Computer-aided design is the use of computer systems to assist in the creation, modification,
analysis, or optimization of a design. CAD software is used to increase the productivity
of the designer, improve the quality of design, improve communications through documentation,
and to create a database for manufacturing. CAD output is often in the form of electronic
files for print, machining, or other manufacturing operations.
Computer-aided design is used in many fields. Its use in designing electronic systems is
known as electronic design automation, or EDA. In mechanical design it is known as mechanical
design automation or computer-aided drafting, which includes the process of creating a technical
drawing with the use of computer software. CAD software for mechanical design uses either
vector-based graphics to depict the objects of traditional drafting, or may also produce
raster graphics showing the overall appearance of designed objects. However, it involves
more than just shapes. As in the manual drafting of technical and engineering drawings, the
output of CAD must convey information, such as materials, processes, dimensions, and tolerances,
according to application-specific conventions. CAD may be used to design curves and figures
in two-dimensional space; or curves, surfaces, and solids in three-dimensional space.
CAD is an important industrial art extensively used in many applications, including automotive,
shipbuilding, and aerospace industries, industrial and architectural design, prosthetics, and
many more. CAD is also widely used to produce computer animation for special effects in
movies, advertising and technical manuals, often called DCC digital content creation.
The modern ubiquity and power of computers means that even perfume bottles and shampoo
dispensers are designed using techniques unheard of by engineers of the 1960s. Because of its
enormous economic importance, CAD has been a major driving force for research in computational
geometry, computer graphics, and discrete differential geometry.
The design of geometric models for object shapes, in particular, is occasionally called
computer-aided geometric design.
Overview Starting around the mid 1970's, as computer
aided design systems began to provide more capability than just an ability to reproduce
manual drafting with electronic drafting, the cost benefit for companies to switch to
CAD became apparent. The benefit of CAD systems over manual drafting are the capabilities
one often takes for granted from computer systems today; automated generation of Bill
of Material, auto layout in integrated circuits, interference checking, and many others. Eventually
CAD provided the designer with the ability to perform engineering calculations. During
this transition, calculations were still performed either by hand or by those individuals that
could run computer programs. CAD was a revolutionary change in the engineering industry, where
draftsmen, designers and engineering roles begin to merge. It did not eliminate departments,
as much as it merged departments and empowered draftsman, designers and engineers. CAD is
just another example of the pervasive effect computers were beginning to have on industry.
Current computer-aided design software packages range from 2D vector-based drafting systems
to 3D solid and surface modelers. Modern CAD packages can also frequently allow rotations
in three dimensions, allowing viewing of a designed object from any desired angle, even
from the inside looking out. Some CAD software is capable of dynamic mathematical modeling,
in which case it may be marketed as CADD. CAD is used in the design of tools and machinery
and in the drafting and design of all types of buildings, from small residential types
to the largest commercial and industrial structures. 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. It
can also be used to design objects. Furthermore many CAD applications now offer advanced rendering
and animation capabilities so engineers can better visualize their product designs.4D
BIM is a type of virtual construction engineering simulation incorporating time or schedule
related information for project management. 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 layout and develop
work on screen, print it out and save it for future editing, saving time on their drawings.
Uses Computer-aided design 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. CAD is one part of the whole Digital Product
Development activity within the Product Lifecycle Management processes, and as such is used
together with other tools, which are either integrated modules or stand-alone products,
such as: Computer-aided engineering and Finite element
analysis Computer-aided manufacturing including instructions
to Computer Numerical Control machines Photo realistic rendering
Document management and revision control using Product Data Management.
CAD is also used for the accurate creation of photo simulations that are often required
in the preparation of Environmental Impact Reports, in which computer-aided designs of
intended buildings are superimposed into photographs of existing environments to represent what
that locale will be like were the proposed facilities allowed to be built. Potential
blockage of view corridors and shadow studies are also frequently analyzed through the use
of CAD. CAD has been proven to be useful to engineers
as well. Using four properties which are history, features, parameterization, and high level
constraints. The construction history can be used to look back into the model's personal
features and work on the single area rather than the whole model. Parameters and constraints
can be used to determine the size, shape, and other properties of the different modeling
elements. The features in the CAD system can be used for the variety of tools for measurement
such as tensile strength, yield strength, electrical or electro-magnetic properties.
Also its stress, strain, timing or how the element gets affected in certain temperatures,
etc. Types
There are several different types of CAD, each requiring the operator to think differently
about how to use them and 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 are created in a way analogous to manipulations of real world objects. Basic
three-dimensional geometric forms have solid volumes added or subtracted from them, as
if assembling or cutting real-world objects. Two-dimensional projected views can easily
be generated from the models. Basic 3D solids don't usually include tools to easily allow
motion of components, set limits to their motion, or identify interference between components.
