MEC435 Computer-Aided Design Chapter 1 PDF

1 Chapter 1 : Introduction Understand the various spheres of manufacturing activity where computers are used What is meant by product cycle with the differences between the conventional and computer based manufacturing systems Definitions of various computer based applications Computer Aided Des...

1 Chapter 1 : Introduction Understand the various spheres of manufacturing activity where computers are used What is meant by product cycle with the differences between the conventional and computer based manufacturing systems Definitions of various computer based applications Computer Aided Design and its applications Various types of manufacturing organizations Computer Aided Manufacturing and its application Meaning of Computer Integrated Manufacturing 2  Computer-Aided Environment Nowadays, computers become very crucial to daily life CAD/CAM are widely used in engineering practice:  Drafting  Design  Simulation  Analysis  Manufacturing 3 4 Computer-Aided Environment Evolution 5 The role of computer in manufacturing may be broadly classified into two groups: 1. Computer monitoring and control of the manufacturing process. 2. Manufacturing support applications, which deal essentially with the preparations for actual manufacturing and post- manufacture operations. 6 CAD – computer aided design. CADD - computer aided design and drafting. CAE - computer aided engineering. CAM - computer aided manufacturing. CAPP - computer aided process planning. CATD - computer aided tool design. CAP - computer aided planning. 7 1. Geometric modeling 2. Computer graphics 3. Design application 4. Manufacturing Applications 8 COMPUTER AIDED ENVIRONMENT IN MANUFACTURING 9  COMPUTER AIDED DESIGN Design is an activity which needs to be well organized and take into account all influences that are likely to be responsible for the success of the product under development. The complexity of the design process increases with the number and diversity of components present in the final part. 10  PRODUCT ENGINEERING Product functions Strength Product Specifications Kinematics Conceptual design Dynamics Ergonomics and Aesthetics Heat Standards Flow Detailed Design Design for Prototype development Manufacture Testing Design for Assembly Simulation Drafting Analysis 11 12 Is faster and more accurate than conventional methods. A very easy task. Editing Never have to repeat the design or drawing of any component. Accurately calculate the various geometric properties Use of standard components (part libraries) 3D (3 dimensional) visualization capabilities 13  COMPUTER AIDED MANUFACTURING 1. Mass production ─ large lots e.g. automobiles 2. Batch production ─ medium lot sizes e.g. industrial machines, aircrafts, etc. 3. Job shop production ─ small lots or one off, e.g. proto-types, aircrafts, etc. 14 Process planning Inspection (CMM) programs Production Organization Process sheets Bill of Materials Route sheets Material Requirement Tooling Production Planning Cutting tools Shop Floor Control Jigs and Fixtures Plant Simulation Dies and Moulds Marketing and Distribution Manufacturing Information Generation Packaging CNC Part programs Distribution Marketing 15 Robot Programs Greater design freedom Increased productivity Greater operating flexibility Shorter lead time Improved reliability Reduced maintenance Reduced scrap and rework Better management control 16  The use of information technology for supporting engineers in tasks such as analysis, simulation, design, manufacture, planning, diagnosis and repair.  CAE tools are being used, for example, to analyze the robustness and performance of components and assemblies including simulation, validation and optimization of products and manufacturing tools. 17 Stress analysis on components and assemblies using FEA (Finite Element Analysis) Thermal and fluid flow analysis - Computational fluid dynamics (CFD) Kinematics Mechanical event simulation (MES) Analysis tools for process simulation for operations such as casting, molding, and die press forming. Optimization of the product or process. 18 Reduce product development cost and time Precise analysis and simulations Early prediction of results Design verification through simulation without having to use physical prototype testing Minimize the time for optimizing products Parallel task can be done along the design stages 19 Example of Assembly Drawing 20 Engineering activities 21 Users of Computers Graphic 22 Mechanical Design 23 Architectural Design 24 Electronic Circuit Design 25  2D Drafting tools  Earliest CAD systems.  Replace traditional design on drawing board.  Engineering drawings using simple geometric and annotation entities: lines, circles, arcs, curves and points; text, dimensions, tolerances, and cross hatching. 26  2D Drafting tools  Provide significant productivity improvements over drawing board i.e. faster time and can easily modify old drawings.  Not a really useful design tool. Only used for documentation of finished design.  