A Challenging Channel - Modeling a Sheet Metal Channel in Fusion 360

On a morning this weekend, while hanging out at home with my coffee in my hand, I decided to play with Fusion 360.  I had a part picked out that looked simple enough.

The finished part. It looks simple, but it hides a suprise

The part I chose looked to be a simple sheet metal part.  It looked to be a simple enough part, but it did have a joggle in it that complicates things a bit.

The joggle that changed how this part was made

Since it's got this joggle, it can't be easily modeled using sheet metal tools.

The sheet metal version wasn't quite what I was after.

So I decided to model it using the "regular" modeling tools.

I also decided I'd document how I did it here, for both posterity's sake, and in the hopes that it might give another struggling user an idea.  I won't go through every single step, but I will give an overview that hopefully encompasses the high points.

The first thing I did was model the envelope.  I nothing more than an extruded rectangle.  A "brick".

The starting point. An extruded rectangle representing the parts outer dimensions.

Next came the process of carving out the shape. I started with the joggle.

The joggles cut into the part. I've turned one of the sketches on to make it more visible.

Once the joggle was in, it was a matter of adding the remaining features, including the outside fillets that represent the outer bend radius.  Notice that the part is still a brick.  It's just a brick with some nice looking features!

The brick has all the features of the sheet metal part now.

This is where my original plan went wrong. My plan was to use the shell command to create the inner profile.

But for some reason, I couldn't select the surfaces I wanted.  I always ended up selecting a surface I didn't want.

So it was time for plan "B".  I switched to the surfacing workbench and used delete face to remove all the faces except those that represented the outer profile of the part.

The part with all but the outer profile removed.  

Now that I had only this surface, I was able to return to the solid workbench and use the thicken tool to get the final shape I needed.

In Conclusion

So is this the only way to do it?  I doubt it.  But it did get the result I was after in a way I was happy with. I'm sure someone out there has a different way of doing it, they may prefer it.  And maybe someone out there has a way that's truly better.  I would be thrilled if they do and I hope they share it!

How would this part be made in real life? 

This is one place that I'm not an absolute expert, so I encourage others to chime in.  But I do have some experience making sheet metal this way.

In production, a blank would be placed in a die, possibly using two of the holes to locate the part.  Then a press would push the two die halves together, forming the part in one operation.

Here's a pretty good video on this process used for the ribs on an aircraft wing.

If the part is made in low production, A form block can be used, made out of wood or metal.  The blank is then formed using a hammer.

He's a video on that process. While this video shows the process being done for steel, aluminum would be done in a similar manner.

The part I modeled in Fusion 360 calls for 24ST aluminum, which is the equivalent of 2024-T3. I know that 2024-T3 can crack when formed around tight bends, so it's possible they would have used 2024-0 (dead soft) and heat treated to the -T3 condition afterward.  But that's one place I'd have to defer to the sheet metal experts, feel free to chime in!

And that's it, I hope this video was informative!

A Final Addendum, Murphy's Law Strikes! 

As I finished up this post, I tried the shell one more time.  Guess what! It worked! It seems I was just not quite getting the picks and clicks right when I tried it earlier.  But I decided to go ahead and share the post anyway because I still feel it's a viable alternative. 

It figures! The shell does work!