Because CAE is used for analysis and is simplified compared with CAD which is used to define build intent. I suspect by CAE you are referring to the rather dull topic of FEA, typically FEA models do not include the essentials of real structures like bend radii, tolerances, surface finishes, and so on.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
CAD and CAE have two different purposes, both very important. CAE helps the engineer refine and improve his design. CAD allows him to communicate that design accurately and completely in the outside world to folks who don't want or need to know about stress levels, but do need to know about fit and finish, fabrication techniques, complete specs of commercial items, etc.
Every CAE tool I've used had very weak modeling tools compared to any CAD tool I've used. Usually I import geometry and only use the CAE modeling to make little tweaks or clean up the model (mostly defeaturing but even that is usually far simpler in the CAD tool).
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There are also practical reasons. Say you have multiple CAE tools from different vendors; would you really want to have the multiple CAD tools from each CAE tool also, and not necessarily be able to cleanly transfer data between CAD tools, just to use the CAE tools?
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
Along the same lines as what IRstuff said, there are multiple downstream uses for CAD data, CAE being only one of them. You can also do CNC programing from CAD models, inspect production, make renderings for sales literature, create owners manuals, etc., etc. Some of that can be done from some CAE models but usually the options are much more limited.
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Of course, some of the CAD, CAE, CAM... packages are pretty integrated these days.
Though many still doubt or have issues with the CAE function of those packages.
Plus if you're in an environment you can make use of full MBD then the drawing aspect goes away - but you still need suitable 'annotation' functionality in your modeller.
CAE systems are typically coded to create geometry for the simple purpose of performing the analysis. Their geometry creation and editing is also usually limited to the resolution and forms that are practical for that analysis context.
CAD systems are coded to create geometry for practically any use. It used to be drawings only, but the 3D / 2D systems really are well suited as the "all around" solution. We have a couple of "CAE" systems (fluid dynamics and structural FEA) and in both cases we find more productivity by modeling in a CAD system not the CAE modeler.
When you're using a system not well suited to the end use, productivity can be nearly impossible.
