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桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 譯文 編號 畢業(yè)設(shè)計 論文 外文翻譯 原文 學(xué) 院 國防生學(xué)院 專 業(yè) 機(jī)械設(shè)計制造及其自動化 學(xué)生姓名 譚鑫 學(xué) 號 1000110110 指導(dǎo)教師單位 機(jī)電工程學(xué)院 姓 名 郭中玲 職 稱 高級工程師 2014 年 3 月 9 日 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 譯文 contents Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing 1 prolonging lifetime ofservice life of die based on deform 13 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 0 頁 共 29 頁 Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing C K Chua1 S H Teh1 and R K L Gay2 School of Mechanical and 2Gintic Institute of Manufacturing Technology Nanyang Technological University Singapore Abstract Rapid prototyping RP is the production of a physical model from a computer model without the need for any jig or fixture or numerically controlled NC programming This technology has also been referred to as layer manufacturing material deposit manufacturing material addition manufacturing solid freeform manufacturing and three dimensional printing In the last decade a number of RP techniques has been developed These techniques use different approaches or materials in producing prototypes and they give varying shrinkage surface finish and accuracy Virtual prototyping VP is the analysis and simulation carried out on a fully developed computer model therefore performing the same tests as those on the physical prototypes It is also sometimes referred to as computer aided engineering CAE or engineering analysis simulation This paper describes a comparative study of the two prototyping technologies with respect to their relevance in product design and manufacture The study investigates the suitability and effectiveness of both technologies in the various aspects of prototyping which is part and parcel of an overall design and manufacturing cycle Keywords Product design Rapid prototyping Virtual prototyping 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 1 頁 共 29 頁 1 Introduction Rapid prototyping RP is emerging as a key prototyping technology with its ability to produce even complicated parts virtually overnight It enables product designers to shorten the product design and development process The coming of age of this technology is clearly reflected in the inclusion of a stereolithography STL file generator in most if not all CAD systems today The STL file is the de facto standard used by RP systems in the representation of the solid 3D CAD models While RP is a relatively young technology virtual prototyping VP has been in steady development since the 1970s in many guises Virtual prototyping is taken to mean the testing and analysis of 3D solid models on computing platforms Today VP is often tightly integrated with CAD CAM software and sometimes referred to as CAE packages It provides the ability to test part behaviour in a simulated context without the need to manufacture the part first 1 2 Definitions of RP and VP Rapid prototyping RP is a widely used term in engineering particularly in the computer software industry where it was first coined to describe rapid software development This term has also been adopted by the manufacturing industry to characterise the construction of physical prototypes from a solid powder or liquid in a short period of time when compared to traditional subtractive machining methods This technology has also been variously referred to as layer manufacturing material deposit manufacturing material addition manufacturing solid freeform manufacturing and threedimensional printing 2 Virtual prototyping VP refers to the creation of a model in the computer often referred to as CAD CAM CAE Virtual or computational prototyping is generally understood to be the construction models of products for the purpose of realistic graphical simulation 1 In this paper VP will refer to thesimulation virtual reality and manufacturing process design domains 3 Nevertheless there are many areas where the distinction between RP and VP is blurred As RP systems rely on CAD systems to generate the files needed to produce the prototype it would seem that RP is a downstream process from VP in the product or part development cycle Indeed Pratt s definition of VP reveals the fact that VP is a term which is loosely used in the prototyping community As such it would be 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 2 頁 共 29 頁 appropriate to clearly define both RP and VP Rapid prototyping will be taken to mean as above the production of a physical model from a computer model without the need of any jig or fixture or NC programming This also includes other related processes and applications which use RP produced objects such as rapid tooling Similarly VP is defined as the subsequent manipulation of a solid CAD model as a substitute for a physical prototype for the purposes of simulation and analysis and is not inclusive of the construction of the solid 3D model VP includes the following functions 1 Finite element analysis 2 Mechanical form fit and interference checking 3 Mechanical simulation 4 Virtual reality applications 5 Cosmetic modelling 6 Assemblability The relationships between RP and VP are shown in Fig 1 Fig 1 Classification of RP and VP 3 Prototyping in Singapore Two selected multi national companies one American and one French based in Singapore with significant product development activities showed differing approaches to both RP and VP Both use RP in their prototyping activities The first company B placed more emphasis on virtual prototyping It 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 3 頁 共 29 頁 manufactures telecommunications equipment such as pagers and handphones It is moving all prototyping applications upstream which is to move prototyping from RP to VP At present their RP models are used only for proof of concept and marketing purposes Other prototyping activities are being carried out with VP The second company C manufactures consumer electronics products such as television sets video cassette recorders and telephones It uses VP only as a tool to create a solid 3D model From the solid 3D model C generates the STL file needed to produce the RP prototype Company C then uses the RP part as a master for silicone rubber moulds to produce a limited number of physical ABS polyacrylonitrite butadienestyrene prototypes for the various prototyping tests and simulation Company B intends to move more prototyping to VP rather than using physical models Virtual prototyping allows for improvements in reliability and quality as well as reducing costs Manipulation of virtual prototypes makes it easier for B to implement design improvements compared to an iterative cycle using physical prototypes Company B drafts the CAD