Hydroforming

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The traditional sheet metal components have been replaced by hydroformed tubes, leading to lesser components, weight saving and an excellent crash performance.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