MIT2_007s09_lec05

MIT2_007s09_lec05 - MIT OpenCourseWare http://ocw.mit.edu...

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.007 Design and Manufacturing I Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms. Introduction to CAD - Basic parts 1 2.007 Spring 2009 Prof. David Gossard Product Development Cycle Costs Cost Design Released For production Mfg docs produced: purchase specs, assy instructions, design drawings for tool/fixtures, instruction manuals, etc. Hard tooling produced: dies, molds, fixtures, etc. Manufacturing, Assembly, Testing Design Ramifications: Early decisions have large leverage Late changes are very costly Time Motivation Computer-based models permit designers to better understand how their products will look and function before physical models are made Make better early decisions Eliminate late changes (Enables you to work on your machine even when the shop is closed...) History of New CAD/CAM Functionality 1960's - Design of complex surfaces, programming of NC machine tools 1970's - Automation of Drawings 1980's Solids 1990's - Parametric Feature-based Solids Key Concept "Parametric", "Associativity" Changes in dimensions propagate between parts, drawings, assemblies Movie Philosophy of CAD Lectures Demonstrate small fraction of available functionality Ideally the most useful fraction... Accelerate your learning process Get you up-to-speed as quickly as possible... Promote self-discovery Motivate you to learn more on your own... Demonstrate use as a design tool Not (just) a detailing/documentation tool Reminder To those who have "seen it before": bear with us help those who haven't Features Sketched 2D geometry (sketch) swept along a 3D path Applied Attached to existing geometry Sketched Feature Types Extrude Constant cross-section along a straight line Revolve Constant cross-section around an axis of revolution Sweep Constant cross-section along a space curve Loft Multiple cross-sections along a space curve Sketched Features May add or subtract material ! Sketched Extrude Revolve Sweep Loft (add) boss/base boss/base boss/base boss/base (subtract) cut Hole Wizard cut cut Require cut more complex mfg methods Applied Features Attached to existing geometry e.g. edges, faces Types Fillet Pattern Shell Draft Rib Injection-molded parts The Drill... Drill... Series of demonstrations/exercises Demonstration: You watch it done Exercise: You do it Demonstrations / Exercises Screen/window layout View control Make a simple part Dimensions & sketch relations Linkages & Blocks Symmetry Make a simple part Dimensions & Sketch Relations Linkages & Blocks Symmetry Case Study Ramp Drop-down ramp (see geometry) Companion robot drives onto ramp Companion robot (150 lb) is lifted off the ground Powered by pneumatic cylinder(s) Geometry Virtual Work Principle: F1 dx1 = F2 dx2 dx2 F2 F1 dx1 END ...
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