Sheet Metal Tote Tray

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Unlike others, I was never introduced to sheet metal forming techniques while in high school or even in college. There was a class we all were required to take on manufacturing processes, where it was briefly discussed, and we also had a shop were we learned to use a few tools and machines, like the lathe, as well as several welding methods. I used to cut and prepare metal for welding, but I can honestly say I never learned how to bend it and form it. I’ve bent tubes in the past, though if that accounts for anything…

Anyway, I’ve been curious about sheet metal, so I’ve been doing some research and, with a little bit of help from here and there, learning about basic techniques with a small leaf brake. One of the beginner’s projects is a tote tray. The pattern seemed really simple, so I thought I would try and model it in SolidWorks. It was certainly a good exercise, and not as simple as I thought.

The tote tray is an assembly of two parts, the main body of the tote tray and a handle, as you can see in the following image.

I started modeling the main body by first creating a rectangular base flange. The pattern called for 24 gauge metal. I assumed it should’ve been galvanized steel, but I only have a couple of tables that come with SolidWorks, and the only 24 gauge metal available was Aluminum, so I used that one. Once I had my rectangular flange, which is actually the bottom of the tote tray, I proceeded to add an edge-flange on one of the short sides. To do this simply select the edge and click on Edge-Flange on the Sheet Metal toolbar.  You will see the Edge-Flange property manager on the left and a preview on the graphics area.

The arrows you see in the preview allow you to modify the direction of the bend to go up or down. You can also modify the angle of the bend through the property manager. I need an angle of 90°.  I’d also like to mention something else that you can’t appreciate from this image: when you first add an edge flange to your part, the shape of the flange is going to be rectangular, just running all along the edge. The reason why my edge-flange looks different is because I modified the sketch used as the flange profile. It’s not hard to do, just click on  Edit Flange Profile in the property manager, modify the sketch and then click on Finish in that little dialog box, as long as it says that your sketch is valid, of course.

Next, and still following the pattern, I added a hem to two of the edges.  From the property manager, I chose a closed hem and material inside option.  Unlike with the edge flange, it does make a difference which edge we choose for the hem. If I had chosen an edge on the outside face of the flange, then the hem would’ve been added to the other side.

After mirroring the first edge flange and its hems, I added another edge flange to one of the sides and then a third smaller one that the pattern calls for and that, I believe, will help close the box. My choices for this one had to be slightly different than for the rest, to accommodate for the material in other parts of the box. The pattern I had didn’t mention this. Anyway, for this flange I had to choose to have the bend outside, since choosing material inside or even material outside would cause interference with the other parts of the box. You can appreciate in the image that there is a small gap between this flange and the second one I made on the side previously.

The rest of the flanges and hems were made in a similar fashion, I mirrored whatever operation could be mirrored and then trimmed the corners.

I had a pattern for the handle of the tote tray, as well, so I first tried to make the part and assemble both together, but it wouldn’t fit right; there was a lot of interference between the two parts. So, I decided to try modeling the handle in context.  For this purpose, I added a plane to Tote Tray 1 (the main body of the tote tray), where the bottom of the handle would be placed.  The first thing I noticed was that I needed to find a way for the sides of the handle to clear the hems of the first part, so while sketching the flange for the bottom of the handle, I left a gap big enough to make sure there would not be any interference (the thickness of the metal plus a little bit more to allow for the gap in the bend of the hem). This can be better appreciated in the following image. Notice how the hem passes behind the flange and both parts don’t interfere with each other no more.

A similar consideration needed to be made for adding what the pattern calls a “hook” for attaching the handle to the main body of the tote tray. I did this with another hem, choosing for it to be open, with the bend outside and a gap distance big enough to clear the gap I had left in the beginning, when sketching the bottom flange, plus the thickness of the metal, as you can see in the image.

Once again, I added a couple more flanges to the sides and mirrored whatever could be mirrored to obtain the final result.

I don’t know if this is the right or even conventional way to do design in sheet metal. When I unfold the parts, they look pretty much like the pattern I had, but the measures just don’t quite match, because mine takes into account all those issues with interference that seemed ignored in that other pattern.  It’s almost as if the other pattern assumed that the bends wouldn’t take space at all. Hmmm…

Comments

[mechanical presswork]

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