Tool Axis Orientation Research Articles

Determination and Analysis of Working Diameters and Working Angle of the Torus Cutter Blade in Multi-axis Machining in the Aspect of Tool Wear

The aim of this study is to provide a theoretical and experimental analysis of the multi-axis milling process by the torus milling cutter of nickel-based superalloy parts in terms of surface quality and tool wear. In the analytical part, using, among other things, matrix calculus and trigonometric relationships, mathematical models were developed to describe the relationships between the tool axis orientation and the geometric parameters of the cutting layer at the contact point. On this basis, mathematical relationships for contact diameter and effective diameter were derived. The basis for these considerations is the very rarely considered working angle of the cutter blade. In part of the experimental study, machining tests were carried out for selected kinematic variants of multi-axis cutting. Based on the results obtained, it was found that as the tool axis inclination angle increases, the contact diameter increases. The effective diameter at the upper characteristic point of the cutting layer increases up to a certain angle of inclination, after which it begins to decrease. The rotational angle of the tool axis does not affect any of the diameters, but it does affect the displacement of the contact point, the values of the working angle of the tool blade and the feed-related component decrease. The result of this displacement is a change from climb milling to conventional milling, which has significantly degraded surface quality and tool life. The best results of the machining test were obtained when only the angle of inclination of the tool axis was used. It was concluded that the parameter tool blade working angle can be a control variable in a multi-axis milling process and has a major impact on the physical aspects of the cutting process.

Toolpath smoothing with reduced curvature and synchronized motion for hybrid robots

G01 commands are the most commonly used toolpath format in Computer Numerical Control (CNC) machining. Due to the discontinuity between adjacent linear segments, toolpath smoothing is necessary to improve machining efficiency and machined surface quality. This paper proposes an analytical C3 continuous local toolpath smoothing and synchronization method for a five-axis hybrid robot. Position and orientation smoothing are decoupled, with quintic B-spline segments replacing the original linear segments. The curvatures of the toolpath are reduced under constrained smoothing errors by weaving transition splines along the linear segments instead of confining them within the corners. A synchronization method based on arc length parameterization tailored to the smoothing method is also proposed. Tool tip position and tool axis orientation are synchronized using another monotonic, C3 continuous spline, which achieves smoother joint motion along the toolpath. For the hybrid robot with highly nonlinear kinematics, improved results in feedrate scheduling considering joint constraints can be realized. Simulations and experiments validate the effectiveness of the proposed method.

Analysis of tool wear, chip and machined surface morphology in multi-axis milling process of Ni-based superalloy using the torus milling cutter

This article presents an investigation into the life of the torus milling cutter with round cutting inserts when multi-axis milling process in high-speed cutting conditions of Inconel 718 under various of kinematic variants of multi-axis machining. The experiments were performed at varying tool axis orientation parameters of; lead angle: 1.37–20° and tilt angle: −18.86–20°. A new research approach was introduced to evaluate the possibility of extending the life of the torus milling cutter by changing the tool axis orientation in multi-axis machining. The analysis performed includes the tool life, tool wear patterns, and mechanisms as well as its relationship with the chip and machined surface morphology and kinematics variants of multi-axis cutting. The experimental results showed that tool wear has begun with smooth abrasion and chipping around the depth of cut line, which then progressed into flank wear and finally notching and flaking via mechanisms of abrasive and adhesive wears. However, for each of the analyzed kinematic variants of multi-axis cutting, the above processes proceeded in a completely different way. Thus, by changing the tool axis orientation in a controlled manner, it is possible to influence the cutting conditions in the tool-chip and chip-workpiece interfaces; hence, efficiently displace the point of contact and thus offset the negative impact of the concentration of tribological interactions at that point. Consequently, it was possible to slow down the tool wear development and prolong the torus milling cutter life to a maximum 78%. There was also a strong influence of multi-axis cutting conditions and tool wear patterns on the morphology of the chip and the machined surface. In conclusion, the kinematic variant of multi-axis cutting (i.e. axis orientation) using the torus milling cutter of Ni-based superalloys plays an important role in the possibility of extending tool life.

