Computer-aided design

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Computer-aided design (CAD) is the use of a wide range of computer-based tools that assist engineers, architects and other design professionals in their design activities. It is the main geometry authoring tool within the Product Lifecycle Management process and involves both software and sometimes special-purpose hardware. Current packages range from 2D vector based drafting systems to 3D solid and surface modellers.

CAD is sometimes translated as "computer-assisted", "computer-aided drafting", or a similar phrase. Related acronyms are CADD, which stands for "computer-aided design and drafting", CAID for Computer-aided Industrial Design and CAAD, for "computer-aided architectural design". All these terms are essentially synonymous, but there are a few subtle differences in meaning and application.

CAD was originally the three letter acronym for "Computer Aided Drafting" because in the early days CAD was really a replacement for the tradition drafting board. But now the term is often interchanged with "Computer Aided Design" to reflect the fact that modern CAD tools do much more than just drafting.

Introduction

CAD is used to design, develop and optimize products, which can be goods used by end consumers or intermediate goods used in other products. CAD is also extensively used in the design of tools and machinery used in the manufacture of components, and in the drafting and design of all types of buildings, from small residential types (houses) to the largest commercial and industrial structures (hospitals and factories).

CAD is mainly used for detailed engineering of 3D models and/or 2D drawings of physical components, but it is also used throughout the engineering process from conceptual design and layout of products, through strength and dynamic analysis of assemblies to definition of manufacturing methods of components.

CAD has become an especially important technology, within CAx, with benefits, such as lower product development costs and a greatly shortened design cycle, because CAD enables designers to lay out and develop their work on screen, print it out and save it for future editing, saving a lot of time on their drawings.

Fields of use

File:Floor Plan.JPG
A commercial floor plan created using AutoCAD 2006

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History Of CAD

[1] [2] [3] [4] [5] Designers have long used computers for their calculations. Initial developments were carried out in the 1960s within the aircraft and automotive industries in the area of 3D surface construction and NC programming, most of it independent of one another and often not publicly published until much later. Some of the mathematical description work on curves was developed in the early 1940s by Isaac Jacob Schoenberg, Apalatequi (Douglas Aircraft) and Roy Liming (North American Aircraft), however probably the most important work on polynomial curves and sculptured surface was done by Pierre Bezier (Renault), Paul de Casteljau (Citroen), Steven Anson Coons (MIT, Ford), James Ferguson (Boeing), Carl de Boor (GM), Birkhoff (GM) and Garibedian (GM) in the 1960s and W. Gordon (GM) and R. Reisenfeld in the 1970s.

It is argued that a turning point was the development of SKETCHPAD system in MIT in 1963 by Ivan Sutherland (who later created a graphics technology company with Dr. David Evans). The distinctive feature of SKETCHPAD was that it allowed the designer to interact with his computer graphically: the design can be fed into the computer by drawing on a CRT monitor with a light pen. Effectively, it was a prototype of graphical user interface, an indispensable feature of modern CAD.

First commercial applications of CAD were in large companies in the automotive and aerospace industries, as well as in electronics. Only large corporations could afford the computers capable of performing the calculations. Notable company projects were at GM (Dr. Patrick J.Hanratty) with DAC-1 (Design Augmented by Computer) 1964; Lockhead projects; Bell GRAPHIC 1 and at Renault (Bezier) – UNISURF 1971 car body design and tooling.

One of the most influential events in the development of CAD was the founding of MCS (Manufacturing and Consulting Services Inc.) in 1971 by Dr. P. J. Hanratty[6], who wrote the system ADAM (Automated Drafting And Machining) but more importantly supplied code to companies such as McDonnell Douglas (Unigraphics), Computervision (CADDS), Calma, Gerber, Autotrol and Control Data.

As computers became more affordable, the application areas have gradually expanded. The development of CAD software for personal desk-top computers was the impetus for almost universal application in all areas of construction.

Other key points in the 1960s and 1970s would be the foundation of CAD systems United Computing, Intergraph, IBM, Intergraph IGDS in 1974 (which led to Bentley MicroStation in 1984)

CAD implementations have evolved dramatically since then. Initially, with 2D in the 1970s, it was typically limited to producing drawings similar to hand-drafted drawings. Advances in programming and computer hardware, notably solid modeling in the 1980s, have allowed more versatile applications of computers in design activities.

