High-speed CNC Machine Tools Research Articles

Improving milling tool wear prediction through a hybrid NCA-SMA-GRU deep learning model

Milling tool wear, a ubiquitous challenge in industrial automation and manufacturing, leads to diminished equipment utilization, escalating costs, and a decline in product quality. The prediction of tool wear is a complex and challenging task, as it involves numerous variables. This paper introduces a pioneering hybrid approach, the NCA-SMA-GRU model. It involves the hybridization of three major components and is designed to enhance the precision and expedite the process of tool wear prediction. The NCA component is adept at filtering and retaining the most relevant features associated with milling tool wear from the raw signals, and it also improves the model’s interpretability. Subsequently, SMA optimizes the GRU network’s hyperparameters, including the initial learning rate, hidden layer neurons, network training iterations, and the L2 regularization factor, to identify an optimal combination that bolsters predictive performance. The modeling steps and the development of fitness function are explained in detail. The model’s efficacy is rigorously evaluated using data from the 2010 High Speed CNC Machine Tool Health Prediction Contest (PHM 2010), which encompasses wear data from both single and multiple cutters. The performance is compared using metrics such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), R-Squared (R2), and computational time. To assess the ability and characteristics of the proposed approach, other popular hybrid models are constructed for comparative analysis. The results demonstrate that the proposed model addresses the limitations of traditional prediction methods and provides insights into the development of deep learning and optimization algorithms for tool wear prediction.

Thermal Error Model of Linear Motor Feed System Based on Bayesian Neural Network

The linear motor feed system has been in service in complex working conditions for a long time, thus causing the nonuniform distribution of the temperature field distribution. Thus, the thermal error has become a key factor affecting system motion accuracy. In order to maximize the accuracy and efficiency of thermal error compensation for linear motor feed systems, an improved modeling method for the thermal error of the linear motor feed system based on Bayesian neural networks is proposed in combination with the strong generalization performance and avoidance of overfitting of Bayesian neural networks. And the specific modeling ideas are as follows: Firstly, the X-Y cross-type two-axis linear motor feed system is taken as the test object. Due to the traditional neural network’s slow convergence, overfitting, and underfitting problems, the Bayesian neural network is used to model the thermal error of the linear motor feed system. Secondly, to avoid the influence of multicollinearity data on the final results, the grey relation analysis method is used to screen the temperature measuring points. The data with a large relation degree is selected for modeling to ensure the prediction accuracy of the neural network. Thirdly, the temperature variables of sensitive points and thermal positioning errors are taken as data input samples. Fourthly, a Bayesian neural network model is established. Fifthly, the hyperparameters of the Bayesian neural network are determined by a calculating method of Hessian matrix by Gauss-Newton approximation. And finally, a thermal error prediction model is established. The comparison and analysis with the neural network constructed by the ordinary Levenberg-Marquardt algorithm after a series of experimental demonstrations see that the prediction accuracy of the proposed method can be enhanced by up to 10%. It also shows that the prediction model has the advantages of high precision, strong generalization ability, anti-disturbance solid ability, and strong robustness, etc. Therefore, the prediction model is expected to be widely used in predicting and compensating thermal error of the feed system of high-speed CNC machine tools in practical machining occasions.

Dynamic Analysis of High Speed Spindle

Assessment of the thermo-mechanical behaviour of machine-tool spindles is a requisite for the reliable operation of high-speed CNC machine tools. The thermal behaviour and applied loads affect the performance of these high-speed spindles. The primary source of heat generation in the spindle is due to friction torque in angular contact ball bearings, cutting forces, centrifugal force, gyratory effects and bearing preload. The spindle shaft is treated as beam element with one translational and one rotational degree-of-freedom at each node. Angular contact ball bearings are modelled to predict heat generation due to load, viscous, and spin-related effects. Mutual interlinkage between the thermal and structural behaviour of both spindle shaft and bearings is modelled using the effects caused due to the thermal expansion and rate of heat generation. The bearing preload is pushed up due to centrifugal force and temperature rise due to high spindle speed. Components matrices are assembled to configure a finite element model for the thermo-mechanical analysis of spindle-bearing systems using Euler-Bernoulli beam theory. Further this work presents ANSYS simulations on CNC spindle system with angular contact ball bearings using 103 Cr1steel material and hybrid type to predict thermal stress. Static and dynamic analysis is carried out on the spindle with and without thermal load and cutting load to predict the displacement and slope.

