Microblasting characteristics of jewellery models built using stereolithography apparatus (SLA)

This paper describes an investigation of the effect of the microblasting process on the surface finish of jewellery models built using stereolithography apparatus (SLA). The layering process of SLA results in visible steps on the model surface. The investigation aims to determine the significant operating parameters of the microblaster deburring process that affect the surface roughness of the SLA jewellery model, to set a practicable range for these parameters for effective deburring and establish the optimum parameters for the best surface finish. A ring model based on the British Standards 28653: 1993 is designed using the Pro-Engineer software. The experimental strategy applies techniques including the full factorial and Yates' method together with the analysis of variance on the deburred samples. The surface roughness of the ring models before and after the deburring process are then measured with a Form Talysurf surface roughness measuring machine. The information obtained is used to identify the parameters for further study. Parameters identified are different nozzle types, blasting time and pressure variation. These parameters are tested for their optimum settings and the microblasting process is found to significantly improve the surface finish by approximately 30% on both the curvature and flat features of the ring model.     

Interface between CAD and Rapid Prototyping systems. Part 2: LMI — An improved interface

The STL (STereoLithography) file format, as developed by 3D Systems, has been widely used by most Rapid Prototyping (RP) systems and is supported by all major computer-aided design (CAD) systems. However, it is necessary to improve the STL format to meet the development needs of RP technologies. In Part 1, several existing and proposed formats have been discussed. This paper, Part 2, will present an improved interface between CAD and RP systems. The new interface is a file format that supports the STL format, removes redundant information in the STL format and adds topological information to balance storage and processing cost. In addition to supporting facet boundary models, the new interface supports precise models by using the edge-based boundary representation. This paper discusses the design considerations of the new interface and data structures for both facet models and precise models. Finally, a comparison of the new interface and the STL file format will be made.     

Creating machinable textures for CAD/CAM systems

Texture is applied on three-dimensionally modelled surfaces in computer graphics to enhance visual effect. This research focuses on the development of three-dimensional textured surfaces which are suitable for manufacturing. Three approaches for creating the three-dimensional texture are presented.The first approach is to process a design from either an artist's sketch or an image from a two-dimensional scan. The second approach uses a three-dimensional scanned texture. Both these approaches depend on the quality of the scanned image and are more tedious than the third approach, which is to convert texture using parameters and is a more direct approach. In the user interface design, two custom-made forms are developed to cater for both regular and irregular textures.The case studies have shown that the textures created are not only good for a visual effect, but are also machinable. The development work is incorporated into the ArtCAM system which is a specialised CAD/CAM system that is capable of generating three-dimensional shapes from two-dimensional artwork.     

Checking for machinability on surface patches

Toolpaths generated from a CAD model do not necessarily produce a part which exactly matches the model part. To close up the gap between a CAD model and a machined model, this paper focuses on the development of a program to check the machinability of surface patches in relation to the cutting tool. A machinability check engine is formulated and implemented for verifying the machinability of surface patches. The structure of the machinability check engine consists of three components: the input parameters, the checking algorithm and the output surface map. The output surface map is called the Chow map. The algorithms for checking a single surface and multiple surface patches are presented. Sample runs of the machinability check engine are performed on three types of surface patch: standard-shaped surfaces, complex surfaces and textured surfaces. The machinability check engine can be incorporated into a CAD/CAM system for better surface design.     

Rapid Sheet Metal Manufacturing. Part 1: Indirect Rapid Tooling

Rapid sheet metal manufacturing (RSMM) is a closed loop process for making sheet metal products which uses advanced computer-aided techniques and computer-controlled machines to produce non-ferrous tooling directly or indirectly. The tooling would be suitable for short-run production or design evaluation of sheet metal products for which prototyping cost and lead time are greatly reduced. The key aspect of this closed-loop process is the method used to fabricate and modify the sheet metal forming tool. Various approaches are adopted in the preparation of the tooling for onward embossing on a sheet metal. The three indirect approaches use selective laser sintering (SLS), stereolithography (SLA), and high-speed computer numerical controlled (CNC) milling to build the masters from computer data models. The masters are used in the vacuum casting process to generate the non-ferrous tooling. Comparisons on quality, lead time and cost are presented.     