Key products for 1981 were the solid modelling packages -Romulus (ShapeData) and Uni-Solid (Unigraphics) based on PADL-2 and the release of the surface modeler CATIA (Dassault Systemes). Autodesk was founded 1982 by John Walker, which led to the 2D system AutoCAD. The next milestone was the release of Pro/ENGINEER in 1988, which heralded greater usage of feature-based modeling methods and parametric linking of the parameters of features. Also of importance to the development of CAD was the development of the B-rep solid modeling kernels (engines for manipulating geometrically and topologically consistent 3D objects) Parasolid (ShapeData) and ACIS (Spatial Technology Inc.) at the end of the 1980s and beginning of the 1990s, both inspired by the work of Ian Braid. This led to the release of mid-range packages such as SolidWorks in 1995, SolidEdge (Intergraph) in 1996, and IronCAD in 1998. Today CAD is one of the main tools used in designing products.

Software providers today

This is an ever-changing industry with many well-known products and companies being taken over and merged with others. There are many CAD software products currently on the market. More than half of the market is however covered by the four main PLM corporations Autodesk, Dassault Systemes, PTC, and UGS Corp., but there are many other CAD packages with smaller user bases or covering niche user areas. See also list of free and open-source CAD software.

Packages can be classified into three types: 2D drafting systems (e.g. AutoCAD, MicroStation); mid-range 3D solid feature modellers (e.g. Inventor, TopSolid, SolidWorks, SolidEdge, Alibre Design, VariCAD); and high-end[7] 3D hybrid systems (e.g. Pro/ENGINEER, CATIA, NX (Unigraphics)). However these classifications cannot be applied too strictly as many 2D systems have 3D modules, the mid-range systems are increasing their surface functionality, and the high-end systems have developed their user interface in the direction of interactive Windows systems.

Capabilities

The capabilities of modern CAD systems include:

  • Wireframe geometry creation
  • 3D parametric feature based modelling, Solid modelling
  • Freeform surface modelling
  • Automated design of assemblies, which are collections of parts and/or other assemblies
  • create Engineering drawings from the solid models
  • Reuse of design components
  • Ease of modification of design of model and the production of multiple versions
  • Automatic generation of standard components of the design
  • Validation/verification of designs against specifications and design rules
  • Simulation of designs without building a physical prototype
  • Output of engineering documentation, such as manufacturing drawings, and Bills of Materials to reflect the BOM required to build the product
  • Import/Export routines to exchange data with other software packages
  • Output of design data directly to manufacturing facilities
  • Output directly to a Rapid Prototyping or Rapid Manufacture Machine for industrial prototypes
  • maintain libraries of parts and assemblies
  • calculate mass properties of parts and assemblies
  • aid visualization with shading, rotating, hidden line removal, etc...
  • Bi-directional parametric association (modification of any feature is reflected in all information relying on that feature; drawings, mass properties, assemblies, etc... and counter wise)
  • kinematics, interference and clearance checking of assemblies
  • sheet metal
  • hose/cable routing
  • electrical component packaging
  • inclusion of programming code in a model to control and relate desired attributes of the model
  • Programmable design studies and optimization
  • Sophisticated visual analysis routines, for draft, curvature, curvature continuity...

Software technologies

Originally software for CAD systems were developed with computer language such as Fortran, but with the advancement of object-oriented programming methods this has radically changed. Typical modern parametric feature based modeler and freeform surface systems are built around a number of key, C programming language, modules with their own APIs. A CAD system can be seen as built up from the interaction a graphical user interface (GUI) with NURBS geometry and/or boundary representation (B-rep) data via a geometric modeling kernel.

A CAD model of a mouse

Hardware and OS technologies

Today most CAD computer workstations are Windows based PCs; some CAD systems also run on hardware running with one of the Unix operating systems and a few with Linux. Generally no special hardware is required with the exception of a high end OpenGL based Graphics card; however for complex product design, machines with high speed (and possibly multiple) CPUs and large amounts of RAM are recommended. The human-machine interface is generally via a computer mouse but can also be via a pen and digitizing graphics tablet. Manipulation of the view of the model on the screen is also sometimes done with the use of a spacemouse/spaceball. Some systems also support stereoscopic glasses for viewing the 3D model.

Using CAD

CAD is one of many tools used by engineers and designers and is used in many ways depending on the profession of the user and the type of software in question. Each of the different types of CAD systems requires the operator to think differently about how he will use them and he must design their virtual components in a different manner for each.

An example of a CAD engineering drawing

There are many producers of the lower-end 2D systems, including a number of free and open source programs. These provide an approach to the drawing process without all the fuss over scale and placement on the drawing sheet that accompanied hand drafting, since these can be adjusted as required during the creation of the final draft.

3D wireframe is basically an extension of 2D drafting. Each line has to be manually inserted into the drawing. The final product has no mass properties associated with it and cannot have features directly added to it, such as holes. The operator approaches these in a similar fashion to the 2D systems, although many 3D systems allow using the wireframe model to make the final engineering drawing views.

