Manufacturing: Metal Forming

Sheetmetal Forming - Hydroforming

 

New all-aluminum frame for the Z06 Corvette features hydroformed side rails and engine cradle

Hydroforming, sometimes referred to as fluid forming or rubber diaphragm forming, was developed during the late 1940's and early 1950's in response to a need for a lower cost method of producing relatively small quantities of deep drawn parts.

Hydroforming, in simple terms, replaces the punch in traditional stamping with liquid--usually water--to provide shaping force. Hydroforming refers to the manufacture, via fluid pressure, of hollow parts with complex geometries. Hydroforming can be used to shape tubes or extrusions—where it finds its greatest use--or to shape sheet blanks.

In tube and extrusion hydroforming, the workpiece is inflated by introducing fluid into the cavity while the tube undergoes axial or radial compression. The tube then expands where permitted by the tooling to the die wall. Such hydroforming in many cases is preceded by forming steps such as bending the tube to distribute where it’s needed—corner radii, usually--for final hydroforming, or bent in order to fit into the die. Hydroforming dies used for tubes or extrusions consist of upper and lower blocks and plates as well as axial units used for sealing and end-feeding of the part.

A sheet blank can be formed via fluid applied directly or through a bladder system to force the sheet to assume the shape of the die wall or punch end. Here, the punch may provide additional pressure to assist in the process.

The hydroforming process requires specialized presses—or specially fitted hydraulic presses--and tooling as well as fluid delivery, storage, disposal and reclamation capability. Fluid pressure can range from the about 3,000 to nearly 100,000 psi.

Competitive processes

Deep-draw stamping, tube bending, fabrication.

Applications -

In automotive, the process delivers hollow parts such as radiator frames, engine cradles, exhaust manifolds, roof and frame rails and instrument-panel supports. Various rails, manifolds and supports find use in aircraft and appliance applications. Parts made through sheet hydroforming, currently a low-volume specialty process, include automotive deep-drawn fuel-tank trays and body panels as well as appliance parts such as panels and sink basins. The process also works well with smaller parts such as fittings and fuel filler necks

Benefits -

Hydroforming results in lighterweight parts in applications where it has replaced traditional stamping, fabrication and assembly methods. In many cases, one-piece hydroformed parts can replace assemblies, thus increasing structural integrity while saving on material costs and reducing scrap. Hydroforming is better suited in producing parts from high-strength steel and aluminum than competing processes. Recently, technology has allowed inclusion of operations such as piercing during hydroforming.

Capacities:

Part size is dependent on press size. Currently, the largest hydroforming press available can churn out parts to nearly 20 ft. long, but typical parts are less than half that size, and can be produced in sizes down to a few inches. Cycle times are slower than traditional stamping methods.

Materials:

High-strength steel and aluminum are the materials of choice in hydroforming parts for automotive use. But any sheet material that can be cold formed is a candidate for hydroforming.