Inventor General Discussion

## Inventor General Discussion

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Posts: 13
Registered: ‎03-13-2014
Message 1 of 13 (398 Views)

# Sheet metal to flat patern bend compensations

398 Views, 12 Replies
03-13-2014 05:42 AM

For my graduate exam I need to design and produce a protecting case for a laser engravingsystem. The case mostly exists out of plate steel.

When you bend a plate the plate will stretch, I've heard the distance stretched is 0,2mm per mm plate thickess per bend.

So if you make two bends in a 3mm thick steel plate it'd mean the plate will stretch 0,2x3x2 = 1,2mm. Therefor to stay within the given tollerances you'd have to make the baseplate 1,2mm shorter to end up with the right dimensions. Many 3D drawing programms don't adjust their base plate of the folded part, one would have to adjust the base plate on the 2D drawing himself.

My question is: will inventor automatically adjusts the dimensions of the baseplate when you convert your part to a flat pattern part, if so will the adjusted dimensions be shown on the 2D drawings or do I have to adjust the steel plates to the right dimensions myself to stay within the specs?

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Posts: 26,352
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Message 2 of 13 (387 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 06:04 AM in reply to: D.D.Koletzki

Inventor will calculate bend allowance.

Model your sheet metal part in finished as-bent dimensions and then attach the file here for suggestions.

The bend allowance is dependent of material, thickness, inside bend radius and bend angle (with perhaps a couple of other considerations).  If you can supply the material information - the other information is in the design.

A general "k-factor" is most often used to calculate the bend allowance.

A bend table could also be used.

Inventor will do the calculations for you to return correct size flat pattern.

If you do not know how to use the sheet metal tools (sounds like this is the case) then simply use whatever modeling techniques you do know how to use and attach your file here and someone will show you how to properly model the part(s) with sheet metal techniques.  The key is - for now - forget the flat pattern, model in the desired finished form.

Please mark this response as "Accept as Solution" if it answers your question.
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Posts: 13
Registered: ‎03-13-2014
Message 3 of 13 (374 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 06:31 AM in reply to: JDMather

Thanks for your quick and complete response.

Contacts from other companies, not working with inventor, told me that their drawing programms don't calculate bend allowance and that they'd have to make their own bending table's. It made me doubt wether inventor would cover this feature or not. Good to know inventor does, it'll save alot of research and drawing time.

I've been using sheet metal for a little while, it took some time to figure it all out but I think I'm quite aware now how the sheet metal features work.

I've attached a sheet metal part, would you mind taking a look at it if the features are properly used and if the bend allowance is calculated within?

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Message 4 of 13 (357 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 06:44 AM in reply to: D.D.Koletzki

0137616 wrote:

Contacts from other companies, not working with inventor, told me that their drawing programms don't calculate bend allowance and that they'd have to make their own bending table's. ..

If you are going to have this part made by a vendor - then give them the detail drawing of the finished part and let them figure out how they are going to make it.

I noticed that several of your sketches are not fully constrained?

Are your critical dimensions on the inside or the outside (think about this as you dimension your drawing).

If I get a chance - I might come back with a slightly different model later today.

I would pay particular attention to the datum(s) used to locate those holes.

Please mark this response as "Accept as Solution" if it answers your question.
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Registered: ‎12-01-2004
Message 5 of 13 (351 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 06:50 AM in reply to: D.D.Koletzki

Just a tip..

NEVER provide a flat pattern to a sheet metal fabricator. Formed drawings only.. Its their job to make the part to the folded dimensions.

K factor/bend allowance is highly process/machine specific.

If you provided the same flat to 2 different vendors there is a good chance you will get 2 parts with different dimension..

Any "good" sheet metal vendor never use your flat pattern and will always create their own.

The ONLY times I will ever do a flat pattern is

#1-If we are forming it in house and I know the kfactor for our specific machine/bend radius,etc..

#2-If that specific vendor provides the kfactor to me.

Did you find this reply helpful ? If so please use the Accept as Solution or Kudos button below.

Down with IDW/DWG files..... Long live 3D PMI... Hurry it up already..
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Contributor
Posts: 13
Registered: ‎03-13-2014
Message 6 of 13 (340 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 07:00 AM in reply to: JDMather

JDMather wrote:

0137616 wrote:

Contacts from other companies, not working with inventor, told me that their drawing programms don't calculate bend allowance and that they'd have to make their own bending table's. ..

I noticed that several of your sketches are not fully constrained?

Are your critical dimensions on the inside or the outside (think about this as you dimension your drawing).

I would pay particular attention to the datum(s) used to locate those holes.

The holes are indeed yet to be constrained to the frame the plate work will be mounted on. The critical dimensions are in the inside. I've got a assambly of the whole safety case and the to be modified frame on where the safety case will be mounted on. The assemblies aren't showing any interferences. I'd need to do some research for correct tollerances tho to prevent interferences once produced.

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Posts: 13
Registered: ‎03-13-2014
Message 7 of 13 (338 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 07:07 AM in reply to: mcgyvr

mcgyvr wrote:

Just a tip..

NEVER provide a flat pattern to a sheet metal fabricator. Formed drawings only.. Its their job to make the part to the folded dimensions.

K factor/bend allowance is highly process/machine specific.

