Currently there are a variety of options that should be considered when reviewing CAD systems, among them some characterize the functionality of the system, or even its applicability integrated with others. Considering the processing of data on the market today there are some variations, followed by a description of the systems on the 2D and 3D.

Systems 2D

One of the advantages of using CAD 2D is the rapid training of users, usually accustomed to the use of common estiradores. But its use is limited, at the risk of transforming the system in a simple electronic drawing, little more productive that the estiradores common.

For some applications the 2D representation is sufficient, such as projects of schemes electrical, hydraulic, circuits and electronic cards, where there is no need for information volume. Also in the creation of various types of sketches, to support production for example, 2D CAD is more appropriate. In this case it should work with a system CAPP, which would be responsible for generating the data represented in sketches (as a list of tools, instructions for assembly and / or inspection, etc. ..) in the mechanical design has been used to represent 2D for the development of drawings of all, because they are more easily changed. At that stage employs a great number of standard parts, which are included in the design of interactive way, which makes a great productivity of this activity. Companies of the mechanical sector of small and medium businesses prefer using 2D systems, as well as lower cost of acquisition and training of its employees, such systems require less powerful machines. Meanwhile, the market exists today a series of 3D systems which they propose to fill that gap. The great return of the use of 2D CAD is the reuse of information, since it is much easier to retrieve and modify an electronic design, than a conventional design carried out.

3D Systems

The 3D modeling shows the difficulties that are themselves the process of design because the designer is required to consider all three dimensions simultaneously. In some cases, the use of 3D model is essential, such as by the application of finite element analysis for verification of tension, flow, temperature, etc.. and even if there is the need to calculate the volume, mass properties of the axis of inertia and verification of interference.

Below are cited the main methods of representation 3D:-Wireframe;

CSG;-Brep;

Hybrid;

Based on Features;

Parametric;

Dynamics.

Modelling by Wireframe

In the past the modelling by wireframe was the main method used by CAD systems, allowing connecting lines between points in 3D space, allowing the creation of spatial models and ensuring consistency of views derived 2D and cotagem associated. With technological advancement and greater processing capacity of computers, these systems began to be replaced by methods based on solid modeling. This also happened partly because of the difficulty of use wireframe when necessary incorporate them into software for analysis or manufacturing, because we do not have any kind of information related to the physical components of the real.

Modelling Solida CSG (Constructive Solid Geometry)

Systems that are capable of shaping the sound is much more powerful that simple modeladores based in wireframe. These programs are used to build components that are solid objects, and not simply a mesh of lines trançadas.

A model CSG is a binary tree consists of primitive objects and Boolean operators. The ancients are represented by the leaves of the tree and objects are more complex us. The root of the tree represents the complete product. Each primitive is associated with a 3D transformation that specifies the position, orientation and dimensions. This method is characterized by composing models from solid. Using solid shape for the components, they start to acquire physical properties as volume, and characterizing their density, we get other features such as weight and mass. So the computer can calculate various physical properties of these components, as a centre of gravity, moment of inertia, etc.. These calculations can be used in or with irregular shapes, where the manual calculation becomes extremely difficult and laborious. In addition to facilitating the use of a software model of analysis. This method has some limitations, and the main the presence of a limited number of operations and primitive, which therefore limits the possibilities for creation by the designer.

Modelling Solida Brep (Boundary Representation)

The Brep modelling is based on techniques for modelling in areas previously existing. The first generation of solid objects modeladores Brep represented only by tables of faces, edges and corners. Thus he supported only objects with flat sides. Areas curves were shaped by linear approximation, in a process called "facetamento." The second generation of modeladores Brep included primitive objects with analytical areas such as cylinders, spheres, cones, etc.. They allow the creation of models much more complex geometry with "accurate". For this was necessary the use of algorithms of intersection much more complex. Other developments in shaping Brep were directed to improvements in the effectiveness of Boolean operations through, for example, the use of directories occupying space, which reduces the number of inspections of interference of light. Another area of development was the expansion of the number of geometric shapes that can be shaped with Brep. The modelling Brep has some advantages over the CGS, primarily concerning the versatility in the generation of complex models and the speed of verification of topological relations. This happens because the way the Brep records the information from the model, storing the parameters of the edges so explicitly.

Solid Modelling Hybrid

The methods of modeling and solid CSG Brep are often combined to create models of components. Each of these methods has its limitations, and components that are difficult to create using one or another, can be generated more easily using a combination of both methods. Most systems modeladores solid commercial hybrids are both using the method CSG as the Brep.

Solid Modelling based on Features

One feature may be defined as a physical element of a piece that has some meaning for the engineering. He must meet the following conditions:

Be a constituent of a physical piece;

mapeável to be a generic geometric shape;

be technically significant from the point of view of engineering;

Tuesday predictable properties.

The technical meaning of feature may involve a function to which a feature is, how can it be produced, which shares its presence should start, and so on. Features can be thought as' primitive engineering 'relevant to some task of engineering. The modeling of features has been gaining ground mainly in the mechanical engineering. The method can create holes, chamfers, tears, and so on. To be associated with other bodies or faces. The modelling by features is based on the idea of drawing using building blocks-blocks of construction. Rather than using analytical forms as parallelepipeds, cylinders, cones and spheres as primitive, the user creates model using the product of more primitive level that are more relevant to their specific application. This approach should make the solid modelling systems were easier to use. Meanwhile, the fixed set of features offered by current modeladores is very limited for industrial use, which limits the possibilities of the designer. Thus it is clear that the features should be adaptable to users and that the library of features to be extended. Efforts to specification language for a formal specification of features which began in 1990, provided that the newest version of STEP include features with the possibility of being defined by the user through a standard language for specification of features.

Parametric Solid Modelling

The solid parametric modeling allows to create models of products with varying lengths. The dimensions can be linked by expressions. Links between the model and bidirectional scheme scaling allow the regeneration automatic models after changes in size and automatic update of related dimensions. Not all parametric CAD systems that provide bi-directionality, given the complexity that this involves, which penalizes the designer, as it has to think about organised links dimensional advance, without which the modification of the model may involve where he is refeito.

• Application of CAD