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Computer-aided design (CAD) is the technology of computer systems to assist in the drawing, modification, analysis, and optimization of a design. Thus, any computer programs that include computer graphics and application program with engineering function in the design process is classify as CAD software. In other words, CAD tools can vary from geometric tools for manipulating shapes at one extreme, to customized application programs, such as those for analysis and optimization, at the other extreme [Zeid 1991]. Between these two extremes, typical tools currently available include tolerance analysis, mass property calculations, and finite element modelling and visualization of the analysis results. The basic role of CAD is to define the geometry of design for an example such as a mechanical parts, architectural structure, electronic circuit, and so on. This is because the geometry of the design is essential to all the subsequent activities in the product cycle. The greatest benefits of CAD is can save considerable time. CAD also can reduce the errors caused by the geometry of the design. There are many CAD software package available as Rhinoceros 3D, SketchUp, SolidWorks, AutoCAD, CATIA and the other few software.
2.1 Computer-Aided Manufacturing (CAM).
Computer-aided manufacturing (CAM) generally allow the user to plan and control manufacturing operations through computer interface. One of the most mature areas of CAM is numerical control (NC). The machine tool is control by using programmed instructions. For an example to control grinds, cuts, mills, punches, bends, or turns raw into a finished part. The computer can now generate a considerable amount of NC instructions based on geometric data from CAD database plus additional information supplied by the operator. Another significant CAM function is the programming of robots. These robots may perform individual task such as welding or assembly or others.
2.2 Computer-Aided Engineering (CAE)
Computerââ‚¬"aided engineering (CAE) commonly applies on a computer system in engineering applications. CAD can be concerned as a subset of CAE. CAE allow the designer to simulate and analyze the design. The software fits into two categories: engineering based and non-engineering specific. The engineering based software for mechanical engineering applications is the software with a CAD system and probably the most widely used method of computer analysis in engineering is the finite element Method (FEM). This approach is used to determine stress, deflection, vibration, and heat transfer (e.g., ANSYS and MSC/NASTRAN). The non-engineering specific computer aided applications contain software for word processing and mathematical solvers (e.g., Mathematica, MathCAD and Matlab).
SolidWorks is the CAD software with three-dimensional (3D) design. The software can run on Microsoft Windows. Dassault SystÃÂ¨mes, S. A. (Velizy, France) is a developer of SolidWorks software. SolidWorks is currently one of a most popular 3D mechanical CAD (MCAD) product on the market.
2.4.1 SolidWorks Approach
SolidWorks is one of the software of a parasolid-based solid modeller and using a parametric feature based approach to create a models and assemblies. Parameters are refers to determine the value of the shape or geometry of the model or assembly. Parameter can be geometric parameters, such as parallel, horizontal or vertical, or numeric parameters, such as circle diameter or line length. Numeric parameters can be refers with each other through the relation, that allow them to capture design intent. Design intent is the part of the creator wants to changes and updates a model. SolidWorks can recognize the design intent and keep all the shape that the user wants. SolidWorks have the shapes and operation to construct the part of a model. A 2D or 3D sketch of shapes is normally begins with shaped-based features. The shapes are then extrude, cuts, or add from the part of a model. Operation-based features is not a sketch-based but it have include features such applying draft to the face of a part. Creating a model in SolidWorks usually begin with a 2D sketch or 3D sketch. The sketches are includes with geometry such as points, lines and others geometry. The parametric on SolidWorks is a dimensions and relations that drive the geometry of the model. SolidWorks have the ability that allows the user to roll back through the history and changes the part of design. SolidWorks also contains additional advanced mating features. The model assemblies can accurately reproduce the rotational movement like an actual component.
2.4.2 SolidWorks Add-in Products.
The main product of SolidWorks contains tools for 3D modelling and freeform surfacing. SolidWorks have capabilities to import and read the numerous file types from the others 2D and 3D CAD programs. An application-programming interface (API) has been included in SolidWorks for custom programming in C#, C++, and Visual Basic (VB). API is a computer program that uses a set of function, procedures, and method or service providers to support the user command. Macros and third party development has been combining in SolidWorks application-programming interface (API). SolidWorks also allows for the integration of the third-party modules design.
2.4.3 Macro in SolidWorks
SolidWorks macro is a shortcut task to perform repeatedly in SolidWorks 3D CAD software. Macro in SolidWorks is a series of command system and actions that and can be stored by safe the macro file. Macro can run within SolidWorks whenever users need to perform the task. SolidWorks allow user to record or build a macro and then play the macro with automatic repeat the series of commands or actions.
2.5 Researcher study
Elasis and FIAT Auto started to test parametric and associative (P/A) techniques since 6 years ago. Fiat is one of the first automotive companies that have test P/A features in development of a new car. Car body design is very critical and time-consuming activity for design modifications during car development of a new car body and the same parametric model is reuse for future platforms are the reasons to develop a new P/A design methodology. The methodology is base on P/A but should have the concept of archetype. An archetype is a set of logical and parametric features of an object. The system can be use to build the relative CAD model. The advantage of the archetype design can generate different components with simply changing its parameter values.
The phase of design methodology were the following:
Define the vehicle reference model( developed with explicit CAD systems and procedure)
Build the design development history (list of modification)
P/A modeling of new vehicle model.
Model update during vehicle development
The traditional process of modeling and the new method based on P/A approach have been compared in qualitative. The development time of model is longer for P/A method, because it is necessary to build P/A library archetypes. P/A library enables to reduce time design because it is reduced the modifying phase. The explicit design take always the same time for every style change.
For the reason, P/A approach seems to be strong enough to manage several style modifications, saving time and costs. 
The authors present an application of Visual Basic Application Programming Interface (API) to develop numerical and procedural algorithm into CAD software. The focus is on Reverse Engineering embedded into SolidWorks. There are many applications is need to remodel the tessellated surface into an editable solid feature, to analyze it and to manipulate. SolidWorks is a widely used commercial software about engineering modeling and computer aided design. SolidWorks is based on parametric definition of component and feature and it can be used in very intuitive way. Other engineering modelers (such as Catia) have dedicated module to reverse engineering, but the purchase of their license may be very expensive. Specific reverse engineering software (such Rapidform) does not allow the building of parametric feature-based models. In many cases there also need to implement specific algorithm to perform dedicated an accurate computation which canââ‚¬â„¢t be found in any commercial software. These are the main reason to API within a commercial software. Resent SolidWorks have improved the method supported by native object and they have been interlaced with very powerful Mathematical Utility. Using API into SolidWorks we can manipulate three kind of object from:
SolidWorks (model native entities)
math utility database (math entities)
User defined entities
The native geometrical objects concern the sketch entities (point, line, circle, spline, etc) and their constrains, the features (extrusion, revolution, loft, etc) the assembly management (mating, inserting, moving, etc). the math native objects concern points, vectors and transformations for manipulate entities (projecting from model space to sketch space and vice versa, performing basic operation on vector, etc). the software without API the user can only access to single model entity and the direct access to internal database is not permitted. Using API database of entity can be directly accessed saving time to execute command and model entities can be interlaced with math and user defined ones.