Least variation in tool orientation control for 5-axis CNC machining

We address the problem of minimizing the variation of the tool axis orientation of a 5-axis CNC machine equipped with a ball-end cutter that is designed to maintain a constant cutting speed, which is ensured by a fixed angle ψ between the tool axis a(t) and the workpiece surface normal n(t) at each point of contact as the cutter moves along a specified toolpath. The configuration can be mathematically translated into a pair of curves a(t) and n(t) on the unit sphere with constant parametric distance ψ, and the least variation of the tool axis orientation is achieved when the overall length of the curve a(t) is minimized under certain auxiliary boundary conditions. Using the calculus of variation we show that the solution a(t) consists of arcs of great circles and offset curves of n(t) on the unit sphere. A numerical approximation scheme based on Euler's method of finite differences is also provided.

Studying the influence of the machining process on the geometrical defects of the standardized S-shape test part

In 2020, an S-shape part was proposed as a 5-axis reception test part in the new version of ISO 10791–7:2020. This test part enables the testing of machine-tool behavior that involves a high variation in tool axis orientation. This test part is formed of an S-shape fillet which is machined in flank milling with an endmill of Ø20 mm. Any defects of the machined part are influenced by the accuracy of the CAD model, the CAM tool path computation, the measurement uncertainty of the free-formed surface by a coordinate measurement machine (CMM), and machine-tool geometric behavior. This article aims to quantify the influence of all these steps on the final defects of machined parts. The proposed conclusion to our work is based on analytical and numerical study and experimental analysis. Finally, we propose an identification process for machine-tool architecture geometrical defects pertaining to the measurement of the machined S-shape part.

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

Tool axis adjustment for 5-axis roughing operations

The increased accessibility of the tool achieved by using 5-axis roughing reduces the overall machining time of complex parts by reducing or eliminating the re-roughing and semi-finishing operations thereby decreasing the volume of remaining material before finishing operations. However, 5-axis milling generates significant variations in tool orientation which, combined with the high tool engagement in the material required by the roughing conditions, can be penalizing. Controlling these variations is therefore mandatory to guarantee the tool life, the productivity and the quality of the roughing operation. Thus, a multi-objective optimization is proposed to define the successive orientations of the tool axis along the path that minimize the feedrate slowdowns and thus the machining time, balance the pushing or pulling machining configurations and respect the programmed scallops heights of the machined surface. In this work, the tool path is defined by two curves, one constraining the position of the tool and the other its orientation allowing for a parametric synchronization to conduct the optimization. From the definition of the weights of each of the minimization objective functions, it is possible to find a tool axis orientation solution that satisfies the given constraints all along the path. The application on a test part by simulation and machining highlights the effectiveness of the proposed approach and the advantages of controlling the evolution of the tool axis orientation in 5-axis roughing.

Optimal tool orientation in 3 + 2-axis machining considering machine kinematics

In 5-axis machining, the initial orientation and position of the part in the fixture on the machine table are chosen to avoid collisions and to ensure that axes ranges are respected. However, kinematics of the machine is rarely considered for workpiece setup optimization although it affects the tool path execution and machining time. Indeed, for complex surfaces, actual feedrate is often lower than the programmed one and can present strong slowdowns, which are critical for the tool cutting conditions and therefore the part quality. This article investigates the use of kinematic manipulability criteria to determine the best orientation of the workpiece setup to maximize the actual feedrate and reduce machining time. The modelling of maximum velocity, acceleration, and jerk of each axis by means of polytopes makes it possible to take advantage of the whole kinematic space of the machine more intuitively. Simulations and experiments are carried out in 3 + 2-axis machining on test parts with a ball-end tool. For stretched surfaces, while the tool centre motion is given by the machining strategy, the tool axis orientation is optimized jointly with the workpiece setup. Experiments confirm that actual feedrate raises faster to better respect the programmed cutting conditions along each path. As feedrate is also higher, machining time is reduced significantly.

