What do these acronyms mean?
CAD – Computer Aided Design, 2D & 3D design on a computer screen
using CAD software
CAM – Computer Aided Manufacturing, using a part geometry database
to control a numerically controlled (NC) manufacturing machine such as a milling machine
or lathe
CAE – Computer Aided Engineering, doing higher level work on a 2D
or more typically 3D part model; for example 3D solid modeling of some type or finite
element analysis to calculate stresses & strains, as well as dynamic, thermal, or
fluidic response to input stimuli. Usually a higher level than plain CAD,
although some lump everything under this term.
DBA - Design by Analysis, design based on FEA rather than
established codes
MCAD - Mechanical Computer Aided Design, synonymous with
MCAE, could be considered a subset of CAE
MCAE - Mechanical Computer Aided Engineering, synonymous with
MCAD, could be considered a subset of CAE
FEA – Finite Element Analysis - stress, thermal, or
dynamic analysis of a part or assembly of parts
CFD - Computational Fluid Dynamics - computing velocities,
pressures, and flow rates in or around a part or assembly of parts
PDM - Product Data Management
PLM - Product Lifecycle Management
EDA - Electronic Design Analysis - electronic circuit
schematic capture and PCB design
IDF - Intermediate Data Format - allows exporting a 3D solid
model of a PCB from the EDA to MCAD tool
Which CAD or CAE Software Should I Use?
Well that depends. Ten to fifteen years when AutoCAD
dominated everything it was a pretty easy choice. Electrical Engineers (EE) were
probably the first to split off and use integer based EE specific CAD tools
which worked much better for them. Architects and Civil Engineers, because of
the types of projects they do and how they work on them, are probably still best
served with AutoCAD and some of the numerous add-ons to it such as Land Desktop,
Survey, and Civil Design. Civil3D is a newer AutoCAD add-on tool that has added
quite a bit of 3D capability for Civil Engineering. For Mechanical, Aerospace,
Ocean, and Nuclear Engineers, people who work on fabricated parts, they are much
better off with the newer 3D solid modelers such as: Autodesk Inventor,
SolidWorks, Pro/Engineer, SolidEdge, Catia, etc. Fabricated parts refers to
parts that are machined, cast, forged, stamped, welded, etc.
How much computer hardware do I need?
Basically as much as you can justify spending for a Windows or UNIX
based workstation. At least one high speed central processor (CPU), two are
better. A 19" to 21"
high-resolution color monitor with a fast graphics board is the norm. CRT's have
much faster dynamic response times than equivalent LCD's and are much better at
real-time rotation of complex 3D solid models. Lots of memory &
fast, high capacity hard drives. A mouse or digitizing tablet plus a C, D, or E sized
plotter rounds out the hardware. You may want a plotter than can handle photographic
output as well as CAD line drawings to handle architectural renderings, 3D mechanical
solid model visualizations, or graphics arts design from non-CAD software such as Adobe
PhotoShop, Corel Draw, or Corel Ventura Publisher. 3D controllers such as the
Labtec SpaceBall are great and improve efficiency. A fast 100 MBPS or 1GB Ethernet connection is
also nice for large file transfers as well as broadband internet access.
How long does it take to become proficient with powerful CAD
software?
With training it takes a relatively short time. Without training, it
takes much longer. Without training, some people will never become proficient. I have had
some people in my AutoCAD courses that have been using AutoCAD for over a year and they
still had terribly inefficient work habits. The three-day Introduction to AutoCAD course
solved these problems for most of them.
What is the difference between an integer based and a floating point based CAD
package?
Integers are whole numbers; i.e., 5, 99, -66. Floating-point, or real,
numbers include fractional parts; i.e., 3678.99, and –0.003. Integer based packages
are very fast due to exclusively using integer arithmetic which is much faster than
floating point arithmetic. Unfortunately this results in limited capability such as
limited discrete zoom ratios which is not satisfactory for Mechanical Engineering, Civil
Engineering, or Architectural work. As the drawing gets larger and larger, the allowed
resolution gets smaller and smaller. For example if you are designing a 1000’ long
bridge and now want to detail a 1" rivet hole your allowable resolution may be a
minimum of several inches or feet – which is useless.
