Iso-scallop Tool Paths Research Articles

An iso-scallop tool path generation method for three-axis machining freeform surface

An iso-scallop tool path generation method for three-axis machining freeform surface

A Simple Point-based Iso-Scallop Tool Path Planning Method for Noisy Point Clouds with High Robustness and Controlled Errors

With the rapid advances in 3D scanning and vision technologies, point clouds have seen a significant increase in their application to CNC machining. As an important way to generate tool paths from point clouds, point-based direct planning methods are, however, now restricted to high-quality point clouds. Most existing methods would have robustness issues if a noisy point cloud is given due to their reliance on the noise-sensitive estimation of differential properties from point clouds. Error control under noisy point clouds is also rarely considered. This paper presents a robust and error-controlled point-based iso-scallop tool path planning method for CNC machining with ball-nosed cutters. It casts the problem of searching for scallop/CL points to another problem of finding circle-sphere intersection points and the maximum/minimum among them. Both circle-sphere intersections and max/min comparisons are easy to implement and robust. It has also been theoretically proved that the intersections and comparisons can ensure an error bound of 2ϵ on the final results if two conditions called ϵ-sampling and ϵ-covering are met. The effectiveness of the method has been demonstrated by a series of examples and comparisons.

A Level-set Non-uniform Offset Method for Iso-scallop Toolpath Planning Based on Mesh Surface Conformal Mapping

A Level-set Non-uniform Offset Method for Iso-scallop Toolpath Planning Based on Mesh Surface Conformal Mapping

An Efficient Iso-Scallop Toolpath Planning Strategy Using Voxel-Based Computer Aided Design Model

Abstract The primary objective of an efficient computer numerical control (CNC) finishing toolpath strategy is to reduce the machining time and maintain desired surface finish (scallop). Among traditional toolpath planning strategies, iso-scallop gives the shortest toolpath while achieving a uniform surface finish. However, it is computationally complex, time-consuming, and sometimes produces topological inconsistencies in regions of high curvature/gradient. This paper presents a novel voxel-based toolpath planning algorithm to address these issues for the three-axis milling of freeform surfaces. Two strategies have been proposed, namely, iso-scallop and hybrid iso-scallop. Gouge-free cutter location (CL) points are initially computed from the voxel-based model, followed by iso-scallop toolpath generation using a binary search algorithm. The hybrid strategy involves region segmentation to generate an adaptive toolpath in high curvature/gradients regions. The overlapping toolpath is stitched and refined to create an efficient iso-scallop-based tool path. The developed system was extensively tested for complex freeform surface parts and was found to be computationally efficient, robust, and accurate in generating a finishing toolpath.

Iso-scallop tool path planning for triangular mesh surfaces in multi-axis machining

• A robust and universal isoscallop tool path planning method for multi-axis machining is proposed. • The tool path with the constant scallop height is generated from the first contour of a normalized geodesic distance field (GDF) on triangular mesh surfaces. • The proposed algorithm starts from the boundary curve and runs forward recursively to ensure that the surface is covered completely by the isoscallop tool path. • The feasibility and superiority are studied by several simulations and experiments. Triangular mesh enables the flexible construction of complex surface geometry and has become a general representation of 3D objects in computer graphics. However, the creation of a tool path with constant residual scallop height on triangular mesh surfaces in multi-axis machining is not a convenient task for current algorithms. In this study, an isoscallop tool path planning method for triangular mesh surfaces, in which the tool path is derived directly from the contours of a normalized geodesic distance field (GDF), without any post-processing is proposed. First, the GDF is built to determine the shortest geodesic distance from each vertex to the mesh boundary. Then, the normalizing process is performed on the GDF to ensure that its first contour meets the isoscallop height requirement considering the mesh curvature and effective cutter radius. To improve the computational efficiency, the GDF is only built in the mesh area related to the first contour by specifying a stop distance. Moreover, an adaptive refinement process is conducted on the mesh to improve the smoothness and accuracy of the tool path. Finally, the triangular mesh is trimmed along this first contour for a new round of tool path planning. The proposed method is organized recursively and terminated when no new paths are generated. Simulations and experiments are conducted to verify the effectiveness and superiority of the proposed tool path planning method.