Solid Modeling There are two types of solid modeling
1). 3D parametric solid modeling allows the operator to use what is referred to as "design
intent". The objects and features created are modifiable. Any future modifications can
be made by changing how the original part was created. If a feature was intended to
be located from the center of the part, the operator should locate it from the center
of the model. The feature could be located using any geometric object already available
in the part, but this random placement would defeat the design intent. If the operator
designs the part as it functions the parametric modeler is able to make changes to the part
while maintaining designed in relationships. 2). Explicit Modellers or Direct 3D CAD Modelers
provide the ability to edit geometry without a history tree. With direct modeling once
a sketch is used to create geometry the sketch is incorporated into the new geometry and
the designer just modifies the geometry without needing the original sketch. As with Parametric
modeling, Direct modeling has the ability to include relationships between selected
geometry. Top end systems offer the capabilities to
incorporate more organic, aesthetics and ergonomic features into designs. Freeform surface modeling
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.
Technology
Originally software for Computer-Aided Design systems was developed with computer languages
such as Fortran, ALGOL 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 modules with their own APIs. A CAD system
can be seen as built up from the interaction of a graphical user interface with NURBS geometry
and/or boundary representation 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.
Unexpected capabilities of these associative relationships have led to a new form of prototyping
called digital prototyping. In contrast to physical prototypes, which entail manufacturing
time in the design. That said, CAD models can be generated by a computer after the physical
prototype has been scanned using an industrial CT scanning machine. Depending on the nature
of the business, digital or physical prototypes can be initially chosen according to specific
needs. Today, CAD systems exist for all the major
platforms; some packages even support multiple platforms.
Right now, no special hardware is required for most CAD software. However, some CAD systems
can do graphically and computationally intensive tasks, so a modern graphics card, high speed
CPUs and large amounts of RAM may be 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.Technologies which
in the past were limited to larger installations or specialist applications have become available
to a wide group of users.These include the CAVE or HMD`s and interactive devices like
motion-sensing technology History
Designers have long used computers for their calculations. Digital computers were used
in power system analysis or optimization as early as proto-"Whirlwind" in 1949. Circuit
design theory, or power network methodology would be algebraic, symbolic, and often Vector
based. Examples of problems being solved in the mid-1940s to 50s include, Servo motors
controlled by generated pulse, The digital computer with built-in compute operations
to automatically co-ordinate transforms to compute radar related vectors and the essentially
graphic mathematical process of forming a shape with a digital machine tool. These were
accomplished with the use of computer software. The man credited with coining the term CAD.
Douglas T. Ross stated "As soon as I saw the interactive display equipment, [being used
by radar operators 1953] I said "Gee, that's just what we need". The designers of these
very early computers built utility programs so that programmers could debug programs using
flow charts on a display scope with logical switches that could be opened and closed during
the debugging session. They found that they could create electronic symbols and geometric
figures to be used to create simple circuit diagrams and flow charts. They made the pleasant
discovery that an object once drawn could be reproduced at will, its orientation, Linkage
[ flux, mechanical, lexical scoping ] or scale changed. This suggested numerous possibilities
to them. It took ten years of interdisciplinary development work before SKETCHPAD sitting
on evolving math libraries emerged from MIT`s labs. Additional developments were carried
out in the 1960s within the aircraft, automotive, industrial control and electronics industries
in the area of 3D surface construction, NC programming and design analysis, 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 Robert Issac Newton from
Pawtucket, Rhode Island. 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 Bézier, Paul de Casteljau,
Steven Anson Coons, James Ferguson, Carl de Boor, Birkhoff and Garibedian in the 1960s
and W. Gordon and R. Riesenfeld in the 1970s. The invention of the 3D CAD/CAM is attributed
to a French engineer, Pierre Bezier. After his mathematical work concerning surfaces,
he developed UNISURF, between 1966 and 1968, to ease the design of parts and tools for
the automotive industry. Then, UNISURF became the working base for the following generations
of CAD software. It is argued that a turning point was the
development of the SKETCHPAD system at MIT by Ivan Sutherland. 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. Sutherland presented his paper Sketchpad: A Man-Machine Graphical Communication
System in 1963 at a Joint Computer Conference having worked on it as his PhD thesis paper
for a few years. Quoting,“For drawings where motion of the drawing, or analysis of a drawn
problem is of value to the user, Sketchpad excels. For highly repetitive drawings or
drawings where accuracy is required, Sketchpad is sufficiently faster than conventional techniques
to be worthwhile. For drawings which merely communicate with shops, it is probably better
to use conventional paper and pencil.” Over time efforts would be directed toward the
goal of having the designers drawings communicate not just with shops but with the shop tool
itself. This goal would be a long time arriving. The 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 with DAC-1 1964; Lockheed projects; Bell GRAPHIC 1 and Renault.
One of the most influential events in the development of CAD was the founding of MCS
in 1971 by Dr. P. J. Hanratty, who wrote the system ADAM but more importantly supplied
code to companies such as McDonnell Douglas, Computervision, Calma, Gerber, Autotrol and
Control Data. As computers became more affordable, the application
areas have gradually expanded. The development of CAD software for personal desktop 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. CAD implementations have evolved dramatically
since then. Initially, with 3D 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 and Uni-Solid based on PADL-2 and the release of the surface modeler CATIA.
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 Parasolid
and ACIS 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 and TriSpective
in 1995, Solid Edge in 1996 and Autodesk Inventor in 1999.
See also
References
External links Learning materials related to Computer-aided
Geometric Design at Wikiversity Learning materials related to Computer-aided
design at Wikiversity Media related to Computer-aided design at
Wikimedia Commons The dictionary definition of computer-aided
design at Wiktionary