Five-axis Tool Research Articles

A practical postprocessor with compensation of tool clamping errors for five-axis tool grinding machine

The runout of the cutting edge significantly affects the cutting force, wear, and the process stability. Generally, the postprocessor of five-axis tool grinding machine ignores the clamping error of blank. Hence, this paper developed a postprocessor method with compensation of tool clamping errors to minimize runout of cutting edge for tool grinding machine. This method includes the kinematic model and the measurement model of clamping error for the tool grinding machine. This kinematic model converts CL data into NC data and converts NC data into CL data. The measurement model for measuring and calculating the clamping error of blank. The clamping error was inputted into the kinematic model of machine to compensate the clamping error. The solution strategy of the kinematic model was built, and is suitable for five-axis tool grinding machine. A postprocessor was subsequently developed according to the algorithm presented. Finally, the effectiveness of postprocessor was confirmed by the grinding experiment.

Optimization of five-axis tool grinder structure based on BP neural network and genetic algorithm

Optimization of five-axis tool grinder structure based on BP neural network and genetic algorithm

Digital mapping of machine tool's volumetric and tracking errors left on the five axis tool paths

Five-axis contouring errors left on the parts contributed by feed drive servos, and intra- and inter-axis geometric errors are predicted along the five-axis tool paths. Quasi-static geometric errors are measured and modeled in the machine's workspace. Servo tracking errors of the three translational and two rotary drives are measured during machining or predicted from the CNC model. All errors are projected to the tooltip using a generalized screw theory-based forward kinematic model. The proposed model is validated experimentally on a CNC machining center for two test parts.

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.

Smoothing interpolation of five-axis tool path with less feedrate fluctuation and higher computation efficiency

Five-axis machine tools are widely used in aerospace, die and mold industries. Most of the time, the tool path is described by connecting a series of short linear segments. The tangency discontinuity of the linear segments leads to the discontinuity of the kinematic profiles, hence generating discontinuous interpolation points, and resulting in fluctuation of machine motion, which reduces the machining efficiency and causes excessive tracking and contouring errors. This paper aims to generate smooth interpolation points at servo sample intervals with the proposed G2 continuous five-axis corner rounding algorithm suitable for reducing feedrate fluctuation along the smoothed toolpath and improving machining efficiency, and the modified jerk-limited feedrate planning algorithm suitable for eliminating feedrate fluctuation within the feedrate planning units and improving interpolation computation efficiency. In this paper, the five-axis linear segments are first smoothed by curvature-optimized cubic Bezier splines, which reduces the number of the feedrate planning units along the smoothed toolpath and improves machining efficiency. Then, the jerk-limited feedrate planning algorithm is modified to ensure that the time interval of each different scheduled feedrate phase is an integer multiple of the axis position control loop closure time (i.e. servo sample interval), which eliminates the feedrate fluctuation within each feedrate planning unit and reduces the interpolation computation load of position command in each interpolation period (i.e. servo sample interval). At last, the effectiveness of the proposed algorithm is demonstrated with simulations and experiments following a five-axis, curved tool path on a CNC (Computer Numerical Control) machine tool.

Efficient cutting path planning for a non-spherical tool based on an iso-scallop height distance field

Iso-scallop height machining means, when machining a freeform surface, the scallop height between any two neighboring tool paths on the surface will be a constant (i.e., the given threshold), which is preferable among various freeform surface machining strategies due to its high machining efficiency as well as better machine tool’s dynamics. However, all the existing iso-scallop height path planning methods pertain to only the ball-end or flat-end types of tools. In recent years, the non-spherical cutting tool has become more and more popular, especially for five-axis machining of complex freeform surfaces, majorly owing to its non-constant curvature which can be utilized to adaptively fit the tool to the surface to both avoid the local gouging and enlarge the cutting width. However, there have been no reported works on iso-scallop height five-axis tool path generation for a non-spherical tool, and, in this paper, we present one. Specifically, we first define and construct two fields on the surface to be machined-the collision-free tool orientation field (vector) and the iso-scallop height distance field (scalar). The iso-lines of the scalar field and their associated tool orientation field vectors then naturally serve as potential iso-scallop height five-axis tool paths, and we present a propagation-based algorithm to construct the desired tool path from the iso-lines. The computer simulation and physical cutting experiments confirm that everywhere on the surface, except maybe near the saddle curves of the scalar filed, the scallop height is exactly the given threshold. By adding the saddle curves as extra tool paths, the final machined surface then is assured of the required scallop height requirement.

