Monocoque and Semi-monocoque

[vex]

I am trying to figure out a way to easily create an assembly that reflects a monocoque or semi-monocoque structure, and I have sort of hit a road block.  My thought process is to use an iParts to place the webbing and stringers based on a simple outline; which was successful and lead me full steam right into my problem.

Actually creating a thin-wall 'skin' to wrap the stringgers in.  The only way I can think of attempting this portion of it is to develop the skin independent of the stringers while having the internal dimensions match the stringers external dimensions.  This seems very work intensive as it would require to know the exact outline of the stringers in space relative to eachother which isn't easily known when using the iPart feature.  I suppose I could create multiple sketches in the assembly view then copy them all into a new part file; loft; and then shell.

Is there a better/easier way to accomplish what I am attempting?  It would seem like such a very handy tool to increase the capabilities of Inventor, especially expanding it into other industries (boats, planes, basically anything that uses such structures).

[blair]

We used to build fiberglass boats, canoes and other fiberglass components. We had molds for the main hull and molds for a number of the tanks and other components.

It might be considerably different if you were just "glassing" in place a stiffener over a structural foam core. These came in sheets and were "scored" so that they could be "snapped" off and placed and "glassed over top.

Possible a picture of what you are trying to accomplish would help.

[vex]

Similar in principle.  Here's the proof of concept I'm working on.  As you can see the skin doesn't conform quite right.  Some of the stringgers/webbing pops through (this was done the way as described in my first post).  I'm currently trying to see if it's even possible; which for the stringgers/webbing it is.  It's just the skin/hull that seems to be the weak link in this attempt.

[blair]

I am thinking that you might want to create a work-plane for each "stringer" to "project the intersecting hull to create each stringer, almost like slices.

[vex]

If I'm understanding you correctly I would prefer not to do that as it would do a number of things that would not be beneficial to the actual design of a component like this.  In essence the more stringers (both longitudinal and transverse) that are connected to the skin the stronger the overall structure will be (not to mention lighter).  Creating an unnecessary amount of strips would also prove more work intensive I think.

Your suggestion does provide me with an idea however; using the same projections that made the loft possible, I could remove a specific amount of material to match the stringgers face area that connects to the skin.  This is still more work than I would like.

Is there anyway to create a tool to be used in assembly that will let you select faces/edges and then use that as the interrior surface and then build material out to a specified thickness.  Once complete allow you to save the skin as a seperate part file similar to how iCopy works?

[vex]

Well.  That seemed to work... but now I've hit another road block on how to do longitudinal stringers that both follow the curvature of the hull and connect the transverse stringers together.  I would have posted the files here for anyone to lookover and see if they could come up with an easy solution to this problem--but they appear to be too big (pack-n-go and zipped comes out to 4.25mb).  I honestly have no idea on how to accomplish this short of being able to loft in assembly.  Maybe I could do it with sweep?  How could I dictate the rails then... Hmmm....

[blair]

You should be able to do a Sweep. It will require a couple of sketches, one for the profile and another for the path.

[vex]

I can do a sweep in Inventor... but it only allows me to remove material rather than produce an independant part based on the geometry in question.  I can get around it by copying the various sketches into their own seperate part file, but there again I run into a trouble in that it would only allow me to do so much.  I would have to figure out some way to allow longitudinal stringers to be placed throughout the assembly based on the skin location  as well as the transverse stringers.

Anyone have any ideas on how to effectively accomplish this without beating my head against a brick wall?

[vex]

I know it's been awhile, and I appreciate the help thus far rendered.  I had, in fact, forgotten about this thread for some time.  I have made some significant improvements upon this process which allows me to create and place stringers at the desired locations without interference:

1. Create a skin and place in an assembly--or the desired shape in the desired thickness; shell works really well.
2. Place work planes at various locations to which stringers/stiffeners are desired to be incorporated.
3. Create part at each work plane
4. Draw the profile of the desired part AFTER using the project cut surfaces tool.  This will ensure that you do not extrude loft into the skin in the next steps.
5. Offset a specific amount from the original profile to incorporate the thickness of the stiffener/stringer.
6. Draw the other profile AFTER using the project cut surfaces tool.
7. Apply guides using either 3D sketch and line tool, and/or using 2D sketch and triming the projected splines to the appropriate shape.
8. LOFT the two profiles using the guides at the various corners.

I must say, that it seems rather silly to me to have such a useful tool as analyze interference and not have the ability to remove the interference as an option.  Having such an option would reduce the total time required for this process significantly while also increasing Inventor's flexibility for streamlined components.

Has anyone else come up with a better way?  Maybe utilizing the frame generator or other design accelerators?

[vex · Accepted solution]

After much searching I found this:
http://inventortrenches.blogspot.com/2011/03/find-interference-and-add-tolerance-to.html

Using this process will actually negate a large portion of the above procedure.  In essence, allowing extrusion, sweep, and lofts of less restraint so long as the individual component does not exit completely through the skin.  You can remove unwanted edges/intersections via this method, and reduces the procedural steps and time required.