Prozessintegrierte Herstellung von Sandwichstrukturen

Process-integrated manufacturing of sandwich structures

 

Motivation

A growing sense of responsibility in the use of resources requires new technologies reducing weight. This goal is now valid beyond the boundaries of traditional industries for lightweight design. Especially sandwich structures have an important role in this field. Their advantage is the high specific bending stiffness and strength. However, this lightweight construction has not yet been economically viable for many applications due to high production costs.

 

Aim

The aim of this research project is to develop a technological basis for sandwich structures made of sheet metal. The economic production will be ensured by a high degree of automation. [Figure 1] shows a prototype of the representative sandwich structure, which shall ensure the achievement of these goals. Among others, brazing is investigated as a joining technology because of its high lightweight potential. The collar connection element provides the distance between both sheets [Figure 2].

Sandwich structure prototype
Figure 1: Prototype of the sandwich structure
Side view on collar connection element
Figure 2: Side view on collar connection element

Process chain

The process chain for the sandwich structure manufacturing consists of hole drilling, collar forming, sheet adjusting and bond creation. At first, holes are drilled in both sheets and used for the collar forming process. Each sheet has its specific collar diameter. After adjusting both sheets, the collars of each sheet can be aligned with one another. In a final step, a mechanical or metallurgical bond joins both sheets.

 

Methodical approach

The development of the sandwich structure is optimized with respect to its assembly and load carrying capacity. Among others, brazing is investigated as a joining technology because of its high lightweight potential. In this context, the process integration possibilities of brazing are investigated to provide an automated production process. In [Figure 3], the arrangement optimization of the collar forming element is shown. Furthermore, the figure shows the soldering optimized design of the collar forming process and the resulting soldering gap geometry.

entwicklungsschritte_sandwichstruktur
Figure 3: Design of the sandwich structure

Methodical approach

The development of the sandwich structure is optimized with respect to its assembly and load carrying capacity. Among others, brazing is investigated as a joining technology because of its high lightweight potential. In this context, the process integration possibilities of brazing are investigated to provide an automated production process. In Figure 3, the arrangement optimization of the collar forming element is shown. Furthermore, the figure shows the soldering optimized design of the collar forming process and the resulting soldering gap geometry.

A mechanical bond is investigated as an alternative to brazing. The joint mechanism is based on a combination of a force-closed and form-closed bond. The geometry of the joining zone as well as the structure and forming processes are designed using FEM and are verified experimentally. The project results are combined in a demonstrator [Figure 1].

 

Significant Results

The project’s aims have been reached and the sandwich structure was realized successfully. The design of the sandwich structure was optimized in regard to bending. Furthermore, the geometry of the collar connection element was optimized within the process window of the manufacturing process collar drawing. By this procedure, an optimized collar connection element was designed for each material used (DC01, DC04, AlMg3 and HC340LA). In particular, the influence of the collar-diameter, the radius in the transition from sheet to collar and the thinning of the sheet were investigated. These parameters have an influence on the distance of the sheets and the bending stiffness and strength. In addition, the arrangement of the collar connection elements on the sheets was investigated. The optimization showed that a shifted arrangement of the collar connection elements with minimal distance has the maximum stiffness and strength. The bending test of a brazed sandwich structure compared with a structure with mechanical joints showed that brazing has no gain for bending stiffness or strength.

 

Acknowledgment

PtU would like to thank the German Federation of Industrial Research Associations (Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. AiF), the European Research Association for Sheet Metal Working and the following companies for their support.

- Graepel Seehausen GmbH und Co. KG

- Haulick & Roos GmbH

- Innobraze GmbH

- KGW GmbH & Co. KG

- Simufact Engineering GmbH

- TOX PRESSOTECHNIK GmbH & Co. KG