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It is very prone to cause large-amplitude cutting vibrations, or even regenerative chatter, when milling thin-walled workpiece due to its low dynamic stiffness. The utilization of fixture support is one of the most effective measures to mitigate vibrations and improve stability limits, which has gained more and more attention. However, the dynamics model of the tool-workpiece-fixture system and the influence of fixture support force have not been fully developed. In this paper, a pneumatic fixture is designed and used to exert controllable support force on the thin-walled workpiece by precisely tunning the air pressure. The position-dependent modal parameters of the thin-walled workpiece under different fixture support forces are identified by combining experimental modal test and finite element analysis. The milling dynamics is then modeled into a delay differential equation with position-dependent coefficients. On this basis, the three-dimensional stability lobe diagrams (SLDs) are obtained in the parameter space of tool path, spindle speed, and axial depth of cut. Both stable and chatter cutting tests are performed to verify the predicted SLDs, and the cutting signals under different fixture support forces are compared in detail. Experimental results reveal that the proposed model can accurately predict the chatter stability of thin-walled workpiece with fixture support, and the stability limit can be successfully improved by tunning the support force. Some important conclusions on the influence of fixture support forces are also drawn based on detailed simulation and experimental analyses.

Stability analysis is rather important in the turning process for achieving a high machining efficiency under the condition of without compromising the surface integrity. However, the occurrence of chatter is not simply attributed to the cutter or the part, and sometimes may be alternating. In this paper, a new chatter stability model is built for the turning process of a typical step shaft with the consideration of the 2-dimensional (2D) compliance of tool and part. Among the model, an accurate dynamic force modeling method is first presented, into which the tool nose radius, the size effect, and the effect of vibrations in chip thickness and width directions are incorporated simultaneously. Then, the position-dependent vibration equations of the 2D compliant turning system are formulated based on the continuous Timoshenko beam theory, and position-dependent modal parameters are subsequently derived by using a matrix recursion algorithm. Further, the dynamic equations for the 2D tool-workpiece compliant system are solved with an extended second-order semi-discretization method. Finally, the simulations and experiments are conducted to verify the built model. The results of stability prediction show a good agreement with the experimental results no matter the flexibility of the cutter or the part plays a dominant role in the turning process.

Thin-walled revolution surface parts are extensively used in various fields. Owing to their low rigidity, there is an inevitable deformation caused by the blank forming and clamping processes. This makes high-precision machining of parts with complex contours for industrial applications challenging. To solve this problem, a shape-adaptive milling method for complex contours on deformed parts is proposed. First, the real geometry of a deformed part is acquired by a developed contact-type on-machine measurement (OMM) system. Subsequently, an orthogonal arc-length mapping is mathematically proposed to establish a one-to-one correspondence between the nominal and real surfaces. The method of adjusting the tool path is based on this correspondence is discussed in detail, using which the nominal tool path can be adjusted to adapt automatically to the shape change of the real part. In addition, the methods of refining the tool path, such as eliminating the overcuts and undercuts and reorienting the cutter orientation, are also presented for achieving a good milling quality. Finally, the experiments of milling complex pattern contours on thin-walled bangles, which are typical revolution surface parts with low rigidity, are presented, and the simulation tests on a general revolution surface are also conducted. Experimental results illustrate that the proposed method can produce clear and complete contours on the deformed revolution surfaces.

Dynamic change of feedrate is almost inevitable in high speed milling along a curved path due to the drive limits of the machine tools. The surface topography caused by the change of feedrate, which has a significant influence on mechanical prosperities and performances of the machined part, cannot be predicted using the existing methods that only consider constant feedrate. To better understand the surface topography formation process in high speed milling and also to more effectively control the machining parameters, in this paper we present a surface topography model for a ball-end cutter, which takes varying feedrate into full consideration. Our model considers the affecting elements including the surface's local geometry, the cutting edge shape, the path interval, as well as the relative motion of tool-workpiece (especially the changes of the tool orientation and feedrate). 3- and 5-axis ball-end milling experiments, in computer simulation and physical cutting, are performed to validate the developed model. The simulation results exhibit good agreement with that of the actual cutting, thereby showing the potential of the developed model for controlling the surface topography and roughness in real NC ball-end milling.

