One correction: The width of the cut is the same as the thickness of the sheet. The depth of the cut is half the thickness of the sheet.
SolidWorks Sheet Metal requires constant material thickness.
What you want to do is build your formed part first without the cut. Then flatten and add the cut after.
If you use Anna's method and want your parts to come out dimensionally correct when they are bent, you will have to use a different K factor for your bends, as half of your material won't actually be there. If you would normally use a K-factor of 0.35, you will probably end up using 0.675 (0.5+0.5*0.35).
I agree with Jerry, but I haven't tried to figure out the resulting K factor or bend deduction that results because I use the 'etch' bends. What I do is not cut all the way across, I leave a short length, 'unetched' at each end of the bend line.
Curious if you ever worked this out? I'll tell you my recent experience:
We have a series of duct nozzles made from .018" thick stainless sheet with half-etched bending channels .025" wide for 90 deg and .050" for 180 deg, for hand-bending and spot welding. Whenever we needed to make custom dimension nozzles I used to manually alter Autocad drawings, such a waste of time....I decided to finally make a SW model.
Unfortunately these etched channels are on both sides of the sheet, so I could not use a half-thickness sheet and then add half-thickness extrusions to the flat pattern. So I ended up using full thickness sheet, then sketched bends at the centerline of the channels, with a bend radius equal to the 1/8 of the sheet thickness and a K-Factor of .25, this is for 90 deg and 180 deg bends. I think this corresponds to a neutral line halfway down the (non-existent) etched channel (ie 1/4 of the sheet thickness).
And then add cut-extrudes to the flat pattern for the etched channels.
So this allows me to get a folded model that corresponds to the correct flat pattern. Haven't had time to try in the opposite direction yet.
A friend gave me the solution:
If I have a part that I want to bend, I create two different parts. The original part (which only exists in my head) is split at the middle of the bend. I then create an assembly which has two "configurations" to combine the two parts into one assemby. One configuration is bend, the other is straight. See attached example.
The downside of this is that I get a lot of small parts and many assemblies, but I haven't found any better solution that actually works for me.
Right, I see. Take a look at the part I have attached. Here I have take a piece of the original Autocad drawing and extruded to the full sheet thickness (I removed most of the folds to make it clearer). Then using the Bend Radius = T/8 and K=.25, when I fold the two tabs tab over twice, I get the correct folded geometry (at least in the sense that the two holes line up and the total folded thickness is correct).
Etched_Bend_example.SLDPRT.zip 124.6 K
I was not able to open the part. I has SolidWorks 2012 and maybe it's too old version?
OK, step by step;
Create a flat sheet metal part, half the final thickness required.
Add material (half the final thickness) to create the "etched" line recess.
Use a Sketch Bend to form the bend.
The trick here is to make the recess wide enough to avoid the edges contacting each other when formed.
Kelvin, I think Daniel and I both require the inside corners to actually touch when bent. Also I need etches on both sides of the sheet so I don't think the half-thickness works.
Previous engineers here (long gone unfortunately) figured out the correct bend allowances for stainless steel thickness T=.018" with half-depth etched bend channels:
For sheet thickness T=.018", Bend Radius R = 0 they use:
Bend Angle A = 90 deg use Bend Allowance BA = .025"
Bend Angle A = 180deg use Bend Allowance BA = .050"
So calculate K-Factor = [(1/PI)*(180/A)*(BA-R)]/T = 1/(20*PI*T)
Thickness T 0.018
Inside Radius 0
Bend Angle A Bend Allowance
If I use this K-factor with R=0 for Daniel's 0.30mm thick sheet, I get these allowances:
Thickness T 0.3
Inside Radius 0
Bend Angle A(deg) Bend Allowance (mm)
Daniel, I attached a SW2012 file with a 90 deg and 75 deg bends on opposite sides, K=.88419, (Inner Virtual Sharp, BendOutside). Sketch6 on the flat pattern shows the etch widths match the table allowances. Do these allowances come close to the etched channel widths that you use? If not I think you could adjust the K-Factor until you get a match.
That's all I can do on this for the moment unfortunately, got to move on....
Thanks for your help. I can open your last example.
I'm new to etching and I got the solution to the problem by an experienced constructor which has developed several train models with this technique, so I will stick to it. It's not perfect, but it works for him. (I haven't yet had sent my sheet for etching). But I hadn't got his answer at the time I asked the original question here.
The good thing with my solution is that I have control. I can add new holes for example, without adding extra trouble.
Uh oh, same problem Daniel has with me, I'm on 2013!