Five-axis CNC Research Articles

Post-processing algorithm of five-axis CNC machine tool under rotation angle optimization

During the operation of 5-axis CNC machine tools, the angle deviation of the rotation axis greatly affects the tool path control. Therefore, a post-processing algorithm of five-axis CNC machine tool with optimized rotation angle was proposed. Firstly, the basic The structure of the machine tool was analyzed, the Hausdoff distance was used to obtain the matching error between the actual machined surface and the difference surface, and the error compensation method was used to compensate the obtained error, and the rotation axis angle of the machine tool was completed according to the processing result. Based on the optimization results, the machine tool coordinate system was established, and the machine tool post-processor was developed through the coordinate transformation results and integrated into the relevant software to realize the post-processing of the machine tool. The experimental results show that the proposed method achieves better processing results when used for post processing of machine tools.

A real-time dual NURBS interpolator with optimised control of flexible acceleration and deceleration for five-axis CNC machining

The limited computing capacity makes it difficult to plan a suitable feedrate profile in real-time for high speed and high accuracy machining of five-axis parametric toolpaths. In this paper, a real-time interpolation algorithm with optimised control of flexible acceleration and deceleration (acc-dec) for the dual NURBS toolpath is proposed. The toolpath is marked as subsegments with similar geometric properties by introducing the five-axis curvature. Machine kinematic and toolpath geometry constraints are considered in the kinematic parameter constraint model. Initial feedrate profiles are solved in a dynamic 3D window which preserves the motion performance of machine tools to a great extent. Convolution is used to smooth the initial feedrate profile to achieve a higher order continuity over the global range. Feedrate fluctuations caused by imprecise parameter interpolation are eliminated through modifying each interpolation periods. Resampling adjusts the position of interpolation points and unify the interpolation periods. All operations mentioned are in series and real-time is strictly guaranteed. Effectiveness of the developed algorithm is validated in simulations and also experimentally on a Self-developed-NC controlled 5-axis machine tool.

Simulation of Motion Nonlinear Error Compensation of CNC Machine Tools With Multi-Axis Linkage

In order to solve the problem of nonlinear error for a dual rotary table five-axis CNC machine tool due to the linkage of rotary and translational axes, the simulation of motion nonlinear error compensation for a multi-axis linkage CNC machine tool is proposed. The adjacent points in the tool position file are selected as the tool position points for building the model, and then the nonlinear error model resolved by the harmonic function is established according to the error distribution in the classical post-processing. The nonlinear error between the two tool position points is quickly predicted by the analytical expression of this model, and the real-time error compensation of the intermediate interpolation points is realized. Finally, MALTLAB simulation analysis is performed on the tool position file of an impeller part machining to verify the effectiveness of the proposed algorithm. The experimental results show that it can be seen from the distribution curve of the nonlinear error that it is about 10% after compensation as before compensation, thus verifying the effectiveness of the nonlinear error compensation mechanism. The correctness of the nonlinear error analysis and compensation method and the effectiveness of post-processing are verified.

Sensitivity analysis and compensation for tooth surface deviation of spiral bevel gear machine tool

To analyze the quantitative mapping relationship between the geometric errors of the five-axis CNC machine tool and the tooth surface deviation of spiral bevel gears, and identify the key geometric errors that affect the machining deviation of the spiral bevel gear tooth surface, a sensitivity analysis method for tooth surface machining deviation of spiral bevel gear based on screw theory and EFAST method is proposed. Firstly, the machining model of the spiral bevel gear tooth surface based on the five-axis CNC machine tool is established. Then, the geometric error transfer model of the machine tool is established based on the screw theory. Combined with the EFAST global sensitivity analysis method, the key geometric errors that affect tooth surface deviation are identified. Finally, the reliability and effectiveness tests are performed by comparing the results to the local sensitivity analysis method and simulating compensation for the key geometric errors. The result of compensation shows that the tooth surface deviation is reduced significantly according to global sensitivity analysis. The feasibility of applying sensitivity analysis to control the tooth surface deviation of spiral bevel gears has been demonstrated.

