Current Status and Development Trends of Internal High‑Pressure Forming Technology

In aviation, aerospace, automotive and other industries, reducing structural mass to save operational energy has long been a pursued goal, and it also represents one of the development trends of advanced manufacturing technologies.

There are two major approaches to achieve structural lightweighting. The first is the material‑based approach: adopting lightweight materials such as aluminum alloys, magnesium alloys, titanium alloys and composite materials. The second is the structural‑based approach. For structures mainly subjected to bending and torsional loads, hollow variable‑cross‑section components can be used to reduce mass while fully utilizing the strength and stiffness of materials. For example, when a hollow shaft with a hollowness ratio (ratio of inner diameter to outer diameter) of 0.85 replaces a solid shaft, the mass can be reduced by nearly 50 % under the same torsional resistance capacity.

Hydroforming is an advanced manufacturing technology for hollow variable‑cross‑section lightweight components developed to meet such demands. The basic principle of hydroforming takes tubular blanks as raw materials. Ultra‑high‑pressure fluid is applied inside the tube, together with axial feeding force, to press the tubular blank into the die cavity and form the desired workpiece. It is suitable for manufacturing hollow components with circular, rectangular or special‑shaped cross‑sections varying along the component axis.

Owing to the working pressure up to 400 MPa, this process is referred to as IHPF (Internal High‑Pressure Forming) in Germany. Based on blank types and forming media, it is also named THF (Tube Hydroforming) in the United States. Early similar processes were known as hydraulic tube bulging.