The experimental determination of stability lobe diagrams (SLDs) in milling can be realized by either continuously varying the spindle speed or by varying the depth of cut. In this paper, a method for combining both these methods along with an online chatter detection algorithm is proposed for efficient determination of SLDs. To accomplish this, communication between the machine control and chatter detection algorithm is established, and the machine axes are controlled to change the spindle speed or depth of cut. The efficiency of the proposed method is analyzed in this paper.

In milling, the dynamic behavior of the tool center point is crucial for estimating surface quality of the workpiece as well as the process stability behavior. Experimental-analytical receptance coupling can be used for predicting the tool tip dynamics but requires accurate analytical modelling of the holder-tool assembly. This includes the reliable identification of the holder-tool joint properties as well as the correct modelling of the fluted segment of end mills. However, the modelling effort associated with accurately representing the dynamic behavior of the fluted segment is significant. In addition, the joint identification requires a reference tool tip frequency response function of the tool assembly clamped in the machine spindle. This is inefficient and can also lead to incorrect estimation of joint properties. This paper provides an efficient method for joint identification and fluted section modelling using an offline, free–free excitation approach. The objective of this paper is to enable a direct comparison of the dynamic behavior of the freely constrained analytical tool assembly model with that of the real freely constrained tool assembly. The comparison of displacement to force frequency response at certain points on the tool assembly allows for the identification of tool model parameters such as the joint properties and effective diameter of the fluted segment. The comparability is realized by extending the analytical holder-tool beam model to include the receptance model of the standard spindle-holder interface. In this study, as an example, a thermal shrink-fit holder-tool beam model is extended to include an HSK-A63 interface. Subsequently, frequency response functions at two points on the real freely constrained tool assembly are measured in order to identify the joint stiffness and effective diameter of the fluted segment using the corresponding proposed formulations. The updated holder-tool model is then coupled with a 4-axis milling machine and validated. Despite the reduced modelling effort, a good prediction accuracy could be achieved for different holder-tool combinations.

Um Stabilitätskarten für Fräsprozesse effizient zu erstellen, bietet sich eine kontinuierliche Variation der Drehzahl an. Jedoch kann die permanente Änderung der Drehzahl zu einer Verfälschung der tatsächlichen Stabilitätsgrenzen führen. Dieser Fachbeitrag analysiert den Einfluss der Spindeldrehzahlvariation auf die Stabilitätsgrenzen bei Fräsversuchen mit verschiedenen Drehzahlbeschleunigungen. Für das Erkennen der Stabilitätsübergänge wird eine Rattererkennungssoftware eingesetzt.   Milling with varying spindle speed allows an efficient determination of instabilities. However, spindle speed variation may also influence the actual stability boundary with constant spindle speed. This paper analyzes the influence of spindle speed variation on the stability limits by evaluating milling trials at different spindle accelerations. For the detection of instability and stability during cutting trials, a time-domain chatter detection software was enhanced, validated and implemented.

Stability boundaries in milling operations can be determined either analytically or experimentally. Since analytical determination depends on several assumptions and approximations, experimental methods offer a realistic alternative. This however, requires numerous milling trials with different process parameters the results of which are then illustrated in a stability lobe diagram. Although the methods for rapid experimental determination of stability boundaries such as continuously increasing depth of cut and continuously increasing cutting speed have been suggested in literature, they have not been adequately evaluated for their accuracy and limitations. In the current paper, the method of continuously increasing depth of cut is analysed. For this, a Poincaré-section based real time chatter detection algorithm was firstly calibrated. Subsequently, this algorithm was run along with milling trials with continuously increasing depth of cut by inclining the work piece. The influence of the inclination angle on the stability boundary could then be analysed.

The article describes modifications to the effector of a manipulator arm proposed in order to increase the accuracy of jaw force measurements. Gripping force measurement is performed using strain gauges. Their proper positioning and connection minimize not only the influence of the position of the centre of gravity of the manipulation object on the jaws but also the effect of temperature changes around the measuring area. The possibility of altering the magnitude of gripping force was incorporated into the robot control application. This greatly increases the security of handling and increases the number of items that can be possibly gripped. Modified effector parts were subjected to stress analysis, with emphasis on the elimination of stress peaks that would not occur in real parts. The article also describes the design of the mechanical modification of the effector, which would allow the continuous rotation of the jaws of the effector.