Dimensional verification and correction of five-axis numerically controlled milling tool paths

A system of algorithms is presented for material removal simulation, automatic dimensional verification and integrated error correction of numerically controlled (NC) milling tool paths. Several different approaches to these problems have been proposed including direct solid modeling, discrete vector intersection, and spatial partitioning. However, each of these methods suffer inherent restrictions that limit their practical application. This dissertation presents a discrete dexel NC verification algorithm based on a spatial partitioning technique (dexel representation) which incorporates the advantages of the discrete vector intersection approach. Hence, real-time animated five-axis milling simulation is supported by efficient regularized Boolean set operations, and dimensional milling errors are verified simultaneously with the simulation process. Based on intermediate dimensional verification results, a reduction of intersection volume algorithm is developed to eliminate detected gouges on the part surface. In addition, a technique for detection and elimination of unexpected collisions between the tool assembly and the workpiece is developed. These combined algorithms automatically correct tool paths to avoid gouges and collisions resulting in tool paths that are ready for immediate industrial application. A major disadvantage of dexel-based spatial partitioning, as originally proposed, is view dependency, i.e., dexels are constructed along a specific viewing vector so reconstruction of dexels is required for each new viewing direction. To overcome this problem, a contour display method is developed to transform dexel-based objects into a set of parallel planar contours thus enabling dynamic viewing transformations. In summary, this dissertation describes a unique hybrid approach to NC milling verification which provides for efficient, accurate and automatic assessment and correction of five-axis milling tool paths

Reaction forces on a milling tool during three-axis milling

This thesis discusses a graphical numerically controlled (NC) milling simulation. Graphical simulations give a better feel for what happens during a complicated process, such as NC milling, than does numerical output from a mathematical model. NC milling simulations can be used to verify tool paths, detect collisions, and check the material removal rate, which can be related to force feedback on the milling tool. A graphical simulation should make calculations and update displays as quickly as possible, while still maintaining a reasonable level of accuracy. This thesis presents a real time NC milling simulation technique that incorporates a cutting force model to calculate forces generated between the milling tool and the workpiece. This information can be used to determine if a piece of the machinery could fail due to driving (feeding) the milling tool too rapidly, creating too large a force on the tool shaft or flutes

Automatic tool path generation for numerically controlled machining of sculptured surfaces

This dissertation presents four new tool path generation approaches for numerically controlled machining of sculptured surfaces: TRI\sb-XYINDEX, FINISH, FIVEX\sb-INDEX, FIX\sb-AXIS\sb-INDEX. All of the above systems index the tool across the object surface in the Cartesian space so that evenly distributed tool paths are accomplished. TRI\sb-XYINDEX is a three-axis tool path generation system which uses a surface triangle set (STS) representation of the surface for tool position calculations. Surface edges are detected with local searching algorithms. Quick tool positioning is achieved by selecting candidate elements of polygons. Test results show that TRI\sb-XYINDEX is more efficient when machining surfaces which are relatively flat while the discrete point approach is faster for highly curved surfaces. FINISH was developed for generating three-axis ball-end tool paths for local surface finishing. It was based on the SPS. Given a surface with excess material represented by a set of discrete points, FINISH automatically identifies the undercut areas. Results show that FINISH provides significant improvements in machining efficiency. FIVEX\sb-INDEX is developed for generating five-axis flat-end tool paths. It uses an STS approximation. Contact points on the surface are derived from edge lists obtained from the intersections of vertical cutting planes with the polygon set. The distances between adjacent end points set an initial step-forward increment between surface contact points. To verify tool movements, some intermediate tool positions are interpolated. The key features of FIVEX\sb-INDEX are: (1) a polygon set representing an object which may be composed of multiple surfaces; (2) Surface contact point generation by cutting plane intersection; (3) simple tool incrementing and positioning algorithms; (4) minimal user interaction; (5) user controlled accuracy of resulting tool paths. FIX\sb-AXIS\sb-INDEX is a subsystem of FIVEX\sb-INDEX, generating tool paths for a tool with fixed orientations. Surface contact points are generated similar to FIVEX\sb-INDEX while tool positions are corrected with the highest point technique along the tool axis direction. Linear fitting is applied to output tool positions. FIX\sb-AXIS\sb-INDEX is preferred for machining surfaces curved in one direction, such as ruled surfaces. Test results show that FIX\sb-AXIS\sb-INDEX can serve as a three-axis tool path generation system but a five-axis machine is required to do it. (Abstract shortened by UMI.)

