Trocken-Scherschneiden von Sandwichblechen

Lubricant free shear cutting of composite materials

 

Motivation

By combining materials with different properties [Figure 1], pre-products with adapted stiffness and strength can be manufactured. Due to the optimal balance of weight and strength, composite materials are broadly used in the aviation sector.

Figure 1: Configuration of a composite material
Figure 1: Configuration of a composite material

Continually increasing exhaust emission standards for automobiles and the increasing environmental awareness in the population urge design engineers to develop new constructive and material concepts. In contrast to the aviation sector, the quantity of processed materials in the automotive industry is significantly higher. Therefore, commonly used manufacturing processes for cutting composite materials, like sawing or milling, are not applicable. Shear cutting promises to be a suitable manufacturing process for high quantities. However, pretrials have shown that with present process layouts flawless cutting edges cannot be manufactured. The main failure modes are cover sheet retraction and delamination of the cover sheets and the core [Figure 2].

Aim

The aim of this research project is the optimization of the shear cutting process in regards to cutting sandwich materials. Hereto, the required process parameters will be determined. In order to minimize the environmental impact as well as reduce costs, the shear cutting shall be performed without using lubrication.

In addition to the process optimization, non-destructive inspection procedures for the detection of delamination, namely ultrasonic measurement, thermography and vibrometry, will be investigated.

Figure 2: Microsection of a cut composite material
Figure 2: Microsection of a cut composite material

Methodical approach

First, the non-destructive inspection procedures for delamination detection are investigated. The inspection procedures will be evaluated based on the following criteria: detectable failure size, reproducibility of the measurement, effort and measurement time.

Within a collateral research project, an innovative counter shear cutting tool is developed for the adjustment of the shear cutting process. With this tool, the impact of different process parameters, like cutting velocity and die clearance, on the cutting edge geometry will be investigated.

 

Significant results

Ultrasound, thermography as well as computerthomography are suitable non-destructive inspection methods for detecting delamination. Depending on the quality requirements, the environmental conditions, and the cycle time, each method has it strengths and weaknesses. Due to the high dampening properties of the core of the sandwich panels, vibrometry is not suitable for de tecting delamination.

Small clearances of the die lead to a low face bending values as well as low fraction angels. Furthermore, dependence between the shear cutting force progression and the used clearance was determined in cooperation with the DFG-Project “Intelligent die for lubricant free shear cutting of composite materials”.

 

Acknowledgment

The PtU would like to thank the “Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. (AiF)”, the Research Association for Steel Application (FOSTA) and the following companies for their support.

- 3A Composites

- F&K Werkstoffprüfung und Labor

- FILZEK TRIBOtech

- Graepel AG

- Oerlikon Balzer Coating Germany

- ThyssenKrupp Steel Europe AG

- Volkswagen AG