Intelligent die for lubricant free shear cutting of composite materials

Intelligent die for lubricant free shear cutting of composite materials

 

Motivation

The increasing requirement for lightweight design in all fields of technic, require the usage of new materials. Composite materials have the possibility to combine positive properties of different materials. So called sandwich beams consisting of strong and stiff facings and light weight cores offer improved stiffness and strength to weight ratios compared to monolithic materials. For a cost-efficient processing of these materials new manufacturing technologies are necessary. In addition to the conventional forming processes shear cutting is one of the most commonly used manufacturing processes. Currently the lubricant free shear cutting is not state of the art. When using normal shear cutting processes there can be especially two different types of failure. On the one hand there could be a high bending in the facings and on the other hand there can be delamination effects [Figure 1].

Figure 1: Failure modes during shear cutting of sandwich beams
Figure 1: Failure modes during shear cutting of sandwich beams

Aim

The aim of the project is the development of a parametric model for composite beams. With the model it should be possible to evaluate the cuttability of different material combinations.

Figure 2: Schematic diagram of the counter shear cutting
Figure 2: Schematic diagram of the counter shear cutting

Methodical approach

In the first step an intelligent experimental die has to be designed and built. With the triple-acting die it is possible to extend the limits of the counter shear cutting process [Figure 2]. In parallel, an analytical model will be developed. With the model it should be possible to estimate different material combinations according to their cuttability. The aim of the last step is the validation and the adaption of the analytic model with an experimental study.

Significant results

The significant results can be summarized by the following three points:

1. Due to the performed parameter study the process knowledge was significantly extended. In a first step the influence of different process parameters on the cutting surface were investigated. Among other things, it could be proved that the temperature of the work piece and the clearance are the main important parameters to reduce the face bending of the upper skin sheet.

2. Based on these fundamental investigations of the shear cutting the important process stages were derived and transferred in a model. In further studies the force requirements and their correlation to the cutting surface parameters were investigated. Also characteristic force displacement curves for different types of sandwich panels were found. In a last step an analytical model was introduced to predict the cutting forces. With this model it is possible to evaluate the cuttability of different material combinations.

3. During the project the counter shear cutting and the extended counter shear cutting were also investigated. Thereby the counter shear cutting without the overlapping of compression stresses did not have any positive influence on the cutting surface. Nevertheless, when using the counter punch to compress the core during the cutting process the face bending can be reduced significant. Furthermore it was shown that the surface parameters can be predicted by a regression model.

Analytical calculated force components for a shear cutting process with sandwich panels
Figure 3: Analytical calculated force components for a shear cutting process with sandwich panels

Acknowledgment

The research project is funded by the German Research Foundation (DFG).