Five-axis Computer Numerical Control Machine Research Articles

An integrated method for compensating and correcting nonlinear error in five-axis machining utilizing cutter contacting point data

In current five-axis computer numerical control (CNC) machining, the use of minute linear path segments as an approximation for the ideal cutter contacting (CC) point trajectory is still prevalent. However, introducing rotation axes leads to a deviation of the actual CC point trajectory from the ideal, resulting in nonlinear errors. An integrated method is proposed in this paper for compensating and correcting both the contour error, associated with the approximation of the part surface by the ideal CC point trajectory and the nonlinear error of the CC point trajectory based on the information in the CC point data. By analyzing the spatial relationship between the tool posture and the CC point path during the five-axis linear interpolation process, two adjacent machining tool positions containing CC point data information are selected as the starting and ending points of the five-axis linear interpolation machining. The ideal tool center point and the actual CC point are calculated during the interpolation process, as well as the distance and the unit vector in the perpendicular direction between the actual CC point and the ideal CC point trajectory segment. In the comprehensive error compensation and correction phase, the obtained unit vectors are used as direction vectors for error compensation, and the tool center point during interpolation is first compensated and corrected. This ensures the actual CC point and the contour curve are on the same plane. The compensation direction for contour error is calculated using the start/end tool axis vectors and the ideal CC point trajectory vectors. The size of the contour error approximating the contour curve is calculated through the chord error. A second compensation and correction are applied to the tool center point for interpolation, ultimately achieving comprehensive compensation and correction of nonlinear errors. The data calculations were conducted in the MATLAB environment using actual machining data. After compensation and correction, the contour error was reduced by 76%, the nonlinear error of the CC point trajectory decreased to below 0.88 μm, and the comprehensive nonlinear error of the CC point trajectory was reduced from 19 to 1.5 μm, a reduction of 93%. This demonstrates significant practical value in enhancing the accuracy of five-axis CNC machining. Through actual machining verification, after using the method described in this paper, the average surface roughness decreased from 1.133 to 0.220 μm, and the maximum surface roughness decreased from 6.667 to 1.240 μm. This significantly demonstrates that the compensation and correction method proposed in this paper can significantly improve the surface quality of machined parts.

Five-Axis Contour Error Control Based on Spatial Iterative Learning

In this paper, a contour error control strategy based on spatial iterative learning control (sILC) is developed for repetitive processing of five-axis computer numerical control (CNC) machine tools. A curve approximation method with an adaptive moving window is developed to achieve accurate tool position and orientation contour error estimation, and a five-axis contour error control strategy based on sILC is proposed. The compensation method is derived using an sILC algorithm to modify the geometric reference path instead of modifying the controller. The experimental results show that the proposed control strategy reduces contour errors of five-axis CNC machine tools, and it outperforms the traditional tracking error control. Note to Practitioners—This paper aims to propose an effective five-axis contour error control scheme. At present, most of the five-axis contour error control methods rely on the modification of the controller, which is not allowed in commercial CNC systems. Therefore, we propose a five-axis contour error compensation algorithm based on sILC, which modifies the system’s reference path. Experimental results show that the proposed method can reduce the five-axis contour errors, while maintaining the machining efficiency.

Compensation of Thermally Induced Errors in Five-Axis Computer Numerical Control Machining Centers Equipped With Different Spindles

Abstract Thermally induced errors are the dominant source of inaccuracy in machine tools today and are often the most difficult type of error to reduce. Software compensation of thermally induced displacements at the tool center point (TCP) is a widely employed error reduction technique due to its cost-effectiveness and ease of implementation. Transfer function (TF)-based compensation methods lead to promising results, as has been shown in previous studies. Furthermore, machine tool manufacturers frequently offer the same type of machine tool equipped with different spindle units. This leads to different thermal deformation behavior depending on the specific spindle unit mounted in the machine tool. To demonstrate this difference, experimental research is carried out on three five-axis computer numerical control (CNC) machining centers of the same type equipped with three different spindle units. The experimentally obtained thermal errors at the TCP of three machine tools with different mounted spindle units are compared, showing a significant variation in thermal errors in the Z-direction depending on the spindle unit. The research presented in this paper shows a dynamic approach to thermal error compensation of five-axis CNC machining centers considering different spindle units. System identification theory is applied to build dynamic thermal error models for three different spindle units based on calibration experiments. Subsequently, the evaluation of model performance through spindle spectrum tests shows that a reduction in thermal error of up to 85% was achieved in the Z-direction after compensation.

