Application of Hydroforming:
Hydroforming benefits include
weight savings, strength improvement, part reduction, and additional design
options. Hydroformed component features can include changing cross sections
with varying corner radii and curved sections. Engineers and part designers
must consider material properties such as yield strength, ultimate strength,
and allowable elongation in the design of a component. Materials commonly
formed are brass, stainless steel, carbon steel, and aluminum. These materials
vary widely in formability characteristics.
The demand for lighter component
solutions remains a primary driver in the automotive industry. Hydroforming is
considered as one of the potential enabling technologies to deliver lightweight
components.
Hydroforming enables manufacturing
of closed sections with non-uniform cross-sectional areas along the length by
using a circular tube as the input material. While conventional stamped and
welded closed sections need a flange area to facilitate welding, hydroformed
closed sections enables weight saving by avoiding the flange area. The capacity
of the Hydroforming process enables a designer to replicate the profile of
brackets / child parts directly on the components, thus reducing the number of
brackets / child parts.
The traditional sheet metal
components have been replaced by hydroformed tubes, leading to lesser
components, weight saving and an excellent crash performance.
Importance
of FEM in Hydroforming:
Although tube hydroforming is a
long known technology, the applications of hydroformed tubular components has
increased in recent times, because of the more advanced pressing control
technology, but also because of the availability of reliable Finite Element
Models (FEM), that eliminate the expensive trial and error process in the development
of the tools and components.
Examples of Hydroforming:
Figure.
Conical hydroformed component
Definition of Tube Hydroforming:
The principal of tube
hydroforming is given in figure. A pre-bended tube is placed in a tool set in a
press which applies the closing force. At the ends of the tube two cylinders
are placed that can apply axial feeding. The tube will be filled with fluid and
the tube will be formed under pressure.
Figure.Tube
hydoforming.
In figure a typical sequence is
shown for tube hydroforming of a simple T-component. First the tube will be
positioned in the die set, the tools will close and the tube will be filled
with water. Axial feeding will build up pressure and enable the inflow of
material into the T-shape. After releasing the pressure, the dies can be opened
and the part be removed.
Figure. Tube
hydroforming sequence for a T-shape
Definition
of Sheet Hydroforming:
In figure the sheet hydroforming
is shown, where the hydraulic fluid is used as a flexible die in a deep drawing
process of cylindrical components.
Figure. Sheet
hydroforming
Apart from sheet
hydroforming as an enhancement of the classical deep drawing process, a special
process has been developed especially for automotive outer components called
the Hydromec process. In figure the
principle of this method is shown where a sheet is pre-formed in one direction
generating a uniform strain in the sheet. After that a mechanical punch will
press the sheet in the other direction giving the component its final shape,
supported by the hydraulic fluid. In this way a component with a lot of pre-strain
will be pressed, which will give the component excellent dent resistance,
especially when so called bake hardening steels are used that raise the Yield
strength of a pre-formed component considerably during the paint cycle.
Figure. The
Hydromec process.
In
figure another special form of sheet hydroforming is shown, the so called pillow hydroforming, where two stacked
sheets are presses together in one toolset into a an outer and inner panel of,
in this case a bonnet, reducing cycle time, tool costs and increasing dent
resistance.
Figure.
A Hydromec bonnet
Figure.
Pillow sheet hydroforming
