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Sheet metal to flat patern bend compensations

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Message 1 of 13
D.D.Koletzki
2726 Views, 12 Replies

Sheet metal to flat patern bend compensations

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?

 

 

 

12 REPLIES 12
Message 2 of 13
JDMather
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.


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Message 3 of 13
D.D.Koletzki
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?

 

Message 4 of 13
JDMather
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.


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Message 5 of 13
mcgyvr
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. 



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Inventor 2023 - Dell Precision 5570

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Message 6 of 13
D.D.Koletzki
in reply to: JDMather


@Anonymous 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.

Message 7 of 13
D.D.Koletzki
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.

Message 8 of 13
mcgyvr
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. 



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Inventor 2023 - Dell Precision 5570

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Message 9 of 13
D.D.Koletzki
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?

Message 10 of 13
JDMather
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).


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Message 11 of 13
D.D.Koletzki
in reply to: JDMather

That is probably what I am going to do, make a few falt patterns and a report to demonstrate I know whats up and let the vendor do the real job.

 

As for the finished form drawings, is this the 3D model or the finished plate in a 2D drawing? And do you perhaps have an example of both a finished form drawing with the needed dimensions and the flat patern drawing showing how to indicate the bend allowance within a 2D drawing? It'd be of great use.

I'm not totally aware if our teacher knows how to do so, we neither have certified autodesk instructors as far as I know. We basically teached inventor ourselfs (or in one of our internships the past years).

Message 12 of 13
JDMather
in reply to: D.D.Koletzki


@0137616 wrote:

...we neither have certified autodesk instructors as far as I know. We basically teached inventor ourselfs (or in one of our internships the past years).


The following response is not directed at you - Where is Carl Bass?  I am so tired of hearing this.  The opportunity exists to develop a digital prototyping legacy that will outlive us deep into the 21 century.


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Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional


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Message 13 of 13
D.D.Koletzki
in reply to: D.D.Koletzki

I think the lack of well educated certified teachers has mainly to do with the sufficient lack of available teachers within the technique sector. Multiple mechanical engineering teachers retired in the past few years, and so far there hasn't been any good replacements, heck we don't even have a CNC teacher anymore. The aging technical community doesn't quite work out either, as some of our older teachers don't get along quite well with the rapidly evolving features the computer has to offer.

 

Besides we recently moved to a new building aswell which had a big expense, in the hope to attract more students. But it did work out, leaving the school with expenses which off course affects the facility's within the school.

 

Anyway, thank you both for the helpfull advice, I think this will do for the rest of the drawings. Smiley Happy

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