Chatter Stability Research Articles

Study of optimization of blade non-uniform allowance process and chatter stability domain

In addressing the phenomenon of chatter during the machining of thin-walled components, a machining strategy involving the implementation of a continuous non-uniform toolpath has been proposed as a remedy for chatter suppression. The methodology commences with a meticulous determination of machining allowances, accomplished by utilizing fitting functions. Subsequently, the stiffness coefficients and natural frequencies inherent to the workpiece-tool system are extracted through modal analysis. A stability lobes diagram is formulated, employing the principles of regenerative chatter analysis. This diagram encompasses both uniform toolpath scenarios and non-uniform continuous toolpath scenarios, with the latter established via the least squares method. The resultant stability lobes diagram effectively delineates the boundaries within which chatter remains stable, under varying depths of cut. The stability lobes diagrams substantiate the effectiveness of the non-uniform continuous toolpath constructed via the least squares method in significantly augmenting the inherent stiffness coefficient of the workpiece-tool system, thereby mitigating chatter. This approach serves as a valuable guide for the manufacturing of intricate curved thin-walled components.

Stability Analysis in Milling Based on the Localized Differential Quadrature Method.

Chatter stability analysis is an effective way to optimize the cutting parameters and achieve chatter-free machining. This paper proposes a milling chatter stability analysis method based on the localized differential quadrature method (LDQM), which has the advantages of simple principle, easy application, and high computational efficiency. The milling process, considering the regeneration effect, is modeled using linear periodic delay differential equations (DDE), then the state transition matrix during the adjacent cutting period is constructed based on the LDQM, and finally, the stability of the milling process is obtained based on the Floquet theory. The accuracy and computation efficiency of the proposed method are verified through two benchmark milling models. The simulation results demonstrate that the proposed method in this paper can accurately and quickly obtain the chatter stability lobe diagram (SLD) of the milling process, which will provide guidance for optimizing the process parameters.

Enhancing Chatter Stability for Milling Thin-Walled Blades by Designing Non-Uniform Allowance

During the milling of thin-walled blades, the removal of material exhibits strong time-varying dynamics, leading to chatter and a decrease in surface quality. To address the issue of milling vibrations in the machining of complex thin-walled blades used in aerospace applications, this work proposes a process optimization approach involving non-uniform allowances. The objective is to enhance of he stiffness of the thin-walled parts during the milling process by establishing a non-uniform allowance distribution for the finishing process of thin-walled blades. By applying the theory of sensitive process stiffness and conducting finite element simulations, two processing strategies, namely uniform allowances and non-uniform allowances, are evaluated through cutting experiments. The experimental results demonstrate that the non-uniform allowance processing strategy leads to a more evenly distributed acceleration spectrum and a 50% reduction in amplitude. Moreover, the surface exhibits no discernible vibration pattern, resulting in a 35% decrease in roughness. The non-uniform allowance-processing strategy proves to be effective in significantly improving the rigidity of the thin-walled blade processing system, thereby enhancing the stability of the cutting process. These findings hold significant relevance in guiding the machining of typical complex thin-walled aerospace components.

Chatter Avoidance by Spindle Speed and Orientation Planning in Five-Axis Ball-End Milling of Thin-Walled Blades

Abstract Selecting suitable cutting conditions is crucial in maintaining chatter stability and achieving acceptable surface quality. However, the selection of a constant set of cutting parameters is not feasible due to the time-varying dynamics of highly flexible thin-walled blades. This paper presents an optimal selection of tool orientation and spindle speed along the tool path as the metal is removed during the ball-end milling of blades. The effects of tool orientation and speed on the mechanics and dynamics of the ball-end milling process are formulated. Test case simulations are used to demonstrate the impact of tool orientation and speed on chatter stability and forced vibrations. The proposed algorithm identifies the optimal spindle speed and tool orientation by continuously updating the workpiece dynamics as a function of time and tool position to achieve improved stability and surface quality. Stability simulations are conducted to assess the optimization approach's performance, and the results are compared with experiments by machining a series of thin-walled twisted fan blades.

