Sorry busy day yesterday. Didn't get up to the house until later. Making parts...
No test bends. You just need to know the science of bending. Easy to say, hard to do unless you did it everyday for 42 years.
Bending is a 80% science and 20% art. The science is getting the correct part size and the art is figuring out how to get the part through the machine using the tooling and machine capability you have on hand.
In your case
@drummerdimitri, you have a machine and 1 set of tools. You can work with that and bend everything that fits in your machine.
Making your tooling last and not damaging it due to "point loading" is a good goal. I stopped up at the plant yesterday and snapped a couple of pics of our "Dies/Punches for carving" drawers. These are Dies and Punches that have been "point loaded" causing damage to the tools. Thus when the force of the material to be bent pushes back greater than than the tooling can handle or was designed for.
This can happen because the material is hard, the Punch is too sharp or the Die is too small...or simply the depth of the bend exceeded the limits of the tooling by traveling to far with too much tonnage. This can be dangerous. Tooling can shatter. I have seen several people take a "lip" from a Die to the chest/stomach when the die lets go. In almost all the situations the operator had the max tonnage too high and or fat fingered the depth of the bend.
In this pic you can see how the tip of this Acute Punch was damaged. The part being formed was narrow and the tonnage per inch exceeded what the tool could handle. Or the Die was too narrow for the material thickness and the tonnage required caused to tool to get damaged.
Here is a Die where, either the top Punch was not aligned with the Die or the Die "rocked" back on the rail and when the operator was starting the next bend on a different tooling set-up on the same rail (Multiple Hit Part) he hit the pedal not noticing the Die tipped and the Punch tip embedded itself in the Die. The machine doesn't see this and it doesn't care.
I couldn't find a split Die due to wrong selection or over tonnage.
Smaller Punch Radii take less tonnage to start the bend. But they also wear faster because of the lack of material or surface area.
Larger Die openings take less tonnage to start the bend. But you loose accuracy because the bend radius will be bigger as it is not "captured" on the tool.
For these reasons I/we have found a good starting point is to design/layout using a .031 inside radius and .44% Neutral Axis for any angle. This will work well for material up to 1/4 in Stainless, Aluminum and Mild Steel.
86° or 88° Tooling for Air Bending (adds to tool life since you not ponding the hammer on the anvil).
At the Machine: Start using a .008 (.2mm) Punch and a Die that is 6 times the material thickness. I know above I said design the part with a .031 ISR and here is why: when you Air Bend the ISR will always be slightly bigger than the Punch Tip radius since you are not coining it. Softer materials the radius will be slightly smaller and the harder the material, like Stainless the actual radius will be slightly bigger. This will get you close.
Now you have options if your tolerance requirements are not met. If you need to take up more material meaning taking material from each flange and pushing it into the Bend you can use a smaller Die opening thus casing the actual bend radius to shrink sucking up material.
If you need to push material out on to the flanges you can use either a bigger Punch tip or a larger bottom die opening causing the ISR to get slightly larger.
Here you can see the effect of changing the ISR slightly. Keep in mind this is theoretical but it the science.
As others have mentioned, keep track of your data per material thickness and type.
As far as galling? Keep your material and tooling clean and you really don't need to do anything. However if you are running material with mill scale on it or Galvanized this can cause issues. Oil can help but I would suggest 2-4 mill plastic over the bottom die, Keep moving the plastic as it rips, and it will rip every hit.
On one offs I have run a strip of masking tape on the die side of the bend line. This works great but usually needs to be wiped down with solvent.
What ever you do, don't use Silicone based lubricants. Paint does not like Silicone and it will stay on the surface of the tooling cross contaminating parts for a long time.
Hope this helps!!!