Improvement in the efficiency of the five-axis machining of aerospace blisks.

Blisks are not easily machined because of their complex curved surfaces and the high-precision requirements of surface machining. Lightweight alloy materials with superior mechanical properties, such as titanium alloy and stainless steel, are popular material choices for manufacturing turbine blisks. However, these materials are difficult to cut and require advanced machine tools and processing technologies. Because aerospace-grade parts are complex and require precise dimensions and high surface quality, machining these parts by using three-axis machine tools is difficult. Using multi-axis machine tools for the machining of complex parts can cause the achievement of precise dimensions, high quality, and the required surface roughness. In the multi-axis machining of aerospace blisks, tool path planning is considered the most difficult task. In this study, we examined the implementation of five-axis machining technology for the manufacturing of an aerospace blisk. Processing modules from computer-aided manufacturing software (NX10) are used for five-axis tool path generating, and 5-axis machining numerical control code is generated through post-processing calculations. Solid cutting simulation software (VERICUT) is used to verify whether tools exhibited overcut or interference. A sensory tool holder (SPIKE) is used to analyze cutting force during the rough machining of a blisk. The sensory tool holder is also adopted to evaluate the spindle runout and tool holding status. In order to obtain a consistent cutting allowance and surface accuracy, the online measurement system is used to generate a measurement path for semi-finish and finish machining. The real cut is performed with SUS304 and demonstrates the practical application. Through improvements in process planning, the machining time was shortened by 16.5%.

A G3 continuous five-axis tool path corner smoothing method with improved machining efficiency and accurately controlled deviation of tool axis orientation

A G3 continuous five-axis tool path corner smoothing method with improved machining efficiency and accurately controlled deviation of tool axis orientation

Numerical implementation of drop spin and tilt method for five-axis tool positioning for tensor product surfaces

This paper presents an extension of multipoint machining technique, called the Drop Spin and Tilt (DST) method, that spins the tool on two axes, allowing for the generation of multiple contact points at varying distances around the first point of contact. The multiple DST second points of contact were used to manually generate a toolpath with uniform spacing between the two points of contact. The original DST method used a symbolic algebra package to position the tool on a bi-quadratic surface; our extension is a numerical solution that allows positioning a toroidal tool on a tensor product Bézier surface, which we tested on bi-degrees 2, 3, 4, and 5. On the three bicubic surfaces we tested, the average number of initial seeds for our numerical method was less than 5 across all three surfaces, and the average number of Newton iterations was less than 20 except when the curvature of the tool closely matches the local surface curvature (in which case more iterations were required). Furthermore, we investigate the spread of possible second points of contact as the tool is spun around these two axes, demonstrating the feasibility of using the method to control the machining strip width.

Global smoothing for five-axis linear paths based on an adaptive NURBS interpolation algorithm

The five-axis tool path generated by CAM software usually consists of a series of linear paths. The tangent direction at the corner of the adjacent line segment will suddenly change, and the curvature is also discontinuous, which will cause vibration and shock during the machining process. Thus, a global corner smoothing algorithm based on cubic NURBS interpolation is proposed to smooth the linear paths in this paper, so as to achieve G2 continuous for five-axis linear paths. The algorithm proposed does not require matrix operations to solve the control points, and it can also reduce the number of control points while satisfying the interpolation error. The algorithm is then used to generate smooth NURBS path for ceramic core burrs and blockage repair. The simulation and experiment show that the algorithm proposed can satisfy the error constraints, reduce the vibration of the motion axis, and improve the surface quality of laser cutting.

Asymmetrical pythagorean-hodograph (PH) spline-based C3 continuous corner smoothing algorithm for five-axis tool paths with short segments