Recent Patents on the Structure of High-Speed Motorized Spindle

Background: As one of the core components of high-speed CNC machine tool, high-speed motorized spindle is the core functional component of high precision CNC machine tool, which has become the key research and development object of the world. Objective: By comparing and discussing the patents of high-speed motorized spindle, some valuable conclusions have been drawn to predict the future research and development of high-speed motorized spindle. Methods: By analyzing the characteristics of high-speed motorized spindle structure, the influence of high-speed motorized spindle on high-speed machining technology was explicated. Combining with the key technology of high-speed motorized spindle, the patents related to high-speed motorized spindle structure were used for investigation. Results: With the rapid development of high-speed cutting and numerical control technology and the need of practical application, the requirement for high-speed spindle performance has increased. Motorized spindle technology has the characteristics of high speed, high strength, high power, high torque and low speed, high precision, high reliability and long life, offering diversified bearing and lubrication cooling methods and serving as an intelligent system. Conclusion: The different levels of improvement and renovation of the structure with high-speed motorized spindle, by adding lubrication and cooling device to the spindle have improve the performance of spindle, addressing the loopholes in the technology and making it more practical.

Error constraint optimization for corner smoothing algorithms in high-speed CNC machine tools

As corner smoothing algorithm is crucial to high-speed CNC machining, a new error constraint optimization method for corner smoothing algorithm is proposed in this paper. Traditional corner smoothing algorithms are all based on a toolpath to generate motion trajectory, and the same allowable error is used for all smoothed corners. However, in using this method, the contour error of workpiece will be invalidated because of the cutting tool radius in real cutting processing, thereby resulting in over-cutting or inefficiency. In this study, the tool offset and corner smoothing algorithm are combined in order to optimize the error constraint. Besides, a cutting process geometry model was established to analyze the error relationship. On the basis of this model, the smoothing error constraints of each corner can be solved according to the allowable contour error of the workpiece. Finally, motion trajectory is planned through a multi-constraint planning strategy, which can balance the contour error in workpiece at each corner and can guarantee the cutting accuracy, compared with the traditional corner smoothing algorithm. Moreover, a test workpiece is designed to verify the correctness of the proposed algorithm through simulation and actual experiments. The experimental outcome proves that the proposed method improves the workpiece cutting accuracy in high-speed CNC machine tool.

Thermal Error Test and Intelligent Modeling Research on the Spindle of High Speed CNC Machine Tools

Thermal error is the main factor affecting the accuracy of precision machining. Through experiments, this paper studies the thermal error test and intelligent modeling for the spindle of vertical high speed CNC machine tools in respect of current research focuses on thermal error of machine tool. Several testing devices for thermal error are designed, of which 7 temperature sensors are used to measure the temperature of machine tool spindle system and 2 displacement sensors are used to detect the thermal error displacement. A thermal error compensation model, which has a good ability in inversion prediction, is established by applying the principal component analysis technology, optimizing the temperature measuring points, extracting the characteristic values closely associated with the thermal error displacement, and using the artificial neural network technology.

Simulation Analysis on the Static Characteristics of High Speed Milling Motorized Spindle

The structure design and the static characteristics of the motorized spindle determine the machining quality and cutting performance of high speed CNC machine tools. In this paper, the ANSYS finite element software is used to analyze the static characteristics of the high speed milling motorized spindle, so as to verify the rationality of the structure design.

A fast and high-smooth velocity planning method for high-speed CNC machine tools

To overcome some shortcomings of the conventional Acc/Dec method, a novel method was proposed to apply for CNC machine tools. Firstly, a fast composite Acc/Dec model was constructed. Secondly, the discretised linear Acc/Dec algorithm was adopted to make velocity planning for machining paths, and the velocity profile of the linear Acc/Dec model was obtained. Thirdly, in the acceleration phase and the deceleration phase, a flexible Acc/Dec method was applied to achieve a fast discretised S-curve Acc/Dec model. Comparing with the linear Acc/Dec model, the presented method improves motional smoothness greatly; comparing with the conventional S-curve Acc/Dec model, the presented method has more efficiency and simpler algorithm. The fast composite method was evaluated by simulation and experimentation. Experimental results have shown that the proposed method can significantly improve the machining efficiency and motional smoothness for CNC machine tools.