G01 blocks are the widespread format of toolpath in computer numerical controlled (CNC) machining. For achieving smooth motion and eliminating the geometrical discontinuity at the block transitions, various local corner smoothing methods have been developed. However, in these methods, the loss of featured information of parts is inevitable. Focused on this topic, this article proposes a new analytical G2 continuous corner smoothing method with G01 shape preserving for five-axis linear toolpath by locally inserting specially designed B-splines into the corners of consecutive segments. First, by analyzing the condition of G01 shape preserving, the configuration expression of control points for B-splines is yielded for passing through G01 point. On this basis, the tool tip position is smoothed by symmetrical B-splines with minimum curvature in the workpiece coordinate system (WCS). Then, another asymmetrical B-splines is used to smooth tool orientation in the machine coordinate system (MCS). After that, the satisfaction conditions of parametric synchronization between tool tip position and tool orientation are mathematically derived at junctions, while the corresponding maximum smoothing errors are also constrained in WCS. Compared with the existing methods, not only the tool tip points and orientation vectors specified in original G01 blocks are preserved but also the optimal control points considering the curvature of smooth splines can be obtained analytically. Finally, simulations and experiments are performed to validate the effectiveness of the developed method.

The G01 tool path, which consisted of linear segments, is commonly used in NC machining. There is the tangential and curvature discontinuity at the junctions of adjacent linear segments, which can ...

The iso-scallop method has been long adopted to achieve a shorter overall machining length. The efficiency and machining performance of this method are largely dominated by the initial tool path. The preferred direction field supplies the local best feed directions. Usually, the offset paths generated by the iso-scallop method largely deviate from the preferred directions, even though the initial path is strictly along the preferred directions. The matching degree of the offset paths and preferred direction field should be taken into consideration when selecting an initial tool path. This paper presents a novel initial path selection method for the iso-scallop method to make whole iso-scallop tool paths and the preferred direction field consistent as much as possible. A surface is re-parameterized to keep the conformality between the surface and parametric domain, which leads to the more regular offset paths on the new parametric domain. By fitting the vector field, streamlines are generated for representing the preferred feed direction on the parametric domain. The offset similarity metric defined by the initial path and streamlines is constructed to measure the matching degree between offset paths and preferred feed directions. Then the feasible path with the best offset similarity for the streamlines will be selected as the initial tool path. In our case study, feed directions with the maximum strip width are chosen. The test results have shown that the tool paths generated by the proposed method achieved a better matching for the selected feed directions and a shorter overall length compared with some existing tool path generation methods.

To improve the detection and recognition performance of DAS in complicated multi-source interfering environments, a blind multi-source separation method is proposed based on the FastICA, which utilizes the independency and non-Gaussianity of different sources.

2-D localization of ground vibration for DAS is realized by extracting the spatial attenuation feature and mapping its relationship with the radial distances by a deep learning network. Field tests prove its effectiveness.

The plasma levels of interleukin-8 (IL-8) and its receptors (CXCR1 and CXCR2) play a significant role in the development of systemic inflammatory response syndrome (SIRS), but it is not clear how t...

When adopting 5-axis machine to mill the parts, it is desired to avoid the drastic change of tool orientation for improving the kinematics performance of 5-axis machining while ensuring no machining interferences. For this purpose, a kinematics performance oriented smoothing method is proposed to plan the tool orientations, which is focused specifically on minimizing the angular accelerations imposed on the rotary axes of 5-axis machine. In this method, with several specified representative tool orientations (RTOs), two B-spline curves, which represent the displacements of the rotary axes, are used to join smoothly the RTOs together and then to determine the tool orientations at other areas. The solutions for the two B-spline curves are achieved by solving a least-square objective function which minimizes the angular accelerations of the rotary axes. To restricting simultaneously the interpolated tool orientations in the geometric feasible domains (GFDs) of tool motion, a simple alternate strategy of first smoothing the tool orientation and then checking the machining interference is developed so that tool orientation planning and its geometric constraints are decoupled and the complicated constraint optimization process of tool orientation can be greatly simplified. Since the proposed method works in the machine coordinate system (MCS), it can not only ensure the smooth motions of the rotary axes without the machining interferences, but also can generate directly the rotary axis orders. Finally, the proposed method is validated by the experiments.

