Optimization of Three-Axis Vertical Milling of Sculptured Surfaces

A tool path generation method for sculptured surfaces defined by triangular meshes is presented in this thesis along with an algorithm that helps determine the best type of cutter geometry to machine a specific surface. Existing tool path planning methods for sculptured surfaces defined by triangular meshes require extensive computer processing power and result in long processing times mainly since surface topology for triangular meshes is not provided. The method presented in this thesis avoids this problem by offsetting each triangular facet individually. The combination of all the individual offsets make up a cutter location surface. A single triangle offsetting results in many more triangles; many of these are redundant, increasing the time required for data handling in subsequent steps. To avoid the large number of triangles, the proposed method creates a bounding space to which the offset surface is limited. The original surface mesh describes the bounding surface of a solid, thus it is continuous with no gaps. Therefore, the resulting bounding spaces are also continuous and without gaps. Applying the boundary space limits the size of the offset surface resulting in a reduction in the number of triangular surfaces generated. The offset surface generation may result in unwanted intersecting triangles. The tool path planning strategy addresses this issue by applying hidden-surface removal algorithms. The cutter locations from the offset surface are obtained using the depth buffer. The simulation and machining results show that the tool paths generated by this process are correct. Furthermore, the time required to generate tool paths is less than the time required by other methods. The second part of this thesis presents a method for selecting an optimal cutter type. Extensive research has been carried out to determine the best cutter size for a given machining operation. However, cutter type selection has not been studied in-depth. This work presents a method for selecting the best cutter type based on the amount of material removed. By comparing the amount of material removed by two cutters at a given cutter location the best cutter can be selected. The results show that the optimal cutter is highly dependent on the surface geometry. For most complex surfaces it was found that a combination of cutters provides the best results

Computer aided process planning for multi-axis CNC machining using feature free polygonal CAD models

This dissertation provides new methods for the general area of Computer Aided Process Planning, often referred to as CAPP. It specifically focuses on 3 challenging problems in the area of multi-axis CNC machining process using feature free polygonal CAD models. The first research problem involves a new method for the rapid machining of Multi-Surface Parts. These types of parts typically have different requirements for each surface, for example, surface finish, accuracy, or functionality. The CAPP algorithms developed for this problem ensure the complete rapid machining of multi surface parts by providing better setup orientations to machine each surface. The second research problem is related to a new method for discrete multi-axis CNC machining of part models using feature free polygonal CAD models. This problem specifically considers a generic 3-axis CNC machining process for which CAPP algorithms are developed. These algorithms allow the rapid machining of a wide variety of parts with higher geometric accuracy by enabling access to visible surfaces through the choice of appropriate machine tool configurations (i.e. number of axes). The third research problem addresses challenges with geometric singularities that can occur when 2D slice models are used in process planning. The conversion from CAD to slice model results in the loss of model surface information, the consequence of which could be suboptimal or incorrect process planning. The algorithms developed here facilitate transfer of complete surface geometry information from CAD to slice models. The work of this dissertation will aid in developing the next generation of CAPP tools and result in lower cost and more accurately machined components

New Approaches to Determining Shortest Cutters and Work Piece Setups without Over-travel for 5-axis CNC Machining

Five axis CNC machining centers are widely used in the industries for producing the complex parts. Due to two more axes as compared to the three axes machining, it provides the efficient and flexible way of the machining. Besides this flexibility, accidental collision possibilities between the cutting system and the other moving parts of the machine tools are also increased. These collisions could be avoided by changing the orientations of the tool during the tool path planning or by adjusting the cutter length and the tool holder size after the tool path generation in the part coordinate system. Collision detection and removal by the optimum cutter length depends on the configuration of five axis machine tools. No. of possible candidates for the collision may vary with the configuration of the machine tools. Since the fully utilization of the existing machining facilities in the industry is also in high demand, therefore, after selecting the one of the critical parameter of the cutter length, the maximum utilization of the work space of the 5-axis machine tools is another critical task. This dissertation comprises of two main works. In the first research work, a comprehensive approach for the determination of the optimum cutter length for the specific configuration of five axis machine tool is developed. The complete cutting system (the tool, the tool holder and the spindle), the work in process model and the fixture are the three possible candidates for the collision. The work in process model and the fixture are represented as the point cloud data and the tool holder and the spindle are represented as a regular shape of the truncated cone and the cylinder respectively. Collision checking is conducted in two steps. In the first step the KD-tree data structure is employed on the point cloud data and a method is developed which confines the searching of the point cloud data in the local region and in the second step a new mathematical model for the collision detection between the points in the local region and the cutting system is established. This model also has the capability of removal collision with the optimum cutter length. In the second research work, kinematics of the table rotating and spindle tilting 5-axis machine is developed and setup parameters for mounting the part on the table are defined. A precise method for the determination of the setup parameters, which gives the opportunity of fully utilization of the work space of the machine tool, is developed. Many machining simulation software such as vericut can simulate the G-codes for the given setup parameters of the part and can verify the over travel limits of the machine tool as well as accidental collision between the moving parts of the machine. In this research, the developed method for the determination of the setup parameters gives the guarantee of complete machining of the part without over travel limits of the machine translational axes. This research is based on the predetermined machining strategies, which means, tool path is already given in the part coordinate system