3D "dumb" solids (programs incorporating this technology include AutoCAD and Cadkey 19) are created in a similar fashion to the way you would create the real world object. Each object and feature, after creation, is what it is. If the operator wants to change it, he must add "material" to it, subtract "material" from it, or delete the object or feature and start over. Due to this, it doesn't matter how the initial operator creates his components, as long as the final product is represented correctly. If future modifications are to be made, the method used to make the original part will not, in most cases, affect the procedure used to make the new modifications. Draft views can easily be generated from the models. Assemblies generally don't include tools to easily allow motion of components, set limits to their motion, or identify interference between components.

3D parametric solid modeling (programs incorporating this technology include Alibre Design, TopSolid, SolidWorks, and Solid Edge) require the operator to use what is referred to as "design intent". The objects and features created are adjustable. Any future modifications will be simple, difficult, or nearly impossible, depending on how the original part was created. One must think of this as being a "perfect world" representation of the component. If a feature was intended to be located off of the center of the part, the operator needs to locate it off of the center of the model, not, perhaps, off of a more convenient edge or an arbitrary point, as he could when using "dumb" solids. Parametric solids require the operator to consider the consequences of his actions carefully. What may be simplest today could be worst case tomorrow. Draft views are able to be generated easily from the models. Assemblies usually incorporate tools to represent the motions of components, set their limits, and identify interference. The tool kits available for these systems are ever increasing, including 3D piping and injection mold designing packages.

Mid range software was integrating parametric solids more easily to the end user: integrating more intuitive functions (SketchUp), going to the best of both worlds with 3D dumb solids with parametric characteristics (VectorWorks) or making very real-view scenes in relative few steps (Cinema4D).

Top end systems offer the capabilities to incorporate more organic, aesthetics and ergonomic features into designs. Freeform surface modelling is often combined with solids to allow the designer to create products that fit the human form and visual requirements as well as they interface with the machine.

The CAD operator's ultimate goal should be to make future work on the current project as simple as possible. This requires a solid understanding of the system being used. A little extra time spent now could mean a great savings later.

Starting the late 1980's, the development of readily affordable CAD programs that could be run on personal computers began a trend of massive downsizing in drafting departments in many small to mid-size companies. As a general rule, one CAD operator could readily replace at least three or five drafters using traditional methods. Additionally, many engineers began to do their own drafting work, further eliminating the need for traditional drafting departments. This trend mirrored that of the elimination of many office jobs traditionally performed by a secretary as word processors, spreadsheets, databases, etc. became standard software packages that "everyone" was expected to learn. Another consequence was that since the latest advances were often quite expensive, small and even mid-size firms often could not compete against large firms who could use their computational edge for competitive purposes. Guggenheim Museum Bilbao (1997) was one of the first buildings designed by a system known as CATIA. Providing a platform to integrate conceptualization, design and manufacture, CATIA belongs to a new generation of advanced computer-aided technology. This technology makes shapes possible that ten years ago would have been unthinkable.

The adoption of CAD studio or "paper-less studio," as it is sometimes called, in architectural schools was not without resistance, however. Teachers were worried that sketching on a computer screen did not replicate the skills associated with age-old practice of sketching in a sketchbook. Furthermore, many teachers were worried that students would be hired for their computer skills rather than their design skill, as was indeed common in the 1990s. Today, however, (for better or worse, depending on the authority cited) education in CAD is now accepted across the board in schools of architecture. It should be noted, however, that not all architects have wanted to join the CAD revolution. Glenn Murcutt, an Australian architect and the 2002 winner of the prestigious Pritzker Architecture Prize has a small office with minimal CAD capacity.

See also

CAD is one part of the whole Digital Product Development (DPD) activity within the Product Lifecycle Management (PLM) process, and as such is used together with other tools, which are either integrated modules or stand-alone products, such as:

Other related topics

References

  1. ^ "History of CAD/CAM". CADAZZ. 2004.
  2. ^ Pillers, Michelle (1998.03). "MCAD Renaissance of the 90's". Cadence Magazine. {{cite web}}: Check date values in: |date= (help)
  3. ^ Bozdoc, Martian. "The History of CAD". iMB.
  4. ^ Joneja, Ajay. "Some Important Events in the Development of Computer-Aided Design and Manufacturing". IELM.
  5. ^ Carlson, Wayne (2003). "A Critical History of Computer Graphics and Animation". Ohio State University.
  6. ^ "MCS Founder".
  7. ^ Yares, Evan (2006.02.03). "What is High-End CAD". Cyon Research. {{cite web}}: Check date values in: |date= (help)

External links


Wikimedia Commons has media related to CAD.

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