Designing sheet metal parts in CAD

[1683cadder]

My team has never really done anything major with sheet metal, but this year we are considering using a sheet metal frame. My question is when you are designing a sheet metal frame, should you design the component in a 3-D model first and then unfold or should you start the design from a piece of sheet metal and then fold it into shape? What is the best bend radius to use? How does bending effect the dimensions (doesn't a bend radius cause dimensions to have really long decimals due to pi? If I make sense) or does getting it laser cut solve the dimension issues caused by bending?

[MetalJacket]

What CAD program are you using? With just about any program out there, the sheet metal tools make it really easy to design parts in three dimensions to make sure everything is the size it needs to be and then unfold it later. This prevents you from having to worry about bend deductions and radii during the actual design phase. As for your question about what bend radius to use, that is generally based on the preferences of the shop you plan to work with. Talk to them and see what they prefer, and what they can work with. The default for most CAD programs though is a bend radius equal to the material thickness.

[Nathan Streeter]

As Jesse said, most CAD programs have a sheet metal tool or part type. In Creo/ProE when you select that you're making a part (rather than an assembly, drawing, etc.) you can select to do a sheetmetal part rather than a solid part. You'll then model the part in it's 3D, bent form.

Assuming you have a sponsor doing the laser-cutting and bending, make sure you find out how they like getting the part files... whether .pdfs of the drawings, STEP or .dxf files, or a proprietary CAD file type. Also, find out what material thicknesses they stock or prefer... and what their preferred bend radii are. The sponsor that has often made sheet metal parts for us (but only infrequently bent) has a wide variety of sheet metal thickness (.050, .063, .083, .100, .125) but they only do bend radii in the multiples of a sixteenth. So, even though the standard is for the bend radius to be the material thickness, for our .100 parts we had to use a .125 bend radius.

In general, you can actually use a surprisingly thin piece of sheet metal as long as you take care to use bends and such as you should. You should rarely need to go over .083 for anything with bends... even AL5052-H32 plate (a relatively weak aluminum that is often preferred for bending) with a thickness of .100 or .125 has a surprising amount of rigidity to it. For a drivebase or other "high-strength" situation it wouldn't hurt to use .083; however, for most other situations .050 or .063 should be fine... as long as bends or stiffeners (angle, standoffs, etc.) are in place.

Feel free to post screenshots or CAD of your sheetmetal parts up here... we'll be glad to help give you tips before you send designs to be made.