models in Pro ENGINEER then uses Patran to pre process the models Static finite element analysis FEA is carried out with ABAQUS Standard whereas dynamic scenarios are analysed with ABAQUS Explicit ALIAS Wavefront is used for cosmetic modelling when presenting different conceptual and actual designs The bulk of the VP carried out by B uses FEA which typically takes 4 6 weeks for a pager design Of all the FEA carried out the majority are concentrated on structural strength static analysis and drop test dynamic analysis Vibration tests are occasionally carried out Some cosmetic modelling is carried out but usually only for presentation purposes Finite element analysis is used to investigate the following problems Relative comparison of different design options to see how one design compares to another Possible failure modes are 1 To evaluate a design change or design correction 2 To assess the possibility of failure based on past experience 3 To make some educated guess correlation with physical testing 4 To try to identify what initiated a failure According to B the drawback of VP is that it cannot simulate process problems efficiently and effectively The accuracy of FEA is also limited because of the 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 4 頁 共 29 頁 inconsistent behaviour of material The amount of computing power also determines the accuracy of FEA The application of RP is rather limited in B The in house laminated object manufacturing LOM RP system is used to produce design prototypes for proof of concept only and not geometrical prototypes Company C uses RP heavily but has very little VP The parts produced using RP range from audio products to 29 in television casings Typically it takes 1 year from the conception of the product to the sale of the product Company C aims to prototype all mostly plastic parts by RP A comparison between numerically controlled NC machining of prototypes from ABS against RP is shown in Table 1 Company C projected 50 savings using an in house RP system versus an NC machining system CAD models are created using I DEAS The STL format is then created for production of the RP part The main purpose of the RP parts is to verify the design Rapid prototyping parts are used for the following functions 1 Form fitting 2 Ergonomics check 3 Proof of concept to confirm design with industrial designers 4 Manufacturability design for tooling design for assemblability 5 Reliability check whether part dislodges or breaks when force applied especially snap on covers 6 Kinematic check Company C offers some insight into the limitations of VP in that VP is unable to model 1 Tactile feeling for buttons not quantified may be able to VP if able to quantify pressing force 2 Assemblability e g PCBs inserted at an angle difficult to visualise 4 Case Study 1 Prototyping of a Telephone Handset This case study investigates the design verification assembly interference check and form fitting aspects of both the RP and VP model The production ABS RP and VP parts or models were evaluated in the above aspects The RP system used here is the stereolithography apparatus SLA Both the ABS and RP parts are shown in Fig 2 Inspection of the RP parts reveal that 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 5 頁 共 29 頁 1 The surface finish was much poorer than in the ABS part 2 Warpage was clearly evident see Fig 3 4 1 Design Verification As a true dimensional physical part the RP model is able to give the designer a sense of size estimation The judgement of a VP part can be erroneous because parts are often automatically sized to fit the viewing window Another advantage of a physical part is that it allows for ergonomic checks ranging from the fit of a telecommunications device in a user s palm to the inspection of potentially dangerous corners and edges Also it offers tactile inspection which is crucial in products for which ergonomics is important such as touch buttons on audio or video products which is not possible on VP systems Rounded edges which appear innocuous on a VP model may prove to be unsafe upon scrutiny of the RP part Above all most RP parts are produced for aesthetic evaluation purposes Aesthetic evaluation is also possible on VP models All CAD software allows the model to be viewed in any spatial orientation along with at least rudimentary rendering capabilities It is then possible to view the part under the desired simulated lighting conditions with millions of shading and colour combinations RP parts cannot be coloured thus surface preparation and painting introduce additional finishing processes Any visibly apparent design discrepancies could be immediately rectified without having to invest in a physical part It also allows designers to evaluate the aesthetics of the design and make corrections if necessary In the case of most multi national companies the design and manufacturing facilities are often a considerable distance apart and in different countries and continents The ease with which CAD files can be sent and received via electronic means greatly helps the design process be it iterative or concurrent With identical or compatible CAD software the prototyping process can be swift and cheap Any design change of the virtual prototype can bemade almost instantly available to all parties involved in the design process 4 2 Assembly Assembly of RP parts must be carried out quickly as warpage and shrinkage increases with time Warpage is a function of both part geometry design and shrinkage All but the bestdesigned parts suffer from varying degrees of warpage and shrinkage Some RP material such as the SLA inherently shrinks and the part is 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 6 頁 共 29 頁 actually built slightly larger to allow it to shrink to its proper dimensions With such arrangements assembly is possible but is often hampered by warpage and or shrinkage Some parts can be mated only with the application of some force Assembly of RP parts allows the user not only to attempt different assembly sequences but also if a part cannot be positioned in a linear movement to insert the part say at an angle before being set into its proper location The drawback in assembling RP parts is that for some RP parts such as SLA the material is weak and brittle and fails when attached using fasteners or under low to moderate loading see Figs 4 and 5 CAD software allows for the assembly of parts and subassemblies in the form of 3D solid or surface models Assembly in the virtual realm is very often used to check for interference and form fitting which will be discussed later The ability of CAD software to assemble parts and or subassemblies allows a product designer to quickly check to see if he or she has designed the part or parts correctly i e