Spiral tool paths for high-speed machining of 2D pockets with or without islands

We describe new methods for the construction of spiral tool paths for high-speed machining. In the simplest case, our method takes a polygon as input and a number δ>0 and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is G1 continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most δ. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in some polygons with no islands than what is obtained by conventional spiral tool paths. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island. Keywords: Spiral-like path, Medial axis, Smoothing, High-speed machinin

Spiral Toolpaths for High-Speed Machining of 2D Pockets with or without Islands

We describe new methods for the construction of spiral toolpaths for high-speed machining. In the simplest case, our method takes a polygon as input and a number $\delta>0$ and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is $G^1$ continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most $\delta$. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in polygons with no islands. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island.Comment: 22 pages, 13 figure

Toolpath algorithm for free form irregular contoured walls / surfaces with internal deflecting connections.

This paper presents a toolpath generation method to efficiently machine free form irregular contoured walls / surfaces (FIWS) containing internal deflecting connections (IDC’s). The toolpath generation method is based on a series of identifications and calculations, where initially a ‘Main Computable Zone (MCZ)’ in the Machinable Areas (Ma’s) of FIWS is identified based on the Tool track dimensions (Td). Then the MCZ’s are divided into Split Computable Zones (SCZ’s) and Split Computable Zones for Internal Connections (SCZI’s) which are subsequently sub divided as ‘Categorized Computable Zones’ (CCZ) with simple-medium-high complexity. The identification of CCZ’s is based on the 10 different types of FIWS representations developed for this study. From the CCZ’s categorization of complexity, they are further split into smaller ‘Machinable Zones (MZ’s)’ using a 4-step algorithm. In the algorithm, the first step calculates a common plane (CP) to cut the steep areas in the CCZ’s where the tool cannot have full access for machining. Once the CP is identified, the second step is to extend it by moving them along the CCZ’s and calculate the necessary ‘Machinable Zones (MZ’s)’ in the next stage. This is done by finding the intersection of CP with the FIWS through a point to point / line plane intersection concept. After this step, the MZ’s are re-iterated by including the open and closed surface criteria and is analyzed for the IDC’s to be combined in the fourth stage. This is achieved by adding up the IDC’s with the existing MZ’s computed by the algorithm. At every stage, the algorithm considers tool collision avoidance and tool rubbing in the CCZ’s and MZ’s . This is by an automatic computation based on the height to fixture clearance for safer neck length which avoids collision and rubbings in the final toolpaths. Finally, a combined tool path is generated for all the MZ’s and has been verified / tested for a sample part and impeller containing similar shapes using UG NX / STEP –NC software

Spiral Complete Coverage Path Planning Based on Conformal Slit Mapping in Multi-connected Domains

Generating a smooth and shorter spiral complete coverage path in a multi-connected domain is an important research area in robotic cavity machining. Traditional spiral path planning methods in multi-connected domains involve a subregion division procedure; a deformed spiral path is incorporated within each subregion, and these paths within the subregions are interconnected with bridges. In intricate domains with abundant voids and irregular boundaries, the added subregion boundaries increase the path avoidance requirements. This results in excessive bridging and necessitates longer uneven-density spirals to achieve complete subregion coverage. Considering that conformal slit mapping can transform multi-connected regions into regular disks or annuluses without subregion division, this paper presents a novel spiral complete coverage path planning method by conformal slit mapping. Firstly, a slit mapping calculation technique is proposed for segmented cubic spline boundaries with corners. Then, a spiral path spacing control method is developed based on the maximum inscribed circle radius between adjacent conformal slit mapping iso-parameters. Lastly, the spiral path is derived by offsetting iso-parameters. The complexity and applicability of the proposed method are comprehensively analyzed across various boundary scenarios. Meanwhile, two cavities milling experiments are conducted to compare the new method with conventional spiral complete coverage path methods. The comparation indicate that the new path meets the requirement for complete coverage in cavity machining while reducing path length and machining time by 12.70% and 12.34%, respectively.Comment: This article has not been formally published yet and may undergo minor content change

Contour parallel milling tool path generation for arbitrary pocket shape using a fast marching method

Contour parallel tool paths are among the most widely used tool paths for planer milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, the applicability of various offsetting methods is restricted because of limitations in dealing with pocket geometry with and without islands, the high computational costs, and numerical errors. Generation of cusps, segmentation of rarefied corners, and self-intersection during the offsetting operations and finding a unique offsetting solution for pocket with islands are among the associated problems in contour tool path generation. Most of methods are inherently incapable of dealing with such problems and use complex computational routines to identify and rectify these problems. Also, these rectifying techniques are heavily dependent on the type of geometry, and hence, the application of these techniques for arbitrary boundary conditions is limited and prone to errors. In this paper, a new mathematical method for generation of contour parallel tool paths is proposed which is inherently capable of dealing with the aforementioned problems. The method is based on a boundary value formulation of the offsetting problem and a fast marching method based solution for tool path generation. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an "entropy condition” in its numerical implementation. The appropriate modifications are carried out to achieve higher accuracy for milling operations. A number of examples are presented, and computational issues are discussed for tool path generatio