Virtual reality based creation of concept model designs for CAD systems

This work introduces a novel method to overcome most of the drawbacks in traditional methods for creating design models. The main innovation is the use of virtual tools to simulate the natural physical environment in which freeform. Design models are created by experienced designers. Namely, the model is created in a virtual environment by carving a work piece with tools that simulate NC milling cutters. Algorithms have been developed to support the approach, in which the design model is created in a Virtual Reality (VR) environment and selection and manipulation of tools can be performed in the virtual space. The desianer\u27s hand movements generate the tool trajectories and they are obtained by recording the position and orientation of a hand mounted motion tracker. Swept volumes of virtual tools are generated from the geometry of the tool and its trajectories. Then Boolean operations are performed on the swept volumes and the initial virtual stock (work piece) to create the design model. Algorithms have been developed as a part of this work to integrate the VR environment with a commercial CAD/CAM system in order to demonstrate the practical applications of the research results. The integrated system provides a much more efficient and easy-to-implement process of freeform model creation than employed in current CAD/CAM software. It could prove to be the prototype for the next-generation CAD/CAM system

Automatic tool path generation for multi-axis machining

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (leaves 67-72).We present a novel approach to CAD/CAM integration for multi-axis machining. Instead of redefining the workpiece in terms of machining features, we generate tool paths directly by analyzing the accessibility of the surface of the part. This eliminates the problem of feature extraction. We envision this as the core strategy of a new direct and seamless CAD/ CAM system. We perform the accessibility analysis in two stages. First, we triangulate the surface of the workpiece and perform a visibility analysis from a discrete set of orientations arranged on the Gaussian Sphere. This analysis is performed in object space to ensure reliability. For each triangle, a discrete set approximation of the accessibility cone is then constructed. Next, a minimum set cover algorithm like the Quine-McCluskey Algorithm is used to select the minimum set of orientations from which the entire workpiece can be accessed. These set of orientations correspond to the setups in the machining plan, and also dictate the orientation in which the designed part will be embedded in the stock. In particular, we bias the search for setups in favor of directions from which most of the part can be accessed i.e, the parallel and perpendicular directions of the faces in the workpiece. For each setup, we select a set of tools for optimal removal of material. Our tool-path generation strategy is based on two general steps: global roughing and facebased finishing. In global roughing, we represent the workpiece and stock in a voxelized format. We perform a waterline analysis and slice the stock into material removal slabs. In each slab, we generate zig-zag tool paths for removing bulk of the material. After gross material removal in global roughing, we finish the faces of the component in face-based finishing. Here, instead of assembling faces into features, we generate tool paths directly and independently for each face. The accessibility cones are used to help ensure interference- free cuts. After the tool paths have been generated, we optimize the plan to ensure that commonalities between adjacent faces are exploited.by Laxmiprasad Putta.S.M

Tool Wear Improvement and Machining Parameter Optimization in Non-generated Face-hobbing of Bevel Gears

Face-hobbing is the dominant and the most productive machining process for manufacturing bevel and hypoid gears. Bevel gears are one of the most important power transmission components, in automobile to aerospace industries, where the power is transmitted between two non-parallel axes. In current industries, the face-hobbing process confronts two major challenges, the tool wear and trial and error experiments to select machining parameters. In the present work, these two problems are targeted. The tool wear in face-hobbing happens at the tool corners of the cutting blades due to the multi-flank chip formation and large gradient of working rake and relief angles along the cutting edge at the corners. In addition, the cutting fluid absence contributes in the tool wear phenomena. In the present work, a cutting tool design method is proposed in order to improve the tool wear characteristics especially at the tool corners. The rake and relief surfaces of the conventional cutting blades are re-designed in such a way that normal rake and relief angles during the face-hobbing process are kept constant and consequently the gradients of these two angles are minimized, theoretically to zero. Using mathematical tool wear characterization relationship and also FEM simulation, the improvements in tool wear are approved. In addition, in the present thesis, semi-analytical methods are proposed to optimize the face-hobbing process in order to select appropriate machining settings. The optimization problem is constructed in such a way that the machining time is minimized subject to the tool rake wear or cutting force related constraints. In order to predict the tool rake wear (crater wear depth), methods are proposed to calculate un-deformed chip geometry, cutting forces, normal stresses, interface cutting temperature and chip sliding velocity. The un-deformed chip geometry is obtained using two proposed methods numerically and semi-analytically. In the numerical method, the workpiece in-process model is obtained and then the un-deformed chip geometry is approximated using the in-process model. In the semi-analytical method, an un-deformed chip boundary theory is constructed in such a way that the boundary curves of the un-deformed chip are formulated by closed form equations. The obtained un-deformed chip geometry is discretized along the cutting edge of the blades. Each infinitesimal element is considered as a small oblique cut. The differential cutting forces are predicted for each individual element using oblique cutting transformation theory. The total cutting forces are derived by integrating the differential cutting forces along the cutting edge. The proposed methods are applied on case studies of non-generated face-hobbing of gears to show the capability of the methods to find the un-deformed chip geometry, predict cutting forces and finally find the optimum machining parameters in non-generated face-hobbing