If you provided the same flat to 2 different vendors there is a good chance you will get 2 parts with different dimension..

Any "good" sheet metal vendor never use your flat pattern and will always create their own.

The ONLY times I will ever do a flat pattern is

#1-If we are forming it in house and I know the kfactor for our specific machine/bend radius,etc..

#2-If that specific vendor provides the kfactor to me.

The thing is, for graduating my education I'd have to live up to 13 competences, correct 2D drawings is one of those. So in this case I'd have to ask the vendor to provide their Kfactors?

Making 2D drawings of parts which have nothing to do with the project or following an "internship" at the vendor for a few days, "helping" the engineer with 2D drawings would be another solution. But the vendor would have to agree on this off course.

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Registered: ‎12-01-2004
Message 8 of 13 (331 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 07:11 AM in reply to: D.D.Koletzki

0137616 wrote:

mcgyvr wrote:

Just a tip..

NEVER provide a flat pattern to a sheet metal fabricator. Formed drawings only.. Its their job to make the part to the folded dimensions.

K factor/bend allowance is highly process/machine specific.

If you provided the same flat to 2 different vendors there is a good chance you will get 2 parts with different dimension..

Any "good" sheet metal vendor never use your flat pattern and will always create their own.

The ONLY times I will ever do a flat pattern is

#1-If we are forming it in house and I know the kfactor for our specific machine/bend radius,etc..

#2-If that specific vendor provides the kfactor to me.

The thing is, for graduating my education I'd have to live up to 13 competences, correct 2D drawings is one of those. So in this case I'd have to ask the vendor to provide their Kfactors?

Making 2D drawings of parts which have nothing to do with the project or following an "internship" at the vendor for a few days, "helping" the engineer with 2D drawings would be another solution. But the vendor would have to agree on this off course.

Are you actually getting this part manufacturered?.. If not just use the "defaults" in inventor.. it will apply some bend correction without doing anything and just using defaults already setup.

and IMO.. a "correct 2d drawing" is a drawing showing the part in its "formed" state.

I've designed thousands of sheet metal parts and not a single one has a 2d drawing showing the flat pattern.

Did you find this reply helpful ? If so please use the Accept as Solution or Kudos button below.

Down with IDW/DWG files..... Long live 3D PMI... Hurry it up already..
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Contributor
Posts: 13
Registered: ‎03-13-2014
Message 9 of 13 (318 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 07:31 AM in reply to: mcgyvr

mcgyvr wrote:

0137616 wrote:

mcgyvr wrote:

Just a tip..

NEVER provide a flat pattern to a sheet metal fabricator. Formed drawings only.. Its their job to make the part to the folded dimensions.

K factor/bend allowance is highly process/machine specific.

If you provided the same flat to 2 different vendors there is a good chance you will get 2 parts with different dimension..

Any "good" sheet metal vendor never use your flat pattern and will always create their own.

The ONLY times I will ever do a flat pattern is

#1-If we are forming it in house and I know the kfactor for our specific machine/bend radius,etc..

#2-If that specific vendor provides the kfactor to me.

The thing is, for graduating my education I'd have to live up to 13 competences, correct 2D drawings is one of those. So in this case I'd have to ask the vendor to provide their Kfactors?

Making 2D drawings of parts which have nothing to do with the project or following an "internship" at the vendor for a few days, "helping" the engineer with 2D drawings would be another solution. But the vendor would have to agree on this off course.

Are you actually getting this part manufacturered?.. If not just use the "defaults" in inventor.. it will apply some bend correction without doing anything and just using defaults already setup.

and IMO.. a "correct 2d drawing" is a drawing showing the part in its "formed" state.

I've designed thousands of sheet metal parts and not a single one has a 2d drawing showing the flat pattern.

The project is going to be manufactured yes, for graduating you need to show a properly working project.

I'd have to ask my mentor if a 2D drawing of a folded part will quallify.

It does bring up a question tho, will the operater calculate the bend allowance himself in this case? or will the engineers from the vendor reshape the 2D drawing in order to cut the plate on the right dimensions from the base plate and make give up the right bending dimensions?

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Posts: 26,352
Registered: ‎04-20-2006
Message 10 of 13 (296 Views)

# Re: Sheet metal to flat patern bend compensations

03-13-2014 08:38 AM in reply to: D.D.Koletzki

For my students - I want them to demonstrate that they understand there is a bend allowance associated with forming sheet metal parts (a large number of posts here would seem to indicate that there is a significant population of paid designers/engineers who are not aware of this fact).  (and I suspect a lot of instructors are not aware either)

I would want them to understand how THEY (or Inventor) could do the calculations working in-house with their people on the shop floor (or in rare cases with VERY good communication with oustside vendor).

I would want them to be able to state why to NOT give anything but finished form dimensions to outside vendors where this communication is not likely to exist.

So for your school work (academic exersice) - you should present an engineering report pointing out all of these considerations and including a dimensioned flat pattern so that you have demonstrated if you were going to work for a company in the business of actually manufacturing sheet metal parts - you would know how to communicate with your shop-floor people.

For actually getting the part made (outside vendor) only give them the finished form drawing (no flat pattern drawing).

Please mark this response as "Accept as Solution" if it answers your question.
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