A G3 continuous tool path smoothing method for 5-axis CNC machining

The chain of short linear tool path segments is the most common form for the five-axis machining by Computer Numerical Control (CNC) machines. The connection points of the linear path segments lead to the discontinuities in position, velocity, acceleration, and jerk, resulting in fluctuation of machine motion which leaves undesired marks on the finished surface. This paper presents a geometric smoothing algorithm by enforcing the continuity of first, second, and third geometric derivatives of the splined path segments at their meeting points for the five-axis machining of curved surfaces. The linear tool path segments are first smoothed by Bezier splines while constraining the path errors within a set tolerance. The tool path segments, that cannot be smoothed within the path error limit, are smoothly connected at the connection points. The tooltip position and tool axis orientation displacements are synchronized to avoid discontinuous displacements along the tool axis. The proposed algorithms are demonstrated with simulations and experiments in following a five-axis, curved tool path on a CNC machine tool. It is shown that the proposed G3 continuous tool path algorithm gives smoother tool-tip and tool axis orientation, reduces the tracking errors, contour errors and amplitudes of jounce at the connections of segments along the tool path, leading to the smoother surface for the precision five-axis machining of sculptured surfaces.

Optimization of Tool Axis Orientations in Multi-Axis Toolpaths to Increase Surface Quality and Productivity

This paper deals with a method to optimize tool axis orientations in multi-axis milling toolpaths. The method is based on calculation of the actual cutting diameter and the cutting speed during the toolpath. Subsequently, the NC code is processed by the interpolator with a machine tool kinematic model. The result is a visualization of the actual cutting speed and the real feed-rate on the toolpath. Based on these results, the vectors used to orient the tool axis along the toolpath can be effectively set up in several iterations. The toolpath are optimized to achieve a more constant cutting speedwhich lead to an improvement in surface quality and increase in productivity.

Tool Path Optimization for Robotic Surface Machining by Using Sampling-Based Motion Planning Algorithms

Abstract This paper develops a tool path optimization method for robotic surface machining by sampling-based motion planning algorithms. In the surface machining process, the tool-tip position needs to strictly follow the tool path curve and the posture of the tool axis should be limited in a certain range. But the industrial robot has at least six degrees-of-freedom (Dof) and has redundant Dofs for surface machining. Therefore, the tool motion of surface machining can be optimized using the redundant Dofs considering the tool path constraints and limits of the tool axis orientation. Due to the complexity of the problem, the sampling-based motion planning method has been chosen to find the solution, which randomly explores the configuration space of the robot and generates a discrete path of valid robot state. During the solving process, the joint space of the robot is chosen as the configuration space of the problem and the constraints for the tool-tip following requirements are in the operation space. Combined with general collision checking, the limited region of the tool axis vector is used to verify the state’s validity of the configuration space. In the optimization process, the sum of the path length of each joint of the robot is set as the optimization objective. The algorithm is developed based on the open motion planning library (OMPL), which contains the state-of-the-art sampling-based motion planners. Finally, two examples are used to demonstrate the effiectiveness and optimality of the method.

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.

Empirical Models for Surface Roughness and Topography in 5-Axis Milling Based on Analysis of Lead Angle and Curvature Radius of Sculptured Surfaces

The orientation of the tool axis and the variable curvature of the machined profile of a sculptured surface have a significant impact on the roughness and topography of the surface in the process of 5-axis milling by means of a toroidal milling cutter. The selection of the orientation of the toroidal milling cutter axis relative to the radius of curvature of the machined surface profile is very important as it can provide a better surface quality and an even distribution of roughness parameters. In this paper, an attempt to carry out model tests to obtain mathematical relationships was made. These relationships were to determine the impact of the tool axis orientation and the variable curvature radius of the machined profile on the surface roughness and its topography in the 5-axis milling process of sculptured surfaces. The tests were conducted on an example of a turbine blade made of Inconel 718 alloy. A measurable effect of the work undertaken was the development of model relationships that can be applied in specialized modules of CAM (Computer Aided Manufacturing) systems supporting the programming of 5-axis machining of sculptured surfaces. The models developed will also make it possible to obtain an evenly distributed roughness on the machined sculptured surface, especially on the surface of the turbine blades of the Inconel 718 alloy, as indicated by the results of the tests carried out.

