Five-axis Machine Tool Research Articles

Research on error tracing method of five-axis CNC machine tool linkage error

Since their ability to machine complex curved surface, five-axis CNC machine tools have been widely used in the machining field. To guarantee the accuracy of the complex surface machining, multi-axis linkage performance detection of five-axis machine tools is necessary. RTCP (rotation tool center point) is one of the basic essential functions for five-axis machine tools, which could effectively reduce the nonlinear errors caused by rotation axes when five axes move synchronously. On the basis of RTCP function, a way to detect multi-axes linkage performance of five-axis machine tools is introduced in this paper. Some simulations that exhibit the relationship between the tool center error trajectories and the factors influencing the linkage performance of the machine tool are established based on the linkage error model. Analyzing the rule of tool center error trajectories, a linkage error tracing method is proposed based on feature extraction and trajectory similarity. The experiments based on RTCP are carried out, and the tool center point error variation is shown to be consistent with the simulation result. Furthermore, the error of the error tracing method is less than 5%, which means the error tracing method could find the mismatch parameters effectively. This attempt provides a theoretical support for linkage performance detection and error tracing of five-axis CNC machine tools.

An efficient error prediction and compensation method for coordinated five-axis machine tools under variable temperature

I n a dual-machine system, the positioning accuracy of coordinated machine tools is one of the most important performances. Considering the quasi-static errors of the developed system, the paper presents an effective error prediction and compensation method for coordinated five-axis machine tools under variable temperature. Firstly, for error prediction at a constant temperature, the workspace of coordinated machines is divided into the subspaces of translation and rotation axes, and an error prediction algorithm is presented with the known errors at sampled points. When the temperature changes, the thermal errors of the coordinated machines are analyzed by the simulation and error measurement, and an interpolation method is proposed to quickly determine the sampled data at any temperature. For error compensation, a recursive algorithm is proposed to compensate the absolute and relative pose error of dual machines. Validation experiments have been conducted to verify the proposed method on the developed system. The results have shown that, compared with previous method, the method presented in this paper is more accurate and time-efficient for error prediction and compensation under variable temperature conditions.

Identification of position independent geometric errors of rotary axes for five-axis machine tools with structural restrictions

Abstract Some of five-axis machine tools, which are widely used for micro-machining, have structural restrictions, such as the center line of tilting rotary axis being close to the surface of worktable or beneath the worktable. In this paper, simultaneous motions of both rotary and translational axes are combined with double ball bar to establish a measurement and one installation-based method for identifying the position independent geometric errors (PIGEs) of rotary axes for this kind of five-axis machine tools. Due to the existence of structural restrictions, the tool ball usually cannot be placed in the center line of the tilting rotary axis, and thus, actual spatial motion of ball bar is considered in the proposed identification procedure. For each rotary axis, two test configurations, i.e. the one along the radial direction of rotary axis and the other along the axial direction, are proposed to carry out the designed measurement and identification. Especially, to well avoid the potential negative problems induced by structural restrictions, rotary and translational axes are simultaneously controlled to carry out the measurement, and in the identification procedure, eccentricities together with angle shift and setup errors are comprehensively involved. Based on this basic consideration, spatial plane, on which the actual trajectory of table ball lies, is accurately constructed to integrate the actual movement of ball bar into the PIGEs identification procedure. Novel fitting strategies are developed to mathematically model both the actual trajectory and the spatial plane of table ball’s motion, which are then adopted to formulate the expressions for identifying location and orientation errors. Both simulation and experimental verifications show that the proposed method is effective and helpful for checking and improving the status of five-axis machine tools.

Interpolation-based contour error estimation and component-based contouring control for five-axis CNC machine tools

High accuracy contour error estimation and direct contour error control are two major approaches to reduce the contour error. However, two key factors make them complex for five-axis machine tools: the nonlinear kinematics and the coupling between the tool position and orientation. In this study, by finding the reference point nearest to the current actual position, and interpolating the point with two neighboring reference points and using the distance ratio, a new contour error estimation method for five-axis machine tools is proposed, which guarantees high accuracy while depending on only the reference points. By adding a weighted contour error on the tracking error in the workpiece coordinate system, and specifying a desired second-order error dynamics based on the error variable, an effective contouring control method is proposed, which can alleviate the problem: when the contour error components are introduced into the controller, the contour errors increase instead in some regions of the tracking trajectory. A series of experiments are performed on a tilting-rotary-table (TRT) type five-axis machine tool. The results reveal that the proposed estimation method has high accuracy, and compared with the case without contour error control, the proposed control approach can reduce the contour error along the whole trajectory.

