Optimized normal and distance matching for heterogeneous object modeling

This paper presents a new optimization methodology of material blending for heterogeneous object modeling by matching the material governing features for designing a heterogeneous object. The proposed method establishes point-to-point correspondence represented by a set of connecting lines between two material directrices. To blend the material features between the directrices, a heuristic optimization method developed with the objective is to maximize the sum of the inner products of the unit normals at the end points of the connecting lines and minimize the sum of the lengths of connecting lines. The geometric features with material information are matched to generate non-self-intersecting and non-twisted connecting surfaces. By subdividing the connecting lines into equal number of segments, a series of intermediate piecewise curves are generated to represent the material metamorphosis between the governing material features. Alternatively, a dynamic programming approach developed in our earlier work is presented for comparison purposes. Result and computational efficiency of the proposed heuristic method is also compared with earlier techniques in the literature. Computer interface implementation and illustrative examples are also presented in this paper

Virtual prototyping with surface reconstruction and freeform geometric modeling using level-set method

More and more products with complex geometries are being designed and manufactured by computer aided design (CAD) and rapid prototyping (RP) technologies. Freeform surface is a geometrical feature widely used in modern products like car bodies, airfoils and turbine blades as well as in aesthetic artifacts. How to efficiently design and generate digital prototypes with freeform surfaces is an important issue in CAD. This paper presents the development of a Virtual Sculpting system and addresses the issues of surface reconstruction from dexel data structures and freeform geometric modeling using the level-set method from distance field structure. Our virtual sculpting method is based on the metaphor of carving a solid block into a 3D freeform object using a 3D haptic input device integrated with the computer visualization. This dissertation presents the result of the study and consists primarily of four papers --Abstract, page iv

A certification method for the milling process of free-form surfaces using a test part

International audienceIt is generally admitted that the manufacturing of free-form surfaces requires the use of a CAD-CAM system. The toolpath accuracy and the dimensional quality of the final shape have to be in accordance with the geometrical specifications. But most of the time, the final parts present deviations from the expected shape. These deviations may be due to either the toolpath calculation (CAM system) or the cutting process itself. In the paper, we propose an analysis of the whole milling process to point out the possible sources of errors. These errors generally lead to geometrical deviations and the final part does not meet the required specifications. As the errors can be linked to geometrical particularities of the shape, we propose a test part associated with check means to bring out problems. The milling of this part using two different techniques of toolpath generation shows that obviously both toolpaths are not error-free and that errors result from different geometrical particularities of the part surfaces

Integrating tolerances in G and M codes using neural networks

Continuous integrated solutions from CAD down to the preparation of NC programs were developed in the recent years. However, if tolerances should be considered, the interaction of human experts is still necessary. A way to fill this gap in the production process is shown in this thesis. The study builds a relationship between the given design tolerances and including these tolerances in machining by generating respective G and M codes. The study focuses on physical phenomena and their inter-relationship while manufacturing. For example how the speed of machining, torque, power, depth of cut, etc. influences machining under specified tolerances. Artificial neural networks (ANN) have been used to generate required outputs because of their capability to learn from a given set of data points. Four different kinds of neural networks, as a module, have been used. with different kinds of learning rules (algorithms) depending on the type of inputs and outputs. The whole model incorporates retrieval of tolerances from a CAD software and running the algorithms for (i) Dimensional tolerance analysis, (ii) Control of feed rate, spindle speed, depth of cut and cutting forces, (iii) Propagation of errors in multistage machining, and (iv) Vectorization of geometrical tolerances. Machining processes would include (i) Milling, (ii) Turning, and (iii) Drilling. Then the corresponding outputs are interpreted and analyzed to generate G and M codes. This study has shown how ANN can revolutionize NC machine manufacturing. A case study illustrates the effectiveness of the proposed method

Tool path generation and 3D tolerance analysis for free-form surfaces

This dissertation focuses on developing algorithms that generate tool paths for free-form surfaces based on accuracy of desired manufactured part. A manufacturing part is represented by mathematical curves and surfaces. Using the mathematical representation of the manufacturing part, we generate reliable and near optimal tool paths as well as cutter location (CL) data file for postprocessing. This algorithm includes two components. First is the forward-step function which determines maximum distance called forward- step between two cutter contact (CC) points with given tolerance. This function is independent of the surface type and is applicable to all continuous parametric surfaces that are twice differentiable. The second component is the side-step function which determines maximum distance called side-step between two adjacent tool paths with a given scallop height. This algorithm reduces manufacturing and computing time as well as the CC points while keeping the given tolerance and scallop height in the tool paths. Several parts, for which the CC points are generated using the proposed algorithm, are machined using a three axes milling machine. As part of the validation process, the tool paths generated during machining are analyzed to compare the machined part and the desired part

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

Ph.DDOCTOR OF PHILOSOPH