000 car sets a day.

My job for a while was carrying the shrink dies back and forth to the carbide grinder, who eventually arrived at the proper blend radii to allow the dies to last for months at a time, vs. a few hundred parts.

The tooling was fairly expensive, so for a few thousand parts, machining from billet makes more sense.

Mike Halloran
Pembroke Pines, FL, USA

RE: Making tube with changing diameter along the length

Ah, there's a similar process known as sizing rubber bushings. Basically the outer metal tube is squished down in diameter to place the rubber in compression. The preferred way to do that is with a cylindrical bush, just push it down a taper. But we often need a flange on the outer, so instead they crush it radially with a hydraulic collet. That needs very little unique tooling.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Making tube with changing diameter along the length

(OP)
Dear Mike : Thank you so much for your great answer !

dear Greg : I could not find a good link to view the operation, despite you gave a great explanation , could you please share some useful links ?

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close