Tube HydroForming

Tube HydroForming

Index

Tube HydroForming.......................................................................................................................................... 1

Introduction ................................................................................................................................................. 1

Parameters ................................................................................................................................................... 1

Process ......................................................................................................................................................... 2

Quality and application ................................................................................................................................ 3

Introduction

A liquid under pressure is used to plastically deform the metallic material and in order to achieve the desired

shape. The mechanical action of the fluid substitutes partially tools and moulds typical of conventional

pressing. During the Nineties, this technology developed for hollow profiles, exhaust and chassis parts in

automotive industry. One of its greatest advantage is the possibility to realize complex geometries at lower

costs than conventional processes: in fact, a decrease of fabrication steps is achieved (no assemblies).

Moreover, the consequent reduction of the number of welds increases mechanical resistance.

The process is based upon the mechanical action of pressurized water or oil on a tube inside a mould

reproducing the final form of the component. The mould is closed under the action of a closure force . The

pressurized fluid is injected into the tube and an axial force is laterally applied through cylinders. The

tube expands into the cavity until assuming the final form of the mould. According to the required part,

additional force can be useful (for example exerted by a transverse punch to set the end of the expansion).

Parameters Considering a cylinder with thin walls in plain strain condition, the radial stress

= = − and it is possible to define an equivalent stress as:

3 2

√1

̅ = − +

1

= / = 1/2, ̅ = /2.

Where and in case of plain strain therefore √3

2 1 1

There are different

processing zones: in the

guided zone, the radial

stress is opposed to the

,

internal pressure of the fluid the hoop stress

= is small and positive and the axial stress

1

= is negative due to large friction. In the

2 ≤ 0

expansion zone, and small, and are positive. Therefore, displacements:

3 1 2

 = > 0

1

 = is positive in the expansion zone and is negative in the guided zone

2

 = is generally negative, but can be positive in the guiding zone

3

Pag. | 1