Step file, bend radius and unfold rules

[sijcooke]

Hi,

All helps is really appreciated here!

We often receive step files of sheet metal parts to manufacture. Our customers don't know the bend radiuses out press brake produces, so therefore their step files always have different radiuses.

For this example, if we imagine their step file has 3 folds and each fold has a different radius e.g. 3mm, 4mm and 5mm. Lets presume our press tooling will product a 6mm radius.

If the bend radius of the final part is not critical and the only important dimensions are the overall finished size, can inventor generate the correct sized flat pattern for this?

What I have done is setup a bend table. I entered all the angles in the left column. Then I added a radius column with radius 0mm, and another radius column with radius 10mm.

I then filled in all the bend allowance numbers which create a correct flat pattern with out machine. 

Is this correct? I expected inventor to look at the bend table for each radius bend (3,4,5mm) and all of these radiuses are between 0 and 10mm, so it will use the same deduction for every bend (if the angles are the same).

Hope that makes sense!

Thanks,

Sijcooke

[Cadmanto]

Hard to know without some pics or a file to work with.  The flat patterns first of all can only be created using the sheet metal.  Within the sheet metal environment, you can dictate what radii you want.  Default radius is the metal thickness.

Next, the OAL, OAW are dictated based on whether the bends are inside or outside of the bend edge.

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[CCarreiras]

"""For this example, if we imagine their step file has 3 folds and each fold has a different radius e.g. 3mm, 4mm and 5mm. Let's presume our press tooling will product a 6mm radius."""

When you receive often parts in step, you can use some steps to create a new radius and flat the part properly.

"""If the bend radius of the final part is not critical and the only important dimensions are the overall finished size, can inventor generate the correct sized flat pattern for this?"""

The final dimensions depend from the size of part pannels plus bend compensations and these compensations are calculated based in the bend radius and part thickness, so, for optimal results, it's better to have those bend radius correct.

To have the proper flat with proper compensation, you must have all bend radius as the machine you gonna produce (in your example, 6mm) and like i said in the previous answer,in a few minutes** you can solve that, even in a step (**I'm talking about the usual sheet metal models without big complexity). 

[SBix26]

Can you post a sample file here?  What version are you using?

I wonder if Feature Recognition could be helpful?

---

Sam B
Inventor Pro 2019.2 | Windows 7 SP1
LinkedIn

[JDMather]

You should be able to Delete Face with Heal option and then place whatever Bends you need.

[sijcooke]

Thanks for the replies.

If I have a step file, and use delete face+heal on the bends, and then put the bend back on I can set the radius.. but how do I know what radius to set it to?

I have done some test folds and it looks to me like a tight over bend has a smaller radius than a bend that is less tight.. is this correct? If this is correct and I have a bend e.g. 67.8 degrees on the step file how do I know what radius to change this to? Surly its not going to be BendRadius for every angle bend???

Thanks,

Sijcooke

[blair]

OD radius less the material thickness will produce the ID bend radius. It could be the same bend radius for all the bend, or each bend could have its own bend radius.

[CadManagerMoffatNZ]

We have found that the best way to get accurate flat patterns is to use bend tables.

And the best way to generate bend tables is to reverse engineer the k-factor from test bends.

There are lots of on-line k-factor calculators. We use Bendworks.

Then once you have this you can calculate your values using the following equation.

 

Straight up K-factor will get you close (ish)

Rule of thumb for inner radius = die opening / 6 (for air bending)

[blair]

I've attached an Excel spread sheet that should help with k-factor

[doug.johnston]

Are you allowed to share the step file on the forum (client approvals, etc.) ??

If so, we could try to give you a better solution and maybe an example.

One thing that I found where I work,  I have to constantly change the K-Factor value to "match" the existing/as-built flat pattern dimensions, regardless of the material thickness.