Prediction of time-varying dynamics and chatter stability analysis for surface milling of thin-walled curved CFRP workpiece

Machining curved surfaces for thin-walled components is always challenging. Due to the strong anisotropic features of carbon fiber reinforced plastic (CFRP), new challenges, such as prediction accuracy loss, have emerged for avoiding the chatter of machining thin-walled curved CFRP workpieces. This paper studied the influence of the anisotropic properties of CFRP workpieces and time-varying dynamics on surface milling stability. An improved damping and time-varying dynamics prediction model was proposed integrated with FEA and numerical calculation considering the change of cutting position, the materials removed, and the anisotropic features of CFRP. Then, the 3D stability lobe diagram (SLD) was achieved by considering the dynamic change at each cutter point on the machining path and dynamic cutting forces based on the instantaneous fiber cutting angle. Based on the obtained 3D SLD, CFRP milling chatter could be accurately avoided, and machining efficiency could be improved. A case study of milling a thin-walled toroidal surface was conducted for validation. In the machining process of CFRP, unlike homogeneous materials such as metals, the natural frequency of CFRP fluctuates nonlinearly with the change curve of material removal within a specific range. Under a higher material removal rate, the surface roughness of the machined surface has been reduced by 74%, Ra below 2.35 µm, based on the selected process parameters of the novel-established SLD, compared to the surface roughness, Ra close to 9.21 µm, obtained by the previous method without considering the time-varying dynamics.

A method to predict chatter stability accurately in milling thin-walled parts by considering force-induced deformation

Thin-walled parts are susceptible to deformation and chatter in milling due to their low rigidity, which can negatively affect machining quality and efficiency. Deformation induced by cutting force has an impact on chatter stability, making it difficult to predict the stability of the milling system accurately. To address the above issue, this paper presents a systematic study on the force-induced deformation and chatter stability, with a fast method for calculating the deformation and predicting the chatter stability accurately. Firstly, a dynamic model for milling thin-walled part and a finite element model for calculating force-induced deformation were established. The mechanism of the deformation on chatter stability was analyzed. Secondly, a method for quickly calculating the force-induced deformation using a surrogate model of radial basis function neural network was proposed. The model was built using a small amount of finite element simulation data, which can accurately predict the deformation and its distribution. Finally, the chatter stability was predicted by the obtained dynamic parameters and validated by the milling tests. The results indicate that this method can reduce computation time and improve prediction accuracy evidently.

Identification and effect of chip shear band on chatter vibration in the turning of Nickel Alloy 718

Shear bands occur during the machining of high-strength materials such as Nickel and Titanium alloys. Shear bands lead to segmented chips, which in turn causes fluctuation in the force that excites vibrations. In some cutting conditions, it is difficult to distinguish regenerative chatter from the shear bands because both originate from chip thickness oscillations. This paper presents the relationship between the chip segmentation and regenerative chatter in turning Alloy 718. The tests are conducted with tool holders having different flexibilities, hence natural frequencies. The chatter stability diagrams with process damping effect are predicted first, followed by experiments in stable and unstable zones. It is observed that, at low-speed machining of Alloy 718, the chip segmentation is caused by chatter. At high speeds, thermo-mechanical induced adiabatic shear dominates the chip segmentation but may become coupled with the relative vibrations between the tool and workpiece. While chatter occurs close to a dominant natural frequency of the structure, shear banding frequency is dependent on the cutting speed and chip thickness and may occur at a distinct frequency.

Reliability analysis of regenerative chatter stability in turning tool systems by modified control variate method

Reliability analysis of regenerative chatter stability in turning tool systems by modified control variate method

Virtual Dynamics Model for 5-axis Machining of Thin-Walled Blades

Abstract The five-axis ball-end milling dynamics of thin-walled blades is presented. The cutting forces are predicted from the ball end mill–blade geometry engagement maps along the tool path. The Frequency Response Function (FRF) of the thin-walled blade is predicted using Finite Element shell elements, and it is updated along the toolpath as the metal is removed. The predicted cutting forces are applied on both the workpiece and tool FRFs to predict the forced vibrations and chatter stability at each tool location. A simplified method to update the cutter–workpiece engagement (CWE) is used to obtain the three-dimensional stability lobe diagram at each desired point on the blade. The integrated model is used to simulate the 5-axis machining of thin-walled blades in the digital environment. The proposed digital model is experimentally validated by machining a series of thin-walled rectangular plates and a twisted fan blade.

Generalized model for dynamics and stability of milling of titanium alloys by integrating process damping, multiple modes and multiple delays

Machining dynamics modelling and chatter stability prediction are important for milling of titanium alloys to improve machining productivity and surface quality. Since titanium alloys are typically machined at low spindle speeds, process damping plays an important role in dynamics and stability of milling of titanium alloys. What is more, multiple modes and multiple delays, resulting from the complexity of milling systems and processes, significantly affect chatter stability of milling. However, there is a lack of comprehensive dynamical models capable of studying how these three factors influence chatter stability. To address this gap, this paper proposes a generalized dynamic model for milling of titanium alloys considering process damping, multiple modes and multiple delays. A time-domain chatter prediction method related to the generalized dynamic model is proposed by extending the Gaussian quadrature-based method. Experiments are conducted on multi-mode cutting systems using both uniform and variable pitch cutters to validate the proposed dynamic model and chatter prediction method. The impacts of multiple modes and multiple delays on chatter stability are investigated considering the presence of process damping. Experimental validation and simulation show that in order to accurately predict chatter stability of milling of titanium alloys at low spindle speed, all dynamic modes should be taken into account whether the modes are well separated or not. Even if the low-frequency modes are much more rigid than the high-frequency modes, low-frequency modes may be dominant in milling of titanium alloys and should be considered in the prediction procedure of chatter stability. In addition, it is observed in both simulations and experiments that variable pitch angles can improve the chatter stability limit in the process damping zone.