In this paper, a new computation method and an optimization algorithm are presented for feedrate scheduling of five-axis machining in compliance with both machine drive limits and process limits. Five-axis machine tool with its ability of controlling tool orientation to follow the sculptured surface contour has been widely used in modern manufacturing industry. Feedrate scheduling serving as a kernel of CNC control system plays a critical role to ensure the required machining accuracy and reliability for five-axis machining. Due to the nonlinear coupling effects of all involved drive axes and the saturation limit of servo motors, the feedrate scheduling for multi-axis machining has long been recognized and remains as a critical challenge for achieving five-axis machine tools’ full capacity and advantage. To solve the nonlinearity nature of the five-axis feedrate scheduling problems, a relaxation mathematical process is presented for relaxing both the drive motors’ physical limitations and the kinematic constraints of five-axis tool motions. Based on the primary optimization variable of feedrate, the presented method analytically linearizes the machining-related constraints, in terms of the machines’ axis velocities, axis accelerations and axis jerks. The nonlinear multi-constrained feedrate scheduling problem is transformed into a manageable linear programming problem. An optimization algorithm is presented to find the optimal feedrate scheduling solution for the five-axis machining problems. Both computer implementation and laboratorial experiment testing by actual machine cutting were conducted and presented in this paper. The experiment results demonstrate that the proposed method can effectively generate efficient feedrate scheduling for five-axis machining with constraints of the machine tool physical constraints and limits. Compared with other existing numerical methods, the proposed method is able to find an accurate analytical solution for the nonlinear constrained five-axis feedrate scheduling problems without compromising the efficiency of the machining processes.

This paper presents a novel method to generate three-axis CNC tool paths for machining freeform surfaces based on a preferred feed direction field. This research was initiated from a fluid dynamics behavior that the energy loss can be reduced when the streamlines of fluid and the small grooves on a surface are in the same directions. In this research, the fluid streamlines above the surface are defined by a collection of vectors. These vectors are regularized into a grid of vectors, and these regularized vectors are further projected onto the tangent planes of a grid of points on the surface to create the preferred feed direction field. Based on the parametric model of the surface, the vectors on the tangent planes of the surface are mapped into vectors in the parametric domain. A scalar function is constructed such that the isolines of this scalar function and the preferred feed direction vectors in the parametric domain are in the same directions. A group of isolines of the scalar function are identified and these isolines are mapped back onto the 3-D surface as the created tool paths considering the tolerance requirement. The developed method has been applied to generate the tool paths for machining surfaces of a compressor blade.

In this paper, a new generalized parametric interpolation method is proposed for optimized five-axis machining with the consideration of both the machine contour errors and the feedrate fluctuation elimination. An analytic processing is presented for linearization of contour errors with respect to feedrate limit. For machine configuration, explicit analytical modeling of the contour error and the tracking error with respect to feedrate is presented; thus, the error constraint problem is nicely converted to a kinematic constraint problem. On this basis, an accurate feedrate upper limit with confined contour errors is further determined by using a shifted Frenet frame with linear computational complexity. With the consideration of both the motion smoothness and machining efficiency, a time-based optimization algorithm is proposed for time-optimal feedrate scheduling. For eliminating the feedrate fluctuation, a new real-time interpolation algorithm is developed for free derivation between the path parameter and the arc length for smoothed five-axis tool path generation. Laboratory testing experiments were conducted for validation and were presented in the paper. And the experimental results indicate that the proposed feedrate interpolation method is capable of confining both the tool tip contour error and tool orientation contour error simultaneously, as well as maintaining a satisfactory interpolation performance in both computation efficiency and accuracy. The presented methods can be used for five-axis machining and the feedrate optimization of complex part machining.

Force-induced deformation is an inevitable phenomenon in thin-wall milling operations, which makes the actual radial depth of cut deviate from its nominal value and changes tool-part engagement angle boundaries. This paper presents an accurate modeling of dynamic milling system with the force-induced deformation effect. Both the thin-walled part and the cutter are discretized into differential elements, such that the influences of the force-induced deformation and multi-point contact structure dynamics can be simultaneously considered at the contact zones. A detail flexible iteration strategy is first presented to calculate the force-induced deformation and the resulting tool-part engagement angle boundaries. After that, time-varying multi-modal dynamic parameters with actual material removal effect are obtained by simultaneously modifying structural static and dynamic stiffness at each tool feed position. The system involving regenerative dynamic displacements is formulated as a matrix of time-periodic delay differential equation. Chatter stability of the system is predicted by an extended second order semi-discretization method. Milling experiments are conducted to validate the proposed approach, and two types of parts with different wall thickness are designed. The results show that chatter can be well predicted by using the proposed approach.

