S.T. Tan

Mould design with sweep operations : a heuristic search approach

Abstract The application of a sweep operation to a solid (a solid sweep) results in a complex solid that can be used for obtaining the core and cavity of injection-moulded or die-cast components. The paper describes a method that is based on solid-sweep operations for modelling mould geometry without the creation of undercut or detached objects. In particular, algorithms based on heuristic search techniques for selecting the parting direction are presented. These algorithms can be used for the selection of the parting direction of a simple 2-piece mould or a mould with external side cores. With the proposed solid-sweep operation, they form a basis for automation of the mould design process.

Heterogeneous object modeling: A review

A review on the recent development in heterogeneous object modeling is provided in this paper. General problems and prevalent solutions to the modeling of heterogeneous objects are investigated. Vigorous heterogeneous object representations are roughly classified into three major categories: evaluated models, unevaluated models and composite models. We reveal their similarities and study their strengths and weaknesses in terms of the representational capacities, intuitiveness, exactness, compactness, efficiency and other criteria. Different design paradigms are briefly reviewed to provide an overview of the state-of-the-art in heterogeneous object design. Finally, open problems and possible future directions are discussed.

A qualitative and heuristic approach to the conceptual design of mechanisms

Abstract Automation of the mechanical design process has attracted much attention over the last decade. This paper reports a method of computational synthesis of the conceptual design of mechanisms. The design algorithm employs best-first heuristic searches in a library of mechanical devices, represented and classified qualitatively from various perspectives. A number of design alternatives can be generated from a specification. The suggested design solutions are compact and compatible with general engineering design principles.

A hierarchical representation for heterogeneous object modeling

Abstract A hierarchical representation for heterogeneous object modeling is presented in this paper. To model a heterogeneous object, Boundary representation is used for geometry representation, and a novel Heterogeneous Feature Tree (HFT) structure is proposed to represent the material distributions. HFT structure hierarchically organizes the material variation dependency relationships and is intuitive in modeling different types of material gradations. Based on the HFT structure, a recursive material evaluation algorithm is proposed to dynamically evaluate the material compositions at a specific location. Such a hierarchical representation guarantees complex material gradations and the users design intent can be intuitively represented. Example heterogeneous objects modeled with this scheme are provided and potential applications are discussed.

Multiple material objects: from CAD representation to data format for rapid prototyping

The representations of contemporary CAD systems do not provide or contain any information with regard to the materials of the objects that the CAD system is used for the design work. The information is usually supplied at the computer-aided manufacturing stage by the production engineers. With the advent of rapid prototyping (RP) techniques, which allow multiple material objects to be produced, this arrangement is inadequate. This paper proposes a scheme for representing multiple material objects in a CAD system. A material tree of the object is built in the CAD systems data structure. By extracting information from this material tree, and outputting a modified version of a STL file format to the RP machines, multiple material objects could be fabricated in a RP machine.

Modeling the material grading and structures of heterogeneous objects for layered manufacturing

Abstract The emphasis of this work is to discuss a scheme for modeling the material grading and structures of heterogeneous objects. To model the material grading of a heterogeneous object, a termed ‘grading source’ is defined. The grading sources are reference features, which specify the type and position of grading, and a material grading function for controlling the material variation within the geometric boundary of the objects. Within the proposed modeling scheme, a concept on representing objects, which are both heterogeneous in material and structure (e.g. composite laminates), will also be elaborated. For downstream layered manufacturing purposes, a contour sub-division algorithm on each layer arising from slicing a heterogeneous object is proposed. Within each slice, the material grading is decomposed into sub-contours according to the different grading variation. A parameter called ‘grading step-width’ is defined to control the number of sub-contours and resolution of the grading. With such discretization, it is, therefore, possible to build a heterogeneous object on layered manufacturing machines of different fabricating precision specification.

Parting Line Formation by Slicing a 3D CAD Model

An effective computer-aided parting line/surface formation algorithm can increase the overall efficiency in the mould design and manufacturing processes. The presence of free-form surfaces in a product model imposes a burden on mould makers to determine the parting line and parting surfaces. Previously proposed algorithms, although available, are few, and mainly deal with product with planar or simple curved surfaces. A new algorithm, which adopts an uneven slicing on the product model, is proposed. The algorithm provides a quick and effective way to locate the parting line and parting surface of a free-form product model.

A simple and effective geometric representation for irregular porous structure modeling

Computer-aided design of porous structures is a challenging task because of the high degree of irregularity and intricacy associated with the geometries. Most of the existing design approaches either target designing artifacts with regular-shaped pores or reconstructing geometric models from existing porous objects. For regular porous structures, it is difficult to control the pore shapes and distributions locally; for reconstructed models, a design is attainable only if there are some existing objects to reconstruct from. This paper is motivated to present an alternative approach to design irregular porous artifacts with controllable pore shapes and distributions, yet without requiring any existing objects as prerequisites. Inspired by the random colloid-aggregation model which explains the formation mechanism of random porous media, Voronoi tessellation is first generated to partition the space into a collection of compartments. Selective compartments are then merged together to imitate the random colloid aggregations. Through this Voronoi cell merging, irregular convex and concave polygons are obtained and the vertices of which are modeled as control points of closed B-Spline curves. The fitted B-Spline curves are then employed to represent the boundaries of the irregular-shaped pores. The proposed approach drastically improved the ease of irregular porous structure modeling while at the same time properly maintained the irregularity that is widely found in natural objects. Compared with other existing CAD approaches, the proposed approach can easily construct irregular porous structures which appear more natural and realistic.

Using dexels to make hollow models for rapid prototyping

This paper presents a simple algorithm for hollowing out a solid CAD model. The algorithm employs voxel elements to do the hollowing. Instead of performing three-dimensional Boolean operations on the solid CAD model, one-dimensional Boolean operations between the ray representations of the model and voxel elements are carried out. The ray representation of the hollowed model in turn, produces the direct slice files as output to the rapid prototyping machine. In order to satisfy strength considerations, square and honeycomb structures are formed in the hollowed object.

Optimal design of functionally graded materials using a procedural model and particle swarm optimization

A new method for the optimal design of Functionally Graded Materials (FGM) is proposed in this paper. Instead of using the widely used explicit functional models, a feature tree based procedural model is proposed to represent generic material heterogeneities. A procedural model of this sort allows more than one explicit function to be incorporated to describe versatile material gradations and the material composition at a given location is no longer computed by simple evaluation of an analytic function, but obtained by execution of customizable procedures. This enables generic and diverse types of material variations to be represented, and most importantly, by a reasonably small number of design variables. The descriptive flexibility in the material heterogeneity formulation as well as the low dimensionality of the design vectors help facilitate the optimal design of functionally graded materials. Using the nature-inspired Particle Swarm Optimization (PSO) method, functionally graded materials with generic distributions can be efficiently optimized. We demonstrate, for the first time, that a PSO based optimizer outperforms classical mathematical programming based methods, such as active set and trust region algorithms, in the optimal design of functionally graded materials. The underlying reason for this performance boost is also elucidated with the help of benchmarked examples.