5-axis Machining Center Research Articles

High Performance Motion Control of Rotary Table for 5-Axis Machining Centers

We discuss motion control techniques of rotary tables for 5-axis machining centers. Three translational axes and two rotary ones are controlled simultaneously in the machining of complex shapes such as impellers. A tilting rotary table powered by a worm gear is generally used as the rotary axes for 5-axis machining centers, and various causes of inaccuracy exist in the rotary axes. In this study, we clarified three causes of inaccuracy exists in the rotary axis: rotational fluctuation in the worm gear, backlash, and measurement delay of rotary encoder for feedback. Motor torque saturation of the rotary axis also causes a problem when rotational velocity is changed rapidly. Based upon investigated results, we propose compensators for improving synchronous accuracy. We avoid torque saturation in the rotary axis through acceleration-deceleration design. To verify the effectiveness of the proposed compensators, we applied them to an experimental set-up including a rotary axis. As the results of experiments, it is clarified that the proposed compensators improve the synchronous accuracy of translational and rotary axes.

Development of High-Speed, High-Precision 5-Axis Integrated Machine Tools

This paper describes the development of high-speed, high-precision 5-axis machine tools which can be used for both milling and turning. Conventional 5-axis machine tools are generally difficult to operate because the visibility is poor. Moreover, their precision is inadequate and the rotary axis speed is insufficient for turning. To deal with these factors, we developed a simple, high-precision 2-axis rotary actuator with high-speed direct drive motors. We studied the machining performance of 5-axis machining centers equipped with such direct drive motors.

반응표면법을 이용한 5축 임펠러 정삭 가공의 최적화

An impeller is a important part of turbo-machinery. It has a set of twisted surfaces because it consists of many blades. Five-axis machining is required to produce a impeller because of interference between tool and workpiece. It can obtain good surface integrity and high productivity. This paper proposes finish cutting method for machining impeller with 5-axis machining center and optimization of cutting condition by response surface method. Firstly, cutting methods are selected by consideration of operation characteristics. Secondly, response factors are determined as cutting time and cutting error for prediction of productivity. Experiments are projected by central composite design with axis point. Thirdly, regression linear models are estimated as single surface in the leading edge and as dual surface in the hub surface cutting. Finally, cutting conditions are optimized.

Dynamic Hybrid Modeling of the Vertical Z Axis in a High-Speed Machining Center: Towards Virtual Machining

This paper describes the modeling and simulation of the Z axis of a five axis machining center for high-speed milling. The axis consists of a mechanical structure: machine head and electro-mandrel, a CNC system interfaced with the feed drive, and a pneumatic system to compensate for the weight of the vertical machine head. These subsystems were studied and modeled by means of: (1) finite element method modeling of the mechanical structure; (2) a concentrated parameter model of the kinematics of the axis; (3) a set of algebraic and logical relations to represent the loop CNC-Z feed drive; (4) an equation set to represent the functioning of the pneumatic system; and (5) a specific analytical model of the friction phenomena occurring between sliding and rotating mechanical components. These modeled subsystems were integrated to represent the dynamic behavior of the entire Z axis. The model was translated in a computer simulation package and the validation of the model was made possible by comparing the outputs of simulation runs with the records of experimental tests on the machining center. The firm which promoted and financed the research now has a virtual tool to design improved machine-tool versions with respect to present models, designed by traditional tools.

A Model for Milling Force Prediction in High-Speed End Milling of P20 Mold Steel

This paper focuses on developing an empirical model for the prediction of milling forces in high-speed end milling of P20 die-mold steel. The spindle speed, feed rate, axial and radial depth of cut are considered as the affecting factors. The data for establishing the model are derived from high-speed end milling experiments conducted on a 5 axis machining center according to the principles of DOE (design of experiments) method. The influences of milling parameters on milling forces are investigated by analyzing the experimental curves. Consequently, multiple-regression analysis is applied in developing the empirical model. Furthermore, the significances of the regression equation and regression coefficients are statistically tested in this paper to validate the model.

