CAD & CAE FAQ's
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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. Fifteen to twenty 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 better served with AutoCAD and some of the numerous add-ons to it; both from Autodesk and 3rd party software developers. 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. 3D solid modelers are CAD on steroids.

How much computer hardware do I need?

Basically as much as you can justify spending for an engineering workstation. At least one high speed central processor (CPU), two or more are better. At least one 22" to 24" high-resolution LCD monitor with a fast graphics board is the norm. Two or three LCD's driven by the same system is a great way of working much more efficiently. Lots of memory & fast, high capacity hard drives. A mouse and 3D controller plus a C, D, or E sized high speed, high resolution printer rounds out the hardware. You may want a printer that can handle photographic output as well as CAD/CAE/FEA drawing or model files of architectural renderings, 3D mechanical solid model visualizations, topographic maps, or graphics arts design from non-CAD software such as Adobe Photoshop, Corel Draw, Rhino, etc. 3D controllers such as the 3DConnexion SpacePilot are great and improve efficiency tremendously. A fast 1Gb Ethernet LAN, fast Wi-Fi, and broadband internet access are great for large file transfers.

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 of course, 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 for these fields of Engineering.

Integer based packages are intended for Electrical Engineering (EE) applications where they work extremely 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, Aerospace, Nuclear, 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 LCD 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 directly. 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 database translator of some sort. The translator opens the source drawing file and looks for specific entity types and then converts and writes them to the output drawing file in the equivalent entity type for the new drawing file.

Or the translator may use a third, neutral database form such as: STEP, 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, neutral 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 technology has improved enormously in recent years. 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 modeling?

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. Usually you need a higher level 3D CAD tool to do high precision 3D surfaces.

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?

Today this is the norm for 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. These are referred to as History based solid modelers.

What is a direct modeler vs. a history based modeler?

A direct modeler is the latest type of 3D solid modeler, one that allows simply picking and dragging on a parts features to change them. SpaceClaim was one of the first developers of this concept. A disadvantage of History based modelers is as the model becomes larger and more complex it can become difficult to make the changes you would like to make. You have become boxed in by how you created the part with the History based modeler. Usually you can change it, but it takes quite a bit of work. Direct modelers have solved this problem quite well but, to date, I have not been so pleased with how the rest of the direct modeling software has worked. SpaceClaim has worked very well at importing geometry from a 3D solid modeler or FEA software tool, that you do not have access to, modifying the geometry and saving it to a neutral file.

What is the difference between prismatic and organic parts?

Prismatic parts refer to mechanical parts that use constant radii curves, and fillets. This is typical of many Mechanical Engineering parts, assemblies, and products. Prismatic parts are typically created with 3D solid modelers or just CAD software.

Organic parts refer to mechanical parts with much more complex variable radii curves. Examples of organic parts include: automobile bodies, aircraft wings and fuselages, and consumer products. Organic parts are typically created with 3D surface modelers.

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 2D design to 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.


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