Region-based toolpath generation for robotic milling of freeform surfaces with stiffness optimization

Abstract Because of industrial robots’ relatively low stiffness, many research efforts have been performed to improve the robot stiffness by optimizing the robot posture. For freeform surfaces with large curvature, however, the expected high stiffness posture may undergo excessive changes that exceed the robot joint speed limit. Therefore, the stiffness optimization may not achieve the expected results in actual machining owing to the limitation of robot kinematics and conventional toolpath pattern. To address this problem, a region-based toolpath generation method is proposed to improve robot stiffness in this study for robotic milling of freeform surfaces. To provide the possibility of higher stiffness robot posture, not only the redundant degree of freedom (DOF) of the robot but also the orientation of tool axis during machining is optimized. Under the influence of surface curvature and position, the change of high stiffness posture has regionality. A surface subdivision method is proposed to divide the surface into multiple sub-regions, so that actual robot posture with better stiffness can be obtained. For each sub-region, the feed direction of toolpath is optimized to further enhance robot stiffness. Simulations and experimental studies are conducted, and show that the proposed toolpath generation method can improve the robot stiffness in freeform surface machining.

Virtual prediction and constraint of contour errors induced by cutting force disturbances on multi-axis CNC machine tools

This paper presents a strategy to virtually predict and constrain the contouring errors contributed by cutting force disturbances on feed drives. The tracking errors on each feed drive are predicted as a linear function of tangential feed by evaluating the product of estimated power spectrum of cutting forces and disturbance frequency response function along the tool path in virtual CAM environment. The corresponding tool tip contouring and tool axis orientation errors are estimated and constrained by scaling the feed along the tool path. The algorithm is experimentally illustrated to improve the machining accuracy on a 5 Axis CNC machine tool.

Modelling of elliptical dimples generated by five-axis milling for surface texturing

Abstract Surface texturing processes that improve workpiece surface properties such as the friction of textured surfaces, the lubrication of sliding surfaces and the adhesion of workpiece surfaces are of increasing interest in industry. The most frequently employed processes for surface texturing are based on laser methods and on chemical etching processes. A widespread application of surface texturing is the improvement of tribological properties in terms of friction and load capacity. In these applications, surface texturing usually consists of generating dimples that are uniformly distributed on the workpiece surface. Five-axis milling with a ball-end mill can be an effective and productive option for these processes in these applications, as it is able to generate surface texturing that consists of periodic elliptical dimples if the tool geometry and the cutting conditions (feed, depth of cut and yaw and tilt angles defining tool axis orientation) are appropriately selected. In this paper, a model that predicts the geometry (shape, dimensions and orientation) of elliptical dimples machined by five-axis milling on flat surfaces for given cutting conditions is developed. In order to achieve this, equations expressing the trajectory followed by the cutting edges in five-axis milling are derived. The model takes into account the effect of tool parallel axis offset on dimple geometry. Next, the influence of cutting conditions on dimple geometry is analysed in order to define the cutting conditions that generate a given dimple geometry. From this analysis, a significant influence of the tool's tilt angle on the elliptical shape of the dimples and a linear dependence of the yaw angle on dimple orientation are observed. In order to mill elliptical-shaped dimples, tilt angles larger than 30° and feed, step over and depth of cut values that avoid interference between the dimples generated by different cutting edges of the ball-end mill are required. Finally, a series of five-axis milling tests was carried out in order to validate model predictions. A low dispersion in the dimensions and area of milled dimples was obtained. The shape and dimensions of predicted and measured dimples are compared and good correspondence between them is observed, the largest error being 7%.

