Flat pattern help (really desperate)

[TechnicalConsultant]

Hi, All

I'm hoping someone can offer me some advice on here as I'm getting really desperate

We have an issue with how we produce our 3D models/flat patterns and how we manufacure our sheet metal components.

Our sheet metal/plate workers always use inside dimensions when bending so inform us (Design office) that they DO NOT require any extra material for inside radiuses. To give them the profile they require we model all our inside radii at 0.01 rad and use the formula below as our bend allowance formula in our flat pattern.

(if(ir==0.01)(0.01)else((Radius+(Thickness*0.44))*rad(Angle)))

This ensures the flat pattern does not give them any extra material. However, from my perspective, I want my models to look how they actually appear, and in my opinion anything over 4mm or so will have some form of radius. The problem we have encountered though is if I model a rad the flat pattern is produced giving them too much material. We can't change just the flat pattern because it can throw other features out.

Any help or info as to how others are using this would be great!

 

[looslib]

You need to set your bend allowance to meet your material conditions. We used the flat patterns directly into our nesting/cutting system.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[TechnicalConsultant]

The bend allowance is set to give 0.01mm of material as requested by the shop floor guys who bend and weld the components.

However, our problem is that although this suits manufacturing it does not give a true reflection of what the component will look like. Imagine bending a 15mm ST ST plate, as it is at the moment our model has perfect sharp corners which would not be the case.

We're really struggling with this one : (

Looslib, what bend allowance formula do you use and I presume your manufacturing guys are happy? Do you work to inside radiuses?

Mark Noyce
Senior Design Engineer/CAD co-ordinator

 

[looslib]

.44 K-factor
mostly bending mild steel plate, A-36

If you want to show the modeled part with the actual bends, then you need to change your modeling practices and adjust NX to give you the correct flat pattern length. Adjusting the K-factor will get you what you want and what the shop needs.



"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[TechnicalConsultant]

What is the K Factor? I recognise the 0.44 as part of the bend allowance formula but don't know what you mean by the K-Factor?

I have created a link to an image which may help explain my problem. The image is of a plate and has been modelled with a sketch for the rectangular sheet with flanges added. Note the flanges have been used in modelling not NX sheet metal (although we do have a license)
The plate has been modelled using an inside radius of 5mm. However when we create a flat pattern it is oversized because as the metal workers do not want extra material for the rads.

It is possible to change the inside radius expression in the flat pattern but doing this makes the flat pattern too small. For example if I change the ir to 0.01 the 440mm dimension becomes 430mm because we work to inside dimesions.

I really hope I'm missing something obvious Thanks for all your comments so far.

http://i106.photobucket.com/albums/m270/mark_noyce/Refs.jpg

Mark Noyce
Senior Design Engineer/CAD co-ordinator

 

[looslib]

This will explain basic sheet metal terminology:

http://www.massey.ac.nz/~odiegel/bendworks/bending.pdf

I modeled your part (in Pro/E) and the overall length is 560 bent and 635.216 with a .439 K-factor.

How is your shop adjusting for the bend allowances? Metal compresses/stretches as it is bent, which is what the bend reduction/allowance formulas account for depending on material and thickness.

Try adjusting the K-factor in NX and see if you can develop the flat length that the shop expects while having your model in its finished formed shape.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[TechnicalConsultant]

Thank you Ben for taking the time to look at this for me.

When creating the flat pattern for this part I'm also coming up with the 635.2mm overall length. However the shop say this is wrong as they calculate using only inside dimensions (and ignoring any bend allowance) and come up with 630mm (5mm short)

Very confusing!

Mark Noyce
Senior Design Engineer/CAD co-ordinator

 

[looslib]

The next thing to check is to take the finished part from the shop and measure it. Does the part match the formed design? If not, then you need to figure out where the process is failing.

I don't see how a 5mm short blank can be used to produce a bent part and meet the design as drawn.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[looslib]

My take on it is: Why go through a bunch of manual steps that the software can produce with no extra effort. Flat patterns need to be associative to the finished part so that when the part changes, the flat pattern also changes.

Make the software work for you. That is how you get productivity gains from it. It may take a little time to get the system configured, but once it is everything after that is already done.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[TechnicalConsultant]

I agree with you that I can't see how they can produce the part correctly with a 5mm short piece of material. The shop are producing some test pieces for me so I can check them. I'll keep you posted!

Mark Noyce
Senior Design Engineer/CAD co-ordinator