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Computer-Aided Design

Computer-aided design (CAD) is use of a wide range of computerbased tools that assist engineers, architects and other design professions 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 base drafting systems to 3D solid and surface modellers.

Origins and terminology

CAD originally meant Computer Aided Drafting because of its original use as a replacement for traditional drafting. Now, CAD usually means Computer Aided Design to reflect the fact that modern CAD tools do more than just drafting.

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. CAM (Computer-aided manufacturing) is also often used in a similar way, or as a combination (CAD/CAM). The term CAD is generally used for graphical design, whereas non-graphical computer-aided design is usually called Knowledge-based engineering (KBE).

 

Introduction
The CAD process.
The CAD process.
Commercial floor plan.
Commercial floor plan.

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 the scope of Computer Aided technologies, with benefits such as lower product development costs and a greatly shortened design cycle. CAD enables designers to lay out and develop work on screen, print it out and save it for future editing, saving time on their drawings.

 

Fields of use
  • The AEC industry- Architecture, engineering and construction
    • Architecture
    • Building engineering
    • Civil Engineering and Infrastructure
    • Construction
    • Roads and Highways
    • Railroads and Tunnels
    • Water Supply and Hydraulic Engineering
    • Storm Drain, Wastewater and Sewer systems
    • Mapping and Surveying
    • (Chemical) Plant Design
    • Factory Layout
    • Heating, Ventilation and air-conditioning (HVAC)
  • Mechanical (MCAD) Engineering
    Fully editable digital multi-CAD mockup
    Fully editable digital multi-CAD mockup
    • Automotive - vehicles
    • Aerospace
    • Consumer Goods
    • Machinery
    • Ship Building
    • Bio-mechanical systems
  • Electronic design automation (EDA)
    • Electronic and Electrical (ECAD)
    • Digital circuit design
  • Electrical Engineering
    • Power Engineering or Power Systems Engineering
    • Power Systems CAD
    • Power analytics
  • Manufacturing process planning
  • Industrial Design
  • Software applications
  • Apparel and Textile CAD
    • Fashion Design
  • Garden design

 

History

[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). Robert A. Heinlein in his 1957 novel The Door into Summer suggested the possibility of a robotic Drafting Dan. 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. Riesenfeld 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
Capabilities
An example of a CAD engineering drawing.
An example of a CAD engineering drawing.
Reuse of component from design library
Reuse of component from design library
Simulation of airflow over an engine
Simulation of airflow over an engine

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
A CAD model of a mouse.
A CAD model of a mouse.

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 of a graphical user interface (GUI) with NURBS geometry and/or boundary representation (B-rep) data via a geometric modeling kernel. A geometry constraint engine may also be employed to manage the associative relationships between geometry, such as wireframe geometry in a sketch or components in an assembly.

 

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. Some CAD systems such as NX provide multiplatform support including Windows, LINUX, UNIX and Mac OSX.

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 the 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.

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 from the center of the part, the operator needs to locate it from the center of the model, not, perhaps, from 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.

Some software packages provide the ability to edit parametric and non-parametric geometry without the need to understand or undo the design intent history of the geometry by use of direct modeling functionality.

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 in the late 1980s, 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 had been 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. Today, however, hardware and software costs have come down. Even high-end packages work on less expensive platforms and some even support multiple platforms. The costs associated with CAD implementation now are more heavily weighted to the costs of training in the use of these high level tools, the cost of integrating a CAD/CAM/CAE PLM using enterprise across multi-CAD and multi-platform environments and the costs of modifying design workflows to exploit the full advantage of CAD tools. CAD vendors have been effective in providing tools to lower these costs.

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.

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