Application of the adaptive Monte Carlo method in a five-axis machine tool calibration uncertainty estimation including the thermal behavior

Calibration of the geometry of five-axis machine tools needs to be performed periodically since the machine accuracy has a direct impact on machined parts. Because mechanical adjustment and a software correction may be done using calibration results, the measurement results must be evaluated. In this paper, the scale and master ball artefact (SAMBA) method is evaluated through the estimation of the uncertainty of the identified machine geometric error parameters. This approach has the multi-input multi-output (MIMO) model and an iterative solution that makes it challenging to apply commonly used uncertainty calculation methods The Guide to the Expression of Uncertainty in Measurement Supplement 2 (GUM S2) gives the opportunity to estimate the uncertainty of a MIMO model through the adaptive Monte Carlo method (MCM). In order to include all the uncertainty sources, the input uncertainty is estimated from the repeated calibration tests performed in different thermal conditions (with and without the warm-up cycle). The uncertainty is calculated for each of the identified machine geometric error parameters along with their covariance. The correlation between the output variables and the impact of the machine state, before and during the repeated calibration, are analyzed. The results demonstrate that the machine tool geometry variations occur even without the warm-up cycle performed before the calibration. Moreover, machine performance has an impact the calibration results.

Geometric error identification and compensation for non-orthogonal five-axis machine tools

This paper proposed a systematic method to identify and compensate the geometric errors of non-orthogonal five-axis machine tools. An efficient ballbar test with a 45° wedge is designed to decouple the position-dependent and independent geometric errors for the non-orthogonal rotary axis. The geometric errors of translational axes are measured by step-size body diagonal tests based on a laser interferometer. After all the error items are measured, the volumetric error is precisely predicted and compensated based on the screw theory. The proposed geometric error identification and compensation strategy are experimentally verified via cone frustum tests on a DMG non-orthogonal five-axis machine.

Chatter stability prediction for five-axis ball end milling with precise integration method

The differential dynamic equation (DDE) considering regenerative chatter effect is derived from an ideal cutting model. At the same time, the ball end mill-workpiece engagement (BWE) in five-axis milling is efficiently extracted by the semi-analytical method, where the machining residual left on the finished surface is taken into account. The explicit precise integration method (PIM) is adopted to translate the DDE into a time series expression, ensuring stability prediction without any discretization error loss. With the relationship of cutter edge and BWE at different instants, the stability lobe diagram (SLD) is constructed by Floquet theory, which is subsequently testified in the five-axis NC machine tool. The experimental results keep good agreement with estimations, validating the proposed method. Compared with traditional method in dynamic cutting forces modeling, the proposed approach is more close to actual processing. In contrast to Runge-Kutta based complete discretization method, PIM shows higher superiority no matter in convergence rate or calculation accuracy. Lastly, the influences of different inclination angles on stability are revealed, which can give a reference to selection of suitable process parameters for higher productivity.

Method for simultaneous measurement of five DOF motion errors of a rotary axis using a single-mode fiber-coupled laser.

The rotary axis is the basis for rotational motion. Its motion errors have critical effects on the accuracy of the related equipment, such as a five-axis computer numerical control machine tool. There are several difficult problems in the implementation of high-precision and fast measurement of the multi-degree-of-freedom motion errors of a rotary axis. In this paper, a novel method for the simultaneous measurement of five-degree-of-freedom motion errors of a rotary axis is proposed, which uses a single-mode fiber-coupled laser with a full-circle measuring range. It has the advantages of high efficiency, low cost, and it requires no decoupling calculation. An experimental system was built and a series of experiments were performed. The standard deviation of stability for 60 min of the five-degree-of-freedom measurement is 0.05 arcsec, 0.06 arcsec, 0.04 μm, 0.03 μm, and 0.19 arcsec, respectively. The repeatability deviation of measuring an indexing table is ± 3.4 arcsec, ± 4.6 arcsec, ± 2.6 μm, ± 2.4 μm, and ± 3.2 arcsec. The maximum deviation of comparison is 3.9 arcsec and 3.2 arcsec. These results demonstrate the effectiveness of the proposed method; thus, a new approach of simultaneous measurement of the multi-degree-of-freedom motion errors of a rotary axis is provided.

Singularity avoidance for five-axis machine tools through introducing geometrical constraints

Abstract Singularities in five-axis machining are a series of deadly positions, which may cause unstable axis movements and deteriorate the performance of machine tools. This paper presents an optimization strategy to locally deform the tool path so that singularities of five-axis machine tools can be avoided. To achieve this purpose, a new concept of “forbidden circle”, which is the projection of the three dimensional “singular cone” associated with tool orientations in a two dimensional space named P-plane, is established for the first time to transform the complicated three dimensional problem into a two dimensional problem. Based on this idea, the projected points in P-plane are interpolated as B-spline first, and then, the B-spline control points are locally optimized by taking the “forbidden circle” as the geometrical constraint to keep the B-spline from crossing it. Especially, in the optimization procedure, the constraints are linearized with the changes of B-spline control points to change the whole optimization problem as a typical positive definite quadratic programming problem, which can achieve one and only global optimal solution. By doing so, singularity is avoided, and at the same time, the machining errors caused by tool path deformation can be minimized. Simulation and experimental results verify the effectiveness of the singularity avoidance method.