A fast and high-smooth velocity planning method for high-speed CNC machine tools

To overcome some shortcomings of the conventional Acc/Dec method, a novel method was proposed to apply for CNC machine tools. Firstly, a fast composite Acc/Dec model was constructed. Secondly, the discretised linear Acc/Dec algorithm was adopted to make velocity planning for machining paths, and the velocity profile of the linear Acc/Dec model was obtained. Thirdly, in the acceleration phase and the deceleration phase, a flexible Acc/Dec method was applied to achieve a fast discretised S-curve Acc/Dec model. Comparing with the linear Acc/Dec model, the presented method improves motional smoothness greatly; comparing with the conventional S-curve Acc/Dec model, the presented method has more efficiency and simpler algorithm. The fast composite method was evaluated by simulation and experimentation. Experimental results have shown that the proposed method can significantly improve the machining efficiency and motional smoothness for CNC machine tools.

Kinematic corner smoothing for high speed machine tools

This paper presents a novel kinematic corner smoothing technique for high-speed CNC machine tools. Typically, reference tool-paths compromised of short G01 moves are geometrically smoothed by means of arcs and splines within the NC system. In this study, a continuous feed motion is generated by directly planning jerk limited velocity transitions for the drives in the vicinity of sharp corners of the tool-path. This approach completely eliminates the need for geometry based path smoothing and feed planning. Contouring errors at sharp corners are controlled analytically by accurately calculating cornering speed and duration. Since proposed approach bases on kinematically planning axis motion profiles, it exploits acceleration and jerk limits of the drives and delivers a near-time optimal motion. Experimental validation and comparisons are presented to show significant improvement in the cycle time and accuracy of contouring Cartesian tool-paths.

Integrated Five-Axis Trajectory Shaping and Contour Error Compensation for High-Speed CNC Machine Tools

A feedforward trajectory command shaping algorithm is proposed to simultaneously reduce the contouring errors and avoid structural vibrations in five-axis CNC machine tools. Trajectory shaping is used to avoid the excitation of the transient, inertial vibrations but at the expense of distorting the reference path due to added delay. The contouring error caused by both trajectory shaping and limited bandwidth of servo drives is predicted based on the trajectory parameters and machine dynamics. The shaped axis commands are then corrected to precompensate the predicted contour errors. The effectiveness of the proposed technique is verified experimentally on a five-axis CNC machining center.

Experimental Study on Backlash Compensation of CNC Machine Tool

The backlash compensation has a great effect on the synthetical precision of CNC machine tool. Here, the measuring and backlash compensating technologies were investigated for high-speed CNC machine tool. Following, the backlash compensation of the synthetical geometric error of the interpolatimg movement and the evaluation system of position accuracy were proposed during CNC machine tool processing. The results indicate that the basic feature of error is established and provides a basis for putting forward the new error measurement method under the essential measuring condition. It also could be applied for different types of error compensation, shows that the backlash of the milling processing could be well compensated.

Real-Time B-Spline Interpolator with Look-Ahead Scheme for High-Speed CNC Machine Tools

NC tool paths of digital CAD models are currently generated as a set of discrete data points. The CNC interpolator must convert these points into continuous machine tool axis motions. In order to achieve high-speed and high-accuracy machining, the development of a real-time interpolation algorithm is really indispensable, which can deal with a large number of short blocks and still maintain smooth interpolation with an optimal speed. In this paper, a real-time local cubic B-spline interpolator with look-ahead scheme is proposed for consecutive micro-line blocks interpolation. First, the consecutive micro-line blocks that satisfy the bi-chord error constraints are fitted into a C1 continuous cubic B-spline curve. Second, machining dynamics and tool path contour constrains are taken into consideration. Third, local cubic B-spline interpolator with an optimal look-ahead scheme is proposed to generate the optimal speed profile. Simulation and experiment are performed in real-time environment to verify the effectiveness of the proposed method. Compared with the conventional interpolation algorithm, the proposed algorithm reduces the machining time by 70%.

Erratum to: Speed optimization control method of smooth motion for high-speed CNC machine tools

Erratum to: Speed optimization control method of smooth motion for high-speed CNC machine tools

Zero transmission and its application in high speed CNC machine tools

Zero transmission and its application in high speed CNC machine tools