B-rep Model Research Articles

Towards declarative CAD modeler built on top of a CAD modeler

Today, industrial CAD software rely on an incremental B-Rep (Boundary Representation) modeling paradigm where volume modeling is performed iteratively using planar sketched contours subjected to mainly extrusion or revolution operations. Even if CAD modelers provide operators (e.g. pad, pocket, shaft, groove, hole, fillet) to get rid of the direct use and manipulation of canonical surfaces and NURBS, working with a CAD modeler is almost procedural with a lot of intermediate operations required to obtain the desired shape of an object. Actually, all those intermediate operations are time-consuming and generate complex construction trees that are not particularly needed to describe the final shape. Moreover, using such a procedural approach, the designers have to make a mental gymnastic to break down the object body into several basic shapes linked to the different operators of the CAD software. Clearly, an approach closer to the designers’ way of thinking is missing and there is still a gap between the ideas designers have in mind and the available tools and operators used to model them. Ideally, it would be more convenient to enter a semantic description of the shape, the CAD modeler being in charge of generating it.

3D CAD solid model retrieval based on region segmentation

3D shape retrieval may find the existing models as reference for design reuse. 3D segmentation decomposes models into new elements with large granularity and salient shapes to replace the faces in a solid model. In this way, it may reduce the complexity of a CAD model and make a local salient shape more prominent. Therefore, a retrieval method for 3D CAD solid models based on region segmentation is proposed in this paper. To deal with the problems of poor efficiency and uncertain results, a three-step segmentation method for CAD solid models is introduced. First, face adjacency graph (FAG) descriptions for query models and data models are created from their B-rep models. Second, the FAGs are segmented into a set of convex, concave and planar regions, and the relations among the regions are represented with a region graph. Finally, the sub-graphs are combined recursively to form optimal region sub-graphs with respect to an objective function through an optimal procedure. To avoid using complex graph matching or sub-graph matching for model shape comparison, region property codes are introduced to represent face regions in a CAD model. The similarity between the two compared models is evaluated by comparing their region property codes. The experiments show that the proposed method supports 3D CAD solid model retrieval.

Recognition of depression and protrusion features on B-rep models based on virtual loops

ABSTRACTLoops are vital elements in B-rep models and are used to describe the boundary contours of faces. A loop is only defined on a single face, which does not reflect real situations in which features mostly lie across multiple faces. The objective of this study is to detect virtual loops across multiple faces and subsequently use them for recognizing depression and protrusion features in computer-aided design models. Three loop types are defined: single, virtual, and multivirtual loops; virtual and multivirtual loops lie across multiple faces with different boundary conditions across faces. The data of the detected loops are then used to develop a feature recognition algorithm for identifying various depression and protrusion types, ranging from simple circular holes on a face to complex irregular pockets on multiple faces with fillets. This paper provides a detailed description of the proposed algorithm and presents several examples to illustrate its feasibility.

On the Development of Blend Faces and Holes Recognition Algorithm for CAE Applications

Mesh generation is one of the key factors affecting computational efficiency and accuracy in finite element analysis.More and more software provides modules for automatic meshes generation. Owing to the complexity and variety of the shape on a CAD model, it needs the recognition of specific features to enhance the success of meshes generation. Holes are one of the fundamental features in 3D CAD models and appear in various types of form. The aim of this study is to present a method for the recognition of different kinds of holes. The primary concept of the proposed algorithm is to detect blend faces first, and then search for holes in accordance with the loop data in the B-rep model. The procedures for the recognition of blend faces and holes are described. Several examples are also presented to demonstrate the feasibility of the proposed algorithm.

On the Development of Virtual Inner Loops for Feature Recognition

Typical feature recognition algorithms in industrial applications are primarily used for solving cases where a feature locates on a single face only. A feature locating on multiple surfaces is quite common in real CAD models, but it has not been received extensive study yet. The reason is because the loop data in current B-rep model is limited to a face only. The aim of this study is to develop a method to search for all kinds of inner loops on a CAD model, including the ones within a face and those across multiple faces. These inner loops are called virtual inner loops because they do not exist in current B-rep model. Several realistic examples are also presented to illustrate the meaning and feasibility of the proposed method.