Robust and efficient tool path generation for machining low-quality triangular mesh surfaces

This paper presents a new method to generate iso-scallop tool paths for triangular mesh surfaces. With the popularity of 3D scanning techniques, scanning-derived mesh surfaces have seen a significant increase in their application to machining. Quite often, such mesh surfaces exhibit defects such as noises, which differentiate them from the good-quality mesh surfaces previous research work focuses on. To generate tool paths for such low-quality mesh surfaces, the primary challenge lies in robustness against the defects. In this work, a robust tool path generation method is proposed for low-quality mesh surfaces. In addition to robustness, the method is quite efficient, providing the benefit of faster iterations and improved integration between scanning and machining. The fundamental principle of the method is to convert the tool path generation problem to the heat diffusion problem that has robust and efficient algorithms available. The effectiveness of the method will be demonstrated by a series of case studies and comparisons.

An efficient iso-scallop tool path generation method for three-axis scattered point cloud machining

Shortening total length of tool path is preferred in numerical control (NC) machining since it can reduce machining time effectively. Compared with iso-planar tool path, iso-scallop tool path is shorter in length due to the pursuing of maximum interval values. However, the process of iso-scallop tool path generation is more complicated and time-consuming. To simplify the computing process and improve efficiency, this paper presents an efficient iso-scallop tool path generation method for three-axis scattered point cloud machining. Avoiding offsetting points or fitting surface, scallop points and iso-scallop cutter location (CL) points are directly calculated based on scattered data points by iterative algorithms. In order to reduce the times of iterative calculations, initial scallop-height points and CL points are calculated to be closer to the wanted theoretical points. Only a small number of key data points are searched for use so as to reduce calculation amount, and the number gradually decreases with the increase of iterations. Two typical point clouds are used to test the presented method. The experiment results indicate that the scallop height on the machined surface is uniform, and total length of the generated tool paths is much shorter than that of iso-planar tool paths. Moreover, the computation efficiency is also improved and is higher than our previous method (Int J Adv Manuf Technol 63: 137–146, 2012).

Initial tool path selection of the iso-scallop method based on offset similarity analysis for global preferred feed directions matching

The iso-scallop method has been long adopted to achieve a shorter overall machining length. The efficiency and machining performance of this method are largely dominated by the initial tool path. The preferred direction field supplies the local best feed directions. Usually, the offset paths generated by the iso-scallop method largely deviate from the preferred directions, even though the initial path is strictly along the preferred directions. The matching degree of the offset paths and preferred direction field should be taken into consideration when selecting an initial tool path. This paper presents a novel initial path selection method for the iso-scallop method to make whole iso-scallop tool paths and the preferred direction field consistent as much as possible. A surface is re-parameterized to keep the conformality between the surface and parametric domain, which leads to the more regular offset paths on the new parametric domain. By fitting the vector field, streamlines are generated for representing the preferred feed direction on the parametric domain. The offset similarity metric defined by the initial path and streamlines is constructed to measure the matching degree between offset paths and preferred feed directions. Then the feasible path with the best offset similarity for the streamlines will be selected as the initial tool path. In our case study, feed directions with the maximum strip width are chosen. The test results have shown that the tool paths generated by the proposed method achieved a better matching for the selected feed directions and a shorter overall length compared with some existing tool path generation methods.

Effect of tool path on cutting force in end milling

Tool path generation is an important task in end milling. In the existing literature, the tool path pattern/style is determined based on geometric analysis. However, there is little analysis from the viewpoint of machining dynamics/cutting force, which is more related to the final manufacturing performance. Although there are many types of tool paths (e.g., zigzag, spiral, and ISO-scallop tool path), they can be decomposed into a number of circular tool paths with various path radii and cutting angles. Firstly, by investigating chip formation mechanism, the effect of tool path radius on uncut chip thickness is obtained. Analysis shows that tool path radius has a significant influence on uncut chip thickness, thus affecting the cutting force, especially when the tool path radius is small. Then, the effect of cutting angle on cutting force distribution is analyzed. It is found that the feed direction could vary the distribution of cutting force in X and Y direction in 3-axis end milling. Based on such analysis, the cutting force prediction model considering tool path effect is established. To validate the proposed model, various experiments have been carried out based on well-designed tool paths. The comparative results show that (1) tool path has great effect on cutting force through the tool path radius, rotation direction, and start/end point, and (2) the proposed model is capable of providing accurate cutting force prediction considering tool path effect. From a physical viewpoint, the proposed method provides huge potential in automated/intelligent tool path optimization towards better surface quality via minimizing cutting force, which significantly contributes to the state of the art in tool path generation.

