Sheet Metal Fold Fails at Intersection with 0.9mm Metal Thickness 1

[cjjatpuresilica]

For several months I have attempted to make the transition from MDT 2009 to Inventor 2011, albeit at the same time being embroiled in a legal battle with the board of directors of a particularly nasty example of a British Bank.

Notwithstanding the latter, I seem to have overcome much of my earlier difficulties in my endeavours to develop a flexible sheet metal model; but I am stuck on just one element for which I would be most grateful for fellow reader’s assistance please?

Although the model attached looks fairly straight forward; when developed fully it does have two more folds and four more flanges.

My failure however, revolves around the mid fold of circa 0.7 degrees, when I choose any of the InnerIntense variants from the model type list within Parameters; which have a metal thickness of 0.9mm driven from the Rule table. It works OK with the two thicker variants of Outer and InnerNormal; that both utilise 3mm metal.

The problems appears to be caused by the fold taking place at the intersection of twin top and bottom edges which are not quite at 90 degrees.

In the past I have requested help and have been advised that my use of such a level of accuracy is misguided; however that seems to be an admission that Inventor is not suitable if one needs to develop an accurate model.

Any meaningful help of how to develop this model without the need to change metal thickness or reduce the level of accuracy would be greatly appreciated.

Thank you.
cjj

 

[rollupswx]

I would not use pink lines for sketches as that is Inventor default for "sick" sketch geometry. (are you using AutoCAD as your sketcher?)

I have not use Zero length dimensions since leaving MDT. Use Coincident Constraints.

I would modle "as folded" and let Inventor figure out the flat rather than using the Fold command.

 

[rollupswx]

I am not aware of an accuracy problem in Inventor?

 

[cjjatpuresilica]

Dear rollupswx,

Thank you for your kind reply.

Would it be possible please to expand on your suggestion to model as folded and let inventor figure out the flat rather than use the Fold command?

Thank you,

cjj

 

[cjjatpuresilica]

Dear rollupswx,

May I also ask you to please explain how to use a coincident constraint to anchor the end of a line on a model whose size is changeable?

I am most grateful,

cjj

 

[rollupswx]

Project Geometry from one sketch to another or from a solid feature to a sketch.

Do the best you can to model a finished part using the standard tools and then I'll show you how to do it with the sheet metal tools.

You might want to read this

http://home.pct.edu/~jmather/skillsusa university.pdf

 

[rollupswx]

Haven't we been through a lot of this before?

http://www.eng-tips.com/viewthread.cfm?qid=286645&page=1

I don't see any progress in technique?

 

[cjjatpuresilica]

Dear rollupswx,

I managed to resolve the fold failure by creating a small flat; perpendicular to the vertical axis, on either side of the proposed fold line.

Would you be so kind as to check to see whether I have created the 2 sketches correctly please and whether my solution is an acceptable one.

I am most grateful.

Thank you.

cjj

 

[cjjatpuresilica]

Dear rollupswx,

You are correct in that you have helped me with a very similar sketch before.

Last time you suggested that I might like to look at using surfaces but I couldn't find any meaningful tutorials on the subject, although it was a format I was relatively familiar with in MDT.

It may seem offensive but I still find many of the command line attributes of MDT preferable if not better functionally than some aspects of Inventor.

In particular I find the inability to ground my view of an object as one could in MDT limiting, certainly for me as a novice. This particular part when folded leaves it's original sketch plane at a compound angle, which makes it difficult to manipulate the model. I am sure it must be down to my lack of understanding of the programme.

I am sorry my progress appears disappointing to you, but my concern has not been to develop my inventor skills per s? but to be able to get a stable version of this particular model that could be used over and over again with different sizes and thicknesses.

Many of the requirements are at odds with Inventor's intuitive functionality which has caused me numerous problems.

To date I have re-modelled it some 150 plus times and every time it has failed on one aspect of the sketch or another.

Thank you for your kind assistance.

Christopher

 

[rollupswx]

... I couldn't find any meaningful tutorials on the subject...