Limitation: Difficult to represent complex 3D shapes. 27  3D Wireframe  3D extension of 2D drafting  Allow designer to represent design in 3-dimensions, improving visualization.  Allow user to view design from any viewpoint, and to rotate the model in real time to visualize any complex shape. 28  3D Wireframe  Can be created using only lines, circles, arcs, curves and points positioned in 3D space to represent the edges and vertices of the parts.  Limitations: - no understanding of object properties - cannot represent the shape of the object faces between edges - incomplete and ambiguous - unable to provide area or volume information  Data is of only limited use for manufacturing. 29  Surface Modelling  Completely defines external shape of an object, faces, edges and vertices.  Each surface represented by a continuous mathematical function.  Created by fitting smooth skin through a wireframe or sweeping a wireframe curve through 3D space. 30  Surface Modelling  Created using many surface patches to define outside shape.  Modelling complex freeform shapes e.g. car body panels, aircraft skins, and plastic injection moulded products  Surface models provide excellent visualization of the geometry.  Surface data from CAD is routinely used to generate tools paths to drive CNC machine tools  Limitations: - Only defines external shapes but not the internal shapes or topology - unable to specify surface connectivity between surfaces (assumes rigid connections) 31  Solid Modelling  The most complete and accurate CAD representation.  Represents external and internal structure of the part.  Generate cross-section, calculate weight, centre of gravity and moments of inertia.  Created by combining simple solid shapes to form more complicated parts.  Basic building blocks are simple solid shapes created using primitive parts from library or extruded/revolved from 2D wireframe. 32  Solid Modelling  Extrusion  Solid Primitives 33  Revolve  Solid Modelling  Boolean operation: joint, subtract and intersect solid parts  Solid models of complex freeform shapes are created using a combination of solid and surface.  Solid modellers can directly be used for manufacturing, finite element and dynamic analyses.  Disadvantage: can be extremely difficult to define (and modify) part geometry. 34 Solid Modelling 35  Computer Aided Manufacture (CAM) The link between a design, and the manufacture of the finished product. Traditional manufacturing: design intent is communicated to manufacturing using engineering drawings e.g. tolerances, surface finish, materials, standard parts. manufacturing process plan developed based on drawings program machine tools to manufacture the part or mold. 36  Computer Aided Manufacture (CAM) In an integrated CAD/CAM:  CAD geometry is transferred to a CAM system using data exchange file and used directly for manufacturing planning.  The tool paths for computer numerically controlled (CNC) machine tools to machine parts can be generated from CAD 37  Computer Aided Engineering (CAE) Kinematics:  analyse movement of mechanism from CAD assembly model.  joints are applied between different parts in the assembly.  can be used to evaluate motion of the mechanism and investigate potential locks or clashes. 38  Computer Aided Engineering (CAE) Finite element Analysis (FEA): A powerful and popular technique developed for numerical solution of complex problems in engineering mechanics and perform stress analysis to predict structural strength of a component STEPS: 1.subdivide the the geometry into small regular finite elements (finite element mesh) 2.apply loads and boundary conditions 3.perform analysis 4.results interpretation 39 CAE - FEA 40 41  CAE  Integrated CAD/CAM/CAE  Can aid product introduction process  Reducing cost  Cutting lead times Objective – to create the product geometry once and reuse it many times Traditional product development – sequential process (design, manufacturing, stress office, logistics etc. 42  Engineering Approach Sequential approach  Allows company to keep tight control over product development  Disadvantage- disciplines later in design process do not see the design until it is well developed, when potential problem may be costly to resolve. Concurrent Engineering and Integrated Product Development Alternative approach to product development where a team made up from specialist disciplines are assigned to a product and have inputs to design from start of the design process. 43 Product development process 44 Linear Engineering Design 45  Model Centered Engineering Design Sharing the 3-D CAD database 46  Model Centered Engineering Design  Sharing of 3-D CAD database  Separation of creative design process and production process no longer necessary.  Non-linear team approach to design that brings together input, processes and output  May result in a better, high quality product, more satisfied customers, lesser manufacturing problems, and shorter time between initial design and final production. 47