# General Concepts of Computer Aided Design

## What is Computer Aided Design

The technology for creating engineering drawings of parts and assemblies keeps advancing with computer aided design. Days of using slide rules and manual drafting techniques, as illustrated the figure, are a thing of the distant past. These manual methods for design are slow and tedious, which makes iterative design procedures very difficult and expensive.

Most engineers of today could not imagine trying to design anything working within the limitations of manual drafting and hand calculations. Computer programs of many different types are commonly used by engineers to become more efficient and reduce errors. Computer aided design (CAD), in the most basic definition, is the use of computer software to assist the design engineer in the overall creation and analysis of parts and assemblies. It should be noted that the acronym CAD also stands for Computer Aided Drafting, but for this course we will focus only on aspects of computer aided design.

Technically, computer aided design could refer to the use of any computer program to aid in design. MATLAB, for example, is a very powerful engineering design tool that is frequently used by engineers. However, for this course we will be focusing mainly on the use of solid modeling software and its use in computer aided design and finite element analysis. Section 4.5 will discuss the use of EXCEL, but focusing only on its use in conjunction with solid modeling software.

### 2D Verses 3D Technology

Many engineers today only learned how to use two-dimensional (2D) software such as AutoCAD. Though 2D software is still utilized and is great for general drafting, it is very limited on applications of true computer aided design. Three-dimensional (3D) solid modeling software allows for a more complete analysis and greater flexibility. Common 3D solid modeling software includes Solidworks, CREO, and Autodesk Inventor. This course will provide screenshot examples from both Solidworks and Autodesk Inventor because they are two very popular programs.

One advantage that 3D software has over 2D software is that it is generally easier to visualize complex parts in 3D. As an example, a part is shown in Figure (a) represented as the standard two-dimensional orthographic views (front, top, and right-side views). The same part is shown in Figure (b) represented in a simple three-dimensional isometric view. Though this part is still fairly basic, it can be much easier to visualize the part when it is represented as a three-dimensional isometric view. Solid modeling software has the added benefit of being able to rotate the part in 3D space to get a complete visualization.

Three-dimensional software allows the user to combine individual part files into an assembly. Assembly files, such as the example provided in the Figure below, are useful to see how parts will work together and will check for interferences between parts. Assemblies can be done in 2D software, but interferences are much easier to detect in 3D software.

3D software allows for more automation compared to 2D software. Once the three-dimensional model is developed, standard two-dimensional orthographic views are automatically generated on a drawing. Depending on how they were generated in the model, holes and bolts (or other fasteners) are automatically called out on a drawing using leaders. Bill of material tables can also automatically generate. Any changes made to the model will automatically update in the drawings. All of these automation features greatly expedites the drawing process and modification processes.

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