Applying geometric constraints for perfecting CAD models in reverse engineering

An important area of reverse engineering is to produce digital models of mechanical parts from measured data points. In this process inaccuracies may occur due to noise and the numerical nature of the algorithms, such as, aligning point clouds, mesh processing, segmentation and surface fitting. As a consequence, faces will not be precisely parallel or orthogonal, smooth connections may be of poor quality, axes of concentric cylinders may be slightly tilted, and so on. In this paper we present algorithms to eliminate these inaccuracies and create “perfected” B-rep models suitable for downstream CAD/CAM applications.Using a segmented and classified set of smooth surface regions we enforce various constraints for automatically selected groups of surfaces. We extend a formerly published technology of Benkő et al. (2002). It is an essential element of our approach, however, that we do not know in advance the set of surfaces that will actually get involved in the final constrained fitting. We propose local methods to select and synchronize “likely” geometric constraints, detected between pairs of entities. We also propose global methods to determine constraints related to the whole object, although the best-fit coordinate systems, reference grids and symmetry planes will be determined only by surface entities qualified as relevant. Lots of examples illustrate how these constrained fitting algorithms improve the quality of reconstructed objects.

Hint-based generic shape feature recognition from three-dimensional B-rep models

Three-dimensional B-rep is often used to convey product models in computer-aided design, computer-aided engineering, computer-aided process planning, and computer-aided manufacturing systems. Meaningful shape features need to be recognized from the B-rep models for product re-design and manufacturing. In this article, a novel hint-based reusable shape feature recognition approach is presented. Its core objectives include (1) definition and classification of isolated generic shape features by analyzing the shape variation or hint for a Boolean operation in computer-aided design modeling; (2) recognition algorithm for isolated generic shape features by detecting such hints or shape variations for each kind of generic shape feature; and (3) recognition of hybrid generic shape features for complex parts by detecting containing, fusing, and intersecting relationships among available generic shape features. Finally, three engineering parts are used as examples to validate the capabilities of the presented approach.

Remanufacturing-Oriented Geometric Modelling for the Damaged Region of Components

The accurate additive manufacturing technology provides an effective and efficient means for remanufacturing or repairing high value and damaged engineering components. Important work to implement this technology is to construct the geometric model of the damaged or worn region, which lays the foundation for the computation of the tool path and the virtual digit repair. This paper discusses several forms of the damaged or worn region and proposes a hybrid B-rep model integrating subdivision mesh and exact boundary representation according to the data sources. A novel method to perform Boolean operations on the triangulated approximation surfaces and exact parameter surfaces is also presented. Finally, a modelling example and discussion are given to illustrate the effectiveness of the approach.

Analysis in computer aided design: Nonlinear isogeometric B-Rep analysis of shell structures

A new concept called analysis in computer aided design (AiCAD) is proposed for design-through-analysis workflow. This concept uses non-uniform rational B-Splines (NURBS)-based B-Rep models for the entire workflow. Such models consist of trimmed NURBS surfaces and are considered standard in the industry, especially for modeling free-form geometries. The newly developed isogeometric B-Rep analysis (IBRA) used in AiCAD is also presented. IBRA can be considered as a generalization of isogeometric analysis (IGA) that uses the boundary representation (B-Rep) of the design model in addition to the same basis functions as in IGA for approximating the solution fields. IBRA provides the framework for creating a direct and complete analysis model from computer aided design (CAD) in a consistent finite-element-like manner. Thus, IBRA allows analyzing a CAD model without remodeling and meshing, even for complex geometries.For the numerical integration of trimmed surfaces, the concept of nested Jacobian approach (NEJA) with NURBS surfaces is introduced. In addition, for enforcing the different types of boundary conditions or mechanical entities, a new finite element type called isogeometric B-Rep element is introduced. Elements of this type permit enforcing, e.g., coupling or Dirichlet boundary conditions. A corresponding formulation based on a penalty approach is presented as well.The proposed workflow is realized exemplarily for surface modeling and the geometrical nonlinear analysis of shell structures. The differences between the standard analysis procedure and the AiCAD workflow are explained in detail. Various numerical examples confirm the accuracy, flexibility, and robustness of the proposed IBRA concept, thus highlighting its advantages for the realization of design-through-analysis workflow with a uniform geometry representation.

