Parallel Is Faster Than Sequential: Passive HPSF Reduces Tool Costs and Becomes a Genuine Alternative to Forming in Stamping Technology

Cycle times in sheet hydroforming are typically longer than in conventional sheet metal forming processes such as deep drawing. Even when processing continuous strip material from coil stock, production rates of only six to eight strokes per minute are generally achievable. This is primarily because the process steps of “opening and closing the press,” “building up the clamping force,” and “forming” are performed sequentially.

Fraunhofer IWU has completely redesigned both the process sequence and the tool structure using its passive high-pressure sheet metal forming technology, enabling these steps to occur simultaneously. In passive HPSF, the forming pressure is generated directly within the tool through a hydraulic cylinder. As the press closes, the clamping force automatically generates the required fluid pressure. Standard presses can be used, eliminating the need for a separate high-pressure water-hydraulic system. Combined with coil-fed production, the technology enables manufacture of bipolar plates at rates of up to 60 cycles per minute for the first time.

At Fraunhofer IWU, passive HPSF is being researched primarily for manufacturing bipolar plates used in fuel cells and electrolyzers. However, the enhanced process could also be applied to the production of smartphone housings, either replacing or complementing deep-drawing processes. Cost-effective tooling enables economical series production even for smaller sheet metal components, which are currently produced by stamping. Additional advantages of passive HPSF include greater design freedom, improved surface quality – because the sheet is uniformly pressed against the die surface by the fluid – more consistent material thickness distribution, and exceptionally short cycle times thanks to the achievements described above.

An Unbeatable Combination in Terms of Cost Efficiency: Hydraulic Forming and Flow Pressing

Metal-plastic hybrid components are used in a wide range of products. In the automotive industry, for example, structural elements of instrument panels (cross-car beams) and front-end assemblies often contain components with permanently bonded plastic and metal elements. Metal and plastic parts are also frequently joined together in furniture legs and similar products.

Today, manufacturing these hybrid components often relies on a combination of hydroforming and injection molding. However, integrating these technologies requires combining two fundamentally different processes – each with demanding requirements as to equipment, process control, and expertise – within a single production system. The result is substantial capital investment in both machinery and tooling, often placing such solutions beyond the reach of small and medium-sized enterprises (SMEs).

To address this challenge, Fraunhofer IWU, together with Chemnitz University of Technology, injection-molding specialist Schicktanz GmbH, lightweight hydroforming press manufacturer IWC Engineering, and industrial designer Felix Monza, has developed a new process combination consisting of tube hydroforming and simultaneous flow pressing of plastic components. The key difference from the established combination of internal high-pressure forming (IHF) and plastic injection molding is that the plastic component is introduced into the tool as a pre-manufactured extruded or injection-molded preform and is reshaped during the forming process rather than molded in situ. This eliminates the need for injection-molding equipment and the complex integration of multiple manufacturing systems.

In the newly developed process, the metal tube and thermoplastic component(s) are heated together and placed into a temperature-controlled tool. During internal-pressure forming of the metal tube, the plastic element is simultaneously pressed into its final shape.

For complex polymer geometries, tool slides can be used to control material flow, while preformed injection-molded parts can be employed where appropriate. Additional components, such as threaded inserts, can also be integrated. After cooling, the finished parts are removed from the tool. Process control largely follows that of a conventional IHF process. Due to the elevated temperatures of both the tool and the workpiece, gaseous nitrogen is used as the forming medium.

Technical Forum on Tube, Profile and Hydroforming Technologies in Chemnitz

Both newly developed processes successfully simplify, accelerate, and reduce the cost of existing forming operations. These and many other innovations in tube manufacturing, downstream processing, and hydroforming will be showcased live at the Technical Forum on Tube, Profile and Hydroforming Technologies on September 30 and October 1, 2026, in Chemnitz.