Additive manufacture of 3 inch nuclear safety class 1 valve by laser directed energy deposition

The additive manufacturing (3D printing) technique, which is feasible for customized, small-scale production, is emerging, and it will be possible to effectively and quickly maintain the industrial facilities of nuclear power plants by replacing parts via ready-made, large-scale production. The 3-inch nuclear safety class 1 valve is a typical safety-grade part used in the pressurized light water reactor. It is difficult to manufacture by conventional laser powder bed fusion (L-PBF) methods because the valve body part weighs 30 kg, has a length of 300 mm, and flow path shape is inside. Therefore, structural stability is a problem and too many non-removable supports are needed. It can be manufactured by means of L-DED with five-axis operation and CNC (Computer Numerical Control) machining, and this method shows satisfactory performance outcomes in terms of dimensional accuracy, assembly, and joining. With this successful fabrication method, mechanical performance tests specifically room-temperature/high temperature tensile, fatigue, and radiographic tests are performed and the detailed process of manufacturing prototypes is described.

General Cutting Dynamics Model for Five-Axis Ball-End Milling Operations

AbstractFive-axis ball-end milling is used extensively to machine parts with sculptured surfaces. This paper presents the general cutting dynamics model of the ball-end milling process for machine tools with different five-axis configurations. The structural dynamics of both the tool and workpiece are considered for the prediction of chatter stability at each tool location along the tool path. The effects of tool–workpiece engagement and tool axis orientation are included in the model. By sweeping the spindle speeds, the chatter-free spindle speeds are selected followed by the prediction of forced vibrations in five-axis milling of thin-walled, flexible parts. The proposed model has been experimentally illustrated to predict the chatter stability and forced vibrations on a table-tilting five-axis computer numerical control machine tool.

Development Trend of NC Machining Accuracy Control Technology for Aeronautical Structural Parts

High-performance five-axis computer numerical control machine tools are widely used in the processing of Aeronautical Structural parts. With the increase of service life, the precision of CNC machine tools equipped by aeronautical manufacturing enterprises is declining day by day, while the new generation of aircraft structural parts are developing towards integration, large-scale, complexity, thin-walled and lightweight. It is very easy to produce dimension overshoot and surface quality defects due to unstable processing technology. The machining accuracy of aircraft structural parts is also affected by complex factors such as cutting load, cutting stability, tool error, workpiece deformation, fixture deformation, etc. Because of the complexity of structure and characteristics of Aeronautical Structural parts, the consistency and stability of cutting process are poor. It is easy to cause machining accuracy problems due to tool wear, breakage and cutting chatter. Relevant scholars have carried out a lot of basic research on NC machining accuracy control and achieved fruitful results, but the research on NC machining accuracy control of Aeronautical structural parts is still less. This paper elaborates from three aspects: error modeling method of NC machine tools, error compensation method, prediction and control of machining accuracy, and combines the characteristics of Aeronautical Structural parts, the development trend and demand of NC machining accuracy control technology are put forward.

