Geometric modeling and processing

This paper details a new method for automatic feature extraction from a Boundary Representation of the solid model. The proposed method is based principally on the evaluation of two topological invariants of concave parts of the modeled object. The result is a decomposition of the object boundary into surface components which represent shape features. Some aspects of the topology of bordered surfaces are discussed. The feature extraction method has been optimized for automatic core pattern design and advice in casting design. The main aspects of the "domain of application" of the method are considered, and six categories of shape features identified. The extraction rules proposed for a specific domain of application could be extended in different feature recognition contexts. © 1997 Elsevier Science Ltd.

Keywords: Feature recognition , Mold design

This work presents a set of methods for simplifying finite element (FE) models without reducing their accuracy in terms of global static and dynamic behavior. The methods were developed to simplify the FE models of carbodies in white without affecting their static and low-frequency dynamics. The simplified models allow structural variations to be theorized and simulated, while accurately representing physical reality.

The application of non-optimized damping and phono-absorbent materials to automotive systems has not proved fully satisfactory in abating noise and vibration. The objective of this work was to develop a simple finite element modelling procedure that would allow optimizing structures such as a car body-in-white in terms of vibroacoustic behavior from the design stage. A procedure was developed to determine the modifications to be made in the mass, stiffness and damping characteristics in the finite element (FE) modelling of a metal structure meshed with shell elements so that the model would describe the behavior of the acoustically treated structure. To validate the modifications, a numerical-experimental comparison of the velocities on the vibrating surface was carried out, followed by a numerical-experimental comparison of the sound pressures generated by the vibrating plate. In the comparison a simple monopole model was used, in which each area of vibrating surface could be likened to a point source. The simulation and experimental procedures, previously validated for the metal structure, were then applied to multi-layered panels. Good agreement between the experimental and simulated velocities and sound pressures resulted for all the multi-layered panel configurations examined. © 1997 Academic Press Limited.

The design of mechanical assemblies is mainly done after having modeled single parts. Most of the CAD systems are still weak for what concerns assembly. For example, they do not support the manipulation or the modification of the part geometry or the mating conditions once the assembly is made. The introduction of a feature-based approach in assembly design, successfully used in the design of single parts, would offer several advantages. This paper describes some results of the research work done within a project funded by the European Union aiming at extending the use of features, to help in the solution of assembly problems in the aeronautical applications.

An approach to the problem of controlling feature semantics in feature-based modeling is proposed by using self validation features, an entity concept developed to implement feature specification replenished with self validation capabilities. Together with this approach the traditional feature definition is extended in order to include the set of rules that allows for feature instances to control the consistency of their shape in respect to functionality associated. In order to realize a tight integration between feature semantics and shape representation an interfacing mechanism, based on an entity monitor, has been studied.

In the present paper, a procedure is described whereby the elastic properties of a ceramic material are evaluated during a biaxial flexure test. The disk specimen is supported on three points and loaded by a uniform pressure on the opposite face. The whole displacement field undergone by the upper face, measured by a digital speckle interferometer, is approximated by a set of polynomials whose weights depend on the elastic properties. This dependence, previously determined by finite element analysis, is exploited to derive the values of the elastic properties from the displacement field experimentally detected. The procedure proposed was applied to a silicon carbide specimen.

Keywords: Biaxial flexural test , Ceramic material , Elastic properties , Speckle interferometry , Zernike polynomials

Within our approach we apply feature-based models and techniques, realized within typed attributed entity (TAE) structures. In particular, we are interested in the handling of additional fabrication relevant form structures and the automatic determination of fabrication parameters. To verify developed methodologies and to demonstrate the applicability of our taken approach, several selected parts, taken from precision machinery engineering and aerospace engineering were modeled and processed.

Due to life cycles of artifacts, which become shorter, rapid prototyping development and tight feedback among product requirements, design, and manufacturing are gaining increasing importance. Classical rapid prototyping technologies such as computer-numerically-controlled (CNC) machinery, which remain still time consuming and expensive, are getting superseded by a growing propensity to apply new solid freeform fabrication (SFF) technologies, which became commercially available since 1987. Although, being on the market for only less than a decade, remarkable progress in various directions such as accuracy, used materials, through-put, and equipment costs, has been achieved in SFF technologies. However, there are still several technological as well as methodological problems left. Within given scope, we would like to tackle some, taken from the methodological field, which seems still weakly developed compared to existing technology. Within our approach we apply feature-based models and techniques, realized within typed attributed entity (TAE) structures. In particular, we are interested in the handling of additional fabrication relevant form structures and the automatic determination of fabrication parameters. To verify developed methodologies and to demonstrate the applicability of our taken approach, several selected parts, taken from precision machinery engineering and aerospace engineering were modeled and processed. An implemented prototype environment and a stereolithography apparatus (SLA) were used for integrated knowledge handling, computation and SFF fabrication.

