The previous sections dealt with the initial and middle stages of reverse engineering. This section highlights a stage which is undoubtedly crucial for product development. After a meshed part is aligned, it goes through either—surface modeling in tools such as Polyworks, which generates a non-parametric model (IGES or STEP format) or parametric modeling where a sketch of the meshed part is created instead of putting it through surfacing (.PRT format). The resultant is generally called, 3D computer aided model or CAD model.
But, what is CAD?
CAD is the acronym for Computer Aided Design. It covers different variety of design tools used by various professionals like artists, game designers, manufacturers and design engineers.
The technology of CAD systems has tremendously helped users by performing thousands of complex geometrical calculations in the background without anyone having to drop a sweat for it. CAD has its origin in early 2D drawings where one could draw objects using basic views: top, bottom, left, right, front, back, and the angled isometric view. 3D CAD programs allow users to take 2D views and convert them into a 3D object on the screen. In simple definition, CAD design is converting basic design data into a more perceptible and more understandable design.
Each CAD system has its own algorithm for describing geometry, both mathematically and structurally.
Different CAD models
Everything comes with its own varieties and CAD modeling is no stranger to it. As the technology evolved, CAD modeling came up in different styles. There are many methods of classifying them, but a broad general classification can be as follows:
- 2 dimensional or 2D CAD: The early version of CAD that most of us are aware of. These are 2-dimensional drawings on flat sheet with dimensions, layouts and other information needed to manufacture the object.
- 3 dimensional or 3D CAD: The purpose of both 2D and 3D models is the same. But what sets 3D models apart is its ability to present greater details about the individual component and/or assembly by projecting it as a full-scale 3-dimensional object. 3D models can be viewed and rotated in X, Y, or Z axes. It also shows how two objects can fit and operate which is not possible with 2D CAD.
3D models can be further classified into three categories:
- 3D Wire-frame Models: These models resemble an entire object made of just wires, with the background visible through the skeletal structure.
- Surface Models: Surface models are created by joining the 3D surfaces together and look like real-life objects.
- Solid Models: They are the best representation of real physical objects in a virtual environment. Unlike other models, solid models have properties like weight, volume and density. They are the most commonly used models and serve as prototypes for engineering projects.
Types of CAD formats
Different professionals use different software, owing to different reasons like cost, project requirements, features etc. Although, software comes with their own file formats, there are instances where one needs to share their project with someone else, either partners or clients, who are using different software. In such cases, it is necessary that both party software understand each other’s file formats. As a result of this situation, it is necessary to have file formats which can be accommodated in variety of software.
CAD file formats can be broadly classified into two types:
- Native File Formats: Such CAD file formats are intended to be used only with the software it comes with. They cannot be shared with any other software which comes with their own CAD formats.
- Neutral File Formats: These file formats are created to be shared among different software. Thereby it increases interoperability, which is necessary.
Although there are almost hundreds of file formats out there, the more popular CAD formats are as follows:
STEP: This is the most popular CAD file format of all. It is widely used and highly recommended as most software support STEP files. STEP is the acronym for Standard for the Exchange of Product Data.
IGES: IGES is the acronym for Initial Graphics Exchange Specification. It is an old CAD file format which is vendor-neutral. IGES has fallen out lately since it lacks many features which newer file formats have.
Parasolid: Parasolid was originally developed by ShapeData and is currently owned by Siemens PLM Software.
STL: STL stands for Stereolithography which is the format for 3D information created by 3D systems. STL finds its usage mostly in 3D printers. STL describes only the outer structure or surface geometry of a physical object but doesn’t give out color, texture and other attributes of an object.
VRML: VRML stands for Virtual Reality Modeling Language. Although it gives back more attributes than STL but it can be read by a handful of software.
X3D: X3D is an XML based file format for representing 3D computer graphics.
COLLADA: COLLADA stands for Collaborative Design Activity and is mostly used in gaming and 3D modeling.
DXF: DXF stands for Drawing Exchange Format which is a pure 2D file format native to Autocad.
Use of CAD
Computer-aided design or CAD has pushed the entire engineering process to the next level. One can actually mould or fold, modify or make a new part from scratch, all with the help of CAD modeling software. The many uses of CAD are as follows:
- CAD is used to generate design and layouts, design details and calculations, 3-D models.
- CAD transfers details of information about a product in a format that can be easily interpreted by a skilled professional, which therefore facilitates manufacturing process.
- The editing process in CAD is very fast as compared to manual process.
- CAD helps in speeding up manufacturing process by facilitating accurate simulation, hence reducing time taken to design.
- CAD can be assimilated with CAM (Computer Aided Manufacturing), which eases up product development.