机械设计类外文参考文献及翻译 第3页
of product design, manufacturing, selling and recycling at the early stage of a design cycle. So that design iteration and changes can be made easily and effectively. The more fluent the feedback is, the higher possibility success of the system has. Design for manufacturing (DFM) and concurrent engineering (CE) require that product and process design be developed simultaneously rather than sequentially [32].
The integrated system of rapid product development is composed of three modules: digital prototype, physical prototype and rapid tooling and functional part manufacturing system. The product development starts from the creation of a 3D model using a 3D CAD software package. At that stage the product geometry is defined and its aesthetic and dimensional characteristics are verified. The main function of digital prototype is to perform 3D CAD modelling. The product and its components are directly designed on a 3D CAD system (e.g. Pro/Engineer, Unigraphics, CATIA, IDEAS, etc.) during the creative design process. If a physical part is available, the model can be constructed by the reverse engineering (RE) technique. RE is a methodology for constructing CAD models of physical parts by digitizing an existing part, creating a digital model and then using it to manufacturing components [33]. RE can reduce the development cycle when redesigns become necessary for improved product performance. Pre-existing parts with features for improved performance can be readily incorporated into the desired part design. When a designer creates a new design using mock-up, it is also necessary to construct the CAD model of the mock-up for further use of the design data in analysis and manufacturing. The three primary steps in RE process are part digitization, features extraction, and 3D CAD modelling. Part digitization is accomplished by a variety of contact or non-contact digitizers. There are various commercial systems available for part digitization. There systems range from coordinate measuring machine (CMM), laser scanners to ultrasonic digitizers. They can be classified into two broad categories: contact and non-contact. Laser triangulation scanner (LTS), magnetic resonance images (MRI), and computer tomography (CT) are commonly used non-contact devices. Contact digitizers mainly have CMM and cross-sectional imaging measurement (CIM). Feature extraction is normally achieved by segmenting the digitized data and capturing surface features such as edges. Part modelling is fulfilled through fitting a variety of surface to the segmented data points [34]. In order to reduce the iterations of design-prototypetest cycles, increase the product process and manufacturing reliability, it is necessary to guide in optimization of the product design and manufacturing process through CAE.
The CAD model can be directly converted to the physical prototype using a RP technique. RP is a new forming process which fabricates physical parts layer by layer under computer control directly from 3D CAD models in a very short time. In contrast to traditional machining methods, the majority of rapid prototyping systems tend to fabricate parts based on additive manufacturing process, rather than subtraction or removal of material. Therefore, this type of fabrication is unconstrained by the limitations inherent in conventional machining approaches [35]. RP potentially offers great benefits when used during the design and manufacturing process. It can help shorten time-to-market, improve quality and reduce cost. Over the last 10 years, RP machines have been widely used in industry. The RP methods commercially available include Stereolithgraphy (SL), Selective Laser Sintering (SLS), Fused Deposition Manufacturing (FDM), Laminated Object Manufacturing (LOM), Ballistic Particle Manufacturing (BMP), and Three Dimensional Printing (3D printing) [36], etc.
RTis a technique that transforms the RP patterns into functional parts, especially metal parts. Furthermore, the integration of both RP and RT in development strategy promotes the implementation of concurrent engineering in companies. Numerous processes have been developed for producing dies fromRP system. The RT methods can generally be divided into direct and indirect tooling categories, and also soft (firm) and hard tooling subgroups. Indirect RT requires some kinds of master patterns, which can be made by conventional methods (e.g. HSM), or more commonly by an RP process such as SL or SLS. Direct RT, as the name suggests, involves manufacturing a tool cavity directly on the RP system, hence eliminating the intermediate
 step of generating a pattern [37]. On the basis of abovetechniques, a novel integrated system of rapid product development is to be established. Its detailed structure is shown in Fig. 1.
 4. The workflow and function design
The workflow of the service system of networkedmanufacturing is shown in Fig. 2. The first step is to log in to the website of SB. Users have to enter their names and passwords. Those without registration or authorization can also enter into the system, but they are limited to viewing the information that is open to the public such as ‘‘typical cases’’ in this system. The password entered by the user will be verified by the system. After entering the SB website successfully, the

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