Geometric error compensation method of five-axis CNC machine tool based on improved genetic algorithm

Geometric error compensation method of five-axis CNC machine tool based on improved genetic algorithm

Study on the material removal mechanism and the exit breakage of ultrasonic vibration-assisted grinding for microcrystalline glass

With the aim of solving problems such as exit breakage and surface microcracks during microcrystalline glass machining, an ellipsoidal erosion model is established by analyzing the motion trajectory and characteristics of single diamond grit in ultrasonic vibration-assisted grinding (UVAG), and the material removal volume of single diamond grit particles is obtained. A simulation model of UVAG of microcrystalline glass is established by the finite element method. The effect of process parameters such as rotational speed, grinding depth, feed rate on grinding force and workpiece edge stress has been investigated. The experiment of UVAG for microcrystalline glass is performed on a five-axis CNC machine with the same process parameters, and the surface morphology, surface roughness, and exit breakage sizes of microcrystalline glass are observed. The results show that with the increase in grinding depth, the average grinding force between the tool and the workpiece increases, and the proportion of material removal in a brittle fracture increases. As the rotational speed increases, the grinding force between the tool and the workpiece gradually decreases and results in an improvement in the surface quality of the workpiece. As the feed rate increases, the surface roughness increases by 16.76%, the width of the edge breakage increases by 109.19%, and the thickness of the edge breakage increases by 104.49%.

Five-axis path smoothing based on sliding convolution windows for CNC machining

Tiny linear toolpaths widely used in five-axis CNC machine tools only meet G0 continuity at the junctions of adjacent paths, the tangential and curvature discontinuities at the corners result in decelerations and fluctuations of machine tools. Although the corner smoothing for the three-axis tool path is relatively mature, the five-axis tool pose path smoothing is still difficult to plan due to the nonlinear motions of the rotational axes and the parameter synchronization between the tool center point (TCP) path and the tool orientation vector (TOV) path. Therefore, this paper aims to extend the smoothing scopes of previously presented mixed tiny path smoothing method based on sliding convolution windows for three-axis CNC machining (Zhang et al. in Journal of Manufacturing Process 102:685–699, [19]). Compared with the previous work, this paper converts the five-axis tool pose path into the tool position signal and tool orientation signal, and the interpolation points of the two path signals in the convolution window are directly processed on the basis of the synchronous motions of all axes. The original parameter synchronization relationship between the TCP path and the TOV path is still maintained. Besides, the smoothing error prediction model is constructed. The proposed five-axis path smoothing method has been integrated into a self-developed open-architecture CNC system and its effectiveness for the five-axis path optimization is validated via the simulation and experiment.

Spherical path planning for multi axis support free additive manufacturing of truss structures

Multi-axis additive manufacturing systems are gaining increasing attention due to their potential for unsupported manufacturing and reduced stair-stepping effects. In response to the challenges of unsupported printing for truss structures, a five-axis path planning method based on spherical slicing has been proposed. Leveraging the implicit expression equation based on cylinders, this study has effectively achieved the generation of efficient surface slicing and five-axis spherical path. The employed path planning method demonstrates significant advantages in both generation efficiency and stability. In the testing experiments, various unsupported path planning schemes are generated for different truss cells and truss structures, including configurations such as the “bridge” and cross-cylinder truss cells. To validate and extend the applicability of this method, two types of five-axis additive manufacturing devices are utilized: one based on a five-axis CNC system and the other employing a UR10 robot. The manufacturing experiments have effectively verified the feasibility of the spherical slicing algorithm in manufacturing various truss unit types, which provides a new technical way for the unsupported manufacturing of truss structures in the future.

Five-axis CNC machining method for eyeglass lens edge profile

Five-axis CNC machining method for eyeglass lens edge profile

Cubic time-spline fitting and interpolation for five-axis CNC machining

Abstract In CNC machining, G01 codes are widely used to represent the tool path. Directly interpolating these G01 codes is time-consuming and may cause discontinuities. In this paper, we propose a time-spline curve fitting method that combines tool path fitting and feedrate scheduling into a single step for five-axis CNC machining. The input for this method consists of a three-dimensional linear path of the tool tip in the workpiece coordinate system and two-dimensional tool orientations in the machine coordinate system (MCS). The output is a fitted tool path in the MCS represented by a five-dimensional smooth time-parametric B-spline curve, simply referred to as the time-spline curve. The time-spline curve provides not only position information but also kinematic information, including velocity, acceleration, and jerk for each axis, directly derived from the first, second, and third derivatives of the curve. To meet fitting error constraints and axial kinematic constraints, our objective is to find the time-spline curve that is time-optimal. We formulate the optimization problem as a nonlinear optimization model and design a recursive algorithm to solve it. The resulting time-spline curve demonstrates high accuracy and fully utilizes the machine’s kinematic capabilities. Along the tool path defined by the time-spline curve, exact interpolation points can be straightforwardly obtained according to the interpolation period. Simulations and experimental results indicate that the proposed method yields a time-optimal time-spline curve with the desired precision and kinematic constraints.

