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1、天津工程师范学院2007届本科生毕业设计A NOVEL INTEGRATED SYSTEM FOR RAPID PRODUCT DEVELOPMENTThis paper presents a novel integrated system of rapid product development for reducing the time and cost of product development. The system is composed of four building blocks digital prototype, virtual prototype, physical p
2、rototype and rapid tooling manufacturing system. It can aid effectively in product design, analysis, prototype, mould, and manufacturing process development by integrating closely the various advanced manufacturing technologies which involve the 3D CAD, CAE, reverse engineering, rapid prototyping an
3、d rapid tooling. Furthermore, two actual examples are provided to illustrate the application of this integrated system. The results indicate that the system has a high potential to reduce further the cycle and cost of product development.Keywords: Rapid product development; rapid prototyping; integr
4、ated system.1. IntroductionDue to the pressure of international competition and market globalization in the 21st century, there continues to be strong driving forces in industry to compete effectively by reducing manufacturing times and costs while assuring high quality products and services. Curren
5、t industries are facing the new challenges: quick response to business opportunity has been considered as one of the most important factors to ensure company competitiveness; manufacturing industry is evolving toward digitalization, network and globalization. Therefore, new products must be more qui
6、ckly and cheaply developed, manufactured and introduced to the market. In order to meet the demand of rapid product development, the various new technologies such as reverse engineering (RE), 3D CAD, rapid prototyping (RP), and rapid tooling (RT) have emerged and are regarded as key enabling tools w
7、ith the ability to shorten the product development and manufacturing time. For example, it has been claimed that RP can cut new product development costs by up to 70% and the time to market by 90%.1 In the form of a better design, more design possibilities, a 3D CAD model can be shown to the custome
8、r for approval and prevents misunderstandings. A virtual prototyping is employed to guide in optimization of the product design and manufacturing process planning, which may result in the accurate determination of the process parameters, and reduce the number of costly physical prototype iterations.
9、 Rapid tooling technique offers a fast and low cost method to produce moulds, and shows a high potential for faster response to market demands. When properly integrated among 3D CAD, CAE, RE, RP and RT, these technologies will play a much more important role to reduce further the development cycle a
10、nd cost of the product production. On the basis of above technologies, a novel integrated system of rapid product development is to be founded so as to meet the requirement of rapid product development.2. Architecture of the Integrated Development SystemThe development process from initial conceptua
11、l design to commercial product is an iterative process which includes: product design; analysis of performance, safety and reliability; product prototyping for experimental evaluation; and design modification. Therefore, any step of the new product development process has a direct and strong influen
12、ce on time-to-market in short order. A good product development system must enable designers or design teams to consider all aspects of product design, manufacturing, selling and recycling at the early stage of the design cycle. So that design iteration and changes can be made easily and effectively
13、. The more fluent the feedback is the higher possibility of success the system has. Design for manufacturing (DFM) and concurrent engineering (CE) necessitate that product and process design be developed simultaneously rather than sequentially. The integrated system of rapid product development is c
14、omposed of four modules: digital prototype, virtual prototype, physical prototype and rapid tooling.The product development starts from the creation of a 3D CAD model using a CAD software package. At that stage, the product geometry is defined and its aesthetic and dimensional characteristics are ve
15、rified. The main function of digital prototype is to perform 3D CAD modelling. The CAD model is regarded as a central component of the whole system or project information base which means that in all design, analysis and manufacturing activities the same data is utilized. The product and its compone
16、nts are directly designed on a 3D CAD system (e.g.Pro/Engineer, Unigraphics, CATIA, IDEAS, etc.) during the creative design. If a physical part is ready, the model can be constructed by the reverse engineering technique. RE is a methodology for constructing CAD models of physical parts by digitizing
17、 an existing part, creating a digital model and then using it to manufacture components. RE can reduce the development cycle when redesigns become necessary for improved product quality. Preexisting parts with features for improved performance can be readily incorporated into the desired part design
18、. Therefore, it is very useful in creating the CAD model of an existing part when the engineering design is lost or has gone through many design changes. 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 d
19、ata in analysis and manufacturing. The three primary steps in RE process are part digitization, features extraction, and CAD modelling. Part digitization is accomplished by a variety of contact or non-contact digitizers. There are various commercial systems available for part digitization. These sys
20、tems 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 as non-contact de
21、vices. 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 fulfiled through fitting a variety of surfaces to the segmented data point
22、s.In order to reduce the iterations of design-prototype-test cycles, increase the product process and manufacturing reliability, it is necessary to guide in optimizing the product design and manufacturing process through virtual prototype (VP). VP is a process of using 3D CAD model, in lieu of a phy
23、sical prototype, for testing and evaluation of specific characteristics of a product or a manufacturing process. It is often carried out by CAE and virtual manufacturing system. Computer aided engineering (CAE) analysis is an integral part of time-compression technologies. Various software tools ava
24、ilable (i.e. ANSYS, MARC, I-DEAS, AUTOFORM, DYNAFORM, etc.) can speed up the development of new products by initiating design optimization before physical prototypes are built. The CAD models can be transferred to a CAE environment for an analysis of the product functional performance and of the man
25、ufacturing processes for producing the products components. It has also proven to be of great value in the design optimization of part geometry, to determine its dimensions and to control warpage and shrinkage while minimizing process-induced residual stresses and deformations. Virtual manufacturing
