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How accurate and reliable is Inventor’s Flat Pattern?

67 REPLIES 67
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Message 1 of 68
Breeze104
1831 Views, 67 Replies

How accurate and reliable is Inventor’s Flat Pattern?

How accurate and reliable is Inventor’s Flat Pattern?  We have clamping bands that we form in a press and then put a final sharp break in one end as a spacer once they are bolted together.  I am using the contoured flange tool to create the part.

 

The reason for the question is that I can’t make these numbers work together to produce a product that resembles this 2D dwg.  What ever you can tell me sure would be helpful.

 

See doc for pic of part

67 REPLIES 67
Message 21 of 68
mrattray
in reply to: Breeze104

It shouldn't be. If it is then that tells me how seriously messed up your file is. Roll the EOP marker to the very top of the model tree so that nothing is visible and save it. It should be small enought to post then.

Mike (not Matt) Rattray

Message 22 of 68
jletcher
in reply to: Breeze104

I dimension from the center for now untill I understand the tabel I may change it but to me it will be easier to manage that way. as far as material you don't add on a bent part you only add material when forming parts like a rib or a form stamping in some cases. Material stretches so when you make the flat pattern the material that stretches needs to be removed to make the flat.

Message 23 of 68
Breeze104
in reply to: JDMather

Does inventor take in to account the loss of material or do i have to add that in?  I did origianlly add it in but the took it out...not sure which is right.

 

either way once I am done if the part doesn't match the original length and hole placements then there is going to have to be several paperwork changes.  Since we use these bands on almost every assembly we make I need to get this one right otherwise down the road there may end up issues with all the assemblies (thats why I am fretting so much about getting this right).

Message 24 of 68
Breeze104
in reply to: jletcher

Here is a link to my files

 

https://www.box.com/shared/1f1rkbpjl8

Message 25 of 68
mrattray
in reply to: Breeze104

I can't handle it anymore. Good luck guys. <unsubscribing>

Mike (not Matt) Rattray

Message 26 of 68
Breeze104
in reply to: mrattray

Sorry didn't think about moving the EOP I will do that then try to attach again...Also, didn't know sending links to places like Box.com was a no-no.  Sorry.

Message 27 of 68
Breeze104
in reply to: mrattray

Also, if you haven't guessed it yet...I am not an engineer.  I Drafter/Systems Admin who is self taught on Inventor so I may not always get what seems obvious to you that are better versed in Inventor and engineering.  As far as the handbook goes, I don't get paid enough to spend $100+ on a book that I would (currently) rarely use..sorry

 

So please bare with me.

 

@JD

If I understand your comment "Model a fully finished part in finished form" I understand the need to get function down first, then worry about dimensions. The part is in its final form and it is the dimentions I am trying to get right.  The problem I am having is that the final length is so far off that I need to make sure that I didn't mess up or miss something.

Message 28 of 68
Breeze104
in reply to: Breeze104

I had never tried it before...but answering from the email I get due too subscribing  included my Signature...Errrr.

Guess we won't be doing that again.. Man Frustrated

Message 29 of 68
jletcher
in reply to: Breeze104

Don't fret we all will get you there. Post your auto cad file for me. Just one or two of them. Plus tell me your sizes...

 

And don't worry about the material Inventor will handle that part once we have it all set up right...

Message 30 of 68
Breeze104
in reply to: jletcher

This part is formed first then the sharp brake is put in last.  Does this fall into the yes category you were talking about?

Message 31 of 68
JDMather
in reply to: Breeze104

I would dimension the holes from center-to-center in the folded part rather than from the end.

This is the critical dimension for parts to go together. 

 

Then once the correct k-factor or bend table is calculated you can dimension the hole location in the flat pattern from the end.

 

Also I would put the hole in from the other side so that it goes all the way through the bend (do you really want it to be in the bent section - usually there is some sort of fastener that would clamp better to the planar face rather than hitting the fillet).

 

The Machinerys' Handbook has k-factors for various materials, but you can simply take whatever dimensions Inventor gives you for the flat (forget the AutoCAD flat dimensions - no bend allowance was taken into account) and make a part from those dimensions.  Compare the finished size to design intent.  Adjust the k-factor (or bend table) to increase or decrease overall length of flat.  Test again.  Should be able to narrow down quickly.

Now that you know the number for your material and processes you can use that k-factor (or bend table) for future designs.  (my understanding is that you could have 5 brand new machines set up "identically" to make the same part and the bend allowance would be slightly different for each machine - such is the nature of bend stretching.  fortunately sheet metal parts usually have generous tolerances so slight difference don't matter.  If tolerences are tight then operator must keep a bend table up to date as machine/tooling wears and you must feed that info into Inventor).

 

BTW - good job in modeling the part.  I see so much stuff here that is unconstrained sketches.