Integer based packages are really intended for Electrical Engineering
(EE) applications where they work very well. All parts for schematic capture fall on a
grid. Not only are parts standardized but they are only shown in schematic form; i.e., a
functional electronic circuit symbol and not the physical housing of the part itself.
Printed circuit board work also is normally done with integer based CAD software although
it is sometimes handled well with a floating point based package. EE based CAD tools also
need to understand part connectivity so that a net-list can be generated. A net-list
describes all of the interconnections in the circuit. If desired, circuit simulation is
done with an external floating point based simulation program.
Mechanical Engineering, Civil Engineering, Ocean Engineering, etc. as well as
Architecture all deal with designing large, complex, and irregularly shaped parts for
which you need powerful graphical drawing tools. From a drawing perspective only, ME, CE,
Architecture, etc. applications have much more stringent drawing requirements than are
those for EE. EE applications, on the other hand, need to understand connectivity. With
AutoCAD, which is floating point CAD software, the zoom ratio is on the order of 16
trillion to one. This allows you to, for example, make a scale drawing of the solar
system, zoom down to the Earth and the Moon, then zoom into a lunar crater, zoom to the
speck that you see in the crater which is the lunar lander, and then zoom inside the lunar
lander and read the control panel!
What is an entity, object, or primitive?
Entities, objects, and primitives are just different names for the same thing used by
different CAD vendors. These are the most basic or primitive parts that you will use to
create your drawings. They include: points, lines, arcs, circles, text, dimensions,
crosshatch, polylines, blocks, 3D surfaces, 3D solids, etc.
What is a CAD drawing database?
This is a software rendition of a paper drawing. Whatever you draw on the screen of the
CRT has to be broken down into its primitive components and then stored in the drawing
database of graphics entities. For example every 3D line would have the X,Y,Z coordinates
of its end points stored, insertion layername, default color, default linetype, etc. All
of the entities in the drawing make up the CAD drawing database. Each CAD, CAE,
FEA, or CFD system uses its own proprietary database format; i.e., by definition
they cannot speak to each other. While they will normally support all or nearly
all of the same entity types they will be implemented and stored differently in
each software system.
How do I translate a drawing from one CAD package to another?
Most CAD software uses a proprietary database to store the actual drawing that you
create. This is not a problem until you want to port one of your drawings between two
different CAD packages. What you need is a drawing translator of some sort. The translator
opens the source drawing file and looks for specific entity types and then writes them to
the output drawing file to the equivalent entity type for the new drawing file.
Or the translator may use a third, neutral database form such as: IGES, DXF,
IDF, etc.. Any
entity type that is not supported by both systems will always create a problem unless they
can automatically be converted into a different and common entity type. You also could do
the non-supported entity conversion manually within the CAD software before or after the
transfer.
How can I get my old paper drawings into a CAD system?
You have several options to do this.
A. Recreate the drawing from scratch
Tape the paper drawing up by your CAD system and manually enter all of the data into a
CAD drawing database. This isn’t quite as bad as it sounds, a fast CAD operator can
work fairly efficiently. They may find old mistakes, which they can correct and they may
create new ones. You may be able to correct old drawing errors.
B. Digitize the drawing with a digitizing tablet
Tape the paper drawing onto a large (C, D, or E sized) digitizer tablet and manually
trace over the drawing with the digitizer puck while entering CAD drawing commands.
Requires a large, properly calibrated digitizer and a sure hand. Can be time consuming and
can create new errors as well as fix old ones. It will replicate any drawing errors from
the original drawing. Smaller digitizers require you to shift, retape, and recalibrate the
drawing. Should be faster than option A, but will input all entities as drawn, not
necessarily as they should be.
