Sheet metal - flat pattern issue

[teak]

Hi. I'm having an issue with a flat pattern not generating. After a quick check of the common reasons for failure,  the material type and thickness seem to match the sheet metal default being used. The design intent got pretty murky through the development of the assmbly, and I just need a flat pattern to cut this part "Back plate_sheave box.ipt".

Please forgive any oversights or omissions...newbie. 

[kacper.suchomski · Accepted solution]

Hi

You have made a plate in inches and set the thickness in mm in the sheet settings.

Btw, classic modeling tools should not be used for sheet metal design unless absolutely necessary.

[pcrawley · Accepted solution]

Missing tangency on the bottom inside radius:

Personally, I would make the bottom sketch line construction - then make the base feature using Contour Flange.   

 

 

[pcrawley · Accepted solution]

Actually... that wasn't all that stopped it flattening.

The units mismatch indicated by @kacper.suchomski also contributed.  I added "d10" shown below:

Then set the Sheet Metal Style "Thickness" = d10.  Now it flattens correctly.

The tip in @kacper.suchomski message about using Sheet Metal Features would have caught all this had you used Contour Flange as the original feature.  Extrusions for Sheet Metal are OK, but you don't get to see this sort of problem until the part looks ready for manufacture and you suddenly realise you can't make it. (Sorry - it sounds like preaching to someone who's already very good with Inventor!)

[teak]

Thank you for your response. I appreciate the insight on sheet metal. Is there an accepted best practice for unit systems as they relate to SM? Some of our projects seem to be easier to model in metric units, while others make more sense in imperial - some SM and others not. Our SM defaults are all set up as imperial gauge sizes. Would you recommend having metric sheet metal defaults? Our focus is on manufacturing, and we can't access material in these sizes, so it hasn't seemed to make sense previously.

[kacper.suchomski]

The list of default settings is intended to speed up work with commonly used variants. In any file you can choose not to use the default thickness and enter the value currently required.

[teak]

Thank you! Contour flange is truly an elegant solution to my fumbling attempts here. Can I ask how you located the missing tangency contraint so quickly? I find that sketch doctor can pinpoint issues, but often gives an error message when attempting to resolve them. I struggle to effectively manage contstraints and often end up being forced to delete the sketch and start over.

[pcrawley]

I wouldn't call what you achieved a "fumbling attempt".  When you develop something from scratch, it's hard to decide the method for creating the model.  What you achieved was an outcome, and that's what pays the bills.  However, if you know that a part will be sheet metal, make it with sheet metal tools because they actually help you find the things (like missing tangency) as you create each feature.  

How did I find the missing tangency... Design Doctor doesn't look ahead for things that aren't acceptable to a given feature (like a flat pattern), so it probably reported things were OK.  None of the features would flatten, so from previous experience, only three things prevent flattening: Non-uniform thickness, self-intersection, and failed tangency.  Given you had already checked thickness - and there's no obvious self-intersection - I just looked at the front & back of the two bends.  On the bottom bend, the inside face was much smaller than the outside face, which means something was wrong in the defining sketch - zoom in and there was the missing tangency.

[teak]

Use SM tools when making SM parts. Thickness, self-intersection, and tangency - three things to check anytime a feature won't flatten. The solution often sounds so simple with a clear and concise explanation. Thank you @pcrawley & @kacper.suchomski so much for making my first experiece posting to the forum a truly pleasant one.