K.M. Yu

Solid reconstruction from orthographic opaque views using incremental extrusion

Abstract The reconstruction of 3-D solids from 2-D projections is an important research topic in reverse engineering. The reconstruction can be grouped into two categories: single-view approach and multiple-view approach. Each approach can be classified as wireframe, BRep or CSG. However, not many CSG approaches have been reported in the literature. The methods are also restricted to uniform-thickness objects or require user interaction. The method proposed in this paper employs the CSG approach. A 3-D solid computer model is reconstructed from 2-D line drawings of six orthographic opaque views, viz. top, front, left, right, bottom and rear views. Firstly, the six views are grouped into three pairs. For each pair of views, segmented areas from one of the two views (called g-view) is incrementally extruded according to the information in the neighbouring view (called d-view). Extrusion primitive solids are generated during the incremental extrusion. All primitive solids are then unioned into an extrusion solid. Finally, all extrusion solids are intersected to give a unique 3-D solution object.

Rapid prototyping for self-similarity design

Abstract This paper proposes a method for the rapid prototyping (RP) of self-similar objects. RP technology makes available the physical generation of a solid object. However, the contemporary design capability of a computer-aided design (CAD) system can atmost use the non-uniform rational B-spline (NURBS) modelling method. When the design has a very complicated shape with self-similarity, contemporary CAD systems can no longer handle the object. In fact, most objects in nature are self-similar. It is valuable to develop a method that can fabricate self-similar objects. Natural objects, such as mountains, clouds, and trees have irregular or fragmented features with self-similarity. These natural objects can be realistically described the by fractal geometry method, while Euclidean geometry is mainly used to represent simple man-made objects such as polyhedra. A typical self-similar fractal solid, the Menger sponge, will be used to illustrate the method. In order to represent a self-similar fractal object for RP, the first task is to develop a method to model the object in a computable form. In this paper, a new data structure, called the radial-blossoming tree (RBT) structure, is proposed and implemented in order to bridge the gaps among CAD, RP and fractal geometry. Based on the RBT representation, an RP toolpath can be traced out more efficiently. The Menger sponge will then be produced layer by layer from the RP machine.

Modeling of multi-connected porous passageway for mould cooling

Abstract Cooling channel design in the plastic injection moulding process is of paramount importance to the performance of the mould, influencing the quality of the parts being produced and productivity of the process. However, cooling channel design is usually limited to relatively simple configurations as well as conventional machining processes, such as straight-line drilling, and milling, etc. The cooling performance may not meet the expectations of the mould engineers. This paper proposes an alternative design method for a conformal cooling passageway with multi-connected porous characteristics based on the duality principle. The proposed method can provide a more uniform cooling performance between the mould plate and the conformal cooling passageway than the existing conformal cooling channel design. Injection mould defects like warpage or hot spots can be avoided. In this study, a 3D mould plate model was offset negatively and the location of the proposed multi-connected porous cooling passageway was identified. The negatively offset model was decomposed into a finite number of cubical cells via the sub-boundary spatial enumerated cell decomposition. Then a duality relationship between the primal and the dual graphs was developed. This provided the preliminary layout of the multi-connected porous passageway for the coolant flow in multiple directions. The cooling channel axis design of the multi-connected porous passageway, illustrated by the skeleton from the dual graph, was created. Following a Boolean difference operation, the proposed multi-connected porous cooling passageway inside the mould plate was able to be generated and fabricated with the aid of rapid tooling technologies. A real-life case study for the design of a multi-connected porous cooling passageway was implemented and examined. The effects of coolant flow and cooling performances, analyzed by computational fluid dynamics simulation, were validated.

Modeling and fabrication of artistic products based on IFS fractal representation

Abstract Contemporary computer-aided design (CAD) and computer-aided manufacturing (CAM) theories and systems are well developed for analytical and free-form objects, but neither can deal with all artistically appealing objects efficiently. Artistically appealing objects are common in, for example, jewellery and furniture decoration. Therefore, it is valuable to explore more suitable modeling and manufacturing method for artistically appealing objects. Fractal geometry has been employed for modeling natural objects that cannot be described easily by Euclidean geometry. In this paper, one type of fractal solid — the Iterated Function System (IFS) fractal — is proposed for modeling artistically appealing objects in a computational form. A Radial-Blossoming Tree (RBT) data structure is worked out for fractal solid modeling in a CAD platform. Traversal algorithms have been devised to extract necessary information from the RBT for generating the toolpath for a layered manufacturing (LM) process, so that a physical fractal object can be built and the fabrication of a fractally represented artistic product can be realized.

Cost-effective solid reconstruction from an X-ray image

Abstract Solid reconstruction of a 3D computer solid model from 2D line drawings has been studied widely over the last two decades. In fact, it is one critical operation in the rapid reverse engineering of a mechanical part. The computer model reconstructed can be used in down-stream operations such as part re-design, engineering analysis, rapid prototyping or CAM. For industrial application, the method should be efficient, cost effective, with minimum human interaction, and reasonably accurate. A new method is studied and implemented using a computer-vision approach to extract information from a mechanical part and generate the corresponding computer model. The method takes advantage of X-rays to capture images of an object with obscured interior details. The reconstruction algorithm will generate an information-complete solid model. The paper explains and discusses the method with examples and explores its cost effectiveness.

Development and evaluation of a mobile platform for teaching mathematics of CAD subjects

ABSTRACTNowadays, Hong Kong has adopted a new 3-3-4 academic structure for senior secondary education and higher education since 2012. Students can admit to most of the university programme without compulsory subject requirement. It means that students can admit to a programme without sufficient background on the underpinning subjects. Recently, it was found that a number of students were admitted to the engineering programmes without sufficient mathematical background, and it is a great challenge for the students study future engineering subjects, especially for the computer-aided product design (CAD) and other subjects that requires demanding mathematical background knowledge. In this project, a mobile learning platform is developed intend to provide a convenient and attractive channel for students to review and study the mathematics concepts and equations that need to be used in class. The platform encourages students’ self-learning and facilitating them to learn other engineering subjects easily. Two ...

3D Fillet Solid Model Reverse Engineering from 2D Orthographic Projections

Recently, the popularity of 3D in computer graphics or image processing boosts the use of reverse engineering. With the aid of computer-aided design, computer-aided manufacturing and computer-aided engineering techniques, various medical images, historical relics, artworks, or products captured in 2D images (e.g. digital photos or engineering drawings) are changed into 3D solid models for recovery, preservation, entertainment, or visualization, or other downstream applications, etc. In some cases, geometric information from a physical object is always obtained by traditional engineering drawings from different 2D orthographic projections without a 3D scanning device. The input for reverse engineering is necessary to change into 3D solid model for various downstream applications. In this study, a 3D fillet solid model construction is proposed from 2D orthographic projections using CSG representation. The uniqueness of the solid model obtained is proved.