Toby's SHEET METAL TIPS & TRICKS - MARCH 28th

[DennisD]

I look forward to this! Your vids are short and packed with great stuff. That's high information density in my book!

When we actually measured scrap sheet metal coupons before and after bending for our in-house press brake operations we were able to develop deadly accurate K-factors and flat patterns. Every one of our engineers participated in collecting the data for our K-factor spreadsheet and therefore valued it. We were able to design features such as pre-punched holes on multi-bend flanges that lined up every time for rivets and rivnuts. Before we calculated the K-factors these holes were mate-drilled and field service was a nightmare. This is the information sheet we used to explain it all.

[jcapriotti]

When we actually measured scrap sheet metal coupons before and after bending for our in-house press brake operations we were able to develop deadly accurate K-factors and flat patterns. Every one of our engineers participated in collecting the data for our K-factor spreadsheet and therefore valued it. We were able to design features such as pre-punched holes on multi-bend flanges that lined up every time for rivets and rivnuts. Before we calculated the K-factors these holes were mate-drilled and field service was a nightmare. This is the information sheet we used to explain it all.

Nice document. I have to constantly explain to new engineers why our SolidWorks gauge table thicknesses aren't the "nominal" values.

[bnemec]

I wish we could buy our sheet/coils from the same mill you guys get yours. You make it sound like they provide a thickness and hardness that's consistent enough to actually model to. We don't update models and dxfs for every heat of every thickness for every order of the parts that use it. Shoot for the mean is the best we can do.

[Frederick_Law]

Technically you need to calibrate for each coil.
And tooling change.

@bnemec
Even with different heat, k shouldn't change that much.
I used same k for a time. Around k=0.3. For most of the sheet gauge.
How thick is your material?

[TTevolve]

We use a 0 radius and .255 K factor for all our sheet metal parts. I told them this isn't correct, but that is how they did it manually and the drawings had to conform. We have a very old hydraulic press break with worn out dies.

We are looking into purchasing a new modern press break that has the system on it to calculate the K factor based on real bends and upload it back into the CAD System using real parts. That should be a real culture shock tot he shop.

[jcapriotti]

We use a 0 radius and .255 K factor for all our sheet metal parts. I told them this isn't correct, but that is how they did it manually and the drawings had to conform. We have a very old hydraulic press break with worn out dies.

We are looking into purchasing a new modern press break that has the system on it to calculate the K factor based on real bends and upload it back into the CAD System using real parts. That should be a real culture shock tot he shop.

Sounds like us to some extent. We even have a top v die where the shop welded a piece of round bar stock down the length to create a larger radius for a part, instead of buying the correct dies.

Funny (and sad) when I hear us outsourcing some sheet metal parts (at greater cost) because of quality issues. Well duh, you didn't buy the needed equipment to produce consistent parts. Sometimes the left hand doesn't know what the right hand is doing I suppose.

[Frederick_Law]

We use a 0 radius and .255 K factor for all our sheet metal parts.

Same here.
Just because they don't know how to fit the bends and corners and it leave gaps.
At least someone was smart enough to use bend table. So the bend radius doesn't really matter.

[bnemec]

Technically you need to calibrate for each coil.
And tooling change.

@bnemec
Even with different heat, k shouldn't change that much.
I used same k for a time. Around k=0.3. For most of the sheet gauge.
How thick is your material?

Agreed hopefully it wouldn't change that much. I don't understand all the ways hardness affects forming operations, along with so many other factors. I do know that our "run of the mill" steel will wander well into the Grade 50 hardness and then back well below it. We learned on some parts that we really needed held to use Grade 50 just because it tends to vary less.

We run steel thicknesses from 16 GA to 3/8" sheets, coils in 16 GA to 1/4"

The forming tool will change how the material bends to some degree. Air bending or bottom forming on break, then in the full progressive dies or blank and form parts, they don't all have the same k for otherwise same bend. On a few parts we have gone back and tweaked the k factor in our model so the flat represents what the tool is doing.

[Frederick_Law]

Bend table may work better for you.
It pair up bend angle and bend radius.
So you can use different allowance/k.
Single k-factor assume same k for all bend angle and radius which we know not true if radius is big. ie 5" rad will be rolled with k~0.5.