A feedrate scheduling algorithm to constrain tool tip position and tool orientation errors of five-axis CNC machining under cutting load disturbances

This paper proposes a model to keep the cutting load induced tool tip position and tool orientation errors of five-axis CNC machines within the desired tolerance limit by scheduling the feed along the tool paths. The cutting forces at the tool tip are transmitted to three translational and two rotary servo drives of the machine tool using its kinematic model. Tracking errors of each axis contributed by cutting forces are modeled using the disturbance transfer function of servo drives. The tracking errors are mapped to the workpiece coordinate system to evaluate the tool tip position and tool axis orientation errors at discrete tool path locations. The cutting forces, therefore the tracking errors, are modeled as a linear function of tangential feed velocity. The feed is adjusted to constrain the tool tip position and tool axis orientation errors at the desired tolerance levels along the tool path. The proposed algorithm has been experimentally validated by milling a curved tool path on a five-axis commercial CNC machine tool. It is shown that the proposed algorithm can significantly improve the part machining accuracy without increasing the machining time.

Wpływ zmiany orientacji osi narzędzia oraz kierunku jego prowadzenia w obróbce powierzchni swobodnej na chropowatość powierzchni

Presented is the effect of the direction of tool driving along parametric curves from a free surface and changes of the tool axis orientation on roughness parameters during finishing machining.

Error compensation in the five-axis flank milling of thin-walled workpieces

Five-axis flank milling is the most commonly used processing method in the aviation industry for the machining of thin-walled parts with complex ruled surfaces. During machining, the tool/workpiece deformations caused by the cutting force often lead to surface errors on the machined components that severely affect the accuracy of the machining results. This article presents an iterative compensation strategy to reduce the tool/workpiece deformation-induced surface error during the five-axis flank milling of thin-walled workpieces by modifying the tool tip position and tool axis orientation. This approach can be implemented in four steps. First, a highly integrated cutter-workpiece engagement extraction method is developed for the construction of a flexible cutting force model that can follow changes in the process geometry. Second, the tool/workpiece deformations are predicted by the cantilever beam model and finite element model, respectively. Third, an off-line error compensation scheme is performed at each cutting location of the tool path to obtain the modified tool position. Fourth, the machined surface of the workpiece model is reconstructed, and the compensated machining code, which can be used directly for actual machining, is generated. A case study is presented at the end of this article, and the effectiveness of the present compensation strategy is verified by machining experiments.

Iso-Planar Feed Vector-Fields-Based Streamline Tool Path Generation for Five-Axis Compound Surface Machining With Torus-End Cutters

This paper presents a new vector-field-based streamline smoothing method in the parametric space and a tool orientation optimization technique for five-axis machining of complex compound surfaces with torus-end cutters. Iso-planar tool path is widely used in the machining of various types of surfaces, especially for the compound surface with multiple patches, but the operations of intersecting the compound surface with a series of planes have depended considerably on the complicated optimization methods. Instead of intersecting the surface directly with planes, a novel and effective tool path smoothing method is presented, based on the iso-planar feed vector fields, for five-axis milling of a compound surface with torus-end cutters. The iso-planar feed vector field in the parametric domain is first constructed in the form of stream function that is used to generate the candidate streamlines for tool path generation. Then, a G1 blending algorithm is proposed to blend the vector fields within the adjacent parametric domains to ensure smooth transition of cross-border streamlines. Based on the smoothened streamlines in the parametric domains, pathlines along with their correspondent side sizes are selected as desirable tool paths. Concerning a high performance machining, detailed computational techniques to determine the tool axis orientation are also presented to ensure, at each cutter contact (CC) point, the torus-end cutter touches the part surface closely without gouging. Both the computational results and machined examples are demonstrated for verification and validation of the proposed methods.