Papers by Keyword: Stability Lobe

Abstract: Chatter vibration in end milling remains a serious problem for manufacturing engineers. Chatter vibration often leaves a characteristic pattern or chatter mark on the machined surface. Chatter marks are generated by the relative displacement of the tool and the workpiece. Closer observation of chatter marks may prove useful in understanding chatter vibration. In this study, we investigated chatter mark patterns on end-milled surfaces. Based on these observations, we proposed and demonstrated the effectiveness of an iterative analysis method to identify stable machining conditions and minimize chatter vibration in various operations without use of sensors under specific conditions.

Abstract: In this paper, time domain simulation has been carried out to study the chatter stability of milling process. Dynamic chip thickness is calculated by analyzing the kinematics of the cutter, and thus dynamic governing equation revealing the dynamic behaviors between the cutter and workpiece is established. Solving framework is constructed by using the Simulink module and S-Function of Matlab software, and dynamic deflection is achieved with the four-order Runge-Kutta algorithm. With the simulated cutting forces, a criterion for the construction of the stability lobe is suggested. At the same time, algorithm for the prediction of the surface topography involving the dynamic response of the machining system is developed.

Abstract: By disrupting the regenerative effect, milling cutters with variable-pitch are usually used to improve stability. Since high interrupted cutting processes, such as low radial immersion case, will result in more nonlinear phenomena and some consequent differences of stability chart, in this paper, an improved semi-discretization algorithm is utilized to predict the stability lobes for variable-pitch milling under low radial immersion ratios, the focus of the current manuscript is to investigate the stability trend caused by tool geometries. In addition, the chart differences in the cases of low and high radial immersion milling are also discussed by comparisons. Under certain combinations of parameters, some phenomena, like bunch of isolated island and flip bifurcation region are described, and some influences of tool geometries on stability trends are shown and explained.

Abstract: Milling is one of the most common materials removal processes used in the production of dies, moulds and various aeronautic components. The process performances such as dimensional accuracy, chatter propagation and tool wear are the common problems which can lead to useless workpiece. The traditional method to avoid these problems is the so-called trial and error method, which often has the characteristics of time-consuming. With the advancement of recent computing techniques, one efficient method to determine acceptable process parameters is development of a comprehensive simulation environment. In this paper, efforts are focused on the introduction of a milling simulation procedure proposed recently by the research group of the authors. The key issues such as development of cutting force model, prediction of dimensional errors and stability lobes are described. At the same time, the crucial issues such as calibration of model parameters and simulation algorithms are also highlighted.

Abstract: Particle reinforced aluminium matrix composites could be used in manufacturing of aviation thin-walled workpiece due to its excellent performances, but it is hard to be manufactured. Rotary ultrasonic machining (RUM) is very suitable for machining particle reinforced aluminum matrix composites with moderate or high volume fraction. Chatter appears very easily in machining process of thin-walled workpiece and it can seriously reduce the quality of components. Based on the dynamic characteristics of machining process, a stability analytical model is built. It is analyzed that the process stability of a thin-walled workpiece of SiCp/Al composites reinforced with 45% volume fraction, and the stability lobe diagram is plotted by using MATLAB. According to stability analysis results, a machining experiment is conducted and the test results indicate chatter could be prevented effectively by this method.

Abstract: The eco-friendly and economic challenges are driving more and more aerostructure components with thin wall and deep pocket features. These features are getting thinner and deeper and become impractical during part manufacturing. Therefore, there is a need to better understand the mechanics, kinematics and dynamics of thin wall machining (which is the focus in this paper). In this paper, the application of a newly discovered relationship between the workpiece geometry and its damping parameters in the machining of aerospace structures is presented. This relationship allows for the prediction of damping ratios, without the use of experimental results for any wall with a different thickness compared to a reference wall. A previously proposed ‘improved stability lobes model’ is used to validate the damping model, as this model considers the nonlinearity of the cutting force coefficients. While a finite element method (FEM) is used to obtain natural frequencies and modal stiffness’s at different locations along the workpiece or toolpath, required in the stability model. The advantage of this new damping model is that, it alleviates the burden of having to carry out modal experiments to obtain the damping parameters required for subsequent stability margin predictions, as the work-piece thickness changes during machining.

Abstract: This paper investigates the effects of the cutting tool edge radius on the cutting forces and stability lobes in micro-milling. The investigation is conducted based on recently developed models for prediction of micro-milling cutting forces and stability lobes. The developed models consider the nonlinearities of the micro-milling process, such as nonlinear cutting forces due to cutting velocity dependencies, edge radius effect and run-out presence. A number of finite element analyses (FEA) are performed to obtain the cutting forces in orthogonal cutting which are used for determining the micro-milling cutting forces. The chip morphology obtained for different tool edge radii using FEA is presented. It is observed that at large tool edge radii the influence of the ploughing effect become more significant factor on the chip morphology. The results related to micro-milling cutting forces and stability lobes show that by enlarging the tool edge radius the micro-milling cutting forces increase while the stability limits decrease.

Abstract: The stability of cutting system is an important research in high-speed machining area. It is widely used in engineering practice. First, this paper studies the milling forces and their change law when milling aluminum alloy through orthogonal experiment. And it solves the milling coefficients. Second, it modal parameters of milling system such as natural frequency, modal mass and equivalent stiffness by hammer experiment. On this basis, it draws the stability lobe about the spindle speed and radial depth of cut and verifies the accuracy of the stability lobe.

Abstract: Milling process will be dominated by multiple delays due to the effect of the cutter runout or the pitch angles of the cutter. In this paper, research efforts are focused on the dynamic behavior of milling processes under different cutting condition parameters such as different radial immersions, feed directions, feeds per tooth and helix angles. To improve the prediction accuracy of stability lobe, the combined influences of feed rate and cutter runout on the stability lobes are also taken into account. The basic principle of the method presented in one existing work is applied to examine the asymptotic stability trends for both down milling and up milling. Some new phenomena for certain combinations of cutting parameters are shown and explained in detail. It is found that as cutter runout occurs, feed per tooth, feed direction and cutter helix angle have great effects on the stability lobes.

Abstract: Flexible parts such as turbine blade, blisk and monolithic components are widely used in the aeronautical industry, and high Speed Machining (HSM) technology is used to increase productivity and reduce production costs. Chatter is an undesirable phenomenon in high speed machining processes because of deteriorative surface finish, early cutting tool failure and unexpected machine tool damage. It can be avoided in higher speed milling processes if stability lobes is determined. In this paper, a non-linear regenerative force model is applied to a bull-nose tool geometry in order to obtain the machine operation stability lobes. An analytical-experimental method is proposed to obtain the stability lobes during high speed milling flexible parts with bull-nose end mills. The method is calculated and validated.