ComputerAided_Design_Engineering_amp_Manufactur.pdf

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esearchers have developed a numerically controlled clamping system integrated with a horizontal milling center for machining of workpieces. The system positions supports, locators, and clamps on servocontrolled turntables, providing a variety of support configurations. The clamping is performed by repositionable hydraulic cylinders. The system can be used for fixturing workpieces such as castings for machining purposes. Phase-Change Fixtures Phase-change fixtures can be divided into two categories: (1) fixtures incorporating materials which undergo an authentic phase change, and (2) fixtures incorporating materials which undergo a pseudo phase change. There have been numerous reports on this class of fixtures, which utilizes materials that undergo a phase change between liquid and solid states. 3,18 Authentic phase-change fixtures are classified according to how the bed material undergoes phase change, which may be temperature induced, electrically induced, or a combination of both. An example of authentic phase-change fixtures is the encapsulation which traditionally has been employed for special purpose machining, such as the milling of turbine blades. The pseudo phase-change fixtures utilize the two-phase nature of materials that undergo a phase change between liquid and solid states. An example of this approach is the fluidized-bed fixture depicted in Figure 3.4. The fluidized-bed fixture consists of a container which retains the bed materials. 7 The container has a porous base through which air passes at a controlled rate. Under these conditions the bed materials behave as fluid into which the workpiece is partially immersed. When the air supply is cut off, the bed materials fall onto the base due to gravitational loading, and are compacted to form a solid mass and thus secure the workpiece. The removal of the workpiece from the fixture is achieved by switching on the air supply to create fluid phase again. The main advantage of this approach is the flexibility of accommodating workpieces of various geometrical configurations by exploiting the fundamental properties of fluids, which are the ultimate conformable surface. However, the approach may generally be employed for low force and torque applications. Furthermore, the workpieces must generally be of prismatic shapes providing surfaces for frictional holding capacity. They must also be placed within the container using an accurate device and be held in the desired position and orientation until the vacuum compaction process is complete. Research efforts have focused on modeling the torsional displacement. 18 Studies have also been carried out on the effect of the workpiece and bed geometries on workpiece lateral displacement. 19 FIGURE 3.4 © 2001 by CRC Press LLC Fluidized bed fixture.
Other Fixturing Techniques There are several other techniques proposed for workholding systems. Examples of these include the multileaf vice, petal collet, and stackable washer fixtures. 1 These have received less attention due to the lack of robustness and the small range of workpieces which they can accommodate. Generally, these techniques do not provide the flexibility, accuracy, and integration capability required in a world-class manufacturing environment. The most suitable approaches for flexible and computer-integrated manufacturing environments are deemed to be modular and reconfigurable fixturing, together with programmable clamps. 3.4 Reconfigurable Fixture Modules In this chapter, attention is mainly focused on reconfigurable workholding. However, most of the planning and integration techniques can readily be applied to other fixturing approaches such as modular or programmable. In fact, for any fixturing system to be acceptable in a manufacturing environment, it must be capable of integration with the CAD/CAM systems and also automation devices such as robots and machine tools. 20 The reconfigurable workholding approach employs a number of adjustable fixture modules to locate and constrain the workpiece in the desired location. For the purpose of establishing the planning and analysis strategies, four types of fixture modules have been developed. 21 These modules include vertical support, horizontal support, horizontal clamp, and vertical clamp, as shown in Figure 3.5. These modules are mainly single axis and have been developed for fixturing workpieces for robotic assembly; however, the concept can be extended for the design of multi-axis modules for panel type workpieces (see Figure 3.6). The fixture setup procedure involves a robot retrieving a number of vertical supports from the fixture magazine and placing these on a fixture platform such as an electromagnetic chuck. The robot proceeds to adjust the height of these modules, which support the workpiece at the required height. The electromagnetic chuck is used to secure the fixture modules once they are placed at the assembly station before any adjustments are to take place. Next, a number of horizontal supports are placed on the chuck where they would be in contact with the workpiece reference faces or locating tabs. The robot then places the workpiece within this fixture layout (referred to as the “initial” fixture layout); a number of horizontal clamps and vertical clamps are then placed on the chuck. The robot adjusts the height of these modules and activates the clamping mechanisms on them, and thereby fixturing the workpiece into the desired position and orientation (pose). The robot may now perform the subsequent assembly operations on the workpiece. It must be noted that other fixture modules have also been developed by other researchers for operations such as assembly and drilling. 