Automated CNC Tool Path Planning and Machining Simulation on Highly Parallel Computing Architectures

This work has created a completely new geometry representation for the CAD/CAM area that was initially designed for highly parallel scalable environment. A methodology was also created for designing highly parallel and scalable algorithms that can use the developed geometry representation. The approach used in this work is to move parallel algorithm design complexity from an algorithm level to a data representation level. As a result the developed methodology allows an easy algorithm design without worrying too much about the underlying hardware. However, the developed algorithms are still highly parallel because the underlying geometry model is highly parallel. For validation purposes, the developed methodology and geometry representation were used for designing CNC machine simulation and tool path planning algorithms. Then these algorithms were implemented and tested on a multi-GPU system. Performance evaluation of developed algorithms has shown great parallelizability and scalability; and that main algorithm properties are required for modern highly parallel environment. It was also proved that GPUs are capable of performing work an order of magnitude faster than traditional central processors. The last part of the work demonstrates how high performance that comes with highly parallel hardware can be used for development of a next level of automated CNC tool path planning systems. As a proof of concept, a fully automated tool path planning system capable of generating valid G-code programs for 5-axis CNC milling machines was developed. For validation purposes, the developed system was used for generating tool paths for some parts and results were used for machining simulation and experimental machining. Experimental results have proved from one side that the developed system works. And from another side, that highly parallel hardware brings computational resources for algorithms that were not even considered before due to computational requirements, but can provide the next level of automation for modern manufacturing systems

Five-axis tool path generation using piecewise rational bezier motions of a flat-end cutter

Master'sMASTER OF ENGINEERIN

Calidad geométrica en el mecanizado de superficies curvas en titanio para aplicaciones médicas

El objetivo del presente estudio, es determinar la influencia de la velocidad de corte, avance por diente y la estrategia de mecanizado; sobre la calidad geométrica de la superficie mecanizada en el fresado con herramienta de punta esférica del titanio grado quirúrgico Ti6Al4V (En este trabajo, se considera calidad geométrica a los parámetros de rugosidad superficial, precisión dimensional y tolerancia de forma). Para ello, las probetas se mecanizaron, por medio de fresado con herramienta de punta esférica. El análisis de la influencia de los factores se realizó, por medio de un diseño experimental factorial 23. Por otra parte, un ANOVA (análisis de la varianza) se realizó, considerando geometrías esféricas cóncavas y convexas del mismo radio; para determinar la influencia de este sobre la calidad geométrica de la superficie mecanizada. Adicionalmente, se realizó; un ANOVA entre geometrías esféricas convexas de radio diferente, con la intención de determinar la influencia sobre la calidad geométrica de la superficie mecanizada. Los resultados del diseño experimental factorial 23 mostraron que el factor interacción velocidad de corte-avance por diente tiene efecto sobre los parámetros de rugosidad superficial Ra y Rt. Por otra parte, el ANOVA para las geometrías esféricas cóncavas y convexas del mismo radio, muestra que el cambio de geometría cóncava a convexa tiene efecto sobre la precisión dimensional. Por último, el ANOVA para geometrías esféricas convexas, muestra que el cambio de radio tiene efecto sobre los parámetros de rugosidad superficial Ra, Rt y la precisión dimensional.Abstract. The objective of this study, is to determine the influence of the cutting speed, feed per tooth and machining strategy; on geometric quality of the machined surface, in the ball milling tool of the surgical grade titanium Ti6Al4V (In this paper, geometrical quality, is considered; parameters of surface roughness, dimensional accuracy and shape tolerance). The samples were machined by means of ball milling tool. Analysis of the influence of the factors was performed by means of a 23 factorial experimental design. Further, an ANOVA (analysis of variance) was performed between concave and convex spherical geometries of the same radius, to determine the influence on the geometric quality of the machined surface. Additionally, an ANOVA was performed; between convex spherical geometries different radius to determine the influence on the geometric quality of the machined surface. The factorial experimental design results showed that factor 23 interaction cutting speed-feed per tooth has an effect on surface roughness parameters Ra and Rt. Furthermore, ANOVA for concave and convex spherical geometries of the same radius, shows that the change of a convex concave geometry has an effect on the dimensional accuracy. Finally, ANOVA for convex spherical geometries shows that the radius change has an effect on surface roughness parameters Ra, Rt, and the dimensional accuracy.Maestrí

Process planning for five-axis milling of sculptured surfaces

Ph.DDOCTOR OF PHILOSOPH

Automated Process Planning for Five-Axis Point Milling of Sculptured Surfaces

Ph.DDOCTOR OF PHILOSOPH