• A real-time C 3 continuous corner smoothing algorithm is proposed for five-axis short linear segments. • The proposed method can achieve lower curvature based on asymmetrical PH splines. • Smoothing errors around the corners are bounded under given constraints. • The arc-length can be analytically calculated to achieve real-time interpolation. • Experiments verify that much lower curvature and higher machining efficiency can be realized. Local corner smoothing is widely used for the G01 motion commands to achieve the motion continuity of transition corners. Most splines constructed by the existing local corner smoothing methods oriented for five-axis machining mainly must be connected by linear segments. However, with respect to the five axis machining of the corners with short line segments, these kinds of methods need that both ends of the constructed splines usually must be shrunk with the same proportion to avoid the overlapping of adjacent splines. This will lead to relatively large curvatures of the obtained trajectories together with relatively low machining efficiency. This article proposes a new real-time corner smoothing algorithm for five-axis machine tools by constructing the C 3 continuous asymmetrical PH splines. The typical characteristic lies in that the control points related to the two ends of the PH spline can be independently adjusted through reasonably introducing two more adjustable variables, which are realized by analytically calculating and then adding two additional control points into the corresponding control polygon. As a result, the PH spline poses the property of the asymmetry about the angular bisector. Based on this, the short linear commands of tool tip and tool orientation can be smoothed only through inserting different lengths of asymmetrical PH splines that can be connected directly. The motion variance of the smoothed tool orientation related to the tool tip displacement is analytically proved to be C 3 continuous, and thus, the synchronization between tool tip and tool orientation is guaranteed. The outstanding advantage of the algorithm for short line segments is twofold. The first is that the performance of the drives can be more fully utilized to reduce cycle time since the curvature around corners are reduced by adopting the asymmetrical profile, and the second is that the synchronization procedure is greatly simplified since the algorithm eliminates the requirement to convert the intermediate line segments into a spline between the adjacent connected PH splines. Both simulation and the experimental results demonstrate that the proposed algorithm can realize a higher machining efficiency.

Real-time smoothing of G01 commands for five-axis machining by constructing an entire spline with the bounded smoothing error

G01 commands generated by computer-aided manufacturing (CAM) software need to be smoothed to eliminate the tangential discontinuities at corners. Although the smoothing methods for five-axis tool paths have been widely studied, it is still challenging to realize the high machining efficiency of short, dense G01 commands with real-time processing. This article proposes a real-time five-axis tool path smoothing algorithm for short G01 commands. The uniform smoothing of adjacent two corners with cubic uniform B-spline is developed. Through connecting the pieces of splines, all the G01 commands are smoothed by an entire B-spline. Therefore, the curvature increment induced by the avoidance of the intersection of adjacent micro-splines is prevented, and thus, high allowable feedrate and high machining efficiency can be achieved. Especially, the smoothing errors are theoretically proved to be constrained by using the convex polyhedron method. At the same time, the required number of control points is greatly reduced by sharing the control points with the adjacent G01 commands. Simulation and experimental results demonstrate that the proposed method can significantly reduce the machining time by more than 26% for short linear trajectories.

Partition-based five-axis tool path generation for freeform surface machining using a non-spherical tool

Freeform surfaces are widely used in many industries for various purposes, and multi-axis CNC machining is the most adopted method for machining them due to its high accuracy and flexibility. The prevailing type of cutter used in machining freeform surfaces is the so-called ball-end type, which is simply a hemisphere and thus has a constant curvature on the cutter surface. Naturally, for a complex surface with a large deviation in curvature, a cutter shape with variable curvature will be more desirable, as we can adaptively choose a portion of smaller curvature on the cutting edge to machine those relatively flat portions on the surface so to enlarge the cutting width and hence reduce the machining time. Towards this objective, in this paper, we present an algorithm which, given an arbitrary freeform surface to machine and a general non-spherical cutter, will generate a five-axis tool path that will strive to match every cutting point on the surface with a locally optimal tool posture (i.e., the contact point on the cutter surface together with the tool orientation) as well as the corresponding optimal feed direction, while both the local gouging-free and global collision-free constraints and the cusp height requirement are all satisfied. The experimental results in both computer simulation and physical machining are also reported, which confirm that, when compared to using a simple ball-end cutter, by using a non-spherical cutter and adaptively adjusting the contacting tool posture and the feed direction, a large improvement in machining efficiency could be achieved, e.g., as much as 60 % achieved in our experiments.