 


-----------------------------------------------------------------------------------------
Autodesk Inventor 2019 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional


The CADWhisperer YouTube Channel


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Message 32 of 68
Breeze104
in reply to: JDMather

"Adjust the k-factor (or bend table) to increase or decrease overall length of flat."  I didn't know this was possible..I guess if you can edit the factor then that should work...just never thought of it.  Knowing this will save me lots of time and your typing fingers...LOL

 

Nope, I don't want the hole in the radius, but currently that is the way they are making them.  I will get the ok to change that once I get things fixed with the K Factor.

 

All the machines we have here are pretty wore out even if we wanted a certain tolerance we couldn't hold it well.  We use a sigle ram press to make the basic shape then brake the sharp angle and basicly WYSIWUG.  So if we get brakes to vary 2 deg in a batch were doing great..LOL.  The guys do a reall good job of getting things as close as they can, but they aren't GOD, so they can only do so much.

 

One thing I did learn early on CONSTRAIN EVERYTHING then dimension.  I also don't leave pieces grounded in assemblies, I remove the grounding and use constraints to lock down parts.  Had to many early assemblies and iAssemblies(especially) blow on me.

 

When I create new drawing in ACAD I try to make sure that loss of material is built in.  But some of the drawings that are much older (ones that hadn't been changed since they were brought over from P&P) and once done by someone else I am not sure of, so that is why I am OCD about my stuff..Sometimes to much...LOL

Message 33 of 68
JDMather
in reply to: Breeze104


@Anonymous wrote:

"Adjust the k-factor (or bend table) to increase or decrease overall length of flat."  things as close as they can, but they aren't GOD, so they can only do so much. 


I forgot to mention that different radii bends can each have a different k-factor (which you can assign by bend).  Especially bend radii that are less than the thickness of the material.  I haven't experimented - but I suspect the other end of the spectrum is also true, that is, the very large radius bend would have a different k-factor than "normal" bends where normal bends radii = material thickness.

Fortunately in sheet metal work the tolarances are usually liberal enough that getting exact isn't critical.

 

Do an experiment - simply change that angle a couple of degrees and measure the length of the flat in comparison. 

Inventor is making an allowance for stretching of the flat in the bending zone.


 


-----------------------------------------------------------------------------------------
Autodesk Inventor 2019 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional


The CADWhisperer YouTube Channel


EESignature

Message 34 of 68

Hi Breeze104, 

 

Attached is a PDF that might help with calculating bend deductions that will match what your shop floor produces. This is more accurate than the K-factor method, although K-factors are often plenty accurate for many shops.

 

This file was originally posted at this link http://inthemachine-autodesk.typepad.com/blog/2008/10/calculating-bend-deductions-using-test-bend-pi... as file_22265.pdf, but Autodesk seems to have broken the link to the file.

 

I'm posting it here in hopes that others might find it if they search in the future (I just searched high and low on the internet and had to resort to digging through my personal stash of reference material that I had squirreled away).

 

Once the test bend information is gathered you can add this information to a bend table in Inventor.

 

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com


 

Message 35 of 68
Breeze104
in reply to: JDMather

Well I was able to get a hold of a 20th edition of the Machinery's handbook.  I found the section on Punches and Dies and from what I can tell it seems I need to use the formula L= (.71*T) + (1.57+R).  I use this formula x2 for each side of the 5" arch and the formula L = L* angle of bend / 90 for the bend over 90deg

 

I then used the formula L= (.71*T) + (1.57+R) * 180/90 to figure out the length arch is supposed to be, but I came up with a number much larger ( 1+ inches lager) than the over all sheared lenght of the original part.

 

Could use some help figuring this out.  If you need more info just ask and it will be yours.

Message 36 of 68
Breeze104
in reply to: JDMather

My numbers used in calculation.

 

Material is mild steel sheet

 

material thickness = .1196

Lg Inner Radius = 5 in

Md Inner radius = .75

Sm Inner Radius = .0625

 

The flat areas are

 

.5625 -> End with double brake and this is the flat with the hole in it.

1.0625 -> End with just one hole and a single brake.

.625 -> This flat for short 110 deg brake.

 

 

This is what I came up with

L = .076544 + 1.1755 = 1.254044 * 2 = 2.508088 (*2 since there is 2 3/4 in brakes)

L = .076544 + .098125 * 110/90 = .213458433

L = .076544 + 7.85 * 2 = 15.85088

 

Total length should be 2.508088 + .213458433 + 15.85088 = 18.57242643

 

I know that going out the number of places I did isn't realistic tolerances but that is what the calculator gave me..LOL

Message 37 of 68
Breeze104
in reply to: Breeze104

It seems I missed a number when typing...the amount 1.1755 should be 1.17655

 

I almost forgot...In order to get the right length I changed the KFactor to .3826 ul.  Does this seem out of line?

 

I attached an updated file.

 

I am not sure...but should I have add the flat lengths into the total length as well?  If so my total lenght of part is 20.543972.....

Message 38 of 68
Breeze104
in reply to: Breeze104

Updated Band files

Message 39 of 68
jletcher
in reply to: Breeze104

Looking good so far.

Message 40 of 68
Breeze104
in reply to: jletcher

I reworked the bands again...sorry they just weren't quite right and I added the 12" band as well

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