A new solution of measurement using 3D artefact to identify all location errors related to rotary axis of five-axis machine tool

In the manufacturing industry, computer numerical control (CNC) machine tool has been applied widely due to their high adaptability and precision in the machining of diversity shape, especially five-axis CNC machine tools. However, more error terms related to rotary axes, in which location errors are always considered as one of the most fundamental error sources, affect directly to machine tool performance. Thus, ensuring that a five-axis machine tool is machining within tolerance is a crucial demand in the market. This study investigates an efficient strategy using a specific 3D artifact to identify and characterize the location errors in rotary axes of a five-axis machine tool. The intended 3D artifact consists of a base plate, 2 standards ball with high roundness embedded on the top surface of the base. A Touch Trigger Probe will be utilized as the calibration instrument to capture the coordinate of 6 arbitrary contact points of the balls, then an optimization algorithm is applied to calculate the coordinate of the centers of the balls. By comparisons the relative position of the imaginary circles made of those centers with the ideal ones, all location errors will be measured individually.

On-line contour error estimation and control for corner smoothed five-axis tool paths

The dimension accuracy of the part is directly affected by the contour error. The improvement of contour accuracy has been one of the research hotspots in five-axis Computer Numerical Control (CNC) machining. Because of the inexplicit mathematical expressions of the point-to-curve distance function for free-form parameterized splines, most existing contour error estimation algorithms of the multi-axis CNC machining are based on linear or circular approximation, while the geometric characteristics of the tool path are not taken into account. However, the corner smoothed five-axis tool paths are composed of straight lines and micro splines with few control points, which have clear and simple mathematical expressions and make it possible to directly calculate the contour error from the actual tool pose to the reference tool path. Considering the geometric characteristics of the corner smoothed five-axis tool paths, this paper proposes an on-line and high-accuracy contour error estimation algorithm for five-axis CNC machining. The estimated contour error components of each axis are compensated to the position-loop controller of each axis to realize contour error control. Simulation and experimental results show that the proposed method has higher precision than the state of art methods, and contour errors are effectively suppressed by on-line compensation.

Reducing the Risks during the Purchase of Five-Axis CNC Machining Centers Using AHP Method and Fuzzy Systems

Nowadays, companies are in the process of renewing their manufacturing lines by equipping them with modern five-axis CNC (computer numerical control) machining centers. The decision to select between different five-axis CNC machining centers, with similar technological capabilities is a difficult process, so the main goal of this work was to develop a method for assisting it. The proposed approach relies on seven technical criteria, four quantitative ones (traverse speed, thrust, spindle power, and spindle speed) which can be expressed by crisp numerical values, while the other three (flexibility, operation easiness, and setup time) are qualitative ones. The analytic hierarchy process (AHP) was used for ordering four variants of five-axis CNC milling machining centers. The qualitative criteria were processed using fuzzy systems to be expressed by crisp numerical values, suitable for AHP. Finally, the four variants of five-axis CNC milling machining centers were hierarchized and the best one was chosen. A sensitivity analysis was also unfolded to certify the robustness of the AHP.

Computer-integrated shaving processing for spiroid face gear on a five-axis CNC machine

To improve the tooth surface finish of spiroid face gear manufactured by die-casting process, a computer-integrated shaving processing of the gear on a five-axis computer numerical control (CNC) machine was developed. Using differential geometry and gear meshing theory, the tooth surface of spiroid face gear generated by shaving processing was deduced. Based on the analyzation of the kinematic relationship between the shaving cutter and the gear, a universal CNC machine model with five degrees of freedom was established, and motion parameters of each movement axis were investigated. The shaving processing for the spiroid face gear and the NC machining program presented in the paper were verified through the simulation process based on the VERICUT software. The shaving machining experiments were conducted on the CNC machine by using the designed shaving cutter, and the tooth surface roughness of the spiroid face gear before and after shaving processing were measured. This work is of great significance for the realization of a computer-integrated manufacturing system, including computer design, simulation machining, and NC manufacturing for the spiroid face gear.

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.

Cross-coupling control method for five-axis computer numerical control machine with dual rotary tables

The contour error cross-coupling control is very important to improve contour accuracy for the five-axis computer numerical control machine. The change in cutter orientation can cause the nonlinear motion of cutter tip, so the contour error calculation and compensation are very complex. For the five-axis computer numerical control machine with dual rotary tables, the forward kinematics model and inverse kinematics model are set up, and the influence laws of feed axis deviation to cutter tip deviation and cutter orientation deviation are studied. Then the simple and accurate calculation models for cutter tip contour error and cutter orientation contour error are established. Finally, the novel contour error cross-coupling control method based on kinematics model is developed. The experimental results show that the developed method can effectively improve contour accuracy of the five-axis computer numerical control machine.