Motion error estimation of 5-axis machining center using DBB method

In order to estimate the motion errors of 5-axis machine center, the double ball bar (DBB) method is adopted to realize the diagnosis procedure. The motion error sources of rotary axes in 5-axis machining center comprise of the alignment error of rotary axes and the angular error due to various factors, e.g. the inclination of rotary axes. From sensitive viewpoints, each motion error is possible to have a particular sensitive direction in which deviation of DBB error trace arises from only some specific error sources. The model of the DBB error trace is established according to the spatial geometry theory. Accordingly, the sensitive direction of each motion error source is made clear through numerical simulation, which is used as the reference patterns for rotational error estimation. The estimation method is proposed to easily estimate the motion error sources of rotary axes in quantitative manner. To verify the proposed DBB method for rotational error estimation, the experimental tests are carried out on a 5-axis machining center M-400 (MORISEIKI). The effect of the mismatch of the DBB is also studied to guarantee the estimation accuracy. From the experimental data, it is noted that the proposed estimation method for 5-axis machining center is feasible and effective.

110 同時2軸制御による円筒面の仕上げ加工精度(OS-3 最新工作機械・多軸複合加工)

An evaluation method for synchronous motion of translational and rotational axes in 5-axis machining centers is proposed. In the proposed method, the X and the C' axes are simultaneously controlled and a circular path is generated under a constant peripheral feed speed. The relationship between the diameter of the circular path and the distance between both centers of the rotary axis and the circular path is useful for evaluating the accuracy. If the diameter of the circular path is smaller than the distance between both centers of the rotary axis and the circular path, the influence of the backlash becomes strongly. If the offset between machine coordinate origin and the center of the C' axis is large, it is difficult to evaluate the inaccurate synchronization appropriately.

Synchronous Accuracy of Translational and Rotary Axes in 5-axis Machining Centers(Precision positioning and control technology)

This paper describes the dynamic synchronous accuracy of translational and rotational axes in 5-axis machining centers. In this study, non-uniform 3-axis synchronous motion was investigated in order to estimate the dynamic synchronous accuracy. A dynamic model of the each axis including a rotary axis was developed, and the synchronous motion was simulated. The dynamic model mainly consists of a moment of inertia, friction forces, a velocity controller and a position one. As the results of experiment and simulation, it is clarified the developed model can express the experimental results accurately. In addition, a method that can improve the synchronous accuracy is proposed, and its effectiveness is verified by the developed dynamic model.

5軸NC工作機械による主軸傾斜曲面加工法に関する研究 (第2報)

Today nearly all die and mold makers use High Speed Cutting or Machining in cavity and core manufacturing. However, finishing processes for injection molding molds and die casting dies are done by EDM because these applications have many thin and deep cavities to be machined. Otherwise, the long solid carbide milling cutters are necessary for machining these molds and dies. To save set-up time and machining time, it is desire to machine by High Speed Cutting or Machining in such machining portions. To solve this problem, mold and die machining by indexing tilted tool axis on 5-axis machining center is proposed in this paper. In the proposed machining process, High Speed Machining is executed on each tilted tool axis. In this machining process, the list of indexing angle should be determined automatically, because the shape of the die and mold is very complex to determine the angle by an operator. Therefore, the main objective of this research is automatic determination method of the list of indexing angle for machining the die and mold. Firstly, we propose the calculation method of optimum indexing angle for required machining surfaces using normal vectors of the surfaces and cutting edge shapes similar to the Gaussian Sphere method. Secondary, we propose the machinable area evaluation method of calculated indexing angle based on inverse offset method with state flag. Finally, we illustrate an example to demonstrate the effectiveness of the proposed methods.

Identification of angular and positional deviations inherent to 5-axis machining centers with a tilting-rotary table by simultaneous four-axis control movements

This paper describes a method for identifying the eight deviations inherent to five axis control machining centers by means of simultaneous four-axis control movements. Some methods to identify the deviations have been proposed. However, a simultaneous four-axis control technique using a ball bar instrument has not been applied to the measurement of relative displacements between the main spindle and the worktable. Furthermore, the method for assessing the deviations from the trajectories has not been proposed. Thus, in this paper, a calibration method based on the simultaneous four-axis control technique is proposed for five axis control machining centers with a tilting rotary table. To confirm the validity of the proposed method, simulations were conducted. The trajectories were obtained by means of a mathematical model into which the eight deviations were substituted. In the first step, four of the eight deviations were estimated by an observation equation for which two measurement trajectories and six reference ones were used. In the second step, the remaining four deviations were geometrically calculated using the values estimated by the observation equation. As a result, it was found that the proposed method was sufficient to identify the deviations accurately.