Comparison of Direct and Indirect Methods for Five-axis Machine Tools Geometric Error Measurement

Geometrical error (GE) is a key criterion for machine tools performance evaluation. GE measurement methods can be classified as direct and indirect methods. As an indirect GE measurement method, the scale and master ball artefact (SAMBA) method can estimate the GE of linear and rotary axes by probing series of master balls and a scale bar artefact installed on the machine tool pallet. The purpose of this study is to research the performance of direct and indirect GE measurement methods (i.e. laser interferometer and SAMBA method) in linear positioning error measurement such as EXX and EYY. These errors of the X- and Y-axis are separately measured on a five-axis machine tool with the two methods. The results reveal that the SAMBA method yields similar results as the laser test in error shape and range. However, there are some minor differences which are discussed.

Self-calibration for motion errors of rotary and linear axes on a five-axis machine tool and workpiece geometric errors

Self-calibration for motion errors of rotary and linear axes on a five-axis machine tool and workpiece geometric errors

Modelling and compensation of dominant thermally induced geometric errors using rotary axes’ power consumption

Thermally induced volumetric errors due to rotary axes’ activity are measured on a five-axis machine tool using a non-contact R-test device with a four-ball uncalibrated artefact and an Invar reference length. The gathered volumetric data allow to estimate intra- and inter-axis machine errors as well as the table expansion via the estimated balls position. Dominant thermal effects are modelled as functions of the measured rotary axes drive power consumption by the superposition of single-input single-output first order transfer functions. The efficiency of the model is validated with different motion sequences and by the compensated machining of a test piece.

Milling of Fir-Tree Slots in Allvac 718 plus

For the machining of profiled grooves in turbine discs made out of nickel based alloys, broaching is still state of the art. However, the broaching process entails some disadvantages like high costs and long delivery times for the machine tools and the broaches in combination with inflexibility with regard to the groove geometry and machining task. An alternative to the broaching process is the integration of the profile slotting on a 5-axis milling center. This paper deals with an approach for machining a fir-tree slot via different milling process chains. The two roughing strategies, ceramic side milling and carbide end milling, are depicted with regard to tool wear and the economy. The finished fir-tree slot will be evaluated in terms of dimensional stability. In addition, the possibility of finish broaching on a five-axis machine tool is shown.

A novel geometric error identification methodology for the tilting head of five-axis machine tools based on double ball bar

The paper proposes a novel geometric error identification methodology for the tilting head of five-axis machine tools using double ball bar(DBB).Firstly, based on the motion condition of the tilting head of five-axis machine tools, three measurement patterns in Y direction, X direction and Z direction are proposed respectively. Then, the relative displacement equations of two balls of DBB in three measurement patterns are established respectively on the basis of homogeneous transform matrix (HTM) and multi-body system (MBS) theory. Finally, the geometric error parameters of the tilting head are identified totally. The presented method is universal and provides a reference for the error identification for the tilting head of five-axis machine tools.

Measurement and analysis of thermo-elastic deviation of five-axis machine tool using dynamic R-test

Thermal errors have a significant impact on machine tool accuracy. Due to their high expense, the conventional shop floors often have poor air conditioning. Even this environmental temperature variation can cause crucial thermo-elastic deviation for precise components. In this paper, a method based on dynamic R-test is presented for the measurement of thermo-elastic deviation of a five-axis machine tool under environmental temperature variation of a conventional shop floor. Due to short measuring time of under 8 minutes, the dynamic R-test enables geometric measurement of a thermal state of the machine tool. The advance in measuring speed is achieved by continuous movement of the machine tool during the measurement procedure. For this purpose, the position of machine axes and measurement data of the sensor are stored synchronously. With a mathematical model, the geometric errors are calculated including all location and orientation errors and important error motions of the five-axis machine tool. The error motions are modelled as a B-spline function of their related axis positions. The measurement is applied repeatedly over three days under environmental temperature variation. The results are presented with the measurement uncertainties and the correlation of the measured errors and temperature.