Generating the tool path directly with point cloud for aero-engine blades repair

Aero-engine is an essential component of the aircraft. Due to the high cost of raw materials and precise structure, the maintenance cost of aero-engine is great. By repairing worn blades rather than replacing them with new ones, the aero-engine maintenance cost can be reduced effectively. For repairing worn blades, existing methods mainly generate tool path based on the reconstructed surface with the aid of CAM software. In this paper, an effective tool path generation method for repairing blades after additive manufacturing process is presented, which overcomes the low efficiency and complicated process weakness of existing methods. The tool path is generated directly with point clouds without surface fitting. By splitting point cloud and analyzing geometric parameters of points, machining areas could be recognized from the entire blade model. The cutter location point is generated by extending on the normal vector direction of the corresponding point. The five-axis tool path could be obtained by connecting cutter location points in turns. Tool path optimization is further studied after the generation process. These algorithms eliminate the time consumption caused by surface fitting operations, and could generate five-axis tool paths for repairing aero-engine blades efficiently.

A decoupled five-axis local smoothing interpolation method to achieve continuous acceleration of tool axis

Five-axis machines are widely used in high-speed and high-precision machining of complex sculptured surfaces for the ability to adjust the tool orientation. But, most of the five-axis machining trajectories generated by computer-aided manufacturing (CAM) software are G01 blocks in the form of a large number of linear segments. The G01 blocks for surface machining show inadequacies as their high-order discontinuities. Although there are a lot of researches to deal with the discontinuities, there are still many problems such as smoothing error control, motion synchronization, kinematic constraints limitation. Besides, the kinematic constraints of the tool orientation motion are always neglected. In this paper, a two-step real-time decoupling local smoothing method is proposed for the problem of the five-axis tool path smoothing. The C2 continuity of the tool path is guaranteed within the error limited. Not only the kinematic constraints of tool tip motion but also the kinematic constraints of the tool orientation motion are considered. The continuous acceleration of each axis motion of the machine tool is realized through feed-rate scheduling by finite impulse response (FIR) filtering. Finally, through numerical simulations and experiments, compared with the existing method and G01 linear interpolation, it is verified that the proposed smoothing interpolation method has a higher computation efficiency and can improve the processing efficiency and surface quality of the tool path while satisfying the specified smoothing error constraints and kinematic constraints.

Smoothing method of generating flank milling tool paths for five-axis flat-end machining considering constraints

Gouging and collision avoidances, tool path smoothness, and geometric deviation should be considered concurrently when generating a five-axis flank milling tool path. The tool orientations of the generated tool path, which can achieve smooth rotary axis motions of the machine tool, can improve the machining quality. Tool orientation planning for five-axis ball-end machining does not affect the position of the ball center point. However, different from ball-end cutters, tool orientation adjustments for flat-end machining will affect the cutter reference point position, which may cause local gouging between the bottom circular edge of the flat-end cutter and the constraint surfaces of the workpiece or excess uncut material left. Hence, generating a smooth flank milling tool path for five-axis flat-end machining which meets all the requirements is a challenge. To deal with this problem, a method of smoothness flank milling tool path generation for flat-end cutters considering constraints is developed in this research, which can minimize the angular accelerations of the rotary axes. B-spline curves are used to represent the displacements of the rotary axes so that the rotary axes’ motions along the tool path can be directly smoothed. The sum of the squares of the first, second, and third derivatives of the cutter reference point trajectory and the two rotary axes’ displacement curves are then utilized as the smoothness indicators for the five-axis tool paths. The method of tool orientation and positioning adjustments for flat-end cutters based on the differential rigid body motion is also presented, ensuring the bottom circular edge of a flat-end cutter is tangent to the constraint surfaces of the workpiece along the tool path. Besides, the discrete vector model is utilized to represent the workpiece geometry, and intersection points between the discrete vectors and the tool swept envelope are calculated to determine the geometric deviation for a flank milling tool path. Finally, a multi-objective optimization problem with constraints is established to generate flank milling paths with flat-end cutters. Numerical examples and machining tests are carried out to confirm the validity and effectiveness of the proposed approach.

A high-precision laser method for directly and quickly measuring 21 geometric motion errors of three linear axes of computer numerical control machine tools

