Milling Process Of Thin-walled Workpiece Research Articles

Исследование влияния элементов режима и шага зубьев фрезы на технологические параметры и температурное поле процесса обработки заготовок тонкостенных деталей

When machining workpieces of thin-walled parts, the temperature field differs from the field, which is formed during massive workpieces treatment. The reason for this is that machining of a thin-walled billet is interfered with its surface, being opposite to the one under machining. It has a significant effect on the temperature field, since the intensity of heat removal from this surface into the environment is significantly less than heat removal into the underlying layers of a massive material blank. In this regard, the problem of finding a rational mode of the machining process of thin-walled workpieces is relevant. The aim of the study is to determine the effects of the elements of the milling mode of thin-walled workpieces and milling cutter teeth space on the technological parameters of the milling process of titanium alloy workpieces and to develop recommendations for choosing this milling mode. For this purpose, a numerical modeling of the technological parameters of the milling process of blanks of massive workpieces and thin-walled parts made of titanium alloy, was performed experiencing various combinations of feed to the milling cutter tooth, cutting speed and milling cutter teeth space. When machining a thin-walled workpiece, due to less intense heat removal from the cutting zone into the workpiece, the temperatures in the areas of chip contact with the front surface of the tooth, the back surface of the tooth with the workpiece and the temperature of the workpiece itself are higher than when in a massive workpiece treatment. The patterns of changes in the parameters of the milling process of thin-walled workpieces depending on the feed, cutting speed and the milling cutter teeth space are established. With a larger tool stepover, the average and maximum temperatures in the areas of chip contact with the front surface of the tooth and the back surface of the tooth with the workpiece are lower in most of the combinations of mode elements used. Equations that establish the effect of feed on the milling cutter tooth, cutting speed and spacing of teeth on the parameters of the machining are obtained. The results of the study will allow choosing a rational milling mode and spacing of teeth in the work on workpieces of thin-walled parts made of titanium alloy.

Early chatter detection in thin-walled workpiece milling process based on multi-synchrosqueezing transform and feature selection

The onset of chatter is extremely disadvantageous to machining process, which will induce poor surface quality, low processing efficiency and severe tool wear, especially in the milling of weakly rigid thin-walled workpieces, so it should be detected as early as possible to avoid further damage. To handle this issue, a multi-synchrosqueezing transform (MSST) based early chatter detection method as well as a novel feature selection algorithm is proposed in this paper to monitor the occurrence of chatter in thin-walled parts machining. MSST is firstly conducted on the sampled vibration signal to generate a time–frequency (TF) representation. The periodic components associated with spindle rotation are removed from the TF matrix and the chatter-related signal is recovered by multi-ridge detection. Then, features in time and frequency domains are extracted from the reconstructed chatter signal. A feature selection algorithm combining multi-feature distance evaluation technique (MFDET) and distance correlation analysis is subsequently presented to determine the optimal feature subset. Compared with other chatter indicators given in existing works, the selected compact feature set is more discriminative and has low redundancy. Furthermore, random forest (RF) is utilized to intelligently diagnose the machining stability. Several experiments under constant and variable conditions are performed to evaluate the performance of the proposed method in terms of early chatter detection. The experimental results demonstrate that the presented chatter monitoring method is highly efficient and robust, which can recognize the chatter onset timely and accurately for thin-walled parts milling under different machining conditions.

Active vibration control of thin-walled milling based on ANFIS parameter optimization

In view of the time-varying dynamic characteristics of thin-walled milling, an optimization method of thin-walled milling control parameters based on the ANFIS system is proposed. Firstly, the control system strategy design and equipment selection construction were carried out, and the fuzzy inference model was built based on matlab platform; Subsequently, the fuzzy inference model of the thin-walled workpiece milling process was obtained by collecting fuzzy inference training data set of and the ANFIS system training. The proportional control coefficient of the controller was optimized based on the input and output relation of the model. Finally, the dynamic response and surface roughness of the controlled thin-walled panel milling process before and after optimization were obtained through cutting experiments, and the effectiveness of the ANFIS method to optimize the control parameters and the reliability of the fuzzy reasoning model were verified through analysis of the reasoning results. The results show that the ANFIS system can predict the vibration response performance of the target by setting the input and output reasonably, and optimize the related variable parameters according to the predicted results, so as to make the thin-wall milling system more stable.

