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1、南通大学毕业设计附录（英文资料翻译）SOUD FREEFORM FABRICATION ISFF) AND RAPID PROTOTYPING11 SOUD FREEFORM FABRICATION ISFF)METHODSSeveral manufacturing processes are available to make the important transition from computer aided design(CAD)to a prototype partSeveral new technologies began to make their appearance aft
2、er 1987In that year，stereolithography (SLA) was first introduced bv 3D Systems Inc，and over the next five years several rival methods also appearedTllS created the family of processes known as solid freeform fabrication fSFFlAs with most new technologies at the beginning of the“market adoption Sshap
3、ed curves”in Chapter 2the SFF domain iS accompanied by a relative amount of advertising“hype”SFF processes are sometimes described as： Parts on demand From arttopart Desktop manufacturing Rapid prototyping At the time of this writing，stereolithography (SLA)，selective laser sintering (SLS)，fused depo
4、sition modeling(FDM)，and layered object modeling(LOM) are being used on a day-to-day basis by commercial prototyping companiesThe three-dimensional(3一D)printing process in cornstarch，plastic，and ceramics is also being used commerciallyThe methods lower on the list show promise but do not seem to be
5、in great use by third party prototyping houses to make their daily incomeCasting is a special caseIt is still used to make oneof-akind prototypesFurthermore，for batch runs in the 10 to 500 category it is a very cost effective method to use once an original mold has been made by a process such as ste
6、reolithographyMachining isalso used to make oneof a kind or several prototypes111 Summary of SFF and Rapid Prototyping ProcessesIn daily commercial use：Stereolithography (SLA)Selective laser sintering (SI S)Laminated object modeling (LOM)Fused deposition modeling (FDM)More at the research and develo
7、pment(R&D)stage：3-D printing in cornstarch，plastic，or ceramic3-D printing with plastics followed by planarization using machiningSolid ground curing(similar to SLA)Shape deposition modeling ra combination of addition and subtraction) Non-SFF(traditional)：MachiningCasting Comparisons done in the earl
8、y 1990s by the Chrysler Corporation revealed that the SLA process was ahead of its rival nontraditional prototyping methods in terms of cost and accuracy(these studies excluded an evaluation of machining and casting)Following the technical descriptions in this chapteradditional figures and tables ar
9、e thus included to compare these costs and accuraciesOver the last decade， SLA has further emerged as the most used SFF process,especially for the generation of the master patterns for casting and injection moldingAt the time of this writing，SLS，FDMand LOM have the most visibility after SLA112 The H
10、istory of SFF MethodsDuring the late 1970s,Mead and Conway(1980)created the groundwork for the fast prototyping of very large scale integrated(VLSll circuitsDesigners were encouraged to think in terms of five two-dimensional(2D)patternsThese patterns defined three stacked interconnection layers on a
11、 metaloxidesemiconductor fMOSl wafer and their mutual connections through holesThe patterns descry bed the actual geometrv of the connection runs and via holes that one would see when looking down onto the circuit chip，regardless of the exact process and number of masking steps that were used to imp
12、lement the chip(see MOSIS,2000) Inspired by this success，beginning in the 1970s,several companies tried to create layered manufacturing for mechanical partsAISO by the mid1980s,severa U.Sgovernment studies analyzed the possibilities of a“mechanical MOSIS”(Manufacturing Studies Board，1990；Bouldin，199
13、4；NSF workshop I，1994，and II，1995) The prospects for a mechanical MOSIS were thus frequently linked to the fabrication processes in the lists mentioned(Ashley,1991，1998；Heller，1991；Kruth，1991；Woo，1992，1993；Au and Wright，1993；Kochan，1993；Kai，1994；UCLA，1994；Wleiss and Prinz，1995；Cohen et a1，1995；Dutta
14、，1995；Jacobs，1992，1996；Beaman et a1，1997；Kumar et a1，1998；Sachs et a1，2000) The introduction of the first commercial SFF technology-stereolithography-was accompanied by the advent of the STereoLithography (STL)representation of a CAD obiect“STUis a modified CAD format that suits a subsequent slicing
15、 operaction and the“downstream”laserscanning paths on a physical SLAFDMor SLS machine Is a soccer ball round? The answer depends on how carefully the balIis measuredNominally,it is a perfect sphereHoweveron closer inspectionthe leather is sewn together from about 20 little hexagonal patches and a fe
16、w pentagonal patches to create the curvatureIn reality it is an approximation to a sphere Likewisethe“STLformat approximates the boundary surfaces of a CAD model by breaking it down into interconnected small triangles-a process called tessellationEach triangle is represented by the xyz coordinates of each of its thre
