Bulging tube

I have a thought, if this is production item setup external clamp die, use explosive under water forming, insert/feed charge into pipe [ alittle goes a long way] water is the tamping, dissapates shock, sound, etc.possibly use nat gas if low press will do job, nitro can exert up to 1000 tons psi force so there is lot of lattitude here. even hard to stretch mat'ls will form well this way...

this is a well known production technique, extrmely close tol can be achieved here.(depends on die } even thread forming, etc...

use a rod to hold/insert & ignite waterproof blasting cap...etc water will tamp [secure at target]J Bo

I have made tooling for hydroforming of ductwork for aircraft. I don't know exactly what pressure was used but the ducts were made of 321SST or inconel. The forming dies were made of 7075-T6 aluminum. The ends of the tube had to have a rolled groove and the end clamps to hold the end plugs were steel and pretty beefy. I will surmise that you are working with aluminum since you are talking about die casting. It shouldn't be too costly to experiment with somesimple dies to geet an idea of the detail you can achieve and what tolerences you can hold.

What do you want to achieve? This technique is used in several directions but requires special steels (if made at low temperatue) and special tools. If you give more informations it is possible (but not sure) to give you some hints.

Currently the piece is made of aluminium, die casting, and I would like to do it in stell (C20-C40) with this bulging process, and afterwards a reworking in order to reach a correct tolerance and shoulder for bearing... I really don't know if this is possible...

Are you talking about forming a large hollow shape or just expanding a pipe?

Various shapes have been made by hydraulic forming into dies using aluminium, steel or titanium, some car exhaust systems are made this way.

Pipes can be expanded, usually to lock them into other components by 'ball sizing' which involves pulling a carbide ball which is slightly larger than the bore of the pipe all the way through the pipe. This is used in the manufacture of heat exchangers & heating elements.

The thickness of this body containing the bearing should be approximately 5 mm....the diameter should be more or less enlarged of 4 mm respect to the initial pipe...the important thing I would like to understand is if this process is able to mantain a certain geometric tolerance, do to the fact that I would like to have in it a correct housing for the bearing. Of course, I think that a reworking is necessary, but as little as possible..otherwise die casting would be cheaper!

The tolerances can be rather tight since repetitivity is not bad. It is nedded to adapt the pressure and degree of plasticisation to the material. Dimensional dispersion depends on the dispersion of following parameters:

- elasticity limit

- how the material behaves after the elestic limit

- how the material comes back since not all the wall is deformed over the elastic limit and there is an elastick back spring effect.

This has to be deteremined as well via simulations (FEA non linear ) as by experimental progressive steps so that you can determine the dimensions of the form. The steel used should have a high deformability. If your part is a cylider then hydraulic forming would be the simplest solition with a usual pressure source + pressure intesifier. It coukd be necessary to work > 1000...2000 bar. The form should be computed for it.

For a 5mm wall which is the internal diameter ? The feasability depends in fact on the ratio wall thickness/diameter. The higher the ratio is the more difficult it is to deform.

Thank you very much for your suggestion, now I have a clearer idea of the important parameters to take into consideration.

The inner diameter should be 14 mm more or less, 17 mm after deformation, with a certain addictional margin of material for the reworking... Having clear the process, the important think is now to investigate from a supplier the feasibility of the piece, and most of all its cost...I have some doubt about the saving respect to die casting...

Sorry...the diameters should also be from 32mm to 35mm ... maybe it is the most critical one...