Sheet Metal Unfold Rule Custom Equation Bending Condition 90 Deg < β <150 Deg

[Anonymous]

I am new to Inventor and will be thankful for the support and guidance from the experts.

I created an “L” of 50x50x20 with thickness of 1mm and bend radius of 2.5. I tried a custom formula and the flat pattern is matching the calculated length up to 90 deg and for any value above 90 Deg the flat pattern was not matching with the calculation. I can say up to 90 Deg - No problem.

As I could not find anything wrong with the formula, I tried with the constant value of Bend Compensation (v) and the flat pattern is not as per calculation. I tried with v = 0 , so that the flat pattern will be of 100mm for any angle. To my surprise up to 90 Deg the flat pattern is 100 but above 90 it is not 100 although v is 0. The observed values are given below. I feel with v=0 the flat pattern should be 100 for any bend angle and this is not the case.

With Bend Compensation (v) = 0

Angle    Flat Pattern

30           100

45           100

60           100

90           100

100         98.658

110         97.003

120         94.876

130         91.988

135         90.101

The same problem was observed with Bend Deduction (δ) = 0.

With Bend Deduction (δ) = 0

Angle    Flat Pattern

45           100

90           100

100         98.658

120         94.876

130         91.988

With Bend Compensation L=L1+L2+v and with Bend Deduction L=L1+L2-δ. Why the flat pattern is not 100 for angle above 90 deg and why the same flat pattern value for Bend Compensation (v) and Bend Deduction (δ).  How to compensate this value. Please advise.

Regards,

Krishnan

[Curtis_Waguespack]

Hi krishnan.p.r ,

I'm not sure if this will answer your question or not, but I suspect that the Backup KFactor setting is being used at some point, and that is why you are not seeing the results you are expecting.

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

[petestrycharske]

Curtis,

I thought the same thing, but when I tried to adjust the values from 0 to 0.5 to 1.0, it didn't seem to make any difference...

I think we might have to wait for an Autodesk representative to help us shed some light on this...

Wish I could have been of more help, but am stumped at the moment.  Hope all else is well and have a most blessed day!

Peace,

Pete

[petestrycharske]

I did some more digging and it seems like this is also related to the radius.  When I set the bend radius to 0 and then sum the two straight edge lengths with the outer bend radius arc length, I get pretty close to the reported flat pattern length.  Not sure if this helps, but something else to hopefully help out the investigation.  Have an awesome and most blessed day!

Peace,

Pete

[blair]

I've attached a great Excel spread sheet for bend allowance and k-factor.

[Anonymous]

Dear Experts,

Thank you for your reply and guidance. I tried unfold rule with the default bend compensation of Inventor and I find even the default formula is not giving correct result for bend angle more than 90 Deg. My observation with default bend compensation values are as below.

Thickness (μ) = 1
Bend Radius (ρ) = 2.5
Length L1 = 50
Length L2 = 50

Bend Angle(β)  Calculated Value          Inventor Flat Pattern
45 Deg             99.8906554487584    99.891
90 Deg             97.5937702991723    97.594
135 Deg           98.3919229741208    89.498

Default Bend Compensation Formula is given below for reference
0 =< (β) >= 90 Deg = π * ((180deg - β)/180deg) * (ρ + (μ/2ul) * (0.65ul + 0.5ul * log(ρ/μ))) - 2ul * (ρ + μ)
90 < (β) >=165 Deg = π * ((180deg - β)/180deg) * (ρ + (μ/2ul) * (0.65ul + 0.5ul * log(ρ/μ))) - 2ul * (ρ + μ) * tan((180 deg - β)/2ul)

I tried unfold rule with Bend Table and the same problem is faced that is the calculated/expected/required value is not matching with the Inventor flat pattern value.

It looks like for angle more than 90 Deg, some calculation is done in the inventor which is not visible to the user.

If it is single bend then we can use the flange in the opposite direction in which case angle will be less than 90 Deg. As I have to make atleast two bends with one bending angle is more than 90 Deg, I am not in a position to use the flat pattern. Will be thankful for any guidance and suggestion.

Thank you and Regards,
Krishnan