Position-Dependent Stability Prediction for Multi-Axis Milling of the Thin-Walled Component with a Curved Surface

Time-varying dynamic behaviors are essential to investigate the stability in the thin-walled workpiece milling process, which is usually affected by material removal and position-dependent characteristics of the workpiece along with the tool feed direction. To predict the milling stability with position-dependent, thin-walled component multi-axis milling, an improved structural dynamic modification method with variable mass is proposed in the paper. Firstly, the extraction of multi-axis milling material and the removal process of thin-walled parts with a complex curved surface and variable thickness is completed with CAM software. Then, the material removal of one cutting path as a modification of the structure is divided into multi-cutting steps with equal length to obtain the corrected FRFs in the machining process on the basis of the extended Sherman-Morrison-Woodbury formula. Furthermore, the dynamic characteristics of the initial un-machined workpiece and final machined workpiece are calculated by both experimental modal analysis and FEM. Finally, the multi-axis milling stability is predicted using the extended numerical integrated method, and an aero-engine blade is used to validate the accuracy and effectiveness of the proposed method for multi-axis milling molding parts.

Dynamic modeling and stability prediction in milling process of thin-walled workpiece with multiple structural modes

Regenerative chatter can easily occur in the milling process of thin-walled workpiece due to the inherently low stiffness. This article aims to predict the stability of thin-walled workpiece in the milling process with a complete dynamic model. First, multiple structural modes of thin-walled workpiece are taken into consideration, and a complete dynamic model of thin-walled workpiece milling system is developed. Then, a numerical integration method is used to achieve the stability lobe diagrams of the milling system and identify the chatter frequency. Besides, the major structural mode, which is responsible for the occurrence of thin-walled workpiece chatter in the milling process, is predicted. A series of milling tests concerning a general cantilever plate are conducted, and the test results agree well with the predicted results, which shows the effectiveness of the proposed method. Finally, the effects of milling tool and structural modes on milling stability are discussed separately, which could provide theoretical basis for the dynamic modeling of thin-walled workpiece in milling process.

Machining vibration monitoring based on dynamic clamping force measuring in thin-walled components milling

In milling of thin-walled structures such as impellers or blisks, critical workpiece vibrations occur due to the excitation by the cutting forces and the dynamic interface between the workpiece and the fixture. Vibrations may cause instable state of the milling process, thus decreasing the production outcome by causing rejects. In respect to the milling process of thin-walled workpiece, a challenging task is to monitor the critical vibrations occurred in the workpiece itself or the contact surface between the workpiece and the clamping system. Vibrations can be reflected in the clamping system, and thus the clamping force variation monitoring is a potential scenario or solution to the challenging task. This article introduces a measurement prototype for the real-time dynamic clamping force monitoring. With respect to the measurement of clamping force, two case studies are carried out by a direct sensing method with PVDF thin-film sensors. In the first study, the measurement prototype with embedded PVDF sensors is located on the dynamometer, and an additional eddy-current transducer is applied for monitoring the workpiece deflection during the milling process. Deflection signals and cutting force signals from dynamometer are used as two referential signals to demonstrate the reliability of the prototype with embedded PVDF sensors. In the second study, milling test with the same tool and workpiece is implemented with only PVDF sensors monitoring. Dynamic clamping signal varying with different cutting durations in time, frequency, and time-frequency domain and different milling surface results is performed. Relationship between the collected signals and machining results is preliminarily analyzed. Case studies with thin-walled workpiece show the performance of the measurement prototype.

Vibration suppression of thin-walled workpiece milling using a time-space varying PD control method via piezoelectric actuator

The vibration suppression and workpiece surface improvement of thin-walled workpiece milling are highly concerned due to the weak stiffness of the workpiece and the time variant of dynamic characteristics during milling process. In this paper, an active vibration control system is developed to suppress the vibration of thin-walled workpiece milling. The dynamic model of plate-actuator milling system is derived using Hamilton’s principle and solved using FEM method. Acceleration sensor and piezoelectric patch are selected as the sensor and actuator in the control system. Considering the time variant of dynamic characteristics and the position limit of sensor and actuator during milling process, a time-space varying PD (VPD) control method is presented and utilized. The VPD control method applies time varying control parameters. Some simulation and experimental validations are carried out to validate the effectiveness of the control system. The overall results indicate that the proposed control system perform well in suppressing the vibration of thin-walled workpiece milling process.

