Chatter Vibration In Milling Research Articles

Cutting force investigation in face milling of additively fabricated nickel alloy 625 via powder bed fusion

The face milling of additively fabricated nickel alloy 625 produced via laser powder bed fusion is experimentally investigated. Typically, cutting forces are the most important factor affects the process outcome in terms of surface finish and chatter vibrations in milling of difficult-to-cut materials. The additively fabricated materials possess different mechanical properties hence their cutting force performance is usually unknown. For additively fabricated nickel alloy 625, the build direction and scan strategy rotation are known to influence the resultant workpiece structure with columnar grains. The peak milling force is found dependent upon the feed direction as well as the layerwise scan rotation employed in fabricating the workpiece. Feeding the cutter against the build direction resulted in lower peak forces with larger deviations, however feeding along the build direction resulted in higher peak forces with lower deviations. The build direction was also observable on fan shaped chip surfaces.

Two-points-based receptance coupling method for tool-tip dynamics prediction

ABSTRACTTool-tip frequency response function (FRF) is essential to predict chatter vibration in milling. This key input can be acquired by experimental tests, but a new test has to be performed for every tool clamped on the machine. To avoid such time-consuming procedures, receptance coupling methods have been developed, allowing coupling of the experimental dynamic response of the machine to the numerical model of the tool. Such techniques require joint rotation response, which is hard to experimentally identify. Inversion of receptance coupling technique is usually performed on additional experimental measurements to overcome this issue. This procedure amplifies measurement uncertainties, reducing accuracy of the coupling approach. In this article, a novel receptance coupling technique is presented. Machine and toolkit are connected through two distinct points, eliminating the experimental phase and computation of rotational degrees of freedom (DOFs). Only translation responses are required, acquired by a single test setup. Proposed technique was experimentally validated on different case studies.

Upgraded stability analysis of milling operations by means of advanced modeling of tooling system bending

The problem of undesired self-excited chatter vibrations in milling is very common. However, only in the last two decades some significant achievements for the theoretical understanding of this intricate phenomenon have been accomplished. Nevertheless, state of the art dynamic models are still not able to completely explain milling dynamics and chatter onset during some conventional milling operations performed by conventional cutting tools. In this research work, a revolutionary model of tooling system dynamics and of the regenerative effect in milling will be presented. The new model introduces a significant correction to the predicted stability borders when the cutter diameter is relatively large in comparison with tooling system overhang and when curved or inclined cutting edges are applied. Accordingly, the new approach may be of great interest for many industrial applications. The model has been successfully validated by performing experimental modal analysis, cutting force coefficient identification and stability lobes diagram determination, through many specific cutting tests. In the considered case study, where the afore mentioned geometrical features of the tooling system were still moderate, a significant shift of the stability borders of about +25% was experimentally observed and correctly predicted by the new approach.

Modeling and Analysis of Spindle with Active Magnetic Bearings for High-Speed Milling Process

AbstractThe high speed milling represents the most important process to produce parts in different fields such as aeronautics, automotive and mould. It allows obtaining parts with complex form and with the best surface quality. So, it remains essential to understand the impact of both the cutting force model and its parameters on the tool tip response. Consequently, the mastering of chatter vibration in milling and surface properties of the work piece is essential. In this paper, the simulation of machining is applied to determine the cutting forces distribution. A spindle system modeling is presented using a new approach: Both rigid and flexible modes of the spindle's shaft are taken into account. The shaft is discretized with the Timoshenko beam finite elements with different circular sections. Nonlinear electromagnetic loads exerted by AMBs are computed in terms of the nominal air gap between bearings and spindle, the control current and the displacement of each node. A parametric study is performed to determine the influence of some parameters, such as the feed rate, the tangential cutting coefficient, the spindle speed and the axial depth of the cut on the cutting forces and the chatter vibrations in milling.

Optimal control for chatter mitigation in milling—Part 1: Modeling and control design

Active structural methods constitute a promising way to mitigate chatter vibrations in milling. This paper presents an active system integrated into a spindle unit. Two different optimal control strategies are investigated. The first one only considers the dynamics of the machine structure in the controller design and minimizes the influence of cutting forces on tool tip deviations. The second one takes explicitly the process interaction into account and attempts to guarantee the stability of the overall closed-loop system for specific machining conditions. The modeling and formulation used for both strategies are presented in this first part. A simulation allows the comparison of their respective working principle. The validation of the proposed concept in experimental conditions is described in the second part.

Stable islands in the stability chart of milling processes due to unequal tooth pitch

The use of unequal tooth pitch is a known means to influence and to prevent chatter vibrations in milling. While the process dynamics of equally pitched end mills can be modeled by non-autonomous differential equations with a single constant delay, the dynamics of unequally pitched end mills lead to differential equations with multiple constant delays. In this paper the process stability of an unequally pitched end mill is investigated experimentally and theoretically. The numerical approximation of the stability limit relies on two fundamental methods: Ackermann's method to control systems with delay and the method of the piecewise constant subsystems. On the basis of these two methods two ways for the theoretical stability analysis are derived. The first way neglects the time dependency of the system by replacing the time varying system matrices by their means. The second way accounts for the time dependency of the system by combining Ackermann's method to control systems with delay with the method of the piecewise constant subsystems, which results in the semi-discretization method. Besides the exemplary investigation of a specific end mill the two methods are compared for a simple one degree of freedom system for different number of teeth, different alternating and linear tooth pitch variations and different helix angles. It is shown, that unlike equally pitched end mills also at high radial immersions the time dependency of the system leads to significant differences between the stability limits of the unequally pitched end mills, predicted by the two methods. Depending on the time variance of the system and the unequal tooth pitch stable islands can arise, which are largely located within the stable peaks of the stability diagram of the system where the time varying system matrices are replaced by their means. The correctness of the results are backed up for several operating points by time domain simulations, taking into account the trochoidal movement of the cutting edges, the time varying character of the system and teeth jumping out of contact.

MAXIMIZATION OF CHATTER-FREE MATERIAL REMOVAL RATE IN END MILLING USING ANALYTICAL METHODS

ABSTRACT Chatter vibrations in milling, which develop due to dynamic interactions between the cutting tool and the workpiece, result in reduced productivity and part quality. Various numerical and analytical stability models have been considered in the previous publications, where mostly the stability limit of axial depth of cut is emphasized for chatter-free cutting. In this paper an analytical stability model is used, and a simple algorithm to determine the stability limit of radial depth of cut is presented. It is shown that, for the maximization of chatter-free material removal rate, radial depth of cut is of equal importance with the former. A method is proposed to determine the optimal combination of depths of cut, so that chatter-free material removal rate is maximized. The application of the method is demonstrated on a pocketing example where significant reduction in the machining time is obtained using the optimal parameters. The procedure can easily be integrated to a CAD/CAM or virtual machining environment in order to identify the optimal milling conditions automatically.

Maximizing Chatter Free Material Removal Rate in Milling through Optimal Selection of Axial and Radial Depth of Cut Pairs

Chatter vibrations in milling, which develop due to dynamic interactions between the cutting tool and the workpiece, result in reduced productivity and part quality. Several stability models have been considered in previous publications, where mostly the stability limit in terms of axial depth of cut is emphasized for chatter free machining. In this paper, it is shown that, for the maximization of chatter free material removal rate, radial depth of cut is of equal importance. A method is proposed to determine the optimal combination of depths of cut, so that chatter free material removal rate is maximized. The application of the method is demonstrated on a pocketing example where significant reduction in the machining time is obtained using the optimal depths. The procedure can easily be integrated to a CAD/CAM system or a virtual machining environment in order to identify the optimal milling conditions.