Design and Analysis of Integrated Manufacturing Systems (1988) / Chapter Skim
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Modeling in the Design Process
Modeling in the Design Process
Pages 167-199
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From page 167... ...
It discusses two (of many) issues that indicate how little we really know about design and about the interplay between design and manufacturing, and it closes with the following assessment: Contemporary modeling systems are most useful for refining and documenting nearly finished designs and for driving a growing array of computer-aided manufacturing modules; they provide little help in the early, conceptual stages of design.
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From page 168... ...
It concludes that modern CAD/CAM systems are best suited to the final "tuning" and "detailing" of parts and products and as sources of data for increasingly automated manufacturing processes; they provide little help in the early, conceptual phases of design. The appendix traces some of the history of design and manufacturing in an effort to understand why manufacturing is ahead of design in terms of scientific understanding and automation.
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From page 169... ...
Nearly all of the pre-1980 systems carried ambiguous representations that required human interpretation to be useful, whereas the new-generation solid modeling systems carry unambiguous representations GEOMETRIC MODELING SYSTEM Deflnitlons of ObJect Geometry ~ Commands : 169 that permit many calculations to be automaten, at least In principle. The Evolution of Computer Modeling Figure 3 summarizes the evolution of modeling technology.
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From page 170... ...
·1972 1 It 1 1 1973- ·1978 ~ 1 ! 1 It 1 1979 - 1984 2-D Systems based on drafting principles; early NC from graphic data bases 3-D Systems; better NC; more convenlence~s Bounded surfaces; better analysis packages; color; more conveniences 1 HOMOGENEOUS INTERACTIVE COORDINATE COMPUTER GRAPHICS (PROJECTIVE)
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From page 171... ...
They continue to be useful today for somewhat different reasons, as will be noted later. Solid Modeling Solid modeling is distinguished by the use of valid and unambiguous representations of solids.
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From page 172... ...
Extensive research has focused on developing fast algorithms and special computer hardware for generating displays from polygon lists, and some of this technology has been incorporated recently in industrial solid modeling systems to build approximate boundary representations. Sculptured Surfaces The sculptured-surfaces stream has the oldest roots, which lie in the mathematics HERBERT B
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From page 173... ...
is a major system-design challenge. An important current goal in solid modeling is installing "exact" sculptured-surface facilities to replace the planar-approximation methods used in some systems.
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From page 174... ...
are difficult to justify in most industrial installations, and thus vendors are using existing packages to provide numerical control and other services while awaiting more advanced modules that can exploit the power of solid modeling." There has been little overt change in the intervening years, and thus Figure 8, taken from the 1983 reference, depicts the current situation reasonably accurately: a few applications are handled automatically from the solid modeler, and the others through human-interactive programs devised mainly for wireframe modelers. The requisite wireframe representations are easy to derive automatically and download from the solid modeler; uploading from a wireframe modeler to a solid modeler requires considerable human assistance.
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From page 175... ...
The modeler also generates the AttrlbLlta n~fInitir~n 1 Solid modeling system with attribute facilltles | | Refinement . I ~~ FIGURE JO An automatic finite-element analysis system.
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From page 176... ...
176 1~1 me, ~ Current Updated Workpiece Cutter Workpiece Swept Region FIGURE 11 The basis of machining simulation. quadtree or octree approximations used in the meshing procedure, plus other aids for managing the process.
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From page 177... ...
Although at least one NC verifier program should be ready for industrial tests in a year or so, automatic NC program generators are farther away. High-level machining programming languages coupled to GO- RAPID *
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From page 178... ...
The advent of solid modeling forced serious thought to be given to the design of user interfaces, beginning about 1980, for HERBER T B VOELCKER several reasons.
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From page 180... ...
Thus far we have focused on graphic interfaces for human users, but, as we noted earlier, automata (programs for automatic finite-element analysis, machining simulation, and so forth) also use modeling systems; indeed, programs are likely to be the major users within a decade.
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From page 181... ...
As noted earlier, efforts to incorporate sculptured surfaces are encountering problems, but given the talent being focused on domain extensions these problems are likely to be solved in one way or another in the next several years. All systems, except for a few optimized for special applications, are slow because solid modeling is computationally intensive.
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From page 182... ...
manual process planning, machine-tool and robot programming, etc., was expensive unless production runs were long. Today, model-based automation of some of the upstream activities is imminent, as discussed earlier, and almost complete "vertical automation" of some important manufacturing processes seems attainable before the end of the century.
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From page 183... ...
But physical testing is expensive and time-consuming, and therefore computational analyses are being substituted as confidence in modern analytical methods grows. Contemporary modeling systems already support automatic mass-property calculation and soon will support automatic finite-element and more specialized kinematic and kinetic analysis procedures.