An analytical local corner smoothing algorithm for five-axis CNC machining

Abstract Linear motion commands of computer numerical control (CNC) machine tools need to be smoothed at the transition corners in order to guarantee continuous and steady machining. However, because of the complex kinematic constraints, very few researches have devoted to developing analytical and high order continuous corner smoothing algorithms of five-axis tool paths, although it is important to guarantee both high calculation efficiency and good dynamic performance of five-axis CNC machining. This paper develops an analytical C 3 continuous corner smoothing algorithm of five-axis tool paths by locally inserting specially designed quintic micro splines into the transition corners of five-axis linear commands. C 3 continuity of the tool tip position and the tool orientation are guaranteed along the entire tool path. The maximal approximation errors of the tool tip position and the tool orientation are both constrained in the workpiece coordinate system. The synchronization of the tool tip position and tool orientation are mathematically guaranteed at the junctions of the linear and spline segments. The proposed corner smoothing algorithm can calculate all control points of the locally inserted tool tip position and tool orientation splines analytically without any iteration, which makes it very suitable to on-line calculation. Experiments on an in-house developed five-axis CNC platform verify that the maximal approximation errors of both tool tip position and tool orientation are constrained, and the proposed C 3 continuous corner smoothing algorithm has higher tracking accuracy and lower acceleration frequency content at higher frequencies than the C 2 continuous algorithm.

On-machine quasi-3D scanning measurement of bevel gears on a five-axis CNC machine

Most commercialized measuring machines for bevel gears have a four-axis structure plus a 3D scanning probe. Because these probes are highly efficient, a large number of high-precision gear grinding and complex machines now apply them to detect tooth surface contour error. Nevertheless, such probes are still too expensive to implement on a milling machine. This paper, therefore, proposes a quasi-3D probe as a better solution for cost reduction. More specifically, the study develops an on-machine measurement system on five-axis machines which are needed for producing bevel gears. It employs a quasi-3D scanning probe whose sensor can detect in xyz directions while outputting only a one-dimensional (1D) deviation. This novel method enables measurement using solely a four-axis movement, meaning that only four coordinates are needed to measure pitch and topography. These coordinates are derived by first establishing mathematical models of bevel gear measurement. Also developed is an evaluation program that communicates between the PC and CNC controller. The proposed mathematical models are then applied to a five-axis CNC (computer numerical control) machine equipped with a Siemens 840Dsl controller and verified by comparing the results of this measurement and evaluation with the accuracy report for the same gear measured on a dedicated gear measurement machine.

Research on shaving processing of spiroid face gear

To reduce tooth surface errors and improve the quality of tooth surface morphology for the spiroid face gear manufactured roughly by die-casting, a method of shaving processing for this type of gears was developed. According to the differential geometry and the meshing theory of spatial crossed axes gears, the kinematics of the shaving processing for the spiroid face gear was analyzed, while the cutting velocity of both contact tooth surfaces was derived to illustrate the feasibility of gear shaving. With the designed tooth geometry of the shaving cutter, the simulation of generation of tooth surfaces for the spiroid face gear was developed. Machining experiments for such type gears were performed on a five-axis computer numerical control machine tool (CNC machine) with the axially grooved shaving cutters. The geometric error measurement of the shaved spiroid face gears was determined by D40 CNC gear measuring center. The research results are of sound great significance to improve the engagement and lubrication for the spiroid face gears.

