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Prediction and compensation of process induced shape deviations in multi-axis high-speed hard finish milling

: Stolorz, M.; Ottersbach, M.; Kalocsay, R.

International Academy for Production Engineering -CIRP-, Paris:
11th International Conference on High Speed Machining, HSM 2014. Proceedings : Advances in Manufacturing Technology, September 11-12, 2014, Prague, Czech Republic
Prague, 2014
ISBN: 978-80-904077-7-0
5 pp.
International Conference on High Speed Machining (HSM) <11, 2014, Prague>
Conference Paper
Fraunhofer IPT ()

In the generation process of sculptured surface machining by means of multi-axis hard finish milling no absolute accuracy can be guaranteed. The relative motion of the applied ball-end milling tool is always performed with systematic deviations. These deviations are influenced especially due to the stiffness of the milling tool, pre-defined process control and disturbance parameters as well as initial environmental conditions with respect to the forecasted relative motion of the milling tool. According to the state-of-the art and the results presented in this paper, the prediction and compensation of machining induced geometrical shape errors on generated work pieces surfaces, is still an interesting research field. Representation models for describing the influence of different process control variables and disturbance factors that influence and provoke shape deviations are well known and provide sufficient accuracy. However, when considering high-precision high-speed hard finish milling applications with long slender ball-end milling tools, adapting existing best practice representation models for describing conventional milling process is not holistically applicable. The reason for this issue are unbridgeable limitations of the economies of scales in modelling of chipping mechanics when considering small values for the thickness of the uncut chip. Especially in finish milling of complex multi-curved sculptured surfaces the description of the work piece (material and geometrical shape) and the designed process layout provoke permanently changing engagement conditions between the work piece surface and the applied milling tool. To predict and compensate machining induced shape errors while generating complex multi-curved sculptured surfaces by multi-axis milling, unique information on the local engagement conditions between the work piece surface and the milling tool geometry is an essential initial condition. For this purpose a novel technique was introduced and verified to derive the local surface curvature radius, which corresponds to each discreet NC tool path point and the orientation of the desired local surface normal vector. By combining the ability of calculating an unique geometrical solution by the vector analysis based technique in combination of the process representation model, a surface feature based life cycle monitoring of a ball-end milling tool becomes holistically feasible. The developed technique was virtually proven by predicting and compensating process induced shape deviations on a high-speed hard finish milling process layout adapted on a specific work piece geometry. At the end the general applicability of the developed technique was proven too. Like proposed before, the engagement conditions between the work piece surface and the applied milling tool geometry changed permanently multiple times during the whole surface generating operation. Local peak amplitudes were noted, which may provoke unacceptable shape deviations while the final physical milling process (not presented in this paper). To satisfy the application-related requirements for higher added value (cost reduction) and greater efficiency (capacities and resources), the developed technique was applied virtually within the process design phase in the scope of seconds, before ramping up the final physical machining process.