Papers by Keyword: Chatter Vibration

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: Chatter vibration generated by coupling a work-piece, machine tools, and cutting tool is a serious problem for engineers. A regular pattern forms the machined surface when chatter vibration occurs. There must be a direct relationship between the relative displacement and machined surface. We propose a method for controlling chatter vibration of end-milling from a machined surface. Hammering tests were first carried out to determine the natural frequencies of machine tools and the tool system, which are likely to be the cause of vibration. We also propose a technique of applying reverse analysis to end-milling surfaces. The machined surface is assumed to include an essential index to easily control chatter vibration at the factory. We found that chatter vibration occurs near the frequency of the cutting tool, tool holder, and their coupling, not at the natural frequency, and the chatter vibration frequency can be calculated by analyzing the surface pattern and cutting conditions. Moreover, the proposed method was effective in analyzing chatter vibrations including more than two kinds of natural frequencies at the same time.

Abstract: Chatter vibrations and tool deflection are common challenges in metal cutting processes. In roughing operations, it is often the occurrence of chatter vibrations which limits the productivity. While finishing, when tolerances are small, the tool deflection can lead to violating tolerances and thus producing scrap parts. Beside the tool and tool holder, it is also the guidance system, especially in the z-axis, which influences the aforementioned phenomena. In this paper the influence of an electromagnetic guided z-axis is presented. It is focused on the influence of the high damping and the high static stiffness of the guide. Further benefits of this technology are outlined.

Abstract: Lapping is possible to produce excellent surface finish with higher geometrical form. Additionally, automated lapping process is perfectly suited with todays industry requirements and also economically advantage over other manufacturing processes. This research is devoted to study the characteristics of the lapping process for mirror-like surface finishing by using the linear motor lathe. In the process of mirror-like finish, various factors that effect on rate of material removal, limit surface roughness and geometrical form improvement were examined on low, medium and high hardness materials by series of experiments. The conclusion shows that active grain characteristics, hardness ratio, lapping pressure, lapping speed, residual stress and chatter vibration on the work surfaces all have influenced on the mirror-like surface finishing process.

Abstract: Chatter vibration in cutting processes usually leads to surface finish degradation, tool damage, cutting noise, energy loss, etc. Self-excited vibration particularly seems to be a problem that is easily increased to large vibration. The regenerative effect is considered as one of the causes of chatter vibration. Although the chatter vibration occurs in various types of processing, the end-milling is a typical process that seems to cause the chatter vibration due to a lack of rigidity of one or more parts of the machine tools, cutting tool, and work-piece. The aim of our research is to propose a simple method to control chatter vibration of the end-milling process on the basis of a coupling model integrating the related various elements. In this study, hammering tests were carried out to measure the transfer function of a machine tool and cutting tool system, which seems to cause vibration. By comparing these results, finite elemental method (FEM) analysis models were constructed. Additionally, cutting experiments were carried out to confirm the chatter vibration frequencies in end-milling with a machining center. In the hammering tests, impulse hammer and multiple acceleration pick-ups are connected to a multi-channel FFT analyzer and estimate the natural frequencies and natural vibration modes. A simplified FEM model is proposed by circular section stepped beam elements on the basis of the hammering test results, considering a coupling effect. In comparisons of the calculated results and hammering test results, the vibration modes are in good agreement. As a result, the proposed model accurately predicts the chatter vibration considering several effects among the relating elements in end-milling. Moreover, it can be seen that the chatter vibration is investigated from a viewpoint of the integrating model of the end-milling process.

Abstract: The paper presents the method of the surveillance of the self-excited chatter vibration. At first, the workpiece modal parameters are estimated based on experimental data which leads to verification of computational model. Then, for selected surface points optimal spindle speeds are calculated. By considering sufficient amount of points it is possible to build a map of optimal spindle speeds. Experimental results show that this map may be used effectively for eliminating chatter in case of the process of ball end milling of a curved flexible detail.

Abstract: Airspace industry components frequently need high added value part including some featuredifficult to manufacture. One of the best example is the thin walls of parts (airplanes frames orthe turbine blades) that have a very low stiffness. The finishing operations for high height to thicknessratio parts lead to chatter vibrations, unacceptable dimensional errors or poor surface finish. The optimalmachining strategy determination is often based on trial and error and may not be cost effective(acceptable conditions can be far from the optimum). Simulation of the milling process is a powerfulmean to accelerate the search for better cutting parameters. Cutting forces, vibrations, geometricerrors or roughness can be predicted before the production of the first parts. The classical mechanisticapproach is even though limited while machining flexible parts because the dynamic response ofthe workpiece changes with the position of the cutter. The objective of this paper is to demonstratethe adaptation of numerical simulation of milling operation for the machining of thin-walled plates.Three complementary approaches are developed: location-dependent stability lobes, quasi static approachand full dynamic simulation. Location dependent stability lobes extend the classical theoryto take into account the variation of dynamic response along the workpiece. Quasi static approach isintended to deal with form error during chatter-free machining operations. Full dynamic simulation isa more complex approach intended to simulate the behavior of the complete tool/machine/workpiecesystem. The numerical approach is compared to experimental tests performed on thin plate of titaniumalloys.

Abstract: The present study considers the state-dependent delay differential equations (SD-DDEs) for the turning process. In general, series expansion of the SD-DDEs turning system is essential in the nonlinear analysis such as the conventional methods of multiple scales and harmonic balance. Unfortunately, the mathematical theory of SD-DDEs, especially for those with an implicit function of delay, was just recently developed and any rigorous mathematical theory has not yet been proven. As one approach for the nonlinear analysis of the SD-DDEs, physically reasonable results could be obtained by extending the general theory of DDEs to the SD-DDEs through the use of the series expansion in conjunction with the implicit function, although there still remains an open issue of its mathematical rigorousness. The other approach may be treating the original SD-DDEs directly. To this end, the high-dimensional harmonic balance (HDHB) analysis is performed in this study in order to investigate the nonlinear behaviors of the turning system in the form of SD-DDEs without its series expansion. The results obtained by HDHB analysis are validated by comparing results with those of direct time integration. Using the resulting bifurcation diagrams, nonlinear chatter behaviors of the turning system are examined and discussed.

Abstract: The research of cutting force and vibration has been gaining significant attention to improve machining efficiency and tool life in processing metals. In this paper, the plunge milling system is reduced to 3-DOF vibration system, and dynamical theoretical model and instantaneous undeformed chip thickness models are established based on dividing cutter tooth into finite number of small differential elements in the radial direction and discrete time domain. Based on regenerative chatter theory, the cutting force and vibration can be simulated by numerical algorithm. Compared the simulation results with experiments data, the milling force and vibration have a good agreement, which testify the correction of those models

Abstract: In this paper, productivity and self-excited vibration are simultaneously optimized using multiobjective optimization in cutting process. At high material removal rate, machining processes accelerates tool wear, poor surface finish and failure of machine parts. The effect of self-excited vibration or chatter prevents high machining productivity. This chatter vibration can be avoided by modifying tool geometry at low material removal rate but not at high productivity. To compensate material removal rate and chatter, multiobjective optimization is applied using ε-constraint algorithm to achieve a Pareto front solution. Differential Evolution as intelligent optimization algorithm is shown better results than traditional technique of Sequential Quadratic Programming.