Nonlinear dynamic modeling and adaptive sliding control of the milling head for efficient and powerful machining

Milling head is an essential assembly in the five-axis computer numerical control machine tools, positioning precision of which directly affects the machining accuracy and surface quality of the processed parts. Considering the influence of nonlinear friction in the transmission mechanism and the uncertain cutting force disturbance on the control precision of the milling head, the static and dynamic performances of the milling head are analyzed; relationships among the drive torque, load torque, motion direction and system parameters are discussed; and, finally, nonlinear dynamic model of the milling head is established. A novel adaptive sliding mode control scheme based on the variable switching gain and the adjustable boundary thickness is proposed for this nonlinear dynamic model; the stability of the closed-loop system is guaranteed by the Lyapunov theory. Experimental results show that the proposed adaptive sliding mode control can reduce the chattering in the traditional sliding mode control and can achieve high control precision without knowing the boundaries of uncertainties in advance.

Development and application of software for open and soft multi-axis EDM CNC systems

This study aimed to develop software for multi-axis electrical discharge machining (EDM) computer numerical control (CNC) systems using open CNC technology and soft CNC technology and to then apply the software to the machining of rimmed turbine blisks. Through the analysis of functional requirements, this study established the hierarchy structure of the software. On the basis of this structure, three main modules and their communications were established with Linux and RT-Linux as the development platforms. The software architecture was also constructed. Through the construction of the modules and communications and the realization of the functions, the multi-axis EDM CNC system software was developed and installed into a five-axis EDM CNC machine to realize the machining of rimmed turbine blisks. Machining results show that the architecture of the software is correct, harmonious, and reasonable. The software is also stable and reliable and features strong real-time capability and accurate movement control.

Additive manufacturing with secondary processing of curve-face gears

In order to process curve-face gears with less material, simpler processes, and high profile accuracy, a method was proposed that uses additive manufacturing (AM) as the primary process, while computer numerical control (CNC) as the secondary process, i.e., obtaining the blanks of the curve-face gear pairs using additive manufacturing and then conducting secondary processing using five-axis CNC machining. The tooth profile coordinate system of the tool, the processing coordinate system of the curve-face gear, the model of rounded corner in addendum angle, the CNC machining model, and the rapid prototyping model were established by applying space gear meshing theory, five-axis CNC machining principles, and fundamental theories in additive manufacturing. The tool’s tooth profile equation, the coordinate transformation matrix from the tooth surface of the non-circular gear to that of the curve-face gear, the fillet surface equation, the five-axis motion equation during machining, and the coordinate transformation matrix during additive manufacturing were derived. The curve-face gear pair was machined by additive manufacturing with secondary CNC processing. Tooth surface measurement of the obtained gear pair was conducted. The results show that while materials wastage and number of processes involved are largely reduced, the tooth surface precision of additively manufactured gear pairs is significantly improved. The design for curve-face gear pairs and the method of additive manufacturing with secondary processing of curve-face gears were proved to be effective.

A precise approach for the determination of the setup parameters to utilize maximum work space of five-axis CNC machine tools

The maximum work space utilization of the five-axis computer numerical control machine tools is a critical task. Cutting system length which includes spindle, tool holder and cutting tool determines the tool tip reachable work space for the five-axis machine tools. Setup parameters for the work piece mounting on the table can be chosen randomly for the post processing, which do not give the guarantee of machining the part without crossing the linear axes travel limits of the machine tools. In this research, a precise method is developed for the determination of the setup parameters of the work piece mounting on the table, which gives the guarantee of machining the complete part without over travel limits. The proposed algorithm has the capability of doing the machining of the big parts in the minimum number of the setups.

Nonlinearity Error Analysis with the Application of the Envelope Surface in Five-axis CNC Machining

Nonlinearity error is the machining error produced due to the linear interpolation scheme of the five-axis computer numerical control (CNC) machine tool. Two cutter movement modes are introduced to illustrate the nonlinearity error: tool path cutter movement and practical machining cutter movement. With these two cutter movement modes, two envelope surfaces of the milling cutter in five-axis CNC machining are obtained as the closed-form representations. Subsequently, an advanced mathematical model is proposed to calculate the nonlinearity error. The proposed method is illustrated with an example, and the result shows that the proposed method is valid.