Stepwise volume decomposition for the modification of B-rep models

During product design, the modification of computer-aided design (CAD) models is frequently required. However, modifying a boundary representation (B-rep) model, which is a typical type of CAD model, is difficult and time consuming. To address this problem, we propose a method for modifying B-rep models. In the proposed method, a B-rep model is decomposed into simple volumes by stepwise volume decomposition. A pseudo feature tree called the composition tree is generated with the decomposed simple volumes. A user can modify the B-rep model by transforming or deleting constituents of the composition tree and then replaying the updated composition tree. To demonstrate the proposed method, a prototype system was implemented, and experiments with test cases are performed. Based on the experimental results, we verified that B-rep models could be easily modified using the proposed method.

A geometric reasoning approach to hierarchical representation for B-rep model retrieval

3D solid model similarity is dependency of many intelligent design applications, such as design reuse, part management, case-based reasoning, and cost estimation. Matching and comparing its intrinsic boundary representation (B-rep) is a critical issue to retrieval. In this paper, we proposed a geometric reasoning approach to generate hierarchy for B-rep model retrieval. We extracted the winged-edge data structure to support series algorithms for underlying geometric reasoning, which is mainly composed of 3 steps to build hierarchy: partitioning, assembling and simplifying. This hierarchical representation is featured with level of detail (LOD) retaining geometric and topological information which is proved to be efficient in both global and partial retrieval. Our approach is based on the standard for the exchange of product information (STEP), which is suitable for data exchange between heterogeneous CAD systems. The result of case studies from prototype implementation demonstrates its effectiveness and efficiency.

Automated identification of complex undercut features for side-core design for die-casting parts

This article describes automated identification, classification, division and determination of release direction of complex undercut features of die-cast parts. The proposed system uses the concepts of visibility and accessibility to identify undercut features from a B-rep model of a die-casting part. The undercut features are then classified using a rule-based algorithm. Thereafter, the identified complex undercut features are separated into simple ones. Finally, the release direction for each simple undercut feature is determined and those having common release direction are grouped. The proposed system is implemented on case study die-cast parts, and the results are verified. This article would help bridge the design-manufacturing integration gaps in the die-casting process.

Toward Mixed-element Meshing based on Restricted Voronoi Diagrams

In this paper we propose a method to generate mixed-element meshes (tetrahedra, triangular prisms, square pyramids) for B-Rep models. The vertices, edges, facets, and cells of the final volumetric mesh are determined from the combinatorial analysis of the intersections between the model components and the Voronoi diagram of sites distributed to sample the model. Inside the volumetric regions, Delaunay tetrahedra dual of the Voronoi diagram are built. Where the intersections of the Voronoi cells with the model surfaces have a unique connected component, tetrahedra are modified to fit the input triangulated surfaces. Where these intersections are more complicated, a correspondence between the elements of the Voronoi diagram and the elements of the mixed- element mesh is used to build the final volumetric mesh. The method which was motivated by meshing challenges encountered in geological modeling is demonstrated on several 3D synthetic models of subsurface rock volumes.

Identification of Weld Beads in Assemblies of B-Rep Models

Computer-Aided Design and Applications is an international journal on the applications of CAD and CAM. It publishes papers in the general domain of CAD plus in emerging fields like bio-CAD, nano-CAD, soft-CAD, garment-CAD, PLM, PDM, CAD data mining, CAD and the internet, CAD education, genetic algorithms and CAD engines. The journal is aimed at all developers and users of CAD technology to ptovide CAD solutions for various stages of design and manufacturing. The journal publishes all about Computer-Aided Design and Computer-Aided technologies.