Regenerative chatter is a pivotal obstacle for achieving required machining quality and efficiency in turning operations, especially when turning of low-stiffness parts. Accurate prediction of chatter stability prior to actual machining is of great significance for the judgment on feasibility and the optimization selection of cutting parameters that are free of chatter. To this end, this paper presents a comprehensive study which allows accurately predicting the chatter stability in turning of low-stiffness parts made of pure iron. The dynamic model for a double-flexible turning system with the regenerative effect is established in orthogonal directions on the basis of a nonlinear turning force model with accurately calibrated nonlinear force coefficients. In the nonlinear turning force model, both shearing and edge effects are considered, in which shearing force components are formulated as the exponential functions of the instantaneous uncut chip thickness to reflect the size effect. In addition, the geometric feature of the tool nose radius is also taken into account by precisely discretizing the instantaneous uncut chip area. The chatter stability of the resulting system is further predicted by an extended second-order semi-discretization method (2nd SDM). To verify the proposed method, a series of cutting tests are conducted on a CNC lathe, and experimental results indicate that proposed method can achieve an accurate prediction of chatter stability in turning of low-stiffness pure iron parts.

Interventions for preventing cognitive dysfunction after traumatic brain injury (TBI) are limited. Given that adult hippocampal neurogenesis after brain injury contributes to cognitive recovery, and hippocampal neurogenesis is potentially affected by nutritional factors, the aim of this study was to examine whether fasting could promote hippocampal neurogenesis and thus ameliorate the cognitive defects after TBI.The present study used 8- to 10-wk-old C57 BL/6 N mice weighing 23 g, half males and half females. The mice were randomly assigned to each group, with 10 to 18 mice per group. All mice were housed in an approved animal facility with a 12-h light/dark cycle. In the metabolic study (food intake, body weight, blood glucose, triacylglycerol, total cholesterol, and β-hydroxybutyric acid ), 54 mice (male:female = 1:1) were randomized to the ad libitum (AL) group (n = 18) and the intermittent fasting (IF) group (n = 36). In the neurogenesis study, 45 mice (male:female = 1:1) were randomized to AL (n = 18), IF (n = 9), IF + scramble (n = 9), and the IF + neuropeptide Y (NPY)_siRNA (n = 9) groups. In the Morris water maze test, 48 mice (male:female = 1:1) were randomized to AL (n = 12), IF (n = 12), IF + scramble (n = 12), and the IF + NPY_siRNA (n = 12) groups.We showed that a 1-mo-long IF regimen enhanced the proliferation of neural stem cells in the subgranular zone of the hippocampus 3 d after TBI, in addition to improving the cognitive performance in the Morris water maze test. Furthermore, an increase in the hippocampal NPY expression was detected in the IF group after the injury, compared with the mice fed AL, and local knockdown of NPY in vivo attenuated the effects of IF on TBI.These findings suggest that IF promotes hippocampal neurogenesis after TBI by a mechanism that involves enhancement of NPY expression, to alleviate cognitive dysfunction caused by injury.

Interventions for preventing cognitive dysfunction post traumatic brain injury (TBI) is limited. Given that adult hippocampal neurogenesis (AHN) after brain injury contributes to cognitive recovery, and that the AHN is potentially affected by nutritional factors, we asked whether fasting could promote AHN and thus ameliorates cognitive defects after TBI. Here we show that a one-month intermittent fasting (IF) regimen enhanced proliferation of neural stem cells (NSCs) in the subgranular zone (SGZ) of hippocampus 3 days post TBI, as well as improved cognitive performance in Morris water maze (MWM) test. Furthermore, an increase in hippocampal Npy expression was detected in IF group after injury, compared to the mice fed ad libitum (AL), and locally knock-down of Npy in vivo attenuated the aforementioned effects of IF in TBI. These findings suggest that IF promotes AHN following TBI by a mechanism involving enhancement of Npy expression, which may offer novel interventions that might prevent cognitive dysfunction caused by injury.

Auxiliary fixtures are widely used to enhance the rigidity of cylindrical thin-walled workpieces (CTWWs) in the machining process. Nevertheless, the accurate and efficient prediction of frequency response function (FRF) for the workpiece-fixture system remains challenging due to the complicated contact constraints between workpiece and fixture. This paper proposes an analytical solution for the comprehensive FRF analysis of the CTWW-fixture system. Firstly, based on the vector mechanics, the mode shape functions of the workpiece are presented using the classical theory of thin shell. The variable separation method is utilized to deal with the inter-mode coupling of the workpiece. Secondly, the motion equation of the CTWW with fixture constraints is established using analytical mechanics from the viewpoint of energy balance. Finally, the FRFs of the CTWW-fixture system are derived by means of modal superposition. Experimental modal tests verify that the predicted FRFs are in good agreement with the measured curves.

