How accurate and reliable is Inventor’s Flat Pattern?

[Breeze104]

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

[jletcher]

It is as accurate as you make it.

I would help but don't understan the problem. Don't understand can't get numbers to work together. And if you want help we will need more info and dims on your part.  What numbers don't work?

You may have to play with the kfactor or set-up a bend table or custom equation.

[JDMather]

Are you familiar with bend allowance?
Are you referring to a pre-existing AutoCAD 2D dwg or to an Inventor 2D dwg created from the flat pattern?

Assuming an AutoCAD 2D, was bend allowance calculated for that "solution"?

When you bend metal it compresses in the inside of the bend and stretches on the outside of the bend.  (This is what most people think should be the flat pattern length - but is incorrect.  Usually their tolerances are not so critical that it matters, or the shop floor operators are already making the necessary allowance by trial-and-error (bend up a couple of parts) and/or experience.)
The neutral plane - where neither compresses or stretches may not be exactly centered between the inside and outside.

Using the Machinery's Handbook as reference the bend allowance depends on material, thickness, inside bend radius and angle of bend.

Inventor uses user adjustable variable named k-factor for the bend allowance calculation.

Inventor can also use a user created experienced-based bend table to calculate the bend allowance.

In short, Inventor is as accurate as the user sets up the k-factor(s) or bend table.

The default settings might not match your processes, so you need to adjust the k-factor or bend table.

[Breeze104]

Here are a couple of video links that will hopefully clear things up.

Video 1 : http://screencast.com/t/RXFzcUCQgQbA

Video 2 : http://screencast.com/t/16GaVRp2Vnf

[jletcher]

Ok can you post the part you have modeled up? I can help just don't feel like redrawing something you have already.

[jletcher]

Also is this going around a pipe? If so what size?

[mrattray]

Inventor's calculations are dead nuts. But, as is explained, Inventor doesn't know your equipment. You have to have the sheetmetal rules set up to calculate it correctly.  If you don't need much precision then I would recommend you set it to use a kFactor of 0.5. This seems to work well on wierd shaped low precision parts. For more accurate parts the only real solution is to have parts test bent and measure the results vs the blank used. Keep track of the measurements and results of each trial, and you'll get an idea of what allowances you need to use in the future.

Bottom line is: nobody on the internet knows your equipment and processes.

[JDMather]

What edition of the Machinery's Handbook are you using (so that I know what pages to reference to you)?

It looks to me like there is something wrong with your Inventor file (see the holes).
Attach it here.

I have ten dollars that says your AutoCAD drawing is wrong as well.

Bottom line - the 3D folded part has a desired design intent.
Worry about getting that right first.  It is what it is.

Attach the file here.

Then we can figure out what is wrong or right after that.

Attach the file here.

Most common mistake I see (AuotCAD) people make is add up the straight line length of centerline of of the flats and arcs and think that is the flat pattern length.  But because of stretching of the material - it is not.
Then they get confused when Inventor (or SolidWork or Creo) results don't match their old 2D drawings.

[JDMather]

I just watched your video again and noticed a couple of things:

1. the folded model in AutoCAD is not fully dimensioned.  Only the folded finished dimensions have any real meaning for sheet metal parts.

2. in your Inventor sketch for the folded part you have a dimension that cannot be held in any manufacturing process.  Use real dimensions.

3. the angle for your tight bend is different than the angle shown on the AutoCAD drawing.  Because of bend allowance (the material stretches when bent) the flat pattern length for this part will be different for the part with 65° angle and part with 80° angle.

In short - the AutoCAD drawing is flawed.
And from the look of the holes (sliver face - hole doesn't go through) in your Inventor model - it is flawed as well.

Attach your files here.

[jletcher]

OK had some fun and did this. I believe this is a better way to control your model I would add a few other things but just want to see if this is what you are after. If so I will help dial in your bend deduction.

[Breeze104]

1. the folded model in AutoCAD is not fully dimensioned. Only the folded finished dimensions have any real meaning. This is because they are the only ones we can do anything about. Due to the fact that that the bands are pressed into the basic form after holes are punched and before the final brake is put in. 2. in your Inventor sketch for the folded part you have a dimension that cannot be held in any manufacturing process. Use real dimensions. I am not sure which dimension (s) you are referring to in the inventor part. But if you are referring to the broke height dimension, that is there so that I can set the center line offset; otherwise the rest of the dimensions are from a straight line dwg before the radiuses were put in. 3. the angle for your tight bend is different than the angle shown on the AutoCAD drawing. Because of bend allowance (the material stretches when bent) the flat pattern length for this part will be different for the part with 65? angle and part with 80? angle. The sharp angle the guys on the floor have changed so that when they are bolted together the sharp angle doesn?t slip off. The AutoCAD drawing is old and the inventor part shows the current dimensional shape. In short - the AutoCAD drawing is flawed. And from the look of the holes (sliver face - hole doesn't go through) in your Inventor model - it is flawed as well. The holes don?t go thru due to the face that they are too close to the radiuses; hence the hole issue, that is an easy fix so I am not that concerned right now. Warren Wetzel Peck Mfg. Co. Network Admin/CAD Drafter & Designer warren@peckmfgonline.com 402-456-7314

[jletcher]

So do you look at my part?

[JDMather]

One last time - attach your part file here.

The finished size is all that matters.
Once the finished size is modeled CORRECTLY then we can work backwards to get the correct flat pattern to start with in your manufacturing process.

At this point the ONLY thing that matters is the desired finished dimensions, not the flat (I know that is what you start with in manufacturing, but don't worry about that yet).

[JDMather]

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Breeze104 wrote:
2. in your Inventor sketch for the folded part you have a dimension that cannot be held in any manufacturing process. Use real dimensions.

> I am not sure which dimension (s) you are referring to in the inventor part.

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The dimension I am referring to should be rather obvious.

I think the entire problem is that I haven't yet convinced you to forget about the flat pattern for now because you know then part is started from a flat.  Forget the flat pattern. Model a fully finished part in finished form with dimensions that would be meaningful for inspection.  Forget the flat!  Attach the part here.

[Breeze104]

Yes, I did. Question.Why dimension holes from center line? I can see doing it to the one that is on the end with the double brake but not the other end. I guess that wouldn't really matter to much but I was just curious as to why you did it that way. I am going thru and try to set dimensions correctly. OUCH!!!! Just had a thought.When you go from bent to flat pattern does the flat patter take into account loss of material or do I need to add that in? I added it in, in the beginning, but later removed it..which is right? Warren Wetzel Peck Mfg. Co. Network Admin/CAD Drafter & Designer warren@peckmfgonline.com 402-456-7314

[Breeze104]

Yes I will post it. I know you already created a band but I will post it for ya'all to look at. Warren Wetzel Peck Mfg. Co. Network Admin/CAD Drafter & Designer warren@peckmfgonline.com 402-456-7314

[Breeze104]

Machinery Handbook????  Whats that?  I don't have one and untill this point..never needed one.

Here is a link to the files Part amd assembly

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

[Breeze104]

Yes these go on tubing sizes of 8", 10" and 12" OD

[mrattray]

EVERYONE needs a machinist's handbook! I don't know how anyone can design anything without one! Go get one ASAP.

Links to third party sites are a no-no. Just post the .ipt as an attachment on this site.

[Breeze104]

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

Files to big to attach