Contour parallel tool path planning based on conformal parameterisation utilising mapping stretch factors

Parameterisation-based methods for planning tool paths on mesh surfaces have been developing for years. The issue of existing mapping deformation which results in machining error has not been sufficiently addressed. And it still needs particular 3D geometric operations when planning iso-scallop tool path. To handle these, an effective approach to directly generating the iso-scallop paths on the parametric domain utilising anisotropic mapping stretch factors is proposed. The conformal parameterisation algorithm, Angle Based Flattening, is first implemented for the mapping between the spatial mesh and the planar mesh. Then a general method to convert 3D path parameters into 2D, which involves the direction mapping and length mapping based on the mapping deformation analysis, is presented. After that, a non-uniform offsetting method is proposed for retrieving the valid 2D offset paths. Finally, the iso-scallop paths on the parametric domain can be generated using the converted 2D path parameters and the present non-uniform offsetting method, and then the corresponding tool paths are obtained by inverse mapping. Simulation and experimental results are given to validate the feasibility and effectiveness of the proposed methods.

Iso-scallop tool path building algorithm “based on tool performance metric” for generalized cutter and arbitrary milling zones in 3-axis CNC milling of free-form triangular meshed surfaces

In order to generate a tool path, scallop height should be under the given precision requirement and the tool path should be as short as possible. Iso-scallop tool path generation method is traditionally used to generate the effective tool path. This paper discussed a new method to generate a iso-scallop and contour-parallel tool path for a generalized cutter and an arbitrary area on free-form surface in 3-axis CNC milling. The milling surface, originally represented as a triangular mesh, and the generalized cutter surface are converted into voxel-based depth maps. Milling zone map with the same resolution as the part depth map is used to define an arbitrary milling area. First, the points on the boundary of milling area are marked in order to build the tool path that can follow a boundary line. Second, different cutter location positions are tried in order to satisfy two conditions: milling the material from the selected boundary points within the tolerance limit and having the maximum material removal rate on the way from the previous cutter location point. The algorithm is repeated until the whole area to mill is finished. Due to the high demand of computational power, graphics processing unit is employed for the most time consuming operations.

Preferred feed direction field: A new tool path generation method for efficient sculptured surface machining

This paper presents a new method to generate efficient ball-end milling tool paths for three-axis sculptured surface machining. The fundamental principle of the presented method is to generate the tool paths according to a preferred feed direction (PFD) field derived from the surface to be machined. The PFD at any point on the surface is the feed direction that maximizes the machining strip width. Theoretically, tool paths that always follow the direction of maximum machining strip width at every cutter contact point on the surface would result in shorter overall tool path length. Unfortunately, overlaps of adjacent machining strips commonly exist for tool paths that follow the preferred directions exactly. Such redundant machining can be reduced by iso-scallop tool paths. Nonetheless, iso-scallop tool paths do not in general follow the preferred feed directions. To improve machining efficiency via generating short overall tool path length, the presented method analyzes the PFD field of the surface and segments the surface into distinct regions by identifying the degenerate points and forming their separatrices. The resulting segmented regions are characterized by similar PFD’s and iso-scallop tool paths are then generated for each region to mitigate redundant machining. The developed method has been validated with numerous case studies. The results have shown that the generated tool paths consistently have shorter overall length than those generated by the existing methods.

Iso-scallop tool-path generation of five-axis computer numerically controlled machining for cyclide splines

This article presents effective algorithms to generate iso-parametric and iso-scallop tool path of five-axis computer numerically controlled machining for cyclide spline surfaces with flat-end cutters. Optimal tool orientations are generated by making the contact order between the cyclide patch and the cutter envelope surface as high as possible. Based on the optimal tool orientation, efficient methods are proposed to generate iso-scallop and iso-parametric tool paths for cyclide spline surfaces. Together with the existing methods of fitting arbitrary surface with cyclide splines, the proposed method can be used to improve five-axis machining efficiency of free-form surfaces.