26、 system (VM) is the natural extension of CAE. It simulates the product functionality and the processes for producing it prior to the development of physical prototypes. VM enables a designer to visualize and optimize a product process with a set of process parameters. The visualization of a virtuall
27、y simulated part prior to physical fabrication helps to reduce unwanted prototype iterations. Therefore, a product virtual manufacturing system may result in accurate determination of the process parameters, and reduce the number of costly physical prototype iterations. 3D CAD model and VP allow mos
28、t problems with unfitting to become obvious early in the product development process. Assemblies can be verified for interference as VP can be exercised through a range of tasks. Structure and thermal analysis can be performed on the same model employing CAE applications as well as simulating down-s
29、tream manufacturing processes. It is clear that VP increases process and product reliability. Although VP is intended to ensure that unsuitable designs are rejected or modified, in many cases, a visual and physical evaluation of the real component is needed. This often requires physical prototype to
30、 be produced. Hence, once the VP is finished, the model may often be sent directly to physical fabrication. The CAD model can be directly converted to the physical prototype using a RP technique or high-speed machining (HSM) process. The 3D CAD model is to be exported not only in the STL format whic
31、h is considered the de facto standard for interfacing CAD and RP systems, but also in the NC coding which can be used by HSM. HSM has a potential for rapid producing plaster or wooden pattern for RT. RP is a new forming process which fabricates physical parts layer by layer under computer control di
32、rectly 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 unconstraine
33、d by the limitations attributed to conventional machining approaches. The application of RP technique as a useful tool can provide benefits throughout the process of developing new products. Specifically, there are serious benefits that RP can bring in the areas of market research, sales support, pr
34、omotional material, and the ever-important product launch. Physical RP can also become a powerful communications tool to ensure that everyone involved in the development process fully understands and appreciates the product being developed. Hence, it can help to reduce substantially the inevitable r
35、isks in the route from product concept to commercial success, and help shorten time-to-market, improve quality and reduce cost. Over the last 20 years, RP machines have been widely used in industry. The RP methods commercially available include Stereolithgraphy (SLA), Selective Laser Sintering (SLS)
36、, Fused Deposition Manufacturing (FDM), Laminated Object Manufacturing (LOM), Ballistic Particle Manufacturing (BMP), and Three-Dimensional Printing (3D printing), etc.Once the design has been accepted, the realization of the production line represents a major task with a long lead time before any p
37、roduct can be put to the market. In particular, the preparation of complex tooling is usually in the critical path of a project and has therefore a direct and strong influence on time-to-market. In order to reduce the product development time and cost, the new technique of RT has been developed. RT
38、is a technique that can transform the RP patterns into functional parts, especially metal parts. It offers a fast and low cost method to produce moulds and functional parts. Furthermore, the integration of both RP and RT in development strategy promotes the implementation of concurrent engineering i
39、n companies. Numerous processes have been developed for producing dies from RP 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 conven
40、tional methods (e.g. HSM), or more commonly by an RP process such as SLA or SLS. Direct RT, as the name suggests, involves the manufacturing of a tool cavity directly on a RP system, hence eliminating the intermediate step of generating a pattern. Soft tooling can be obtained via replication from a
41、positive pattern or master. Soft tooling is associated with low costs; used for low volume production and uses materials that have low hardness levels such as silicones, epoxies, low melting point alloys, etc. RTV silicone rubber moulds, epoxy moulds, metal spraying moulds, etc. are some of these ty
42、pical soft moldings. Hard tooling is associated with higher volume of production, and the use of materials of greater hardness. Keltool process, Quickcast process, and the ExpressTool process are some of these hard toolings. Electrical discharge machining (EDM) seems to be an interesting area in whi
43、ch rapid tooling finds a potential application. Some methods of making EDM electrodes based on RP technique have developed, such as abrading process, copper electroforming and net shape casting, etc. On the basis of the above techniques, a novel integrated system of rapid product development is to b
44、e proposed. Its overall architecture is shown in Fig. 1.3. Case Studies3.1. Case study 1: ImpellerA total of thirty plastic impellers, with a relatively complex geometry, were required by a customer within fifteen working days from the receipt of a 2D CAD model. There were many factors to be conside
45、red in deciding the most appropriate route for producing the impellers. These factors mainly involved cost, lead-time, the number of parts required, the final material for the parts, and the part geometry. In order to maximize the benefits in terms of time and cost reduction for the parts, it was de
46、cided to use silicon rubber mould and the parts were eventually produced by vacuum casting process. Silicon rubber mould is an easy, relatively inexpensive and fast way to fabricate prototype or pre-production tools. It can be utilized for moulding parts in wax, polyurethane, ABS, and a few epoxy ma
47、terials. The process is best suited for projects where form, fit, or functional testing can be done with a material which mimics the characteristics of the production material. The casting parts with fine details and very thin walls can be easily and rapidly produced. The whole process flow involved
48、 the 3D CAD modelling, producing master pattern (RP prototype), silicon rubber mould, and casting green parts. The time sequence for the fabrication of impellers was described as follows. Due to the complexity of the impeller, the task of generating the 3D CAD model using Pro/Engineer software packa
49、ge took almost 3 calendar days. The master pattern for this project was built on a SPS 600 machine in 2 calendar days. SL process was chosen because it was cost effective and the surface finish was good. The next step involved creating a roomtemperature vulcanized (RTV) silicone rubber mold which was completed within an additional 3 calendar days. Finally, the ABS materials were cast into silicon rubber mould under the vacuum casting condition, and the green parts were achieved in 4 calendar days. The required 30 components were produced successfully and complet
