Use of the MSR165 acceleration data logger in a study of process dynamics in the machining of CFRP components

In addition to lightweight design and sawing technology, the "Lightweight Construction Technologies" department at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA is particularly concerned with the machining of comparatively new lightweight construction materials such as carbon or glass fiber reinforced plastics.

In addition to the machining process with all associated sub-processes, the focus is on extraction technology, tool design, digitalization, cooling and lubrication systems and robot-assisted machining.

Components made of carbon fibre reinforced plastics (CFRP) are manufactured close to the final contour so that they only need to be machined in the area of the edge and for functionalization, for example by inserting holes. Due to the largely open and large-surface component design, these are usually unstable and tend to vibrate despite their high rigidity, which impairs both the service life of the tools used and the machining quality.

In order to avoid such effects during machining, clamping templates are typically used, which represent a negative image of the CFRP component. This means that the component is supported over the entire surface and can be clamped with low vibration using a vacuum. The disadvantage is that the clamping template can only be used for one component geometry at a time. Even the smallest design changes to the component blank can necessitate a new design.

As part of the BMBF-funded research project CFK Complete, a modular clamping system was therefore developed that can be used for finishing different CFRP component geometries. Depending on the geometry, this clamping system consists of several units of freely configurable vacuum clamps in combination with lockable support pins and can be optimally adapted to a wide variety of component contours.

In order to investigate the suitability of the modular clamping system for the machining of CFRP components, the dynamic behavior of the workpieces clamped with the modular clamping system during the machining of the component contour was recorded using the MSR165 acceleration data logger. For this purpose, the accelerometer was placed in the center of the component and mechanically fixed with screws. As a reference, machining tests were carried out in which the workpieces were clamped with a conventional clamping template.

Fixing the acceleration data logger

The tests showed that the workpieces exhibited significantly stronger dynamic behavior when clamped with the modular clamping system during machining of the contour than was the case when clamped with the conventional clamping template.

The results can be explained by the fact that the modular clamping system offers a smaller contact surface compared to the clamping template, so that the component vibrates more during machining due to the dynamic influences of the cutting forces. As a result, this leads to shorter tool life and poorer machining quality. Against this background, the modular clamping system proves to be an economical alternative, particularly for small series and in prototype construction, while a conventional clamping template is preferable for large quantities and in series production.