22–23 3.5 Fixture Task Planning and Analysis An important objective of any flexible workholding system is to provide for rapid design of fixture configuration and analysis, and automated generation of fixture setup programs. 13,17,24 The fixture planning and analysis system must reside within the overall process planning of the manufacturing system. An approach is now presented describing an interactive computer-aided fixture planning and analysis (CAFPA) system for reconfigurable fixtures. In the proposed approach, the CAFPA consists of six submodules comprising pre-processor, planning, analysis, verification, interference checking, and postprocessor (Figure 3.7). The following sections describe the individual submodules and their functionalities. Pre-Processor Phase The first operation in the pre-processor segment is to access the CAD data base and retrieve the model data of the workpiece. The boundary representation (B-Rep) scheme provides an excellent structure for manipulation of appropriate data and has a format as shown in Figure 3.8. There are several CAD systems © 2001 by CRC Press LLC
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COMPUTER-AIDED DESIGN, ENGINEERING,
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Library of Congress Cataloging-in-P
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Editor Cornelius T. Leondes, B.S.,
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Chapter 1 Chapter 2 Chapter 3 Chapt
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the implementation of the IPD syste
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In our IPD system implementations,
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2. Specification of analysis-specif
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FIGURE 1.2 base or the design insta
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FIGURE 1.4 System architecture of t
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of a beam is considered for FEA. Th
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FIGURE 1.7 through the control expe
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2. machining facility (e.g., gang m
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from the FBDS. The user also specif
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Depending on the type of feature to
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TABLE 1.6 Tolerance synthesis is de
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FIGURE 1.12 Display of the NC tool
Page 33 and 34: component geometric entities and va
Page 35 and 36: FIGURE 1.14 The system architecture
Page 37 and 38: TABLE 1.10 User Input for the Toler
Page 39 and 40: TABLE 1.11 Tolerance Specifications
Page 41 and 42: 7. Z. Young and I. R. Groose. A rul
Page 43 and 44: FIGURE 2.1 Tool paths generated for
Page 45 and 46: FIGURE 2.2 sented by instances of f
Page 47 and 48: TABLE 2.1 A CAD-Generated Hole Conf
Page 49 and 50: FIGURE 2.6 mounted on the rotary ta
Page 51 and 52: FIGURE 2.8 fixture for the machinin
Page 53 and 54: FIGURE 2.10 or best-fit, or the cur
Page 55 and 56: FIGURE 2.11 Linear approximation of
Page 57 and 58: FIGURE 2.13 Circular approximation
Page 59 and 60: FIGURE 2.14(b) Circular approximati
Page 61 and 62: FIGURE 2.16 Types of biarcs. FIGURE
Page 63 and 64: FIGURE 2.18 Approximation of scanne
Page 65 and 66: FIGURE 2.20 A touch trigger probe c
Page 67 and 68: TABLE 2.4 Substitute Elements in CM
Page 69 and 70: FIGURE 2.21 CMM planning requiremen
Page 71 and 72: Product Model Representation for Co
Page 73 and 74: © 2001 by CRC Press LLC TABLE 2.5
Page 75 and 76: TABLE 2.7 Partial Listing of Dimens
Page 77 and 78: 24. Makinouchi, S., Okamoto, M., an
Page 79 and 80: Bijan Shirinzadeh Monash University
Page 81 and 82: FIGURE 3.1 Trends in flexible manuf
Page 83: FIGURE 3.3 and constrain different
Page 87 and 88: FIGURE 3.6 contact point. The geome
Page 89 and 90: FIGURE 3.8 The vertical support fix
Page 91 and 92: and moments about the contact point
Page 93 and 94: een identified, the normals are use
Page 95 and 96: one of choosing the variables: such
Page 97 and 98: Fixture Module Location An importan
Page 99 and 100: FIGURE 3.15 Illustration of functio
Page 101 and 102: FIGURE 3.18 Minimum separation test
Page 103 and 104: direction) the face, respectively.
Page 105 and 106: FIGURE 3.21 Software structure for
Page 107 and 108: 3.8 Conclusion A reconfigurable fix
Page 109 and 110: Heui Jae Pahk Seoul National Univer
Page 111 and 112: FIGURE 4.1(b) Conceptual framework
Page 113 and 114: 4.3 Measurement Points Sampling and
Page 115 and 116: Surface S2 Measurement Path FIGURE
Page 117 and 118: FIGURE 4.4 Rough phase alignment ba
Page 119 and 120: deviation between the nominal CAD d
Page 121 and 122: FIGURE 4.6(a) Sum of squares distan
Page 123 and 124: FIGURE 4.7(c) Trailing edge. (c) th
Page 125 and 126: FIGURE 4.8(a) Profile tolerance of
Page 127 and 128: The calculated minimum form error i
Page 129 and 130: FIGURE 4.11(a) A typical mold havin
Page 131 and 132: FIGURE 4.11(d) Inspection results f
Page 133 and 134: FIGURE 4.12(c) Maximum deviation (p
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5.1 Introduction Developments in th
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process plan for a part (Figure 5.3
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FIGURE 5.5 leading to the developme
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the previously stored process plan
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FIGURE 5.7 Techniques of defining a
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Feature Recognition and Extraction
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in relation to another feature (e.g
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FIGURE 5.9 Framework for building a
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FIGURE 5.10 Process plan content.