A Study of the Microstructure and Mechanical and Electrochemical Properties of CoCrFeNi High-Entropy Alloys Additive-Manufactured Using Laser Metal Deposition

This work demonstrates the successful additive manufacturing of an in situ-alloyed CoCrFeNi HEA with a single phase (FCC) structure via the laser metal deposition (LMD) technique. In this work, bulk specimens of the CoCrFeNi high entropy alloy (HEA) of size 15 mm × 15 mm × 45 mm were additive-manufactured (AMed). An H320-type additive-subtractive manufacturing all-in-one system with a 2 kW fiber laser with a coaxial nozzle head integrated in a five-axis CNC machine was used. The effect of varying laser powers (1000 W, 1300 W, and 1600 W) on the microstructure and mechanical and electrochemical properties of the AMed HEA specimens was investigated. The AMed specimens were analyzed for their microstructure, elemental distributions, microhardness, and mechanical and electrochemical properties. An increase in the laser power led to a non-uniform cooling rate and non-steady solidification rates of the molten area during the AM process. As a result, the crystal constant decreased, and the microhardness fluctuated within a narrow range across the specimen. Among the three laser powers, the AMed CoCrFeNi HEA at 1300 W had the optimal mechanical properties and the best electrochemical behavior in 3.5 wt.% NaCl solution.

A novel simulation model of three-dimensional surface topography for five-axis CNC milling using bull-nose tool

A novel simulation model of three-dimensional surface topography for five-axis CNC milling using bull-nose tool

Research on Machining Error Control Method Driven by Digital-twin Model of Dynamic Characteristics of Machining System

The position of each component structure in the machining space of the machining system directly affects the machining quality of the workpiece. In this paper, RBF neural network is used to study the spatial dynamic characteristics of the translational axes of five-axis CNC machine tools. It is the basis for building an evolvable knowledge base. Process evaluation, information feedback, and iterative optimization of thin-wall parts were carried out using digital-twin technology. Firstly, the model simulation of the translational machining space of a three-dimensional five-axis CNC machine tool is carried out by using the finite element method. The RBF neural network predicts the natural frequency of a translational machining space dynamic characteristics. It is further used to construct the dynamic characteristic spectrum of the translational space of CNC machine tools. Secondly, the machine tool flush space cutting process is built with a digital-twin system to optimize the iterative mechanism for machining process optimization. Finally, the method’s effectiveness was verified by experiments on milling thin-walled parts on a dual-turntable five-axis CNC machine and by contouring error measurement experiments. The results show that the average error of the optimized thin-wall contour is reduced by 26.9%. The iterative mechanism can continuously optimize the machining error and improve the machining accuracy. The iterative mechanism can continuously optimize the machining error and improve the machining accuracy.

A novel method to minimize the five-axis CNC machining error around singular points based on closed-loop inverse kinematics

A novel method to minimize the five-axis CNC machining error around singular points based on closed-loop inverse kinematics

Five-axis parallel mechanism system (PMS) CNC partial link control system based on modified inverse kinematic of 6-DOF UPS parallel manipulator

This paper presents a control system algorithm for a five-axis parallel mechanism system (PMS) CNC milling machine based on a 6-DOF Stewart platform parallel manipulator with a universal-prismatic-spherical (UPS) configuration. The control system reads the G-Code commands as standard CNC machine language, then extract data points and interpolates them to generate the robot trajectory patterns as motion references. Then, the control system uses the modified inverse kinematic equation to determine the length of each link to move the end effector to track the trajectory patterns from the previous G-code extraction process. The inverse kinematic equation is modified especially for the five-axis PMS CNC milling machine by including machine-offset and tools-offset parameters so it will be easier for the control system to implement the kinematic equation. As expected, the system simulation results successfully followed the G-Code program moving commands. The average error of the length control system is 0,1 mm, while the average error of the length change rate control system is 1,8 mm/s. The maximum error is 26.9 mm was caused by the system's inability to follow the motion profile in transient. It can be concluded that 6-DOF Stewart platform parallel structures,which provide better performance than serial structures, can be implemented as a new concept for the motion mechanism of five-axis CNC milling machines. The five-axis PMS CNC milling machine also promises better performance than conventional five-axis gantry structures CNC.

Optimization of cutting parameters based on surface partitioning

With the rapid development of science and technology, five-axis CNC machine tools are widely used in the field of complex surface parts processing and manufacturing, so the part geometry model of the complex surface becomes more and more complex. Most traditional machining methods use fixed cutting parameters to calculate and generate five-axis machining toolpaths. If the fixed cutting parameters are used to generate the 5-axis machining toolpaths, the optimal cutting condition will not be obtained in some parts, and the generated machining toolpaths will be less adaptable. In this paper, the complex surface is partitioned and the cutting parameters are optimally adjusted to different parts of the workpiece during the cutting process to respond to the change in the cutting state.

