1,721,329 research outputs found
Breakthrough of regenerative chatter modeling in milling by including unexpected effects arising from tooling system deflection
No full textSelf-excited anomalous vibrations called chatter affected milling operations since the beginning of the industrial era. Chatter is responsible for bad surface quality of the machined part and it may severely damage machining system elements. Although the significant advances of recent years, state of the art dynamic models are not yet able to completely explain chatter onset even when some conventional cutting tools are applied for conventional milling operations. In this work, a more general model of regenerative chatter is presented. The model takes into account some additional degrees of freedom and cutting forces which are neglected in the classical approach. By so doing, a more accurate representation of milling dynamics is obtained, especially when considering large diameter cutters. An improved mathematical formulation of regenerative cutting forces is provided with respect to a very recent publication where the new model has been first outlined. This approach allows -45 % of computation time. Moreover, here a new, independent, and stronger experimental validation is provided, where the new model successfully predicts an increase of about +(50 A center dot 100) % of the stability boundaries with respect to the classical prediction, thus showing the potential breakthrough of the new approach
RCPM - a New Method for Robust Chatter Prediction in Milling
No full textThe reliability of conventional chatter prediction algorithms is limited by the inaccuracy of machining system dynamic models. In this paper, a new probabilistic algorithm for a robust analysis of stability in milling, which performs the stability analysis on an uncertain dynamic milling model, is presented. In this approach, model parameters are considered as random variables, and robust analysis of stability is carried out in order to estimate system’s probability of instability for a given combination of cutting parameters. By so doing, probabilistic instead of deterministic stability lobes are obtained, and a new criterion for system stability based on level curves and gradient of the probabilistic lobes can be applied to identify optimal robust stable cutting conditions. Experimental validation consisted of different phases: firstly, machining system dynamics were estimated by means of pulse tests. Secondly, cutting force coefficients were determined by performing cutting tests. Eventually, chatter tests were performed and the experimental stability lobes were compared to the predicted robust stable regions
State aid and Brexit: the temptation for political intervention
No full textState aid is currently regulated by the EU and, after Brexit, the government intends to transpose the rules into UK legislation, with the Competitions and Markets Authority overseeing the issue. Totis Kotsonis (Eversheds Sutherland) explains why future governments could be tempted to allow political intervention that EU membership precludes
Development of a modular dynamometer for triaxial cutting force measurement in turning
No full textAccurate and reliable measurement of cutting forces in turning is essential for tool geometry, tool trajectory and cutting parameters optimization, as well as for tool condition monitoring and machinabilty testing. In this work, an innovative dynamometer for triaxial cutting force measurement in turning, specifically designed to be applied at a milling-turning CNC machine tool endowed with an indexable head, is presented. The device is based on a piezoelectric force ring integrated into a commercial toolshank, and its modular design allows the easy change of the cutting insert without altering sensor preload. The prototype device was assembled and experimentally tested by means of static calibration and dynamic identification, which evidenced good static and dynamic characteristics. Eventually, the sensor was tested in operating conditions by machining a benchmark workpiece. (C) 2010 Elsevier Ltd. All rights reserved
Upgraded Regularized Deconvolution of complex dynamometer dynamics for an improved correction of cutting forces in milling
No full textIn order to characterize cutting mechanics during high-speed milling and micromilling applications, high-end piezoelectric dynamometers with a wide frequency bandwidth are necessary. Nevertheless, when installed into the machine tool their signal bandwidth is limited by the dynamic behaviour of the machining system. Thus, special filters have to be adopted for dynamics compensation. State of the art filters are based on a simplistic 3 × 3 dynamic model of device transmissibility without taking into account the influence of input force location with respect to the centre of the sensing platform. The Upgraded Augmented Kalman Filter has been recently proposed for solving this problem. Although it outperformed the other state of the art filters, it was based on the preliminary identification of a parametric mathematical model that is generally a difficult and non-automatic task. Here a novel non-parametric filter is introduced, that was based on a more general and abstract model of dynamometer dynamics considering both input force direction and location. By so doing, impressive results were found both from modal analysis and from real cutting tests, showing the potential of the new method for an effective and almost completely automatic cutting force dynamic compensation