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FIGURE 5.12 Schematic sketch of the
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Several techniques of defining a fe
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TABLE 5.1 Data Structure for Repres
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FIGURE 5.16 Classification of the t
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system to ensure that the part bein
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FIGURE 5.19 Graphical model of the
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TABLE 5.4 Data Structure for Repres
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FIGURE 5.20 Mapping between machini
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algorithms. (Some details of the pr
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FIGURE 5.24 An example rotational p
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FIGURE 5.26 Down_face-turn-up_face
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FIGURE 5.27 Procedure for machine t
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FIGURE 5.28 Determining the number
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DL is needed to be set only if the
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FIGURE 5.31 Operation sequencing co
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Cutting Tool Selection Selection of
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1. A tool is searched for in the da
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FIGURE 5.32 Inputs to optimization
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When these values are substituted,
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Usually, maximum and minimum speed
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FIGURE 5.33 Solution methodology.
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TABLE 5.6 Process Plan Internal Rep
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In a strict theoretical perspective
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18. Domazet, D. S. and Lu, S. C. Y,
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63. Prasad, A. V. S. R. K., Rao, P.
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CAD systems. The sample consists of
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learn to master the new system. An
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Although researchers appear to agre
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Link and Zmud28 found that organic
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Informal Training Informal CAD trai
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informal training programs, felt th
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6. C. A. Beatty, Tall Tales and Rea
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A.Y.C. Nee National University of S
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FIGURE 7.1 Planning, design, and ma
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A metal stamping can have the follo
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FIGURE 7.3 Strips used to notch out
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A Skeletal Approach for the Recogni
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These findings can be used to devel
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Semi-Direct Piloting In cases where
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a larger value, the die operations
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FIGURE 7.9 Symbolic relationship be
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FIGURE 7.11 The shape of the envelo
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TABLE 7.1 Schema for the Generation
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strong reasons to support a move to
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FIGURE 7.16 3-D CAD model of a part
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References Cheok, B.T. et al. (1994
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include the once forbidden generati
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A temporal matrix (T-Matrix) is pro
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FIGURE 8.1 A basic process. (From R
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FIGURE 8.4(a) Generate a new IG usi
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Note if the pair of nodes are both
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TABLE 8.1 Summary of the Rules Cond
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The correctness of these rules is e
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needs to show that after each full
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ule is violated, a warning should b
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Π1 Π3 Π4 FIGURE 8.8(a) After add
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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A ik � ‘U’ and is in a cycle
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FIGURE 8.12(a) Add [p2 t7 p7 t8 p4]
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FIGURE 8.12(c) Add a token to p8 vi
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FIGURE 8.12(e) Add [p8 t9 p14 t10 p
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FIGURE 8.13 An example of rule TT.0
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FIGURE 8.14 A GPN model of a machin
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FIGURE 8.15(b) The first exclusive
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FIGURE 8.15(d) The last exclusive T
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FIGURE 8.15(f) After entering the a
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FIGURE 8.15(h) Completion of Compon
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FIGURE 8.15(j) Two PP-generations:
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FIGURE 8.15(l) The last exclusive T
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t1 t5 p1 p5 t6 (a) t2 t3 t4 2 2 p2
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FIGURE 8.17 An example of partial f
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Theorem 10: If pi → pk in a synth
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Note that control transitions are o
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t j than the lower at , it indicate
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• Programming logic and VLSI arra
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7. Chao, D. Y. and D. T. Wang, Appl
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53. Villaroel, J. L., J. Martinez,
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q u : the numerator of the least ra
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geometric modeling, engineering ana
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In dimension driven or parametric d
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FIGURE 9.3 configuration of bodies
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FIGURE 9.6 FIGURE 9.7 Geometric Int
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FIGURE 9.8 Intersection of degrees
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will introduce a way to propagate p
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Completeness of Dimensions Complete
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FIGURE 9.12 3-D constraints. © 200
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The distance constraint from pt �
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therefore: Now merge the lists and
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Quantity analysis methods have the
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y a revolute joint. By selecting al
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