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Chapter 1 Introduction to Computer Aided Design CHAPTER 1 INTRODUCTION TO COMPUTER AIDED DESIGN Computer Aided Design, which is currently known as CAD, is in fact the integration of computer graphics, geometric modeling, and design. Computer graphics provides the visualization techniques. Geometric modeling provides the platform for modeling purposes, whilst the design is a process to come up with certain design. CAD is applicable to many areas, however the scope of CAD in this book is focused on the application to mechanical engineering. 1.1 HISTORY OF CAD The invention of SKETCHPAD in 1962 remarks the birth of CAD. Before the invention of SKETCHPAD, computer has been used for numerical simulation using keyboard and punch card. With the invention of SKETCHPAD by Ivan Sutherland in MIT Lincoln Laboratory, for the first time human can give command to computer using light pen. In fact, the graphical user interface using light pen was firstly done with the invention of SKETCHPAD. Push button technique is used to give command to the computer and the geometrical input can be done using light pen. The invention of SKETCHPAD was in fact contributed to many new inventions, constraint based drawing, 3D solid model with the ability to hide the hidden edges, and even hierarchical data structure that have been implemented in object oriented programming. Throughout the 1960s, companies were interested to develop the CAD software for their own companies such as CADD by Mc-Donnell Douglas, CADAM 1-1 by Lockheed etc. In Europe, researchers were focused on the development of 3D complex curve and surface formation, such development of Bezier curve based on the inventor name at Renault become the breakthrough in the development of algorithm for complex curve. At the late 1960, the development of the commercialized CAD packages becomes the interest. Avions Marcel Dassault, a French aerospace company in 1975, purchased a source-code license of CADAM from Lockheed to develop 3D CAD software program that was named as CATIA (Computer Aided Three Dimensional Interactive Application). In 1970s, the development of solid modeling becomes the research interest. The introduction of Constructive Solid Geometry (CSG) and Boundary Representation (BReps) were the core for PADL and BUILD solid modeler respectively. Later in 1980s, most commercial CAD packages started to use these modelers for their solid kernel. Then the development of CAD packages relies on the development of the platform; mainframe (late 1970s), Unix Workstation (first half of 1980), and Windows NT (early 1990s). With the invention of Unix system, the parametric modeling becomes reality as its first concept introduced by SKECTCHPAD. Amongst the leading vendors are Computervision (CADDS), Intergraph (IGDS and InterAct), McDonnell-Douglas (Unigraphics), GE/CALMA, IBM/Dassault (CADAM and CATIA), SDRC (I-DEAS) and Parametric Technology (Pro/Engineer). These vendors were supported by B-Reps solid kernel developer such as Spatial Technology (ACIS), EDS-Unigraphics (Parasolid) and Ricoh (Designbase). 1-2 When Microsoft developed Windows NT and Intel developed Pentium processor with 32 bits capability, PC has now the capability to run parametric solid modeler and this cause the CAD industry to be totally revolutionized. In 1993, Jon Hirschtick developed SolidWorks based on windows platform with the aim to make 3D CAD technology more accessible. Then 1995, SolidEdge become the competitor to SolidWork and 1999 CATIA is fully implemented using Windows NT based. The trend of parametric modelling has extended to include the usage of tool to keep track the data related to particular model as it is called as Product Data Management (PDM). The PDM will include technical specifications of the product, specifications for manufacture and development, and the types of materials that will be required to produce goods. In the early 2000’s, full-fledged CAD packages with the integration of design process is implemented. Start with concept, and finally engineering analysis and manufacturing have been integrated and this reduces the time taken for design. Then, Product Lifecycle Management (PLM) is integrated to the CAD packages to manage the entire lifecycle of a product efficiently and cost-effectively, from ideation, design and manufacture, through service and disposal. Currently, CAD packages can be divided into three categories; upper range price packages (CATIA, Unigraphics, etc), mid range price packages (Solidworks, Inventor, etc) and freeware CAD packages (CadStd, CADVANNCE, etc). 