Hydroforming

Process Definition & Working Principle

Hydroforming (Innenhochdruck-Umformen – IHU) is a specialized metal forming process utilizing high-pressure fluid (typically 500 to 4000 bar) to deform metal blanks (tubes, profiles, or sheets) inside a closed die cavity until the material completely conforms to the tool geometry. This process enables the manufacturing of complex, lightweight, seamless three-dimensional components with high structural integrity, which cannot be fabricated using conventional stamping and subsequent welding.

Process Physics and Mechanics

Hydroforming relies on a multi-axial stress state. Unlike conventional sheet metal drawing, which subjects the material primarily to uniaxial or biaxial tensile stresses, tube hydroforming (THF) applies a synchronized combination of internal fluid pressure ($P$) and axial feed displacement ($S$) via horizontal hydraulic rams.

The process is divided into three distinct physical phases:

Kinematics, Axes, & Machine Configuration

A typical hydroforming system consists of four primary assemblies: the vertical clamping press, the horizontal axial cylinders, the ultra-high-pressure hydraulic intensifier, and a closed-loop CNC control unit.

Tooling & Cutting Geometry

Hydroforming tooling consists of a split-die assembly (upper and lower halves), sealing punches, counter punches, and venting networks. Developing these tools requires precise consideration of die deflection under extreme internal pressures.

Tooling Design Elements:

1. Die Design: The die halves meet along a parting line. The cavity replicates the outer contour of the finished part, compensated for material springback and the elastic expansion of the tool itself. The design incorporates mechanical die locks to prevent lateral shifting of the halves under load.

2. Sealing Punches: Seal the tube ends and inject fluid. They are classified into three designs: