Tool Path Generation Method Research Articles

Toolpath generation for partition machining of T-spline surface based on local refinement

Toolpath generation is one of the most challenges facing today’s freeform surface machining, and partition machining methods are widely investigated for toolpath generation of freeform surface based on sampling and clustering. However, due to the inherent drawbacks of NURBS, there are two limitations for the partition machining of freeform surface in the current research: (1) global sampling method is imposed by reason of rectangular topology of NURBS, which will introduce redundant sampling points and increase computation costs, (2) partitioned region boundaries are represented using analytical curves or discrete points, and freeform surface behaves like trimmed surface, which will introduce gaps near partitioned region boundaries. T-spline has been proven to perform excellently in the field of CAD/CAE/CAM with the charming characteristics of less control points, flexible topology, and local refinement. However, T-spline does not be introduced for the partition machining in the current research. In the paper, T-spline is firstly introduced for the partition machining of freeform surface to solve above limitations. A partition method is proposed for T-spline surface based on its flexible topology and face-by-face sampling, which will improve the partition efficiency. Clustering parameters are analyzed, and curvature parameters are chosen for surface partition, which can extract isolated features. T-spline local refinement and sliding box method are introduced for the boundary construction of partitioned regions, and partitioned regions are described by a set of rectangles, which can guarantee the continuity near the partitioned boundaries and avoid the gaps. Different sizes of tools are used for toolpath generation of partitioned regions, which can reduce toolpath length. The proposed method is tested using two synthetic T-spline surfaces and the comparison with existing toolpath generation methods is provided.

Tool-path generation for industrial robotic surface-based application

Industrial robots are widely used in various applications such as machining, painting, and welding. There is a pressing need for a fast and straightforward robot programming method, especially for surface-based tasks. At present, these tasks are time-consuming and expensive, and it requires an experienced and skilled operator to program the robot for a specific task. Hence, it is essential to automate the tool-path generation in order to eliminate the manual planning. This challenging research has attracted great attention from both industry and academia. In this paper, a tool-path generation method based on a mesh model is introduced. The bounding box tree and kd-tree are adopted in the algorithm to derive the tool path. In addition, the algorithm is integrated into an offline robot programming system offering a comprehensive solution for robot modeling, simulation, as well as tool-path generation. Finally, a milling experiment is performed by creating tool paths on the surface thereby demonstrating the effectiveness of the system.

Research on the double-sided incremental forming toolpath planning and generation based on STL model

In order to take the advantages of the double-sided incremental forming (DSIF) that can freely switch the pressing and supporting functions of the two tools and realize the forming of the sheet parts with protruding features in both the positive and negative directions of the sheet (the sheet part with bidirectional protruding feature), a method for the double-sided incremental forming based on the stereo lithographic (STL) model was proposed. The method first classifies the forming features according to the protruding direction and the position relationship of the model into the different types of the features to be formed. The main forming surface and the supporting surface are determined by the types of the forming features, and the pressing and supporting tasks of the main tool and slave tool heads are assigned. Then, the cutter location points of the main tool and slave tool are generated, and the toolpath of the main tool and slave tool are planned out according to the forming sequence and the forming methods of the different forming features. Finally, a method of the interference detection and correction between the forming tool head and the sheet part is proposed. The finite element numerical simulation and the forming experiments of the sheet part with bidirectional protruding features show that the proposed toolpath generation method for the DSIF is applicable; the DSIF toolpath generated based on the STL model can fabricate the sheet part with the bidirectional protruding feature.

Region based five-axis tool path generation for freeform surface machining via image representation

Abstract This paper inaugurates a brand new five-axis tool path generation method for freeform surface machining, which is solely based on digital image processing. By utilizing image representation, a freeform surface can be digitized into a uniform grayscale image. With this novel representation, we come up with a region based five-axis tool path scheme with remarkably enhanced utility towards freeform surface machining process. The image representation possesses sufficient geometric data for us to evaluate the surface normal distribution and split the surface area accordingly via image processing algorithms. Since each partitioned region contains a limited surface inclination range, one rotary axis is locked with a certain angle during the processing of this region. In addition, by further exploiting the potential of the image representation, the cutter contact (CC) curves are extracted purely from the image of each partitioned region. Preliminary results show that this method is more than adequate for the tool path computation. The computed tool path outperforms the benchmarks by reducing the machining time for as much as 40%, as verified in the physical cutting test.

Generating gouge-free tool paths for ball-end cutter CNC milling of cloud of point by projecting guide curves

This paper presents a gouge-free tool path generation method for direct ball-end cutter CNC milling of cloud of point. In this method, a base surface with simple geometry, which can approximately reflect the features and the changes of surface shape, is first constructed, and the guide curves with different patterns of the cutter motion are then planned on it. After the cloud of point is offset by a distance of the ball-end cutter radius, the guide curves are deformed onto the offset of cloud of point by point projection operation along the computed direction instead of the traditional z-axis direction, thereby forming the desired tool paths directly on the cloud of point. In projecting guide curves, the computation of the projecting direction and construction of the weight function are discussed in detail to eliminate the projection error as much as possible. The technique of adjusting the path points is also presented to eliminate the unfavorable undercuts and overcuts. Since the cloud of point is offset a distance of the cutter radius, the gouge between the cutter and the point set surface can be automatically avoided. Also, various patterns of the cutter motion can be conveniently planned on the simple base surface, such that the cloud of point can be milled along the generated tool paths with the most suitable topology. Finally, several examples are given to validate the proposed method.

Plunge milling with constant scallop height by adaptively modifying the step interval for pocket wall

Plunge milling plays an important role in machining of components with cavity structures. As a non-continuous material removal strategy, residual material is inevitably remained between two adjacent plunge cutter locations, also named as scallop. Large scallop height causes machining error, as well as fluctuations of cutting width in the following machining operation like semi-finish milling. As such, a constant scallop from plunge milling is essential to improve machining stability and tool life in following operation. In this paper, a new plunge milling toolpath generation method with adaptive interval is developed to restrict the maximum scallop height within a given value. Geometric relationship between plunge tool location and cusp of the constant scallop is firstly analyzed to determine the curves that the cusp of the constant scallop and plunge tool location located on. Then an iterative cusp of the constant scallop calculation algorithm is constructed based on the constructed geometric relationship. The next plunge tool location is obtained through a similar algorithm. Therefore, interval between current and its previous tool location is determined. In this way, the generated plunge milling toolpath can satisfy the given machining error allowance and keep a constant scallop height. It also has minimum number of plunge cutter locations to achieve maximum machining efficiency. Advantages of the proposed method are validated through a machining experiment by comparing the machining results with conventional plunge milling toolpath with constant step interval.

Toolpath generation in sub-regional processing with constraint of constant scallop-height at boundary for complex curved surface

Complex curved surface parts are widely applied in the manufacturing industry for specific functions. With the continuous improvement of the geometric complexity and the machining requirement, the conventional processing technology with uniform processing parameters is no longer applicable for this kind of parts, and the sub-regional processing with variable parameters is proposed. However, the obvious machined trace at the boundary between sub-regions appears easily in this way, which restricts the processing quality of complex curved surface parts seriously. To reduce the machined trace and realize the precise toolpath stitching, a toolpath generation method in sub-regional processing with constraint of constant scallop-height at boundary for complex curved surface is proposed. Firstly, the formation mechanism of the machined trace at the boundary between sub-regions is analyzed. Taking into account the geometric feature of the curved surface, the calculation model for the distance between boundary and cutter contact (CC) point is built. With constraint of constant scallop-height, the critical curve of CC points for the boundary between sub-regions is constructed. Then, the geodesics for the critical curve of CC points are calculated in side-step direction with a numerical method. The theoretical CC points on the geodesics are generated according to the estimated scallop-height and modified by the sensitivity analysis. Finally, the toolpaths are generated by connecting the theoretical CC points orderly and the actual CC points are determined in feed direction. A comparison experiment is carried out to verify the feasibility of the proposed toolpath generation method. The experimental results show that with the proposed method, the maximum of the profile deviation and the profile arithmetic average error at the boundary between sub-regions are 9.0 μm and 2.3885 μm respectively, which decrease by 74.43% and 34.98% compared with the results for the iso-level method. This research proves that the proposed toolpath generation method can realize the precise toolpath stitching and improve the processing quality in sub-regional processing, which provides guidance for the precision machining of the complex curved surface parts.