<Emphasis Type="Italic">Development of a Tissue Engineering Scaffold Structure Library for Rapid Prototyping. Part 1: Investigation and Classification</Emphasis>

In tissue engineering (TE), a porous scaffold structure may be required as a template to guide the proliferation, growth and development of cells appropriately in three dimensions. Although TE scaffolds can be created using one of many conventional techniques available, most will suffer from a lack of mechanical strength and/or uniformity in pore distribution and sizes. This study is focused on creating scaffolds using rapid prototyping (RP) techniques. Utilising these novel techniques, a computer-aided design (CAD) of the scaffold structure must first be modelled. The scaffold structure is then fabricated directly from CAD data using a RP system. The objective of this research is to (1) investigate and select various polyhedral shapes suitable for scaffold modelling, (2) classify the selected unit cells, (3) create a parametric library of scaffold structures and (4) verify by building the CAD models using the selective laser sintering process. The first two objectives are covered in Part 1 of this two-part paper. The remaining objectives will be described and discussed in Part 2. ID="A1"Correspondance and offprint requests to: Dr C. K. Chua, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mckchua@ntu.edu.sg     

一种有效提高紧缩场反射面精度的CAD／CAM技术

介绍了一种利用计算机技术和数控技术对反射面进行加工的CAD／CAM技术，从加工精度、加工工艺、生产周期等方面对比分析了这两种成形方法。加工成形后经过三坐标测量，对测量结果分析得精度为15．4μm，较反射面板蜂窝夹层结构成形技术的精度极限（20μm）提高了近5μm。经用户使用证明，它是一种可以提高紧缩场反射面精度的新方法。     

Rapid tooling technology. Part 1. A comparative study

Rapid tooling (RT) is the technology that adopts rapid prototyping (RP) techniques and applies them to tool and die making. Research into RT techniques has shown that it is gaining more importance and is starting to pose a serious threat to conventional machining. In this paper, several popular RT techniques are discussed and then classified. A comparison is also made on these techniques based on tool life, tool development time and cost of tool development.     

Selecting and prioritizing key factors for CAD/CAM software in small- and medium-sized enterprises using AHP

In today’s fast-paced world, computer-aided design/computer-aided manufacturing (CAD/CAM) systems have become a necessary element in manufacturing industries. Prior to investment in a CAD/CAM system, it is essential for investor to know how to maximize their benefits from buying a new or by changing an existing CAD/CAM system. The purpose of this study is to provide a methodology to assist small- and medium-sized manufacturing companies of Pakistan in selecting a CAD/CAM system. It will also facilitate the software providers in recognizing the current state of affairs as well as preceding problems regarding the application of CAD/CAM in manufacturing firms when assisting them in choosing the direction for future development simultaneously. To accomplish this purpose, data have been collected about current CAD/CAM systems. Important criteria for system selection and parameters for evaluation have also been identified and prioritized. Analytic hierarchy process (AHP) is used as a decision-making technique for identifying and prioritizing important factors for CAD/CAM software selection. Expert Choice (AHP-based software) has been used to validate the results.     

交互式虚拟设计与同步制造技术算法与图形系统研究

产品的创意外形设计与快速试制对于更好地满足产品多品种、短开发周期、优美外形、提高市场竞争力等需求具有重要意义,而现有的CAD/CAM和快速原型制造技术在这一方面仍然存在一些不足,这里提出的交互式虚拟设计与同步试制系统利用虚拟现实技术和计算机数字雕刻技术,在交互设计、创意设计、快速试制、材料多样性等方面都有所突破。文章阐述了在设计过程中工作描述、刀具轨迹包络计算、图形布尔运算、以及高速逼真图形显示等关键技术。实际工作设计与制造实验证明所开发的系统技术可行,已经可以进行基本的产品外形设计与同步制造。     

A method for assessing geometrical errors in layered manufacturing. Part 1: Error interaction and transfer mechanisms

Geometric accuracy of components is one of the most important quality characteristics in layered manufacturing processes on which most rapid prototyping (RP) techniques are based. Layered manufacturing is an approximate fabricating process in which the final geometric error of the physical part is affected, not only by the approximation technique used, but also by the fabrication process. Errors that occur in one layer could propagate and transfer to other layers causing an accumulated error effect in the process. In this paper, a concept of disturbance error is introduced to describe the effect of accumulated errors in the fabrication process. A physical model is presented to describe error interactions and error transfer mechanisms in the layered manufacturing process. A geometrical model is developed using surface approximation techniques to describe the relationships of the geometrical errors. It is shown that although the complexity of the part geometry is not directly related to the manufacturing process, it will affect the geometrical errors of the part produced.     