Error compensation has become an important means of improving the manufacturing and processing accuracy of computer numerical control (CNC) machine tools. Quick and precise measurement of the various geometric motion errors (GMEs) of CNC machine tools is crucial. We propose a novel laser method for the efficient and direct high-precision measurement of the 21 GMEs of a three-axis CNC machine tool, or three linear axes of a five-axis tool. A corresponding system was developed, comprising a fiber-coupled laser unit, sensor head, target unit, and beam-steering unit. The beam-steering unit was designed to perform high-accuracy 90° rotation of the measuring beam, and the target unit was designed to be sensitive to 18 GMEs of the three linear axes. Stability, repeatability, and comparison experiments were conducted to verify the performance of the proposed system. The results showed that the stability of the position error measurement is ± 6.3 nm. For straightness error measurement, the stability, repeatability error, and residual are within ± 60.3 nm, ± 0.5 μm, and ± 0.7 μm, respectively. These are within ± 0.12 arcsec, ± 0.5 arcsec, and ± 0.5 arcsec for the pitch and yaw measurements, and within ± 0.37 arcsec, ± 1.5 arcsec, and ± 1.0 arcsec for the roll measurements, respectively. For squareness error measurement, the repeatability error and residual are within ± 0.6 arcsec and ± 1.6 arcsec, respectively. Compared with a laser interferometer, the proposed system can measure the 21 GMEs of a three-axis machine tool with one-step installation. Without accuracy loss, the measurement efficiency is approximately 45 times higher than that of a laser interferometer, thus providing a new quick and accurate measurement method of GMEs and error compensation of CNC machine tools.

Study on a 2D field-based multi-objective tool-axis optimization algorithm based on covariant field theory for five-axis tool path generation

In five-axis machining, drastic change of tool axis has negative effects on machining efficiency and quality. Our published work proposed a unified mathematical framework to generate smooth tool-axis field and implemented in 1D domain (Yan et al., J Manuf Syst 48:30–37, 2018). In this paper, we extend the mathematical framework to 2D domain and the framework is an integral functional problem converting diverse machining requirements, such as gouge and collision free, smoothness, into mathematical expressions. A tool-axis vector field (TAVF) defined on the freeform surface is calculated by optimizing the integral functional problem. The surface is discrete into triangular mesh, and the discrete TAVF calculation problem is solved by a numeric 2D finite element method (FEM). Subsequently, the proposed algorithm is implemented to generate field-generated tool path (FGTP). The tool path has been used in machining hub of blade disk (blisk). The blisk is a complex workpiece that impellers should be gouge avoided. Machining experiments indicate that tool path generated by the proposed algorithm can avoid collision and improve smoothness on the whole surface. The freeform surface machining quality is highly improved compared with that machined by region-partitioned tool path (RPTP).

A Voxel Model-Based Process-Planning Method for Five-Axis Machining of Complicated Parts

Abstract This paper presents a new process planning method for five-axis machining, which is particularly suitable for parts with complex features or weak structures. First, we represent the in-process workpiece as a voxel model. Facilitated by the voxel representation, a scalar field called subtraction field is then established between the blank surface and the part surface, whose value at any voxel identifies its removal sequence. This subtraction field helps identify a sequence of intermediate machining layers, which are always accessible to the tool and are free of self-intersection and the layer redundancy problem as suffered, respectively, by the traditional offset layering method and the morphing method. Iso-planar collision-free five-axis tool paths are then determined on the interface surfaces of these machining layers. In addition, to mitigate the deformation of the in-process workpiece and avoid potential dynamic problems such as chattering, we also propose a new machining strategy of alternating between the roughing and finishing operations, which is able to achieve a much higher stiffness of the in-process workpiece. Ample experiments in both computer simulation and physical cutting are performed, and the experimental results convincingly confirm the advantages of our method.

Developing continuous machining strategy for cost-effective five-axis CNC milling systems with a four-axis controller

ABSTRACTThis paper investigates the five-axis continuous machining strategy on cost-effective five-axis CNC milling systems, which is limited by simultaneous control of any four axes at a given time. The proposed strategy consists of (1) generation of five-axis continuous milling tool path for conventional five-axis machines using a CAD/CAM software, and (2) conversion of the generated tool path to four-axis tool trajectory based on a novel interpolation algorithm. The interpolation algorithm is built on the relationship between the position data of the tool and the displacement of the machine tool axis. The position of the interpolation point is determined by the offset distance of the interpolation point, and the error of the interpolation is controlled by the dichotomy method. Furthermore, two simulation case studies are conducted to verify the effectiveness of the proposed algorithm. One case study is on a standard ‘S’ test piece, and the other study is on a more complicated geometry – an impeller part. The generated five-axis continuous paths are converted to the four-axis trajectory by the proposed algorithm. Machining simulations are performed using both the five-axis continuous path and the converted four-axis continuous path. The conversion quality is found to be satisfactory for both cases.