Contour parallel milling tool path generation for arbitrary pocket shape using a fast marching method

Contour parallel tool paths are among the most widely used tool paths for planer milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, the applicability of various offsetting methods is restricted because of limitations in dealing with pocket geometry with and without islands, the high computational costs, and numerical errors. Generation of cusps, segmentation of rarefied corners, and self-intersection during the offsetting operations and finding a unique offsetting solution for pocket with islands are among the associated problems in contour tool path generation. Most of methods are inherently incapable of dealing with such problems and use complex computational routines to identify and rectify these problems. Also, these rectifying techniques are heavily dependent on the type of geometry, and hence, the application of these techniques for arbitrary boundary conditions is limited and prone to errors. In this paper, a new mathematical method for generation of contour parallel tool paths is proposed which is inherently capable of dealing with the aforementioned problems. The method is based on a boundary value formulation of the offsetting problem and a fast marching method based solution for tool path generation. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an "entropy condition" in its numerical implementation. The appropriate modifications are carried out to achieve higher accuracy for milling operations. A number of examples are presented, and computational issues are discussed for tool path generation

A new geometric-and-physics model of milling and an effective approach to medial axis transforms of free-form pockets for high performance machining

Mechanical part quality and productivity depend on many parameters in CNC milling processes, such as workpiece material, cutters, tool paths, feed rate, and spindle speed, etc. To pursue high performance machining, the cutting parameter optimization is in high demand in industry, though it is quite challenge. This innovative research successfully addresses some essential problems in optimizing the cutting parameters by developing a new geometric-and-physics integrated model of milling and proposing an effective approach to the medial axis transforms of free-form pockets. In this research, an original geometric model of 21/2- and 3-axis CNC milling is developed and integrated with a well-established mechanistic model. A main research contribution is that this integrated model can predict complex milling processes in higher fidelity with instantaneous material remove rates, cutting forces and spindle powers, compared to prior machining models. In the geometric model, an in-process workpiece model is introduced by using a group of discrete Z-layers and applying the B-Rep scheme to represent the workpiece shape on each layer, in order to accurately represent instantaneous cutter-and-workpiece engagement in 2Yz- and 3-axis milling. Hence, the un-deformed chip geometry can be found even for complex part milling, which is then fed to the mechanistic model to predict instantaneous cutting forces. By using this integrated model, cutting parameters can be optimized for profiling, pocketing, and surface milling to ensure steady cut and the maximum material removal rates. This model has been verified by experiments, and will be implemented into a software tool for Bombardier Aerospace. Another important research in this work is to propose aggressive roughing of free-form pockets for ultimately high cutting efficiency. For this purpose, an accurate, efficient approach to the medial axis transforms of free-form pockets and an optimal approach to multiple cutters selection and their path generation are proposed. The main contributions of this research include (1) a new mathematical model of medial axis point, (2) an innovative global optimization solver, the hybrid global optimization method, (3) an optimization model of selecting multiple cutters for the maximum material removal rate. This research can substantially promote aggressive roughing in the machining industry to increase cutting efficiency of free-form pockets. The technique has been validated using considerable number of cutting tests and can be directly implemented into commercial CAD/CAM softwar

Modeling and optimization of micro scale pocket milling operations

Ankara : The Department of Industrial Engineering and The Graduate School of Engineering and Science of Bilkent University, 2014.Thesis (Master's) -- Bilkent University, 2014.Includes bibliographical references leaves 121-127.Manufacturing of micro scale parts and components made from materials having complex three dimensional surfaces are used in today’s high value added products. These components are commonly used in biomedical and consumer electronics industries and for such applications, fabrication of micro parts at a low cost without sacrificing quality is a challenge. Micro mechanical milling is a viable technique which can be used to produce micro parts, however the existing knowledge base on micro milling is limited compared to macro scale machining operations. The subject of this thesis is micro scale pocket milling operations used in micro mold making which are used in micro plastic injection in mass production polymer micro parts. Modeling of pocket milling while machining of basic pocket shapes are considered first. The developed milling model is then extended to more complex mold shapes. Minimum total production time is used as the objective to solve single pass, multi pass, and multi tool problems. Case studies are presented for each problem type considering the practical issues in micro milling. A software has been developed to optimize machining parameters and it is shown that the developed pocket milling optimization model can successfully be used in process planning studies.Sert, BengisuM.S

From 3D Models to 3D Prints: an Overview of the Processing Pipeline

Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step, in particular along the Process Planning pipeline, can now count on dozens of methods that prepare the 3D model for fabrication, while analysing and optimizing geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and Innovation action; Grant agreement N. 68044