A high-efficiency generation method of integral impeller channel tool path based on parametric domain template trajectory mapping

Integral impeller is a complex part commonly used in petroleum, chemical, shipbuilding, aerospace, and other industries. The manufacturing of the integral impeller involves the multi-axis machining of free-form surface, which is a time-consuming and error-prone process. Tool path planning is regarded as a key issue in this process, but there is still short of systematic solutions. In this paper, a parametric domain template trajectory mapping algorithm is presented to calculate the tool path of impeller channel machining. Through generating the template trajectory in the parametric domain, and mapping the template trajectory to the physical domain with the aid of the mapping model, and then the actual machining tool path can be obtained. The proposed method can realize the rapid acquisition and easy modification of the impeller machining tool path. Firstly, the trajectory mapping model from the parametric domain to the physical domain is established using the morphing technique, and the template trajectory mapping method in the parametric domain is given. Secondly, the clean-up boundary of the impeller channel is determined in the parametric domain, and the quasi-triangular and streamlined template trajectory of the impeller channel is defined. Finally, the template trajectory given in the parametric domain is mapped to the physical domain through the mapping model, and the streamlined and quasi-triangular tool paths of the impeller channel are calculated. An example analysis shows that the calculation difficulty of the tool path for impeller channel machining is greatly decreased, and the calculation efficiency is also improved. The simulation and actual machining are carried out. The result shows that the tool path generation method presented in this paper is effective and feasible, and it offers a new way for tool path planning of NC machining for impeller complex parts.

A region-based tool path generation approach for machining freeform surfaces by applying machining strip width tensor

In freeform surface machining, the cutter should move along the feed directions with maximal machining strip widths (MSW) as much as possible to improve machining efficiency. However, since the optimal feed directions usually vary among different regions over a complex freeform surface, only local optimal machining result could be achieved by most existing tool path generation methods which consider the whole surface as one machining region. This research proposes a tensor-based approach to generate regional tool paths for more globally optimal machining result. A rank-two tensor is first constructed to enable the evaluation of the MSW over the whole feed direction space at the cutter contact point (CCP). To make this MSW tensor usable for generic APT cutters, the concept of effective cutting surface (ECS) is raised. The tensor is then obtained by modeling the geometric approximation between the ECS and the part surface around CCP. A MSW tensor field is then induced over the entire part surface. The regional distribution of the optimal feed directions is associated with the degenerate points within the tensor field. Then, the surface may be divided into several machining regions by constructing inside boundaries starting from the trisector degenerate points. At last, tool paths will be separately calculated in each sub-surface. Since the optimal feed directions in each sub-surface vary continuously, the cutter movements can follow the optimal feed directions closely based on the generated regional tool paths which refer to shorter tool path length and machining time. Two parts with freeform surface are selected from the real industry as test cases and the comparisons to other traditional methods are also provided.

Smooth fillet-end cutter tool path generation method on triangular-mesh surface based on Modified Butterfly subdivision

Triangular-mesh surfaces are widely applied in the design of aerospace, automobiles, ships, etc., because of their high computational efficiency and robustness compared with parametric surfaces. In order to improve the tool path continuity and reduce the cutter load fluctuation, a smooth tool path generation method on triangular-mesh surfaces based on Modified Butterfly subdivision is proposed. The machining model at the cutter-contact point is constructed based on the geometric analysis of the triangular-mesh surface and fillet-end cutter. The minimum cutter tilt angle and maximum machining stripe width are obtained to avoid the interference of cutter and workpiece. And then, the Modified Butterfly subdivision method is applied to the triangular-mesh surface to ensure the tool path interval within the strip width. The boundary of the surface is selected as the initial tool path based on which the subsequent tool paths are generated along the edge of triangular mesh, and the cutter location points are obtained according to the geometric model of the fillet-end cutter. The Discrete Domain of Feasible Orientation (DDFO) model is constructed to eliminate the singularity problem of the machining process, and Modified Butterfly subdivision is applied recurrently to guarantee the whole surface within the scallop height requirement. Finally, the spiral tool path with good continuity and smoothness is generated according to the specified cutter parameter and scallop height requirement, which can reduce the cutter load fluctuation.

