In detail: What is hydroforming?
As a pioneer in hydroforming, we deliberately rely on the process for which we are known worldwide as experts for the production of bipolar plates. The advantages of hydroforming are obvious:
Hydroforming – or external high-pressure forming – is an active media forming process. A metal foil is inserted into a tool gravure and expanded into the forming tool with very high pressure by means of a water-oil-emulsion (see sketch).
Thanks to the even pressure distribution over the entire foil surface, an homogeneous material thickness distribution is achieved, and abrupt stress transitions are avoided. This allows forming even the smallest radii. The material spring back remains low.
The advantages of hydroforming
With so-called external high-pressure forming, extremely filigree structures can be realized in series using extremely thin materials from 50 μm. In contrast to mechanical forming, which at first glance may seem more cost-effective, especially for series production, hydroforming offers numerous advantages that pay off in the long term.
Since bipolar plate production is all about repeatable precision, attention to detail and high value, we believe that hydroforming is the optimal process – and one of the quality features that makes Graebener® Bipolar Plate Technologies your sustainable competitive edge.
Properties of a Graebener® hydroforming plate and a mechanically produced plate
| Criteria | Graebener® hydroforming plate | Mechanically produced plate |
| Repeat accuracy in the process | Very high |
Good |
| Elasticity after forming | Highly elastic through gentle forming with integrated cooling | Significantly reduced through strain hardening |
| Wall thickness variation | Very homogeneous over the entire duct cross- section | Heterogeneous (constrictions) |
| Suitability for pre-coated materials | Ideal: no friction on the water side | Only limited use due to friction in the tool |
| Contact areas | Almost ideal shaping of the flat contact surfaces | Good shaping |
| Use of different material thicknesses in one tool | Flexible: different material thicknesses can be used per tool | Not possible |
| Adaptation of the manufacturing parameters in the forming process |
Flexible |
Not possible |
| Tool costs | Low: less wear and fewer tools | High |
| Number of tool stages | One | Several (multi-stage forming tool) |
Exemplary Graebener® hydroforming plates
Foil thickness: 100 μm, Material: Alleima Sanergy® LT (316L)
Foil thickness: 50 μm, Material: 304L
Foil thickness: 100 μm, Material: Titanium Grade 1