There aren't any that I am aware of that cover this topic in any significant detail. It is an advanced topic with a small audience. There is some information here - but not much

http://au.autodesk.com

 

[mcgyvr]

Chris,
Do you have a drawing or something of what you are actually trying to model (finished with all the details)?
Right now I'm really failing to see how anything about this is difficult.

And one must have the proper "inventor skills" BEFORE you can get stable models that can be used over and over again. Walk before you try to run.

 

[cjjatpuresilica]

Dear mcgyvr,

Thank you for your observations.

It would seem that the problems I have encountered have been those associated with using Inventor's Sheet Metal technology to design a model that is not in any way a traditional looking box.

Whilst it is easy to recognise the many attributes of Inventor I would willingly stay with MDT 2009 but for its inability to cope with sheet metal models in the way that Inventor does.

It would certainly be more helpful, if fellow readers actually looked at the model and tried to understand why it is failing, rather than pass simplistic judgemental criticism willy nilly on my skills or lack of them.

I thought the purpose of such postings was to enable those readers with greater expertise to assist new fledgling users, not to sit it patronising judgement and offer one line meaningless help?

 

[rollupswx]

The problem is that you are going about it all the wrong way. Forget Fold. Forget that it is a sheet metal part for now. Model the external geometry as though it was a solid part in finished form. Then someone will show you how to model it as a sheet metal part (probably not limited to using just the sheet metal tools).
Keep in mind that the sheet metal tools are simplistic tools for creating common geometry. But sheet metal is simply constant thickness material. Other techniques can be used for more complex geometry that still results in uniform thickness part.

 

[rollupswx]

Here is an example of a relatively simple part that would be exceedingly difficult to model with Fold or other standard Sheet metal tools and get the desired end dimensions.
But it is trivially easy and robust in editing if going about it with other techniques as shown.
And it isn't limited to the CAD appication - it is all about geometry rather than the particular program used.
I haven't met anyone who could use MDT right either.

 

[cjjatpuresilica]

Dear rollupswx,

Thank you for your kind further guidance.

I am just about to open the model you provided and will then set about modelling my end component as per your suggestion, ready for your further kind help.

I am sure you are correct about MDT. For my sins I used it on and off for some 13 or more years but never professed to have anything but a smattering of knowledge on the subject. I suspect that Inventor and MDT before it, are a bit like the UK’s taxation laws as implemented by Gordon Brown. They are so complex and far reaching that there is not a single accountant in the country that has a thorough and complete understanding of them.

Nevertheless it would be most beneficial if I could find my way around Inventor in a meaningful manner.

I will post again once my model is complete.

Thank you once again.

Christopher

 

[cjjatpuresilica]

Tuesday morning

Dear rollupswx,

I have endeavoured to produce a finished model but I am struggling with the bottom flanges.

They do not want to from part of the main model and either will not thicken with it or enable a radii to be applied to the adjoining edge.

I realise I am doing something fundamentally wrong and would be most grateful if you could please elucidate what it might be.

I am most grateful.

Christopher

 

[cjjatpuresilica]

Dear rollupswx,

I have stitched the bottom flange surfaces to the main body and thus I hope, overcome that problem correctly.

I am now faced with the problem that has been dogging me for some while; namely the bottom flanges per se.

In the model I obviously cannot apply fillets to the intersections between the bottom flanges and the side faces without introducing some form of rip.

I accept that I could thicken the model without the bottom flange surfaces and then add these as standard flanges under the sheet-metal option.

However, regardless of how wide I set the mitering gap under auto corner mitering, the end result always diminishes the very bottom of what I describe as the hip beam or corner. It is imperative I retain the hip/corner for its entirety, thus the rectangular cut-outs through the corners of the bottom flanges.

Hence I am back to requiring a rip at the end of each of the bottom flanges to allow a radius to be formed.

Do I just form the rips by simple extrusions or is there an automatic simpler means?

Or am I going about this in entirely the wrong manner?

Thank you for your kind help,

Christopher