Rapid tooling technology. Part 2. A case study using arc spray metal tooling

In this case study of arc spray metal tooling, the feasibility of implementing arc metal spraying on a master, produced using an RP technique, to produce the tool is tested. This tool is then used to produce plastic parts in injection molding. In this project, the tool was completed in less than 2 weeks and at an approximate cost of $4180. Compared to traditional tool shop methods, this method would provide time and cost savings of at least 50%.     

NURBS曲线在快速原型制造系统中的应用

大多数快速原型制造系统采用 STL 文件作为与 CAD系统之间的数据交换接口。但是 ,STL 文件是通过用一系列的三角片逼近实际零件表面而产生的 ,STL 文件本身及其创建过程均存在许多问题。要提高模型的精度 ,就必须增加三角片的数量 ,同时减小三角片的尺寸。这必然造成 STL 文件庞大 ,后续处理时间较长 ,而且易产生缺陷 ,使后续处理不能进行。针对上述问题 ,本文分析了 STL文件的不足 ,提出一种 CAD系统与 RPM系统之间新的数据交换方法。该方法对 CAD系统中的真实模型直接切片 ,将切片后所得到的轮廓数据作为 CAD系统与快速原型制造系统之间的数据交换接口。该切片算法已在“超人 2 0 0 0 CAD/ CAM”系统中实现 ,算法表现稳定     

A method for assessing geometrical errors in layered manufacturing. Part 2: Mathematical modelling and numerical evaluation

Layered manufacturing based rapid prototyping processes are subjected to not only a staircase effect owing to the approximating process used, but also an accumulated error transfer between layers. Certain types of error such as surface tilting and layer thickness variations that occur in one layer can transfer to other layers above it. This paper describes a mathematical model based on the physical and geometrical models discussed in Part 1 of the paper. The model uses the matrix transformation method to analyse the effect of transformation of local errors to the multiple layer global errors. A data preparation error transformation matrix is used to describe the error interactions between layers during the data preparation stage. A disturbance error transformation matrix is used to describe the error interaction within each layer and error propagation between layers during the part building process. This model describes geometrical error analysis involving profiling error, layer inclination and layer thickness variations. Numerical evaluation of the model is carried out for a typical benchmark component.     

用于高精度小尺寸零件制作的光固化快速成型技术的现状与发展

用于高精度小尺寸零件制作的光固化快速成型技术源于快速原型技术 ,利用光诱导树脂固化 ,实现逐层堆积的原理制作零件原型。本文回顾了近年来该领域中开发出的主要工艺方法、原理及系统构成 ;本文还提出了以变形反射镜器件为核心构建新型动态视图发生器 ,采用整层曝光固化工艺实现原型快速制作的新方法。和其它方法使用的动态视图发生器相比 ,本文提出的新型动态视图发生器具有更高的分辨率和更高的对比度 (可达 10 0 0∶1)。     

发动机气道曲面反求及其模具设计

应用CATIA软件中的数字曲面编辑器和自由造型模块,对发动机气道的点云数据进行曲面拟合处理,再利用Pro/E软件对已逆向生成的吊钩实体进行模具设计,这种快速原型技术的方法可以提高产品设计的准确性,并大大缩短产品研发,模具设计和加工周期,从而降低产品开发、模具设计成本.     

<Emphasis Type="Italic">Development of a Tissue Engineering Scaffold Structure Library for Rapid Prototyping. Part 2: Parametric Library and Assembly Program</Emphasis>

Rapid prototyping (RP) techniques have been found to be advantageous for tissue engineering (TE) scaffold fabrication due to their ability to address and overcome the problems of uncontrollable microstructure and the feasibility issues of complex three-dimensional structures found in conventional processing techniques. This research proposes a novel approach for TE scaffold manufacture using RP techniques. The approach involves the integration of medical imaging devices (CT/MRI) for the acquisition of anatomic structural data, three-dimensional CAD modelling for designing and creating the digital scaffold models and RP for fabricating the physical scaffolds. To aid the user in CAD modelling, a standard parametric library of scaffold structures is designed and developed. With the library, a user can select the geometry of the scaffold unit cell and size it to suit the end application of the TE scaffold. A developed application program will then assemble the scaffold structure from the selected unit cell, following the surface profile of the anatomic structure to be replicated. A physical scaffold will then be built using an RP system. ID="A1"Correspondance and offprint requests to: Dr C. K. Chua, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mckchua@ntu.edu.sg     

Rapid Prototyping Applications in Medicine. Part 1: NURBS-Based Volume Modelling

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prostheses for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the extended opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In this paper, Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. Part 2 deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.