Feature-based simplification of boundary representation models using sequential iterative volume decomposition

When computer-aided design (CAD) models generated in the design phase are used for engineering activities such as engineering analysis, distributed collaborative design, and virtual prototyping, a process for simplifying the CAD models is needed. In this study, a feature-based simplification method of boundary representation (B-rep) models using sequential iterative volume decomposition is proposed. This method generates a feature-based model from a B-rep model by sequentially and iteratively applying the four volume decomposition methods (fillet, round, and chamfer decomposition; wrap-around decomposition; volume split decomposition; and cell-based decomposition). Then, feature-based simplification is applied to the generated feature-based model. To demonstrate the proposed method, a prototype system is implemented, and experiments with test cases are performed. Based on the experimental results, we verified that the proposed method successfully simplified B-rep models.

Automatic Process Intermediate Model Generation in Process Planning

In process planning of machined part, three-dimensional process intermediate models are necessary for process design, documentation, and downstream applications including clamping design, NC programing, and process analysis. An automatic process intermediate model generation method is proposed in this paper for machined part represented in B-Rep solid model. Machining features are recognized and classified according to process type. Process plan is expressed in terms of machining features and feature surface modification operations in solid model. Local modification operations are applied to part model to move, replace or remove feature surface resembling machining process. Process intermediate models are generated automatically in a batch manner by applying geometry and topology modification operations directly on B-Rep model for each machining operation. The proposed algorithm is implemented in a CAPP tool developed in solid modeler ACIS.

Brep Model, VOXEL Model, and its Inner Attributes

By using dexelization algorithms, a Brep model is transformed to the three direction DEXEL model and VOXEL model. In the VOXEL model, every VOXEL could have its attributes such as color, or transparence. The attributes of the VOXEL model could be set and the inner attributes of a 3D model could be expressed. The VOXEL model and its inner attributes setting are very important for the design of complex models with complex inner attributes. Under Java2.0 and Java 3D, these algorithms were tested and some design examples were given.

The Design, Rapid Manufacture, and Materials of Artificial Porous Bone Structure

By using dexelization algorithms, the Brep model of artificial bone is transformed to the three direction DEXEL model and VOXEL model. By setting the transparence attributes of VOXELs in this VOXEL model, the artificial porous bone structures are designed. In order to preserve bio-activities of materials when we manufacture the artificial porous bone structure, the low-temperature deposition manufacturingLDM is used. By using the blended materials poly-lactic-coglycolic acid (PLGA) and tricalcium phosphate (TCP), we could manufacture the artificial porous bone structures.

설계 특징형상 인식을 고려한 단계적 볼륨 분해

To modify product design easily, modern CAD systems adopt the feature-based model as their primary representation. On the other hand, the boundary representation (B-rep) model is used as their secondary representation. IGES and STEP AP203 edition 1 are the representative standard formats for the exchange of CAD files. Unfortunately, both of them only support the B-rep model. As a result, feature data are lost during the CAD file exchange based on these standards. Loss of feature data causes the difficulty of CAD model modification and prevents the transfer of design intent. To resolve this problem, a tool for recognizing design features from a B-rep model and then reconstructing a feature-based model with the recognized features should be developed. As the first part of this research, this paper presents a method for decomposing a B-rep model into simple volumes suitable for design feature recognition. The results of experiments with a prototype system are analyzed. From the analysis, future research issues are sug

Conservative sampling of solids in image space.

Conservative sampling samples boundary-representation (B-rep) solid models into layered depth images (LDIs). The resulting models have a closed boundary and are guaranteed to bound the input B-rep models on the rays of LDIs. This approach can be fully implemented by shader programs supported by various graphics hardware. Experimental results demonstrate this approach's efficiency; applications of it to evaluating intersecting volumes and computing Minkowski sums show its versatility.