Vibrations occurring during milling operations reduce process efficiency and result in rougher surfaces as well as in high tool wear and workpiece scrap. A trial and error approach to process design is frequently adopted in a bid to minimize vibration This is both time-consuming and costly. In a two-year research project known as "FixTronic", the Fraunhofer Institute for Production Technology IPT and its partners developed a clamping system and simulation software to systematically minimize vibration occurring during milling operations, thereby ensuring more stable, cost-efficient milling processes.
The aim behind the "FixTronic" project was to develop a system capable of reacting autonomously to dynamic changes in the milling process and to actively reduce vibration and instabilities. To this end, the engineers developed firstly an active clamping system for the workpiece and secondly, simulation software which optimizes spindle speed so as to ensure that no natural workpiece vibration is stimulated.
In order to actively stabilize the milling process, sensors permitting the condition of the workpiece to be monitored throughout the milling operation were integrated within a clamping system. Piezo actuators then generate targeted counter-vibrations on the workpiece as required in order to minimize milling tool vibration. Trials have shown that workpiece vibration can be reduced autonomously by over 70 percent when this method is applied.
Additionally, the clamping system can be networked with the machine tool, permitting effective workpiece monitoring in real time. This stabilizes the entire milling process. Thus, the active clamping system itself becomes a cyber-physical production system (CPPS) in accordance with the principles of Industry 4.0.
In order to further reduce workpiece vibration, the engineers at the Fraunhofer IPT also used simulation software they had developed themselves. This software allows the milling process to be simulated prior to the actual machining operation. As a result, critical spindle speeds which cause excitation of natural workpiece frequencies when there is particularly strong vibration, can be avoided. The software developed by the researchers in Aachen involved a "multi-frequency stability diagram", which takes account of changes to the workpiece geometry throughout the course of the machining operation. In trials, it has already been shown to achieve a further significant reduction in vibration: surface roughness of the parts tested, fell by over 50 percent.