Spiral Tool Path Generation Method on Mesh Surfaces Guided by Radial Curves

This paper presents a new spiral smoothing method to generate smooth curved tool paths directly on mesh surfaces. Spiral tool paths are preferable for computer numerical control (CNC) milling, especially for high-speed machining. At present, most spiral tool path generation methods aim mainly for pocketing, and a few methods for machining complex surface also suffer from some inherent problems, such as selection of projecting direction, preprocessing of complex offset contours, easily affected by the mesh or mesh deformation. To address the limitations, a new spiral tool path method is proposed, in which the radial curves play a key role as the guiding curves for spiral tool path generation. The radial curve is defined as one on the mesh surface that connects smoothly one point on the mesh surface and its boundary. To reduce the complexity of constructing the radial curves directly on the mesh surface, the mesh surface is first mapped onto a circular region. In this region, the radial lines, starting from the center, are planned and then mapped inversely onto the mesh surface, thereby forming the desired radial curves. By traversing these radial curves using the proposed linear interpolation method, a polyline spiral is generated, and then, the unfavorable overcuts and undercuts are identified and eliminated by supplementing additional spiral points. Spline-based technique of rounding the corners is also discussed to smooth the polyline spiral, thereby obtaining a smooth continuous spiral tool path. This method is able to not only greatly simplify the construction of radial curves and spiral tool path but also to have the ability of processing and smoothing complex surfaces. Experimental results are presented to validate the proposed method.

HSM toolpath generation with capsule-based region subdivision

High-speed machining (HSM) has become a research hotspot in the manufacturing field these years. In HSM, it requires the toolpath to be very smooth. Any sharp corners will cause decelerations of the feed axes. However, corners are inevitable in the toolpath generation process. This work focuses on smooth toolpath generation for HSM pocketing. The concept of region subdivision is proposed and implemented. With this concept, the input pocket is firstly subdivided into two classes of sub regions: the HSM regions and the low-speed machining (LSM) regions. For the HSM regions, very smooth path curves are filled and high machining speed is set. For the LSM regions, sharp corners are allowed and low machining speed is set. In this work, the HSM regions are extracted as capsule-shape regions inside the pocket. For these capsules, paperclip-shape curves are used as the HSM toolpath. These curves are smoothly connected by semicircles and line segments. The path intervals are strictly controlled so that constant radial cutting depth can be achieved. For the rest regions inside the pocket, conventional offset curves are filled as the LSM toolpaths. The proposed capsule-based HSM toolpath generation method is tested with several comparative examples. Results show that the proposed method could generate larger HSM regions and more efficient toolpaths than the maximum inscribed circle-based method from the authors’ previous work.

A region-based 3 + 2-axis machining toolpath generation method for freeform surface

Due to the geometric complexity, tool orientations usually change dynamically during freeform surface machining with 5-axis machine tool. As the kinematic performance of the rotary axes is usually weaker than that of the linear axes, the real cutting speed is difficult or even impossible to reach the desired level, which further leads to low machining efficiency. This paper presents a region-based 3 + 2-axis machining toolpath generation method with 5-axis machine tool. The surface is first divided into several preliminary sub-surfaces using K-means clustering algorithm. A post processing procedure is then carried out to optimise the preliminary sub-surfaces to ensure the machinability. For each sub-surface, gouging-/collision-free tool orientations are first calculated and then the optimal combination of the fixed tool orientation and the feed direction is determined by maximising the average machining strip width for toolpath generation. The proposed method is tested by a case surface and the comparisons to some other traditional methods are also provided.

A discrete simulation-based algorithm for the technological investigation of 2.5D milling operations

Many applications are available for the syntactic and semantic verification of NC milling tool paths in simulation environments. However, these solutions – similar to the conventional tool path generation methods – are generally based on geometric considerations, and for that reason they cannot address varying cutting conditions. This paper introduces a new application of a simulation algorithm that is capable of producing all the necessary geometric information about the machining process in question for the purpose of further technological analysis. For performing such an analysis, an image space-based NC simulation algorithm is recommended, since in the case of complex tool paths it is impossible to provide an analytical description of the process of material removal. The information obtained from the simulation can be used not only for simple analyses, but also for optimisation purposes with a view to increasing machining efficiency.

Automated Flexible Forming Strategy for Geometries With Multiple Features in Double-Sided Incremental Forming

Double-sided incremental forming (DSIF) is a dieless sheet metal forming process that uses two generic tools to form a part of arbitrary geometry from a clamped sheet via the accumulation of small localized deformations. In DSIF, there is a need for an automatic toolpath generation method to separate geometric features coupled with a strategy to form these features in the correct sequence such that they can be accurately formed. Traditional CNC machining toolpaths are not suitable for DSIF because these toolpaths are designed for material removal processes, which do not have to account for the motion of the virgin material during the process. This paper presents a novel and simple way to represent geometric features in a hierarchical tree structure during z-height-based slicing along with algorithms to generate different forming strategies using this tree structure. The proposed approach is demonstrated through physical experiments by forming a complex part with multiple features.