Prediction of in-process frequency response function and chatter stability considering pose and feedrate in robotic milling

Prediction of in-process frequency response function and chatter stability considering pose and feedrate in robotic milling

Prediction of a chatter stability of thin-walled parts during high-speed milling considering a variation of dynamic characteristics based on surface roughness measurement

Prediction of a chatter stability of thin-walled parts during high-speed milling considering a variation of dynamic characteristics based on surface roughness measurement

A Hybrid Full-Discretization Method of Multiple Interpolation Polynomials and Precise Integration for Milling Stability Prediction

As milling chatter can lead to poor machining quality and limit the efficiency of productivity, it is of great significance to learn about milling chatter stability and research the effective and fast prediction of milling stability. In this study, a hybrid full-discretization method of multiple interpolation polynomials and precise integration (HFDM) is proposed for milling stability prediction. Firstly, the third-order Newton interpolation polynomial, third-order Hermite interpolation polynomial and linear interpolation are applied to approximate the state term, delay term and periodic coefficient matrix, respectively. Meanwhile, the matrix exponentials can be calculated based on the precise integration algorithm, which can improve computational accuracy and efficiency. The numerical simulation results indicate that the proposed method can not only effectively generate a stability lobe diagram (SLD) but also obtain better prediction accuracy and computation efficiency. A milling experiment is offered to demonstrate the feasibility of the method.

Prediction of Chatter Stability in Bull-Nose End Milling of Thin-Walled Cylindrical Parts Using Layered Cutting Force Coefficients

During the bull-nose end milling operations of thin-walled structures, chatter usually occurs and adversely affects cutter performance, finished surface quality, and production efficiency. To accurately predict chatter stability, a suitable dynamic model with effective system parameters is required. In this article, a three-degree-of-freedom (3-DOF) dynamic model is developed to analyze the milling stability of the thin-walled cylinders, in which the dynamics of the bull-nose end mill along the x-axis and y-axis directions and the dynamic of the workpiece along the z-axis direction are taken into account. Then, the cutter-workpiece engagement (CWE) is extracted by employing a slice-intersection-based approach. And the layered cutting force coefficients are identified by considering the influences of varying cutter diameters on the cutting speed. Thereafter, the semi-discretization method (SDM) is adopted to compute the stability lobe diagram (SLD). In the end, a group of milling tests are carried out on a thin-walled cylinder to validate the accuracy and reliability of the proposed model, and the results show that the model predictions agree well with the experimental data.

Dynamic Modeling and Stability Prediction of Robot Milling Considering the Influence of Force-Induced Deformation on Regenerative Effect and Process Damping

Undesirable chatter is one of the key problems that restrict the improvement of robot milling quality and efficiency. The prediction of chatter stability, which is used to guide the selection of process parameters, is an effective method to avoid chatter in robot milling. Due to the weak stiffness of the robot, deformation caused by milling forces becomes an unavoidable problem, which will change the tool–workpiece contact area and affect the stability prediction. However, it is often simplified and neglected. In this paper, a multipoint contact dynamic model of robot milling is established, which considers the influence of force-induced deformation on the regenerative effect and process damping. The tool–workpiece contact area is discretized into a finite number of nodes along the axial direction so that the force and deformation at each node can be calculated separately. The different contact forms of the tool–workpiece under different process parameters are discussed in different cases, and the interaction process between cutting force and force-induced deformation is analyzed in detail. An iterative strategy is used to calculate the deformation of each node and the result of the tool–workpiece contact boundary. Finally, chatter stability of robot milling is predicted by a fully discrete method. Robot milling experiments were carried out to verify the predicted results. The results show that force-induced deformation is an important factor improving the stability prediction accuracy of robot milling, and a more accurate prediction result can be obtained by simultaneously considering force-induced deformation and process damping.