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From page 184... ...
If we associate the three terms with artifacts (call them "specifications" for present purposes) linked by transformations, we are led to the view shown in Figure 15, which extracts a portion of Figure 1: Form is induced from function through design, and fabrication is induced from form by manufacturing planning.
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From page 185... ...
MODELING IN THE DESIGN PROCESS inspection plans, inspection-machine programs, etc. We are learning how to represent these specifications formally and model their effects mathematically and computationally.
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From page 186... ...
with little or no loss in their ability to meet functional requirements. We believe that this conjecture warrants exper~°Interested readers should consult Samuel et al.
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From page 187... ...
PADL - 2.8 128 120 110 100 90 a' 80 Al o ED 53 E z E c' 70 60 50 40 30 1 _ 20 _ 10 o EXPLICITLY SPECIFIED GEOMETRIC DETAILS DEFINED AS AtrRIBUTES 1 1 1 2 _ 1 1 1 1 111 ,_~ PADL- 2.0 ~PADL- 1.6 -1.0 PADL- 1.4 100 90 80 70 _~ PADL- 1.0 ~S 60 `t ~D 50 ~ u) o ~D ~n ~_ ~ ~D q, 30 2n _ 10 1 1 1 1 1111 1 1111 1 1 11 1 1 11 1 1 o 15 20 25 30 40 50 70 80 100 150 200 300 400 500 650 3 4 5 6 7 8 910 Number of Primitive Instances FIGU~ 16 Some resulb from the Xerox part survey.
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From page 188... ...
(Or perhaps one should say that gauging and tolerancing practices have had a profound effect on manufacturing-planning and factory-organizing principles.) Figure 19 shows a simple limit-tolerancing specification in which C = A + B (Requicha, 1977~.
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From page 189... ...
models provide primitives for planning automata now wholly in the research stage that eventually should produce complete sets of plans and programs for making, inspecting, and assembling parts automatically. Now consider design: Mechanical-design automation and, more fundamentally, the understanding of mechanical design in a scientific sense are progressing slowly if at all.
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From page 191... ...
Figure 20e shows that versatile artisans were replaced with specialist builders of standard parts and specialist assemblers and that "gauge artisans" appeared as the precursors of manufacturing planners; products emerged through the intrinsically parallel, hierarchical tree of Figure 21b. From Figure 20e it is a relatively short step to the contemporary product cycle shown earlier in Figure 1.
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From page 192... ...
Flnite-element 1940 MMC Computer 1944 True Computer graphics poalUon sImulatlon 5O11d 1973 ANSI Y14.5 Manufacturlng Technology l Free cutters Gulded cutters Water-powered cutters Coupled-motlon cutters Steam-powored— cutters I Preclelon metrology 1000 BC O BC 1000 AD 1400 AD 1600 AD 1700 AD Mechanl2atlon 1800 AD Interchangeabillty Mechanically programed cuttem Eloc~lflcadon Group technology NC and robot programing] languages Electronic control NC machine tools Industrlal robots FIGURE 22 Historical evolution of component technologies in the product cycle.
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From page 193... ...
Drafting began to be "computerized" in the late 1950s with the advent of computer graphics, and now drafting is being replaced by solid modeling as the primary medium for design specification. The evolution of tolerancing practice warrants special discussion.
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From page 194... ...
FUGUE 23 A twelfth-century drawing of an undershot waterwheel. Drawing is from "Hortus-Deliciarum," a manuscript containing drawings compiled by the Abbess Herrad of Landsperg in about 1160.
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From page 195... ...
The 1920-vintage drawing of Figure 25a contains no explicit tolerances but specifies manufacturing processes (bore) for two holes and a precision for one hole through a functional requirement running-fit (R.F.)
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From page 196... ...
Alas, all of this work on tolerancing lacks mathematical foundations and thus, in the current era of informationally complete solid modeling, tolerancing stands as an open problem in engineering science. Design Analysis Tools The evolution of design analysis tools followed closely developments in mathematics, physical science, engineering science, and now computer science.
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From page 197... ...
Today the relationship between gauges and tolerances is clear: Gauges are built to reflect tolerances given in design specifications, and hence tolerances implicitly specify inspection procedures. Thus, we have, for example, "Principle 5: The gage designer should not have to make arbitrary decisions regarding gage element size or location, since a complete product specification dictates these design and interchangeability criteria.
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From page 198... ...
1987. Automatic finite element mesh generation and self-adaptive incremental analysis through solid modeling.
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From page 199... ...
Pp. 93-97 in Proceedings of the Thirteenth NSF Grantees Conference on Production Research and Technology.
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