Inventor Bend Table Question/help

[AARON_DEANE7AQ78]

I'm Currently Creating a Gutter Which Consists Of 3 Internal Bends and 3 External Bends. I have created a Bend table For how I would manually do it in this case its 3mm so -5.2 for an external and add 0.8 for an internal and half for an obtuse so -2,6 which would give me 1211.8 For the Inventor file I have attached however the blank size is coming out at 1218.494 for what I can see the internal bends aren't adding enough material other than that I'm a bit unsure on how to fix this the bend table I have made is.

The bend radius i am using is 1.5.

IF anyone has any clue on what's happening or can even explain how the bend table works within inventor and how the values interact or how to achieve the blank i want that would be appreciated.

[YannickEnrico]

Hey there.

Your question had me investigate bend tables, as I've only ever worked with the K-factor.

Based on this video I learned that the bend tables work on the bend deduction approach described.

https://www.youtube.com/watch?v=eTY0hyF5_lY

So for a given inner bend radius (magenta) at a given angle (blue) it'll deduct this amount (green) from the bend allowance.

I have developed a flat pattern based on this drawing where you can see the corresponding measurements and can tell that 2mm has been deducted from the flat pattern on the bend between A and B

Edit:

Keep in mind anything bend related is usually developed by test bends, as deductions varies from material to material, as well as machine to machine

[piotrekdoro94]

If your final sheet metal part has dimensions slightly different from what you would expect, it's probably because of KFactor value. It represents a ratio of distance from the internal side of a sheet bend to the neutral axis (thickness of the compressed area) and sheet total thickness. If you've assumed that an imaginary line separating streched and compressed areas goes through the middle of the sheet then that might be the reason.

 If I understand it correctly, you could try and set KFactor  to 0,5 to get that imaginary line to go through the middle of the sheet, but you have to keep in mind that neither 0,44 nor 0,5 might be a correct value. Both might be good enough approximations, but the only advice I can give on that matter is to try to bend a piece of material and calculate what the KFactor really is if you want very accurate results 

[AARON_DEANE7AQ78]

Thankyou for this and the drawing and i understand the bend table will deduct the amount you put however I'm wondering how it choses to add material when its an internal fold as you know depending on thickness you add material when its an internal fold due to compression but the bend table doesn't seem to have a way to account for this.

Also how have you found just using k factor is it reliable with using different thicknesses and internal and external folds?

[YannickEnrico · Accepted solution]

Hi again

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... however I'm wondering how it choses to add material when its an internal fold as you know depending on thickness you add material when its an internal fold due to compression but the bend table doesn't seem to have a way to account for this.

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For uniform materials like steel and other metals, it doesn't matter what direction the sheet is bent.

If I were to bend some material with different properties in one way than the other, I'd draw one way with one radius, and the other way with another radius - That would allow my bend table to apply different K factors to each bend

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Also how have you found just using k factor is it reliable with using different thicknesses and internal and external folds?

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+/-0,5 has been an acceptable tolerance in the sheet metal factories I've been working in, and as such K factor is enough, even if it's only derived from 90 degree bends.

Edit:

On this drawing, I changed my bend table for 2mm to -2mm for a 90 degree bend. As you can see, the numbers correspond with 4mm longer flat pattern

[johnsonshiue · Accepted solution]

Hi Aaron,

Here is a simple test to check if the Bend Table yields a reasonable result. Set the Unfold Rule to K factor and set the value of K to 0 (inner side). Measure the Flat Pattern length. Repeat the same test by setting K to 1 (outer side).

In your case, when K = 0, the Flat Pattern measure 1212.37mm. And, when K = 1, the Flat Pattern measures 1236.66mm. Your Bend Table leads to 1218.94mm. It is between the range. I would say the result is reasonable. Your expected length of 1211.8mm does not make sense. Please show how you calculated the length.

Many thanks!

[AARON_DEANE7AQ78 · Accepted solution]

Thanks for your Reply Johnsonshiue i have managed to get the bend table working so i will accept a solution but for ease of mind i will explain why the blank was coming out wrong for if anyone else is getting the problem the bend table works and gives a reasonable answer.

i would calculate how many internal and external folds are on the profile which is 3 internal and external i would then minus -5.2 for each external however there is an obtuse angle so it half's this is also done with internals 0.8 for each and half of one because its an obtuse angle which i then add all lengths giving me 1225 subtracting  these i get 1214 the model I sent wasn't correctly done as the dims i was working of was taken from the front of the material therefore the obtuse angles were wrong with the flange settings I was using this is the flange settings below to correct this. 

so it wasn't actually the bend table that was causing the issues but was the flange which was adding two gauges on which is why the inventor blank came out wrong.

Thankyou all for the responses they have been very helpfull.😊