Tool Path Generation for Local Interference Region Machining of Triangular Mesh Model

In this paper, a novel method is proposed for identifying local interference region and generation iso-scallop tool paths based on triangular mesh model for 3-axis ball-end milling. With our method, the principal curvatures and directions at vertices have been computed first and a recursive merging algorithm for segmenting local interference regions is developed. In addition, a method of generation tool path with constant scallop height for local interference region is also presented. Some illustrative examples are tested that indicate the feasibility and availability.

Iso-Scallop Toolpath Generation for Orthogonal Turn-Milling of Ruled Surfaces

This paper presents a new method of computing constant scallop height tool paths for orthogonal turn-milling of ruled surfaces. Indeed, the traditional tool path generation method in orthogonal turn-milling leads to unevenly distributed scallop-height between adjacent toolpaths, which prevent from reaching the required quality. The proposed approach is adequate for orthogonal mill-turning whose toolpath topology is parallel-pattern or spiral-pattern and the constant scallop height is guaranteed by modifying the path-interval distance through adjustment of the offset distance.The machining results obtained show that this method can reduce uneven distribution of scallop height.

Analysis of drift in iso-scallop planning—machining by regions

Computer-aided manufacturing (CAM) occupies an increasingly significant role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. Our present work is devoted to the integration of a module for automatic generation of cutter paths into a CAM program to machine freeform surfaces by end milling. The study addresses the more global issue relating to the adoption of tool path planning with constant scallop height. For present purposes, the cutter geometry is taken as given and does not enter into the study’s parameter choices. The main problem posed by planning for iso-scallop tool paths lies in the management of drift in trajectories, which leads to the path looping due to the fact that global programming over the surface remains unattainable. The proposed solution is to define surface subdivision criteria (machining by regions) enabling iso-scallop planning to be implemented in each region. We conducted our study on a three-axis numerical control machine tool.

Power Series Solution for Isoscallop Tool Path Generation on Free-form Surface with Ball-end Cutter

In this paper we propose a method to compute symbolically a curve of constant scallop height on the surface swept by a ball-end cutter when it traces a free-form cutter-contact curve on a free-form surface. We give explicit formulas for power series solutions to the curve of constant scallop height and the next cutter-contact curve, when the initial cutter-contact curve is given. To make the symbolic results useful in practice, we propose a method to approximate the solutions unilaterally in the parametric plane by piecewise Chebyshev polynomials and exponential functions.

A novel iso-scallop tool-path generation for efficient five-axis machining of free-form surfaces

Tool-path generation is the most important factor in effective machining. A novel iso-scallop tool-path generation strategy was developed for the efficient five-axis machining of free-form surfaces. In the developed iso-scallop method, the cutter paths were scheduled so that the scallop height formed between two adjacent machining paths was constant. The tool orientations along the tool-paths are optimized to maximize material removal and to avoid local gouging. For this aim, the effective cutter radius was adjusted to the surface curvature and then side step was calculated for a constant scallop height. An effective binary searching algorithm was proposed for side step and step length determination. A surface curvature analysis procedure was applied to the entire surface for determination of the minimum radius of curvatures along the feed and side-step directions. Additionally, a feasible flat-ball-end tool selection method is presented by using the concave radius of curvatures which are calculated by surface curvature analysis procedure. Local and rear gouging was analyzed for all cutter contact points. Based on the results, the iso-scallop method reduced the total path length by about 22–50%. Three-dimensional (3D) free-form surfaces were delineated with the STEP-AP214 format, and the “B-spline-surface-with-knots” entity was used to define the B-spline surface geometry. Windows®-based software written in Borland® Delphi has been developed according to the algorithm presented.

5-axis Iso-scallop Tool Paths along Parallel Planes

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Iso-scallop tool path generation in 5-axis milling

This paper presents a new method of computing constant scallop height tool paths in 5-axis milling on sculptured surfaces. Usually, iso-scallop tool path computation methods are based on approximations. The attempted scallop height is modelled in a given plane to ensure a fast computation of the tool path. We propose a different approach, based on the concept of the machining surface, which ensures a more accurate computation. The machining surface defines the tool path as a surface, which applies in 3- or 5-axis milling with the cutting tools usually used. The machining surface defines a bi-parametric modelling of the locus of a particular point of the tool, and the iso-scallop surface allows to easily find iso-scallop tool centre locations. An implementation of the algorithms is done on a free-form surface with a filleted end mill in 5-axis milling.