whether a boss is tall enough to accept a screw inserted through another part or if two slots are aligned to form a larger slot The advantage of assembling in a virtual environment is that no physical parts need be produced and thus this reduces cost The absence of physical parts also means that tooling time is eliminated The assembly in a virtual environment can be done in a matter of minutes or up to a few days but is much faster than producing the physical parts and then assembling them The user can also build or change a part or modify its attributes when all instances of the part will be changed accordingly Assembly relationships can be written in engineering parameters part dimensions and orientation dimensions The equations are solved variationally to allow for flexibility while working with the assembly Evaluation of the tolerance specifications of the design to optimise the engineering performance at the lowest possible cost can be carried out This allows the user to measure the sensitivity of a critical dimension in an assembly to changes in individual constraints Manufacturing cost can then be reduced by tightening the tolerances which contribute most to the overall variation of a critical dimension and loosening tolerances that have little impact 4 3 Interference Check and Form Fitting Again interference checking and form fitting is hampered by warpage and shrinkage of the RP part Therefore the problem of parts which interfere or fit poorly may be due to one or more of warpage shrinkage or design error Even when RP 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 7 頁 共 29 頁 parts fit well there is no assurance that the parts are dimensionally correct as shrinkage of two or more parts in the same direction or directions could still produce a good fit When such situations arise CAD models are often used to determine whether the interference or poor fit is due to design flaws The ability to check for interference as well as form fitting is very widely used in CAD systems It gives the user the ability to fit two parts together and check for interference without having to produce a part or parts which are potentially dimensionally incorrect thereby increasing cost The interactive nature of the process in a CAD system also frees the user or designer from the need to manually interpret engineering drawings to detect interference This process also allows the user to establish tolerances which are crucial in the manufacturing process The advantage of interference checking on a CAD system is not evident when an assembly consists of a small number of parts For complex assemblies with a large number of parts there are often many features on a particular part that must be mated or aligned with features on one or more other parts CAD systems allow not only the detection of any misalignment or interference but also immediate rectification of the problem Interference checking is performed by the CAD system on an assembly when required by the user and is relatively faster and more accurate and precise than other methods The CAD system would also identify and list the features which interfere The user can then view the entities to rectify the situation 5 Case Study 2 Prototyping of a Knee Prosthesis 5 1 Background Rapid prototyping has applications in the field of medicine However in this application the STL file is no longer obtainable from a CAD model There is a need to generate the necessary STL files from data acquired by medical equipment Swaelens and Kruth 4 proposed three approaches to producing an RP part from computer assisted tomography CT scanner data see Fig 6 In most cases STL interfacing was used In STL interfacing a CT scanner maps the contour of a 3D surface This data is then converted into triangular file format which is then converted into the STL format required by RP machines There is a direct conversion of data from the CT scanner to the RP machines In effect the scanned surface is faithfully reproduced by the RP machine 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 8 頁 共 29 頁 When used in this fashion VP plays an almost negligible role in RP assisted surgery prototyping as a viewer to verify the contour of the surface Jacob et al 5 constructed 3D models from CT scanner data using CTrans from Proform They reported that the decisive advantage lies in the clearness and manual getting in touch as the surgery proper is elaborate manual craftsmanship The model can be viewed and palpated from any angle and could even be operated upon In that way surgeons could literally grasp the problem This study shows VP as a viewer for a 3D model While the study did not state whether the 3D model was a solid model it opened the possibility of integrating CAD software into the process data exchange problems notwithstanding This contrasts with the CAD system route shown above Researchers in the University of Leuven Belgium identified contours from CT scanner data and introduced them into CAD software to generate surface models The physical model of a hip was produced with much effort and the whole procedure took several working weeks The procedure of converting CT scanner data to a solid 3D model is tedious and prone to error Given the triangulation points from the CT scanner they must be joined to the appropriate adjacent points to form curves Confusion sometimes occurs when a surface folds back while a point below is the nearest point it may not be an adjacent point These curves must then be individually and manually selected to define surfaces Again care must be taken to ensure that the appropriate surfaces which approximate the original surfaces are formed After the surfaces are formed they are connected to form patches or quilts These quilts are then combined to form a surface model If the surface model is fully enclosed the CAD system may then convert it into a shell or solid 3D model The complexity and shape of the human body also presents problems Most of the extracted outlines are represented as complicated Bezier curves A mapping algorithm sometimes fails to combine these Bezier outlines to form 3D data So it is necessary that this process be supported by hand 6 Human supervision is also required where software is unable to recognise features such as joints where bone structures abut The data must be separated into individual components disarticulation in order to evaluate a function e g a jaw joint Direct interfacing has two major problems The data from the CT scanner are in 桂林電子科技大學(xué)畢業(yè)設(shè)計 論文 外文翻譯 原文 第 9 頁 共 29 頁 the form of shaded images and are automatically segmented While it is possible to calculate triangles from the images they do not contain enough surface information Therefore it is difficult for the RP system which requires supports