119 5軸工作機械を用いた3+2軸制御加工法に関する研究([4]多軸制御加工・工作機械(2))(OS3 最新工作機械)

Recently, high precision machining and high-speed cutting are required in the die and mold machining. To solve this problem, die and mold machining by 3+2 axis control machining, which is a method of indexing by 2-axis rotary motion and machining by 3-axis feed motion, on 5-axis machining center is proposed in this paper. In this machining process, the list of indexing angle should be determined automatically, because the shape of the die and mold is very complex to determine the angle by an machining operator. Therefore, the main objective of this research is automatic determination method of the list of indexing angle for the die and mold machining. Firstly, we propose the calculation method of optimum indexing angle candidates for required machining surfaces using normal vectors of the surfaces and cutting edge. Secondary, we propose the machinable area evaluation method of calculated indexing angle based on inverse offset method with state flag. Finally, we show the examples to demonstrate the effectiveness of the proposed methods.

Sculpture Surface Machining by Automatically Indexing Tilted Tool Axis on 5-axis Machine Tools (1st report)

Today nearly all die and mold makers use High Speed Cutting or Machining in cavity and core manufacturing. However, finishing processes for injection molding molds and die casting dies are done by EDM because these applications have many thin and deep cavities to be machined. Otherwise, the long solid carbide milling cutters are necessary for machining these molds and dies. To save set-up time and machining time, it is desire to machine by High Speed Cutting or Machining in such machining portions. To solve this problem, mold and die machining by indexing tilted tool axis on 5-axis machining center is proposed in this paper. In the proposed machining process, High Speed Machining is executed on each tilted tool axis. In this machining process, the list of indexing angle should be determined automatically, because the shape of the die and mold is very complex to determine the angle by an operator. Therefore, the main objective of this research is automatic determination method of the list of indexing angle for machining the die and mold. Firstly, we propose the calculation method of optimum indexing angle for required machining surfaces using normal vectors of the surfaces and cutting edge shapes similar to the Gaussian Sphere method. Secondary, we propose the machinable area evaluation method of calculated indexing angle based on inverse offset method with state flag. Finally, we illustrate an example to demonstrate the effectiveness of the proposed methods.

5軸マシニングセンタの幾何偏差が加工精度に及ぼす影響(G.S. 機械加工,OS4:ダイナミクス・コントロールの基礎とその応用技術)

5軸マシニングセンタの幾何偏差が加工精度に及ぼす影響(G.S. 機械加工,OS4:ダイナミクス・コントロールの基礎とその応用技術)

116 球と変位計を用いた5軸制御マシニングセンタの幾何精度測定方法([3]多軸制御加工・工作機械(1))(OS3 最新工作機械)

116 球と変位計を用いた5軸制御マシニングセンタの幾何精度測定方法([3]多軸制御加工・工作機械(1))(OS3 最新工作機械)

임펠러의 효율적인 5축 NC 황삭가공에 관한 연구

This paper proposes a roughing path generation method for machining impeller with 5-axis machining center. Traditional researches are focus on finishing for machining impeller. To achieve efficient machining, roughing method must be studied. The proposed method consists two steps : One is to select optimal tool size and tool attitude by dividing cutting area into two regions to reduce cutting time. The regions are automatically divided by character point on the geometry of impeller blade. After dividing, the tool of the optimal size is selected for each divided region. The other is avoidance of tool interference. Tool interference in cutting areas is avoided by checking the distance between tool axis vector and ruling line on blade surface or approximated plan between ruling line. Using this method, the cutting time is reduced efficiently.