C. Video scan the drawing
This can be challenging. Doing a video scan of the drawing is trivial and works very
well, but all you have is a digitized video image of the piece of paper and
what's on it. It doesn’t
have any intelligence in the form of a drawing database of graphics entities. Converting
the video digitized image into a CAD drawing database of entities is the hard part. This
is done with powerful artificial intelligence software that looks at items in the video
image (raster file of pixels) and tries to turn them into equivalent CAD entities that it
can then store into a CAD drawing database. Considering the enormous complexity of the
task, this scanning software is remarkably successful. It will normally require some
manual clean up of each drawing. This is potentially the fastest method for large
quantities of drawings.
What is 3D wireframe design?
Drawing with 3D line entities. The model can be complex but it can only be
displayed as a wireframe model. Not only are surfaces not visible, but it is impossible to
do any type of "solid" computations. It is possible to draw objects that
physically cannot exist. For example look at some of the German artist, Escher's, prints.
What is 3D surface modeling?
Surface modeling is one step up from wireframe modeling. It allows the creation
of complex 3D curved surfaces similar to what you would require for an automobile fender,
a Clorox bottle, or a jet engine inlet nacelle. Some solid modelers support this to
varying degrees.
What is 3D solid modeling?
Designing with 3D solid primitives such as: rectangular boxes, cylinders,
cones, spheres, etc. Creating a complex 3D model by performing Boolean operations on two
or more primitives via: join, cut, intersect, and union. The final model will be
mathematically correct. By definition, it cannot be an optical illusion.
What is a 3D parametric, feature based solid modeler?
This is a newer and more powerful version of solid modeling that eliminates
some of the problems associated with older modelers. Older solid modelers created models
that were very difficult or impossible to change. Parametric feature based solid modelers
have the ability to scale the model up or down and change dimensions of any of its
features. Features could include the length, width, height, and wall thickness of a model
as well as hole, groove, and fillet locations, and their dimensions. Any geometric feature
of a model can be changed. Model features can also be driven from a spreadsheet containing
all of the model dimensions.
What are the advantages of solid modeling over 2D CAD work?
Working from a single, common 3D geometry database. You don't have to recreate
geometry multiple times for: 3D visualization, 2D detail design & drafting, 2D or 3D
Finite element analysis, 3D NC manufacturing, and creating visualization diagrams for
advertising, marketing, or a manual. It's also much easier and faster to make changes to the model.
Change is a fact of life for any design project so it's better to have tools that are
powerful enough to easily cope with the inevitable changes.
It's also normally very easy to port the 3D solid geometry to an FEA software tool. This is an
enormous time saver, easily paying for the entire cost of converting from 2D/3D CAD to a
parametric, feature based solid modeler all by itself. The end result is a virtually
seamless "end to end" set of software tools for mechanical engineering.
Everything from 3D solid design and visualization to 3D FEA, to detailed 2D drawings, to
3D NC CAM is handled by a single geometry database.
What are the disadvantages of solid modeling over 2D CAD work?
The disadvantages of solid modeling over conventional 2D CAD design are: the
requirement for faster and more powerful hardware to run the solid modeling software;
increased cost of the hardware, and software; getting up the learning curve of the solid
modeling software; and learning to think differently about the design process. Just as you
had to when converting from manual design and drafting on a drawing board to 2D CAD, the
thought processes change when going from 3D wireframe design to 3D solid modeling.
Also the process of porting your 3D solid model to 3D FEA and getting it to mesh
properly isn't always as easy as advertised and can be a problem.
What are efficient CAD work habits?
Take our Introduction to AutoCAD course and find out. If you don’t learn to work
efficiently, you probably won’t. I've had numerous students in the
Introduction to AutoCAD course who have already been using AutoCAD for one to
two years and they still were working pretty inefficiently.
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