Requirements of intelligent CAD systems are aimed to enable them to support the designer throughout his/her entire activity, starting from conceptual design and ending with, according to given specifications, an almost complete design object description. Cunent approaches featuring geometrical constraint-based systems with parametric or variational models, allow the designer to consider the realized design object description as an archetype of a family, based on a unique morphological model with unambiguous sets of parameterized rules. However, functionality for both design and reasoning, are limited to the low geometric level, leaving most of related information from the design intend and related technology unconsidered. Our objective of given study is, to extend the present functionality of existing approaches by integrating different types of knowledge and incorporate dedicated semantics in form features and feature-based methodologies. As a basic representation, typed attributed entity structures (TAE) are used. Computation is performed over domain structured alphabets of attributed symbols using a conditional attributed rewriting system. An application example in form of a wing rib, taken from aerospace engineering, is used, to verify and demonstrate the modeling and consistent handling of knowledge formations within our developed framework. Current limits of our new approach are discussed and a comparison related to the functionality of existing systems is undertaken, to direct the focus on further enhancements and extensions of our approach.

The realization of sculptured shapes using CAD systems is still today a very complex and time consuming operation. For these reasons, design by physical modeling is still in use and remains in force in many industries (automotive, ski boots, sport articles). For the manufacturing of complex free-form surfaces, in situations in which it is more desirable to proceed from a physical model to a numerical definition rather than use mathematics to derive the physical part, copy milling techniques are widely used. This paper gives a brief overview about copy milling techniques for 3 axis copy milling machines, and proposes a feature based method to support an automatic tool path generation for the super-finishing phase. The proposed method is divided in two parts: super-finishing features recognition and tool path generation. Using copy milling techniques, the model of the object to be milled is obtained by digitizing. Therefore a global mathematical surface description of the model does not exist. In such a situation a model interpretation phase is required to recognize the super-finishing features and thus proceed to the tool path generation. A two step algorithm for super-finishing feature recognition on a digitized model is proposed: features are recognized on the basis of the digitized point density and the normal vectors of the triangles generated by the surface reconstruction (based on Delaunay triangulation method). The tool path is then generated using a method based on the calculation of the Voronoi diagram on the area identified as super-finishing feature. The super-finishing feature recognition and tool path generation modules have been integrated as part of a more general CAM system for copy milling called HICAM. The architecture of such a system will be presented together with examples of solutions obtained by means of the use of the implemented prototype modules.

According to the general design theory a design process is an evolutionary process which step by step transfers the model of the design object from the design specification to the design solution. In our framework, design object specification and iterating evaluation are performed over different contexts using feature-based design, and feature recognition/transmutation. These activities are integrated to achieve consistency between given design requirements and design objects. Features are used to relate elements of different domains, in order to represent design objects with shape and meaning within a context. The basic concept of topology and attributed entities is used to define a homogeneous architecture of the modeling space of our reference kernel. It is reflected in the uniform use and structure of an attributed feature graph, an attributed boundary representation, and a knowledge representation in form of conditional attributed rules. For design by feature and feature recognition we propose to use a conditional attributed rewrite system as a generative as well as a recognition device to represent knowledge of control and operationalization in a uniform way. Morphisms realize a bi-directional mapping between the entire modeling space of the reference kernel and an alphabet of attributed symbols, which together with rewrite rules define our rule-based design object specification. Knowledge representation for reflective functionality and strategies of design and recognition are specified with a conditional attributed rewrite system on a meta level. Central components of a prototype implementation, according to our proposed reference model kernel, will be introduced and discussed together with first results of modeled and evaluated objects.

In the present paper a methodology is described whereby the subdivision of a multiply connected planar domain into mappable regions is automatically performed. The technique proposed, which was developed to be applied within an interface between a geometric modeler (b-rep type) and a 3-D BEM code for elastic stress analysis, can be as well applied to 2-D finite element discretization problems. At the present stage of development, the technique operates over planar domains which are externally and internally bounded by polygonal contours and may contain any number of circular holes.

The paper deals with the automatic feature recognition of workpieces and families formation. To generate part families, the used approach utilizes a frame based representation system both for data and for features. A clustering method is used to toke into account the morphology, the dimensions as well as the manufacturing sequences of parts. Being the procedure a self learning one, the introduction of new parts into the families is relatively simple. © 1991 CIRP.

Keywords: Cluster analysis , Feature-based models , Group Technology