Bend Radius and Fusion's Sheet Metal module

[ZephyrSurfer]

I've been looking for a more powerful CAD tool for my 3D printing. I'm a Mac user, though I do keep a relatively capable Windows 11 laptop to work on my car since that software is Windows only. I had Solid Edge, Shapr3D, and Fusion on my short-list.

I'm really drawn to Shapr3D since it is so easy to use, and I was about to go that direction until I ran across a Sheet Metal K-Factor video for calculating cuts for folded sheet metal parts. ok, that's cool and sets it apart from Shapr3D. Especially if it I can design a part and have it print out where the bend-lines are as well as the overall flat-plane dimensions.

So, has anyone used it to get the 2D pattern and lines for bending sheet metal? They list a "K-Factor" for calculating the bend radius of various metal sheet, but I'm curious if they have embedded the proper math do follow the FAA spec of AC 43-55 on bend radius. The YouTube video I ran across said the user would need to experiment with setting the "k-factor" until they got a satisfactory result with the material they are bending.

 

[terrye]

"K factor" in CAD software is a bit of a black art. I'm using Solidworks and it defaults to 0.50. I usually change it to 0.45 (toward the inside of the bend) and have had good results with 2D stretchouts, but I don't have a CNC brake and am not making precision parts (like Vans), mostly just brackets. I think Vans in the past used Solidworks, I don't know if they still do. In any case, the "K factor" needs to be adjusted in the CAD model with some test bends to verify. I suspect the second decimal point would change depending on the alloy but haven't tried this.

 

[Snowflake]

Give FreeCAD or the slightly upmarket version OndSel a try... I *think* it has a sheet metal module. It's also free, so there's no cost to try it other than your time.

 

[JRichichi]

The "K-factor" everyone is talking about varies depending on the material you use (and heat treat or temper) and the process how you bend the metal. If you use the same material (and heat treat or temper), and the same bending process (box brake, air brake, etc.), you can change the thickness, bend radii, and angle of bend using the same K-factor and you should get the same results. If you start making large changes in thickness, bend radii, or angle, you might start getting some variation in the K-factor. Typically, for thin materials and only a few bends, the actual different the K-factor makes between the "real number" and "0.5" is small. However, if you want to be more precise (or use thicker material and/or more bends), the actual K-factor should be used.

There are two ways that I know of on how to determine the K-factor. One is based on actual tests (the more accurate way of course). The second is based on using the ultimate and yield strengths of the materials. I've attached a few PDF's that should help you out. The "Standard Bend Radii" PDF lists the proper bend radii for various materials, heat treats/tempers, and thicknesses. The "Sheet Metal Bend Allowance" PDF is the method to determine the K-factor based on material ultimate (Ftu) and yield (Fty) strengths of a material. I tried to attach an Excel spreadsheet that does the number crunching for you, but I don't think the software will allow this. If someone knows a way to attach an Excel spreadsheet, please let me know and I'll upload it.

I hope this helps.

Jeff

 

[hgerhardt]

Lately I've had several bent sheet metal parts made by SendCutSend. Amazingly accurate and reasonable $$ too. Below is an avionics support shelf I designed and had SCS make.

On their website they list alloys and gauges of sheet metal which they have available and the corresponding K-factors as well as bend radii. Plug the given K-factor and radius into your CAD and send the generated flat pattern as a dxf to them and 5 days later you have nice parts. Of course if you want to make parts via your own brake, well, can't help you there, other than you could take SCS's bend criteria and use that on your own parts.

 

[azrv6]

Just to add to the list, I'm on Mac and am using Onshape. It is free. Based on and very similar to Solidworks. Has a sheet metal module and can handle K-factors. Youtube channel "Too Tall Toby" has a ton of video tutorials including an entire sheet metal playlist.

 

[Snowflake]

Just to add to the list, I'm on Mac and am using Onshape. It is free. Based on and very similar to Solidworks. Has a sheet metal module and can handle K-factors. Youtube channel "Too Tall Toby" has a ton of video tutorials including an entire sheet metal playlist.

OnShape was developed by people who left Solidworks because they wanted Solidworks to move towards an online interface and Solidworks said no. But last I checked, OnShape wasn't any cheaper than Solidworks to use... Is there a free version now that limits you somehow?

 

[jmpratt]

OnShape was developed by people who left Solifworks because they wanted Solidworks to move towards an online interface and Solidworks said no. But last I checked, OnShape wasn't any cheaper than Solidworks to use... Is there a free version now that limits you somehow?

Yes, Onshape is free but only allows you to save files to a public folder. If you want to keep your designs private, you have to pay for it.

 

[rdamazio]

My experience with SendCutSend has been great, except for bends - they got every single bend I ordered off by a little bit, even though I used the correct K factor they specified (maybe I still messed up somewhere? but I didn't want to keep spending $$ until I found out why/how). Ordered the same part from Oshcut (uploading the 3D STEP file), and the part was perfect. https://www.airplane.build/2022/03/baggage-area-o2-mount-box.html