1-3 1.2 CAD IN DESIGN PROCESS When talking about design, it is eventually talking about design process. Figure 1.1 shows the design process. Design starts with problem or need. When the need has been defined, a research background is carried out. The objective of the research background is to have in depth understanding related to the needs. The research background should come out with product design specification (PDS). PDS is the boundary of the design, all the concepts that will be developed in the next step must fulfill all the statements in the PDS. When PDS is developed, now it is the time to develop the solutions or most people will say design concepts. Important to mention here that the more solutions are, the better will be the final design. The key of producing a good solution is to have larger number of solutions to be considered. Then the the final appropriate design is selected. This final design can one of the designs or a new design resulting from the combination of two or more design. A good method to select final design should allow the design to be combined with other design to give more alternative designs. After the final design is developed, then detail design is carried out prior the development of the prototype. At this stage, a number of tools can be applied such as Design for Manufacturing and Assembly (DFMA), Failure Mode Effect Analysis (FMEA), or Value Engineering. Engineering analysis on the part of the design is also done at this stage. This stage will ensure every consideration has been taken into account. Then, the design is built and a number of testing is carried to ensure the final product serves its initial needs. Then, the engineering drawing, is produced as the final documentation to allow the design to be fabricated and manufactured. 1-4 Figure 1.1 Design Process 1.2.1 APPLICATIONS OF CAD Following will discuss the engineering applications of the CAD. 1.2.1 Modeling Most users use CAD packages to model parts and even the whole assembly of the design. Currently, parametric modeling becomes the modeling method adopted by most CAD packages. Even the drafting software has started to introduce parametric modeling, such as it has been introduced in AutoCAD 2012. The modeling process starts with part model, and then a number of parts will be assembled to produce assembly model. Based on the part and assembled part, a complete documentation include detail and production drawing can be generated. Since all the files, part, assembly and drawing files, are linked to each other, any changes that is carried out on one of the files will cause similar alteration to be done on other files. To link between part and documentation, concept of work space and paper space is well adopted. The difference between the CAD packages, the implementation 1-5 of the concept. AutoCAD implements the concept in a single file, whilst most of the other CAD packages uses different file format in the implementation of the concept. 1.2.2 Design Review and Evaluation Each model comprises the geometrical properties and attributes. Geometrical properties will ensure the spatial requirement for the model, whilst attributes will keep the properties of the model such as material, surface texture, or color. Both the geometrical properties and attributes of the model are the properties of the model and these properties are retrievable. Retrievable properties will allow the user to review and evaluate the design. For instance, mass and centroid of the parts are amongst the essential information to analyze the part. Even some of the modeling techniques are adopted from specific applications such as sheet metal, weldment, and mold. As such, when the model is created using sheet metal method, the model should be created based on base flange, then process such as folding or bending can be applied to create final part. In addition to the method of modeling based on the applications, models can also be reviewed whether it can be produced using the intended application. As such, CAD packages will indicate whether the specific model on the parts can be produced by certain machining process. Most of CAD packages provides features for user to review and evaluate the the part as well as assembled model. Interference checking is used to check whether the part will obstruct other part or will be obstructed by other parts. 1.2.3 Full fledged design platform 1-6 When PDM and PLM are integrated to the model, CAD packages become the tool for full-fledged design platform. It commences from the modeling and follows with the design review and evaluation of the part and assembled model. Finally engineering analysis on design is carried out to ensure reliability of the design. Currently, motion analysis and finite element analysis becomes common features in most of CAD packages. Motion analysis will focus on the kinematics and dynamic effect of the parts when the assembly model in operation. Most of the application is moving part such as mechanism, piston etc. FEA will analyze the part when the load is applied to part during operation. Hence, all the related parameters on the design can be determined and geometrical properties of the design can be finalized. Nowadays, the modeling techniques to build the part are already established. Therefore, vendors are now developed very specific engineering applications for the CAD packages, as such human activity analysis becomes one of the applications for CATIA software.
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