Sheet Metal Flat Pattern is not working consistently

[Lifeisriding]

Hello, 

I have a work flow that HAS worked great where I use Sheet Metal components to design multi piece parts with intersecting curves. I then can make flat patterns from each of the Sheet metal components and cut on the CNC and get great results. 

I have spent the last few work days battling some really weird results however where there are issues selecting the sketch line to create the first sheet metal flange also unfolding it when I am able to get it to work. I have also had Fusion freezing for very long periods of time with multiple crashes while working on this which is very unusual for my experience. 

As I said above I have done this before and just recently with great success and a almost identical shape. 

I thought maybe it was the use of Splines in the initial sketch instead of curves but that seems to only help some of the time.  Here is a screen shot of what the unfolded components are coming out like sometimes. 

Here is a link to a stripped down version of my working file that shows the strategy I am using as well as the unusable results.

I tried finding another workflow recommended on the autodesk forums for Inventor usere where they export a .stl and use Unfold command in meshmixer but had not success there either. 

Any help would be greatly appreciated. 

Thanyou, 

-Marc 

[hfcandrew]

When you export the model as an .stl from your link it is non-manifold with internal walls. This will cause unwrapping/flattening algorithms to fail.

[Lifeisriding]

@hfcandrew What you are saying makes sense HOWEVER, what I tried was a work flow suggested by AUTODESK Support as you can see here. 

Really, I would just like the sheet metal workspace to be reliable in fusion since I know my work flow has recently worked just fine with an almost identical shape. 

[hfcandrew]

Wow, just read that. That workflow for MM is wrong. lol

Do NOT thicken/offset/extrude etc. You must have a zero thickness model for accurate and meaningful sheet metal unwrapping in MM.

Also remeshing to a much high density is required. See attached.

Was you scaling off? You model is 2730mm long... i scaled it down

[WeekenderSolutions]

I have a hard time trying to get sheet metal models to work if I start with a regular model then try to "convert to sheet metal".  It never works reliably for me.  If im working with sheet metal models then I have to start with a sketch under sheet metal then use "flange" and a sheet metal rule to give the component its thickness.  That is the only way I can get bends and flat patterns to work properly since its using the sheet metal rules for bending.

[TheCADWhisperer]

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@WeekenderSolutions wrote:

I have a hard time trying to get sheet metal models to work if I start with a regular model then try to "convert to sheet metal".  

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If you follow the 4 rules - Convert to Sheet Metal will ALWAYS work as expected.

@Lifeisriding 

Your model does not match the real world (cuts not perpendicular to the flat).

I would not use this workflow.

[Lifeisriding]

@TheCADWhisperer " does not match the real world"

That is cute, thanks for chiming in with your helpful advice. 

I guess this picture "I attached below" of a very similar part made with the EXACT same work flow last week is from a different world then the "Real World".  

[Lifeisriding]

@WeekenderSolutions, I also start my sheet metal components as an actual Sheet metal component with a sketch line that is extruded as a (First) flange to get the initial body for the component. Every time, including in this file above as well as in the time before when it worked fine. I think its the only way? I have never tried converting a body into a sheet metal component. Thanks for taking a look and my problem.

[Lifeisriding]

@TheCADWhisperer How would you model these two curved parts so that you can cut them out from flat stock if not similar to how I do it? 

[PCprincipal]

I also have an issue with the only tool I know of that allows me to change the cuts angles without altering the perpendicularity of the cut: draft.

It was working perfectly before and suddenly it's acting up. First requiring you to unfold the bend in order to execute the draft. OK, I can always refold and edit feature till I get it right, but now it wants to move any other previous draft in the same bend synchronously WITH the draft I'm trying to apply. It's driving me nuts!

[Lifeisriding]

@hfcandrew Since that link to the file is literally a Fusion file it should be scaled correctly. 

I was designing in inches, and if you exported and imported into MM that might be the issue. One of the unfolded parts should be over 8' long but since I can't unfold it in fusion without wired errors I can't actually tell you how long it is exactly. 