With the widespread application of product recommender systems, there exists significant scope to enhance predicting customers’ purchasing possibility. Then 4 supervised classification models are constructed based on the data from a financial corporation, including logistic regression model, decision tree, bagging and random forest, to anticipate which customer is more likely to adopt the proposed health insurance policy. After comparing 𝐹1 score using an undersampling train set considering unbalanced sample data, the logistic regression model ultimately represents a superior prediction accuracy for clients’ buying propensity, and therefore has the potential to improve targeted selling system for this company.

The plastic deformation produced in the machining process can cause residual stress. As an effective way to control the residual stresses, the cryogenic process is used in modern industries such as aerospace, automobile, and shipping industry. Focusing on the minimization of surface stress in the cryogenic process of pure iron, the Taguchi design is used in this paper. The effect of cryogenic temperature (77–193 K), holding time (8–24 H), cooling rate (2–6 K/min), and warming-up rate (0.5–1.5 K/min) on surface residual stress is discussed and the optimal combination of cryogenic parameters is obtained using signal-to-noise (S/N) ratios. To overcome the weakness of the Taguchi method that cannot calculate stresses, an exponential model to predict residual stresses considering cryogenic parameters is developed. The coefficients of this mathematical model are obtained using multilinear regressive analysis based on the database of the Taguchi experiment. After this, the optimization process is conducted with this model using the genetic algorithm (GA). The optimized results using both ways coincide with each other. The optimal cryogenic parameters are obtained, i.e., cryogenic temperature of 193 K, holding time of 24 h, cooling rate of 2 K/min, and warming-up rate of 0.5 K/min. When the optimum cryogenic parameters are used, the surface residual stress is reduced by 42.9% in the cutting direction and 46.2% in the feeding direction. The method can be applied to the actual machining engineering to realize the low-stress control on the cutting surface.

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.

In order to meet the growing industrial demand of high quality and high efficiency machining, long cutters with larger axial depth of cut are extensively implemented in peripheral milling of deep pockets, grooves, and thin-wall parts. However, due to their high flexibilities, chatter easily occurs during the machining process. It has been demonstrated that milling cutters with variable pitch and/or variable helix angles can mitigate the chatter, which are gaining increasingly important applications. Although this kind of cutters have been studied in some detail in previous research, few studies have focused on the interaction dynamics complicated by actual cutter runout in long tool-part contact zone. This paper systematically studies the dynamics and stability of variable-pitch/helix milling system with long end cutters. The cutters are divided into a series of axial disks, and each axial disk includes several cutting elements which are equal to the number of teeth. Variations of pitch and helix angles, cutter run-outs including radial offset and axial tilt, and mode shapes with the cross terms in the orthogonal direction, are assigned to these cutting elements. The system, involving multiple regenerative delays as well as the axially varying dynamics, is formulated as a matrix form of time-periodic delay differential equation with multi-modal dynamic parameters. An updated cross-axis and cross-point modal testing method is then proposed to obtain the dynamic parameters, which can effectively avoid multiple hits when impacting the cutter with hammer. The stability lobes are predicted in state space by developing an improved semi-discretization method, by which the pitch variations and actual runout effects on stability are investigated. It is shown that the stability lobes differ significantly when the combined effects of cross-axis and cross-point FRFs and actual cutter runout are considered. A series of cutting experiments is conducted to demonstrate the proposed model and method. Results show that these lobes well agree with the experimental results.

Surface profile is one of the foremost aspects to evaluate milling performance. Its generation mechanism is affected by a variety of factors such as tool geometry, runout values, and process parameters and thus still deserves further investigation. This paper aims to propose a unified method to study the surface generation mechanism and to predict the machining quality for variable pitch tools considering runout. First, a Floquet theory based algorithm is extended to analyze the machining stability and output the dynamic responses of the machining system. The resultant trajectories of cutting edges are obtained by kinematic synthesis of system vibrations, tool rotations, and machining feed. Next, both the surface location error (SLE) and the surface roughness are simultaneously extracted from the edge trajectories. A series of cutting tests are performed to validate the prediction results. Some new characteristics of the machined surface profile in terms of form errors and teeth marks are discovered and theoretically explained. Finally, the joint influences of tool geometry, runout values, and process parameters on the surface generation mechanism and quality are analyzed in detail with the proposed method.