A new approach to generating trochoidal tool paths for effective corner machining

In conventional corner machining, the cutter machines the workpiece in a large engagement angle which could even be π. More cutting edges are engaged at each cutting moment; thus, the cutting force is great, and the un-cutting time of each cutting edge is less for the cutter releasing heat; thus, the cutting temperature is high. It is common that the cutter in corner machining often wears out quickly and the tooling cost is high. Recently, the trochoidal tool path has been recognized in industry; however, due to no well-established trochoidal tool path generation method, this path is not widely used yet. In this paper, a new approach to generating trochoidal tool path is proposed. First, the trochoidal tool path is represented with two parameters. The material removal rate and the cutting force in trochoidal machining are formulated. Then, an optimization model of the tool path that is established to achieve the machining time is the shortest while the cutting force is expected. Relationships of the trochoidal tool path with the material removal rate and cutting force are analyzed, and a method of choosing the optimal trochoidal parameters is proposed. Finally, a practical example is rendered and the results demonstrate validity of this proposed method.

Flexible punching system using industrial robots for automotive panels

Abstract A new flexible punching system based on industrial robots is proposed for tailor-made automotive panel. A robot end effector for industrial robot punching - punching plier is designed. Meanwhile, according to the shape feature of the punching plier, the interactive tool path generation method is proposed in 2D space instead of 3D space. This system can be adjusted easily to punch all kinds of holes, reducing the cost of developing new cars and shortening the development cycle. Finally, the practicability of this system is verified through application in real production of automotive panels.

A new mathematical method of modeling parts in virtual CNC lathing and its application on accurate tool path generation

In industry, many taper shafts are designed with tolerances of a few microns. To cut them in finish turning, paths of the tool in virtual machining should be accurately generated beforehand. For this purpose, the dimension errors and surface roughness of the virtually cut workpiece should be predicted. Unfortunately, the current tool path generation methods cannot accurately calculate the errors and the roughness, resulting in the taper errors larger than the part tolerance. Our research formulates equations of the effective turning edge to accurately calculate the dimension errors and the surface roughness, and then proposes a new approach to CNC programming for high-precision CNC turning. It lays a theoretical foundation of modeling parts in virtual turning and can generate tool paths to machine taper parts with high accuracy.

Efficient tool path generation for five-axis machining of a difficult machined centrifugal impeller

This article presents an efficient tool path generation method for five-axis machining of a difficult machined centrifugal impeller. Geometry of centrifugal impeller is analyzed, and the inherent low efficiency of the machining of difficult machined centrifugal impeller is obtained. The tool path curves which are calculated by the most common iso-parametric method are shown to testify the waste in machining. The new type machining layers are calculated, and the new machining regions are achieved. The new tool path curves in each new machining region are calculated, and they are sparser and triangular. For the inherent low machining efficiency of difficult machined centrifugal impeller, the machining time can be greatly reduced just by the optimizing tool path generation method in this article. Numerical simulation and a real test impeller are presented as the test of the proposed method.

5-Axis CNC incremental forming toolpath generation based on formability

To the problem of the existing CNC incremental forming that mostly adopts the 3-axis CNC incremental forming method and cannot form the complex sheet metal part containing the surface by one-stage forming, which cannot be visible in the positive and negative directions of the Z-axis and whose forming angle is larger than 90°, a multi-directional slant and multi-directional pressing toolpath generation method for the 5-axis CNC incremental forming was proposed to accomplish the forming of the complex sheet metal parts by fully considering the differences of the forming angles at each position of the surface and the accessibility of the extrusion tool to the surface. In this method, the posture of the forming toolpath is adjusted individually according to the forming angle at each position of the surface so that the posture of the sheet metal is constantly adjusted in the forming process, which ensures all the forming angles of the surface to be less than the forming limit angle. Moreover, the posture of the extrusion tool is also adjusted according to the accessibility of the extrusion tool to the surface and the features of the surface, which makes the extrusion tool to press the sheet metal along the needed directions so as to control the deformation state and material flow efficiently, and then accomplish the forming of the complex sheet metal part. The results of the research show that the 5-axis CNC incremental toolpath generated based on the method mentioned earlier can form the complex sheet metal part containing the surfaces whose forming angle is larger than 90° and that is invisible from the positive and negative directions of Z-axis.