Identification and compensation of systematic deviations particular to 5-axis machining centers

This paper presents an algorithm for identifying particular deviations such as angular deviations around linear axes relating to rotary axes in 5-axis machining centers. In this study, three kinds of simultaneous three-axis control motions are designed for each rotary axis to identify the deviations. In the measurement, two translational axes and one rotary axis are simultaneously controlled keeping the distance between a tool and a worktable constant. Telescoping ball bar is an effective instrument for measuring the relative displacement to the reference length in the work volume because its attitude is freely changed. In these three-axis control motions, the sensitive direction of the ball bar is kept constant. In order to determine the deviations, we derive eight equations from the relationship between the eccentricities obtained from the measured circular trajectories and the approximations derived from the mathematical model based on the simulation. In the simulation, a mathematical model considering the particular deviations is developed and then the characteristic diagrams are prepared for every deviation and every three-axis control motion. Based on the results, we propose a procedure for identifying the particular deviations in 5-axis machining centers and its procedure has been applied to identify the deviations actually. From both the simulation and the experiment, it has been confirmed that the proposed method gives precision results and is able to apply to the measurement of 5-axis machining center which is a tilting rotary table type.

５軸制御マシニングセンタのキャリブレーション方法に関する研究 （第２報） 同時３軸制御運動を用いた位置偏差および角度偏差の推定

Various types of 5-axis controlled machining centers have been developed to produce molds, dies and mechanical parts with complicated shape as well as aero parts. The most fundamental cause of the machining errors is the deviation of the configuration of the machining center. However, any calibration method for the 5-axis machining centers including two rotary axes has not been investigated. In this paper, a calibration method using simultaneous 3-axis control technique is proposed for 5-axis machining centers with a tilting rotary table. The ball-bar system is used as a measurement instrument. In this method, one rotary axis and two linear axes are simultaneously controlled and the sensitive direction of the ball bar system is kept constant in radial, tangential or axial accordingly. The influence of the positional and angular deviations on 3-axis motion is evaluated through the characteristic diagrams. In the experiments, the positional and angular deviations existing in the 5-axis machining center are estimated by the proposed method. The results show that the deviations can be estimated with high accuracy.

５軸加工機における回転軸系の運動誤差原因の診断に関する研究（第１報）―回転誤差の診断法と診断手順―

Critical motion error sources of rotary axes with respect to linear axes in 5-axis machining center (MC) include: 1) the alignment error of rotary axes, and 2) the angular error due to e.g. the inclination of rotary axes. Each motion error has a particular "sensitive" direction where it causes the largest motion error in DBB measurement plane. In this paper, the diagnosis method for the motion error sources of rotary axes is proposed as: the first is to find out such the sensitive direction of each motion error source by using numerical simulation, and the second is to determine the diagnosis procedure according to the simulation results. Moreover, the applicability and effectiveness of the proposed diagnosis method is validated by this experiment.

５軸制御マシニングセンタのキャリブレーション方法に関する研究（第３報）―５軸制御マシニングセンタの構造形態に対応した測定方法―

In this paper, the structural configurations of 5-axis machining centers are researched, and a proposed method is applied to the measurement of the geometric deviations of the available machines, and the effectiveness of the method is discussed. The structural configurations of the 5-axis machining centers are divided into three types. The ball-bar technique is applied to the measurement of simultaneous 4-axis control motion, and the error motion is simulated using the motion analysis software. As the results, the geometric deviations in three types of 5-axis machining centers can be estimated by the proposed method. 5-axis control motion using a simplejig is proposed as alternative measurement method, and it is found that the proposed method is effective to evaluate the geometric deviations as well as 4-axis control motion.

335 General Calibration Methods of 5-axis Controlled Machining Centers According to the Structural Configurations

In this study, the axis compositions of five-axis machining centers (MCs) are collected through websites and catalogues. The analysed 5-axis MCs are divided into three types. The deviations of the axes motion are discussed. Telescoping magnetic ball bar (TMBB) is applied in the measurement method of the effectiveness of deviations. The proposed procedure of ball-bar setting is evaluated for general structural codes of all types according to the simultaneous motion of four and five axes. They are simulated using software of dynamic analysis and design system (DADS). The influence of deviations in the measurement method is discussed. The results show that the geometric deviations can be estimated by the proposed method. The simultaneous motion of five axes using a simple jig is proposed as an alternative method of measurement. It is found that the proposed method is effective to evaluate the geometric deviations in simultaneous five-axis motion as well in simultaneous four-axis motion.