Gilles Cazenave-Larroche. Integration of dynamic behaviour variations in the stability lobes method: 3D lobes construction and application to thinwalled structure milling. International Journal of Advanced Manufacturing Technology, Springer Verlag, 2006, vol. 27, pp. 638-644. 10 Integration of dynamic behaviour variations in the stability lobes method: 3D lobes construction and application to thin-walled structure millingAbstract Vibratory problems occurring during peripheral milling of thin-walled structures affect the quality of the finished part and, to a lesser extent, the tool life and the spindle life. Therefore, it is necessary to be able to limit these problems with a suitable choice of cutting conditions. The stability lobes theory makes it possible to choose the appropriate cutting conditions according to the dynamical behaviour of the tool or the part. We introduce the dynamical behaviour variation of the part with respect to the tool position in order to determine optimal cutting conditions during the machining process. This generalization of the classical lobes diagram leads us to a 3D lobes diagram construction. These computed results are compared with real experiments of down-milling of thin-walled structures.

& Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thinwalled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.

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Résumé -Les problèmes vibratoires rencontrés lors de l'usinage en contournage de parois minces affectent la qualité de la pièce finie et dans une moindre mesure, la durée de vie de l'outil et de la broche. C'est pourquoi il est nécessaire de pouvoir limiter ces problèmes par un choix approprié des conditions de coupe. La théorie des lobes de stabilité permet de choisir les conditions de coupe adéquates en fonction du comportement dynamique de la pièce ou de l'outil. Nous introduisons ici les variations de comportement dynamique duesà la position de l'outil, dans le but d'obtenir des conditions de coupe optimales tout le long de l'usinage. Cette généralisation du tracé classique des lobes de stabilité nous conduità représenter les lobes en trois dimensions. Ces résultats théoriques sont comparésà des usinages expérimentaux de pièces minces, en avalant.Mots clés : Lobes de stabilité 3D / fraisage de paroi mince / comportement dynamique Abstract -Influence of the tool position on the dynamic behaviour in milling of thin walled structure. Vibratory problems encountered when milling a thin walled structure affect the surface quality of the finished workpiece and to a lesser extent, the life of the tool and the spindle. This is why, it is necessary to be able to limit these problems by an appropriate choice of the cutting conditions. The stability lobes theory allows to choose the suitable cutting conditions according to the dynamic behaviour of the workpiece and the tool. We introduce here the variations of dynamic behaviour due to the tool position, in order to obtain optimum cutting conditions all along the machining. This general implementation of the classical stability lobes graph leads us to represent the lobes in three dimensions. These theoretical results are compared with experimental milling of thin walled structure, in down-milling.Key words: 3D stability lobes / milling of thin walled structure / dynamic behaviour