Implementation of Inerter-Based Dynamic Vibration Absorber for Chatter Suppression

AbstractChatter is one of the major issues that cause undesirable effects limiting machining productivity. Passive control devices, such as tuned mass dampers (TMDs), have been widely employed to increase machining stability by suppressing chatter. More recently, inerter-based devices have been developed for a wide variety of engineering vibration mitigation applications. However, no experimental study for the application of inerters to the machining stability problem has yet been conducted. This article presents an implementation of an inerter-based dynamic vibration absorber (IDVA) to the problem of chatter stability, for the first time. For this, it employs the IDVA with a pivoted-bar inerter developed in the study by Dogan et al. (2022, “Design, Testing and Analysis of a Pivoted-Bar Inerter Device Used as a Vibration Absorber, Mechanical Systems and Signal Processing,” 171, p. 108893) to mitigate the chatter effect under cutting forces in milling. Due to the nature of machining stability, the optimal design parameters for the IDVA are numerically obtained by considering the real part of the frequency response function (FRF), which enables the absolute stability limit in a single degree-of-freedom (SDOF) to be maximized for a milling operation. Chatter performance is experimentally validated through milling trials using the prototype IDVA and a flexible workpiece. The experimental results show that the IDVA provides more than 15% improvement in the absolute stability limit compared to a classical TMD.

A whole discretization method for milling stability prediction considering the discrete vibration velocities

The discretization methods have been widely used for chatter stability prediction and can be divided into two categories: semi-discretization methods (SDMs) by discretizing the time-delayed displacements, and full-discretization methods (FDMs) by discretizing both the present and time-delayed displacements. In this paper, a whole discretization method is proposed to achieve a faster and more accurate prediction for the milling stability. In addition to the discrete vibration displacements, the discrete vibration velocities are included in the solution by rebuilding the integrated matrix. The prediction error caused by the separate discretization of the cutting force coefficient matrix and vibration state variables can be avoided. The milling stability is determined with the discrete map of the state based on the Floquet theory. The proposed model is compared with the zeroth-order SDM and the first-order FDM which also approximate the solution with two neighboring discrete state variables. It is shown that the local discretization error based on the proposed method achieves o((Δt)5), which is three orders higher compared to the zeroth-order SDM and the first-order FDM. In addition, when the same prediction errors are required, the computational time of the proposed method is 11–14% of the zeroth-order SDM, and 24–27% of the first-order FDM. The results prove that considering vibration velocity can increase the efficiency and accuracy of the chatter stability prediction compared to existing SDM and FDM algorithms.

Chatter stability of robotic rotary ultrasonic countersinking

In recent years, industrial robots have received extensive attention in manufacturing field due to their high flexibility and great workspace. However, the weak stiffness of industrial robots makes it extremely easy to arouse chatter, which affects machining quality inevitably and generates noise pollution in severe cases. Compared with drilling, the chatter mechanism of robotic countersinking is more complex. The external excitation changes with cutting width and depth in countersinking. This characteristic results in time-varying and nonlinearity of robotic countersinking dynamics. Thus, it is urgent to propose a new method of chatter suppression and provide an accurate stability analysis model. As a new special machining technology, rotary ultrasonic machining has been proved to improve robotic drilling and milling stability effectively. Based on this, robotic rotary ultrasonic countersinking (RRUC) is proposed to improve the robotic countersinking stability in this paper. A three-dimensional stability domain method of RRUC is established. First, the countersinking process was divided into ρ parts. The dynamic model of every unit was constructed based on ultrasonic function angle (γ) and dynamic chip area. Then, the stability region of RRUC is obtained based on the semi-discrete method (SDM). Compared with the robotic conventional countersinking (RCC), RRUC improves the stability by 27%. Finally, the correctness and effectiveness of the stability region model are proved by robotic ultrasonic countersinking experiments.

Predictive model of surface roughness in milling of 7075Al based on chatter stability analysis and back propagation neural network

Predictive model of surface roughness in milling of 7075Al based on chatter stability analysis and back propagation neural network

A State-of-the-Art Review on Chatter Stability in Machining Thin−Walled Parts

Thin−walled parts are widely used in many important fields because of performance and structural lightweight requirements. They are critical parts because they usually carry the core functions of high−end equipment. However, their high−performance machining has been facing severe challenges, among which the dynamics problem is one of the most important obstacles. The machining system is easily subjected to chatter due to the weak rigidity of the thin−walled structure and slender cutting tool, which significantly deteriorates the surface quality and reduces the machining efficiency. Extensive studies aiming at eliminating machining chatter have been carried out in the recent decades. This paper systematically reviews previous studies on the identification of system dynamic characteristics, modeling and prediction of chatter stability, and chatter elimination/suppression methods and devices. Finally, existing problems are summarized, and future research is concluded.