State Prediction Model of Five-axis Machine Tools based on the "S" Test Piece Surface Finish

With the development of industries and advanced manufacturing technology, the performance of the machine tools plays an important role for the product quality. Nowadays five-axis linkage machining centers (5-axis MC) have been applied in the aerospace industry widely. During the thin-walled aircraft parts machining process of the 5-axis MC, the stochastic chatter phenomenon has important influence on the machining precision and quality of the parts. It has been the research hot point due to predict the 5-axis MC state hard with the complex operating process. “S” test work-piece(S test piece) is with the features of aerospace thin-walled parts. A State Prediction model for 5-axis MC based on the S surface finish is presented. Firstly, the movement principle of 5-axis MC during the S test piece processing is analyzed by using VERICUT Simulation tool; Then the information coupling method during geometry, operating process, monitoring and S test piece surface finish is built based on external export directions. By using the Geometry-Process-Monitor-Surface Quality information coupling method, the monitoring signal information data included vibration signals and acoustic emission signals are obtained while a S test piece finishing processing; the 5-axis MC state is predicted by using the ensemble empirical mode decomposition(EEMD) method with three indicators: fractal dimension (FD ),standard deviation (SD)and Power spectral entropy (PSE). By using a coordinate measuring machine (CMM) and a Scanning Electron Microscope to measure the machined S test piece, the actual geometry and surface finish of the S test piece can be obtained. Finally, the mapping relationship during the geometry-operating process-monitoring-surface finish of a S test piece are constructed. The prediction system is developed by using LABVIEW and MATLAB. This model is applied to the 5-axis MC and the experimental results show that this model will be the effective means for predicting the state of the five-axis machining center.

Primena neuronskih mreža za predviđanje rešenja kinematskih grešaka kod trohoidne obrade petoosnom glodalicom matsuura MAX-330

The prediction of machining accuracy of a Five-axis Machine tool is a vital process in precision manufacturing. This work presents a novel approach for predicting kinematic errors solutions in five axis Machine. This approach is based on Artificial Neural Network (ANN) for trochoidal milling machining strategy. We proposed a multi-layer perceptron (MLP) model to find the inverse kinematics solution for a Five-axis Machine Matsuura MX-330. The data sets for the neural-network model is obtained using Matsuura MX-330 kinematics software. The solution of each neural network is estimated using inverse kinematics equation of the Machine tool to select the best one. As a result, the Neural Network implementation improves the performance of the learning process. In this work trochoidal trajectory generation formulation has been developed and simulated using the software Matlab Inc. The main advantage of the trochoidal path is to present a continuous path radius leading the machining process to take place under favorable conditions (no impact, less marking of the part, ...). Obtaining the toolpath is to allow programming of the toolpath according to ISO 6983 (which defines the principles of the G code). For this, numerical study of trochoidal strategy and experimental result are presented with aims to full milling and to ensure a control of radial engagement.

转台-摆头式五轴机床几何误差测量及辨识

转台-摆头式五轴机床几何误差测量及辨识

Effect of the Dynamic Characteristics of a Five-axis Machine Tool on the Surface Quality of Complex Surface

Due to complex machining process on five-axis milling center, a complex surface usually has uneven quality distribution. To achieve high quality in a unified surface, a machine tool must has good dynamic behavior and possible defect surface also should be known in advance. In this paper, the dynamic stiffness of machining is discussed by studying the processing characteristics of a machine tool. The effect of the dynamic stiffness on surface quality is evaluated using the force-excited model. The relationship between the parameters of vibration and surface quality is established to analyze the influence. In the results, a complex surface S shaped part is evaluated as an example. A method for measuring surface quality, including roughness and waviness, is also considered in this paper.

Prediction and compensation of geometric error for translational axes in multi-axis machine tools

This paper proposes an integrated geometric error prediction and compensation method to eliminate the positioning inaccuracy of tool ball for a double ball bar (DBB) caused by the translational axes’ geometric errors in a multi-axis machine tool (MAMT). Firstly, based on homogeneous transform matrix (HTM) and multi-body system (MBS) theory, the positioning error model only considering the translational axes of a MAMT is established. Then, an integrated error parameter identification method (IEPIM) by using a laser interferometer is proposed. Meanwhile, the identification discrete results of geometric error parameters for the translational axes are obtained by identification experiments. According to the discrete values, the optimal polynomials of 18 position-dependent geometric errors (PDGEs) are founded. As a basis, an iterative compensation method is constructed to modify the NC codes generated with the ordinary compensation method in self-developed compensation software. Finally, simulation verification is conducted with these two compensation methods. Simulation results show the positioning errors for test path of tool ball calculated with the iterative compensation method that are limited within 0.001 mm, and its average accuracy and accuracy stability are improved by 79.5 and 52.2%, respectively. In order to further verify the feasibility of the presented method, a measuring experiment is carried out in XY plane of a five-axis machine tool by using DBB. The experiment results show that the maximum circularity error with the iterative compensation method is reduced about 40.4% than that with the ordinary compensation method. It is therefore reasonable to conclude that the proposed method in this paper can avoid the influence of the translational axes’ geometric errors on rotary ones during a DBB test.