I really appreciate you trying to help me out, I downloaded the file you posted but don't have a program that seems to be able to open it. I havent yet tried meshmixer which is on my other computer at the office if thats the way to go. 

[Lifeisriding]

@PCprincipal When did the problem start happening for you? 

I think for me it started mid last week. Previously everything worked very well on multiple projects. 

[TheCADWhisperer]

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@Lifeisriding wrote:

@TheCADWhisperer How would you model these two curved parts so that you can cut them out from flat stock if not similar to how I do it? 

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It will take me some time to create a video.

I have the components modeled up - I just need to show how I would model the components, how to use MeshMixer to Unwrap and a bonus of how Unwrap works in Autodesk Inventor Professional.

Editing videos takes me longer than the actual CAD modeling... ...and I am in the middle of another big job.

[Lifeisriding]

@TheCADWhisperer Impressive that you were able to get a nice result in the picture you shared although it looks like you are using Inventor and the Unwrap function? Is that correct? If so I do not have access to that program. 

[TheCADWhisperer]

When I get a chance I will run Unwrap in free MeshMixer.

[PCprincipal]

I think it was about the same time.

[TheCADWhisperer]

@Lifeisriding 

As mentioned by @hfcandrew you only need Surface Body to make a roundtrip to MeshMixer - Unwrap and back to Fusion 360 to get the DXF...

[Lifeisriding]

@TheCADWhisperer  It was a very busy time and I am just getting to watching your video now. Thankyou very much for taking the time to make a video and help me with unfolding this sheet metal part. 

Replies to some of your comments in the video. 

-The K factor will not be 0 or 1 as you say in our case because we are kerf cutting the back side of the plywood around the bends and the part does stretch just like it would in metal. 

-The file I posted on here was copy and pasted from a much larger more complicated file. That is why sketches are not fully defined in the example you downloaded, the were fully defined in relation to other parts and geometry that I stripped away for my Help Post. 

-The imperial measurements that are not rounded to the closets 1/8" and bother you are the result of tracing a large Mesh file to get the proper interaction between our parts and the parts from the real life source of the mesh. So they are what they are and make no difference to the CNC , the installer or the client. 

-I modeled this part to the be a " Perfect fit " and then in CAM I add my tolerance for fitment with negative stock to leave.  Since when actually cutting on the CNC is when and where you find out if you need to add a little more tolerance. I have found it a much faster work flow to get parts that fit then trying to guess the perfect tolerance during the design, or going back to the change the tolerance in the design and redoing all the CAM ( some small changes in the design can mean big changes when you go back to CAM). Design it "prefect", then make test cuts, measure the joints when the part is still on the machine and adjust the stock to leave settings for a perfect fit.  Using different tooling, speeds and feeds as well as different materials all can have a big effect on the tolerance. 

-Using surfaces is an interesting way to model, I almost always go from sketch to solid bodies. Thanks for sharing that I will try it out. I guess that is also why i could not unwrap in meshmixer since my "Loop" was an .stl from a body not a surface. 

-Lastly thankyou again for all the time you took to help me out. It is funny that I was able to make these parts and different ones previously all within Fusion and now cannot. I hope what ever changes happened between the updates where it was working to now get sorted out and we can once again do in one platform. 

All the best, 

-Marc

[Lifeisriding]

@TheCADWhisperer The very last step in your video does not work as you intended. When you convert the Mesh to a surface the geometry changes of the part.  Look at time 9:28 in the video and then look at the shape after you convert it around 9:30, the end are curved upwards loosing all the critical geometry to make this work flow usable. 

I am playing around in the mesh workspace trying to figure out a work around that isn't me trying to trace the shape by hand with a sketch overlay. 

Do you think there is an easier way?

[TheCADWhisperer]

I was in a hurry and didn’t verify the conversion.

Try the faceted option, otherwise if that doesn’t work you will have to trace over the mesh.

I have another video where I show tracing over the mesh that I will post tomorrow.

If you Project a few key points and use a Fit Point Spline you will likely find that it takes very few points to get well within any possible manufacturing tolerance.