Gear evaluation deviations-based crucial geometric error identification of five-axis CNC gear form grinding process

The gear form grinding accuracy is significantly affected by crucial geometric errors. The gear form grinding process is a special line contact forming method. There are exclusive evaluation standards for gear grinding accuracy. While the existing sensitivity analysis for spatial point errors cannot meet the final gear report requirements. Hence, a novel method for analysis of geometric error influence on the key gear evaluation deviations (GED) is proposed. First, the actual digital tooth surface considering geometric errors and gear form grinding mechanism was constructed according to the homogeneous transformation matrix (HTM) and multi-body system theory (MBS). Second, the GED of the digital tooth surface was gained according to the modified gear meshing equations. Third, the analytic mapping relationship between the GED and machine tool geometric errors was first established. Then, the crucial geometric errors affecting the GED were identified based on a proposed Morris method. Finally, the identification results were compared to the existing publications, and the compensation discussions of crucial errors were demonstrated to validate the advantages of the proposed method. It can be found that the compensation results of GED-oriented key errors are better than those of the traditional methods, which is beneficial to the improvement of evaluation reports.

Real-time estimate and control contour errors for five-axis local smoothed toolpaths based on airthoid splines

Five-axis linear commands are blended as the local smoothed toolpaths by inserting clothoid and airthoid splines at corners in five-axis CNC machining. The contour error is the bottleneck to achieve the precise dimension of the machined parts, when following the local smoothed toolpaths. This paper presents a contour error estimation and control method for the five-axis smoothed toolpaths with airthoid splines, according to the geometric characteristics of the toolpaths. The tool-tip contour error is analytically calculated based on the expression of the smoothed toolpaths. Consequently, the tool-orientation contour error is obtained by synchronizing the tool-orientation contour point with the tool-tip item based on the motion time through the designed time scale coefficient, when the toolpaths are scheduled by the time-synchronization scheme. Furthermore, a contour error compensation strategy is constructed to adaptively determine the compensator gain. It can be qualified to maximally eliminate the contour errors and steadily hold the control stability of the feed drives, in spite of the modeling error between the nominal and actual control models. The simulation and experiment results show that the estimation algorithm has higher accuracy than traditional methods, and the compensation strategy effectively eliminates the five-axis contour error.

Parasitic Motions of 3-PRS Parallel Mechanisms with Two Different Branch Chain Arrangements

The kinematics of 3-PRS parallel mechanisms (PMs), an important category of 2R1T PMs, is very important for the motion control and error compensation of PMs. In order to produce a spindle head that could meet the requirements of various machining accuracy levels, a definite kinematics analysis of the PMs par should be taken with caution firstly. Here, the mathematical models of two 3-PRS PMs with different branch chain arrangements were established using the Euler angle. The kinematic equations of two 3-PRS PMs were obtained by establishing the closed-vector loop equation according to structural conditions. Parasitic motions that would cause a great effect were obtained, and their variations with structural and kinematic parameters were also obtained through MATLAB. Since the relationship between parasitic motions, and the given structural and kinematic parameters, is inextricable, an analysis is performed for the purpose of reducing or eliminating parasitic motion to ensure the accuracy of end-effector movement. The caused effect of parasitic motion can be improved with scale optimization and precision compensation. Lastly, two improved 3-PRS PMs without the parasitic motion of different branch chain arrangements used as the spindle head were obtained. Parasitic motion was related to the mechanism configuration and could be avoided in the configuration design stage with the comprehensive optimization of the structural and kinematic parameters, which provides a reference to obtain a sufficient workspace and improve the precision of traditional five-axis CNC machine tools.

Rotation-Angle Solution and Singularity Handling of Five-Axis Machine Tools for Dual NURBS Interpolation

Dual NURBS interpolation has been proven an essential technique for high-speed precision machining of complex surfaces. The solution of rotation angles and their derivatives is the basis of kinematic transformation and feedrate optimization in dual NURBS interpolation. The characteristics of the rotation motion of five-axis machine tools with different structures are analyzed. A generic model of dual heads of the vertical five-axis machine tool is established to unify the solution of rotation angles. Then, a generic method for solving the rotation angles and derivatives based on the vector inner product is proposed, and the solution space is analyzed. A singularity handling is given to avoid abrupt rotation angles based on the higher derivatives of the tool orientation vector. The proposed method obtained smooth rotation angles at the singularity points in the cardioid dual NURBS interpolation experiment. It reduced the machining time by 43.3% compared with the simple inverse trigonometric method based on kinematic transformation. Experiment results demonstrate that the proposed method is feasible and effective, and has significant theoretical and practical value for optimizing five-axis CNC machining.