Chatter mitigation for the milling of thin-walled workpiece

During the milling process of thin-walled workpiece, chatter is the major obstacle in achieving desired accuracy and productivity of the final part due to its low rigidity. In this paper, a novel method is proposed to mitigate the chatter of the thin-walled workpiece by submerging the milling system in viscous fluid. To evaluate the effectiveness of the presented method, the influence of the viscous fluid on the milling force coefficients is investigated, and the modal parameters of the thin-walled workpiece are identified under dry and viscous conditions respectively. It is found that compared with the dry milling, the milling force coefficients reduce significantly under viscous fluid condition due to the lubrication. Besides, the damping of the milling system increases substantially under viscous fluid condition, and the natural frequencies of the milling system decrease owing to the added mass of the viscous fluid. The milling stability lobe diagrams are predicted based on the numerical integration method by taking multiple modes of the thin-walled workpiece into consideration. A series of milling tests are conducted to verify the stability lobe diagrams and confirm the effectiveness of the proposed approach. The vibration displacement signals are measured and then analyzed in time-frequency domain to demonstrate the state of the milling process. Moreover, the surface finishes of the thin-walled workpieces are compared. The results show that the thin-walled workpiece chatter could be suppressed greatly with the proposed method and higher stability limit can be achieved.

Application of Sherman–Morrison–Woodbury formulas in instantaneous dynamic of peripheral milling for thin-walled component

How to consider the mass loading effects and stiffness modification effects of materials removed on dynamic characteristics in a thin-walled component milling process is an essential problem. Sherman–Morrison–Woodbury formula can be employed and extended to estimate the corrected frequency response function (FRFs) without the material removing effect. In the paper, a novel method, named as structural dynamic modification method with equal mass, to predict the dynamic stable lobe diagram (DSLD) of the thin-walled workpiece milling process is proposed. The whole cutting process is divided into multi-cutting steps with equal length. The presented method is to regard material removal of each cutting step as a modification (or reanalysis) of structure so as to estimate the corrected FRFs based on the so-called Sherman–Morrison–Woodbury formula. The input data of the method is only two sets of the dynamic characteristics of original (unmachined) and finial (machined) structures, which can be easily obtained using experimental modal analysis (EMA) or finite element method (FEM). The accuracy of the method is dependent of the number of cutting step. FEM is highly recommended, and EMA mainly enables the damping ratio of FEM model to be readjusted. The efficiency is higher than one of the methods reported in literatures because it is not necessary to re-build and re-mesh FEM model each time, and the modal analysis can be implemented automatically through pre-programs. Meanwhile, using Sherman–Morrison–Woodbury formula at active coordinates only can greatly improve computational efficiency. Additionally, the probability of singularity occurring is very low comparing with that in the existing methods. Once the dynamic characteristics changing with respect to tool positions are identified, a specific DSLD can then be predicted by using these characteristics along the machining direction. And the cutting parameters for thin-walled components milling can be also optimized to avoid chatter vibration and improve the chatter-free material removal rate and surface finish. Finally, the results are verified by dynamic and milling tests with thin-walled workpiece.

Systematic Simulation Method for the Calculation of Maximum Deflections in Peripheral Milling of Thin-Walled Workpieces with Flexible Iterative Algorithms

Due to the deflection of tool and workpiece induced by cutting force, there is a high complexity associated with the prediction of surface form errors in the peripheral milling process of thin-walled workpieces. And the prediction of surface form errors induced by cutting deflection is the precondition for process optimization and error compensation. This paper proposes a systematic simulation procedure suitable for surface form errors prediction in peripheral milling of low rigid thin-walled workpiece. Some key algorithms with the judgment of contacts between the cutter and the workpiece, the flexible iterative algorithm as well as the tool/workpieces deflection prediction using FE model are developed and presented in detail. Comparisons of the form errors and cutting forces obtained numerically and experimentally confirm the validity of the proposed algorithms and simulation procedure.

A New Approach to Build a Heat Flux Model of Milling Processes

During the finishing milling process of thin-walled workpieces, deformations occur due to the mechanical and thermal influences. Hence, the manufacturing quality may be affected. The aim of a research project at the iwb is to simulate thermally caused deformations and deriving methods to reduce them. Two approaches subsume the term “reduction methods”: the use of less deformation-causing process parameters or alternatively – if this approach is insufficient – to compensate the deformation.Simulating thermally induced deformations necessitates a description of the heat input, which is caused by the milling process. Furthermore, this description needs to be valid for the whole spectrum of process parameters recommended for the used tool. The model of the heat source is based on milling experiments with an in-process measurement of the thermally caused deformations. The experimental results allow differentiating between thermally and mechanically induced deformations due to the restriction on an end milling finishing process. However, these measurements only provide a relation between process parameters (variation of cutting speed vc, feed per tooth fz and width of cut ae) and deformations. The simulation model, which will be described within this paper in detail, provides the relation between a variable heat input and its resulting deformations. The experimental and the simulative relations together are leading to a heat source model in dependence of the process parameters.