Polynomial Chaos-Kriging approaches for an efficient probabilistic chatter prediction in milling
No full textAfter more that 60 years of investigation, chatter vibrations in metal cutting are still a major cause for poor surface finish and machine tool damage. In order to avoid undesired machining conditions, chatter prediction algorithms may be applied to draw stability charts that allow a preliminary identification of the safe areas. Nevertheless, the stability boundaries are sensitive to the variations and uncertainties of the dynamic milling model coefficients. Thus, the accuracy and reliability of the obtained predictions can be inadequate for many industrial applications. For solving this problem, robust methods were recently devised that are fast but usually too conservative. On the other side, probabilistic approaches were also developed to estimate the probability of instability for a given combination of cutting parameters, by taking into account the statistical distributions of model coefficients. Probabilistic approaches allow a less conservative, risk-aware selection of stable cutting conditions. Unfortunately, their application is still very limited due to the required large amount of computational power and time. In this work, three novel probabilistic methods based on Polynomial Chaos and Kriging metamodels (PCE, KRI and PCK) were compared to state of the art probabilistic algorithms (MC, MC-SPA, DRM-SPA, RCPM). The numerical analysis and the experimental validation proved that MC-SPA, DRM-SPA, RCPM and PCE are too rough and thus needless for industrial applications. On the contrary, KRI and in some cases also PCK showed an excellent accuracy together with significantly shorter elaboration time than that required by the reference Monte Carlo (MC) technique
Superior optimal inverse filtering of cutting forces in milling of thin-walled components
No full textMeasuring the cutting force when milling slender/thin-walled parts is difficult because of the large and long-lasting structural vibrations that cause inertial disturbances in the measured signals. Under these conditions, signal filtering is the only option to significantly extend the dynamic bandwidth of the device above 3 kHz. Non-parametric filters are typically preferred over parametric ones because they are more practical and easier to apply in industrial applications. Currently available parametric filters cannot address this problem because they are based on oversimplified transmissibility models or are affected by computational problems when the impulse responses of the device are excessively long. In this study, the novel non-parametric Superior Optimal Inverse Filter was developed to address the limitations of state-of-the-art filters. It is a non-trivial extension of the Optimal Inverse Filter to a higher dimensionality, and it can process long transients and generic (possibly aperiodic) signals. Thus, outstanding results were obtained both from modal analysis and from an actual case study, demonstrating the potential of the new filter for an effective and almost completely automatic cutting force dynamic compensation when milling thin-walled structures. The proposed filter was compared with parametric Kalman filters and with the existing non-parametric filters, and it offered a considerably better performance, particularly for compensating for cross disturbances and for input force position-dependent dynamics
Robust Analysis of Stability in Internal Turning
No full textWhen machining high precision mechanical parts, self-excited chatter vibrations must be absolutely avoided since they cause
unacceptable surface finish and dimensional errors. Such unstable vibrational phenomena typically arise when the overall
machining system stiffness is relatively low, as in the case of internal turning operations performed with slender boring bars. In
general, it is not easy to determine stable tooling system configurations for a given machining operation, since data available in
literature are often incomplete or inaccurate. In this paper, a new probabilistic algorithm for a robust analysis of stability in
internal turning is presented. In this approach, model parameters are considered as random variables, and robust analysis of
stability is carried out in order to estimate system’s probability of instability for a given boring bar geometry and material, tool
geometry, workpiece material and cutting parameters. By so doing, robustly stable tooling system configurations and cutting
conditions may be identified in the preliminary production planning phase. The proposed approach was experimentally validated
by considering different boring bar geometries and materials (including special boring bars made of high-damping carbide), tool
geometries, workpiece materials and cutting conditions. For each machining system configuration, the developed approach was
capable of successfully estimating the maximum ratio between boring bar overhang L and bar diameter D which assures process
stability for most cutting parameters combinations
Divergence, at what cost?
No full textThe EU-UK Trade and Cooperation Agreement is a free trade agreement like no other: the first between parties negotiating from a position of regulatory convergence; the first trade deal in which the EU has accepted the principle of no tariffs and no quotas, but also the first trade deal which not only incorporates provisions that can broaden and deepen the Agreement’s scope, but also narrow it. However, at what cost are the parties willing to increase divergence, asks Totis Kotsonis (Pinsent Masons LLP)
- …