In-Process Deformation Measurement of Thin-walled Workpieces

During the finish milling process of thin-walled workpieces, deformations occur due to the mechanical and thermal influences. The measuring method outlined in this publication allows an accurate assignment of these deformations to their respective cause in size and form, due to the high temporal and spatial resolution of the used optical measurement system. Furthermore, dividing the dis-placement into its mechanical and thermal proportion allows a fully decoupled validation of process models. Especially the simula-tion results of thermal models, which are mainly validated by measured temperature fields, can be further ensured.

Modeling and Analysis Effects of Material Removal on Machining Dynamics in Milling of Thin-Walled Workpiece

In aerospace industry, thin-walled workpieces are widely used in order to reduce the weight and to fulfill the high demands of their later applications. These workpieces are usually highly sophisticated and difficult to machine according to their geometry and material choice. In this paper, influence of material removal within the thin-walled workpiece machining operation on the dynamic properties of the workpiece and the machining process system is discussed. Aiming at learning about dynamic properties evolution during the machining operation, different milling processes of thin-walled plate are studied. Numerical simulation methods are employed in the study to investigate the dynamic properties evolution and machining stability with the material removal process in the milling process of thin-walled workpiece. The investigation results are expected to be used for designing optimized material removal sequence, which will guarantee highly material removal rate as well as highly machining accuracy of thin-walled workpiece.

Prediction of simultaneous dynamic stability limit of time–variable parameters system in thin-walled workpiece high-speed milling processes

A method for predicting simultaneous dynamic stability limit of thin-walled workpiece high-speed milling process is described. The proposed approach takes into account the variations of dynamic characteristics of workpiece with the tool position. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method. The curvilinear equation of modal characteristics changing with tool position is regressed. A specific dynamic stability lobe diagram is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The results show that, during thin-walled workpiece milling process, material removing plays an important part on the change of dynamic characteristics of system, and the stability limit curves are dynamic curves with time–variable. In practical machining, some suggestion is interpreted in order to avoid the vibrations and increase the chatter free material removal rate and surface finish. Then investigations are compared and verified by high-speed milling experiments with thin-walled workpiece.

Stability analysis in milling of thin-walled workpieces with emphasis on the structural effect

Regenerative chatter easily occurs in milling and has become the common limitation to achieve good surface quality and high productivity. For the purpose of chatter avoidance, the structural effect of the thin-walled part should be considered for the milling chatter stability analysis for the optimization of axial cutting depth and spindle speed pairs. The main objective of this paper is to examine the link between the structural modes (i.e. modal shapes) and the chatter stability limits in the case of finish milling thin-walled workpieces. In this paper, the dynamic stability of the milling process of thin-walled workpieces is investigated through a two-degree-of-freedom mechanical model. The mathematical relationship between the critical axial depth and the thin-walled part modal shapes is deduced and an optimal calculation process of milling stability lobes is presented. Peripheral milling of aluminium alloy (2A70 Al) plates is carried out on a computer numerically controlled (CNC) five-axis super high-speed machining centre to validate the method. The experimental results agree with the prediction by the presented method. Additionally, the experimental results show that the cutting stability is also influenced by the modal frequencies of the thin-walled part, which have a great influence on the milling stability analysis when the tool passing frequency (i.e. the inverse of the tooth passing period) harmonics are close to the modal frequencies of the part. The presented method is effective in the prediction of milling chatter limits in the thin-walled case for the optimization of machining parameters.

Stability Prediction during Thin-Walled Workpiece High-Speed Milling

A method for predicting the stability of thin-walled workpiece milling process is described. The proposed approach takes into account the dynamic characteristics of workpiece changing with tool positions. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method (FEM). The workpiece frequency response function (FRF) depending on tool positions is obtained. A specific 3D stability chart (SC) for different spindle speeds and different tool positions is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The dynamic optimization of cutting parameters for increasing the chatter free material removal rate and surface finish is presented through considering the chatter vibration and forced vibration. The investigations are compared and verified by high speed milling experiments with flexible workpiece.

Systematic simulation procedure of peripheral milling process of thin-walled workpiece

Abstract A systematic procedure is developed to simulate the peripheral milling process of thin-walled workpiece. The procedure integrates the cutting force module consisting of calculating the instantaneous uncut chip thickness (IUCT), calibrating the instantaneous cutting force coefficients (ICFC) and the cutting process module consisting of calculating the cutting configuration and static form errors. It can be used to check the process reasonability and to optimize the process parameters for high precision milling. Key issues such as the theoretical calculation of the IUCT, efficient calibration scheme of ICFC, iterative correction of IUCT, the radial depth of cut and material removal are studied in detail. Meanwhile, the regeneration mechanism in flexible static end milling is investigated both theoretically and numerically. Comparisons of the cutting forces and form errors obtained numerically and experimentally confirm the validity of the proposed simulation procedure.