Outsourcing sheet metal folding

[hotponyshoes]

Just looking at having some sheet laser cut and noticed the suppliers are now offering sheet folding as well (although they are closed until next year so I cant ask any questions!)

Just to keep things simple:

A channel, internal dimensions of 200mm base with 2x 100mm sides.
6mm sheet.

The guide from the folders shows a minimum internal bend radius of 8mm.

So, I presume the external bend radius will end up as 14mm.

First question, should I design to this minimum radius they have given or will I get better results going over the minimum (I would prefer it as small as possible)

Second question, if I draw this profile out and add up the leg lengths I get different lengths for the inside and outside of the profile.
Do I just take the center line of the profile and use that as the dimensions for my flat sheet cutting?

Final question, when adding bend lines to the drawing I presume they just go in the centre of where the bend will be?

 

[pressbrake1]

First need to know how long the bends are and how many tons their pressbrake is so we know what size vee they will use as sometimes you use a slightly larger vee to reduce bend pressure
Bendlines are tool centre lines

 

[hotponyshoes]

It wont actually be 6mm sheet, I just used this as an example because the bend radius specified was a nice round number.

Its only 2mm and 3mm aluminium, Max of 1250mm lengths. If somebody on here has a press break and wants the job I would prefer passing it to them!!

I presume fold will be V die, air bending. The exact profile of the bend is not critical but I am planning to have holes and locators cut into it at sheet stage so it all needs to line up afterwards.

I suppose all I am trying to work out at the moment is how much allowance I need to put into the drawings for the bends?

 

[Mr Roo]

To be honest with you, you should be able to draw it as-finished and the company shouldn’t have any issues cutting it to size and folding it to suit.

i know whenever I’ve had a stair to make or any folded and holed sections, I’ve just been given final sizes and it’s down to operator to get the cut and fold right!

 

[hotponyshoes]

Originally I was planning to have the sheets cut and fold them in house, it's only when I went to get some pricing on the cutting I saw they offer folding as well which I thought might be a bit more precise that trying to do 1m+ sheets by hand on my edwards.

The actuall parts are for drawers, all the same width/depth but varying heights. I thought if I can draw them out as flat sheet with the allowance for the bends in there i can have the holes cut for the runners and handles and locks then fold them up.
If I want a different height of drawer it will be simple to change the drawing.

I am planning to have tabs cut into both ends of the channel for the front and rear panels to locate into but I could have all 4 sides folded up if I can work out the initial dimensions accurately enough.

 

[pressbrake1]

2mm will bend like paper so internal measurements will give bend allowances
3mm will rad slightly
Do some test folds on your edwards on some scrap material

 

[bricol]

Talk to 'em first. give them the dimensions they need, not what you think they need. Annoys the heck out of me at work when colleagues use the super duper sheet metal option in the 3D CAD and spend hours coming up with flat patterns etc - having no idea what the supplier actually needs, or will use due to his own equipment. Or indeed, any idea themselves of sheet metal!

 

[hotponyshoes]

Talk to 'em first. give them the dimensions they need, not what you think they need. Annoys the heck out of me at work when colleagues use the super duper sheet metal option in the 3D CAD and spend hours coming up with flat patterns etc - having no idea what the supplier actually needs, or will use due to his own equipment. Or indeed, any idea themselves of sheet metal!

This is exactly what I am trying to avoid

I have done these before on the Edward's,
For a 200mm wide x 100mm high drawer in 2mm I would draw it out with 100mm sides and a 204mm base. Clamp the sides in the folder and push the base up.
This comes out close enough, if it's a long piece I would add 2.5mm each side as the folder seems to produce a bigger radius over a longer section.

I have found the outer width dimension are pretty critical for the runners to work smoothly plus I want to add tabs to locate the front/rear panels so i need to be a bit more precise with it really.

 

[cianh91]

I’d talk to whoever your looking at dealing with . In 3mm il use 16mm or 24mm v-blocks dependence on specs from customer 2mm will be on a 16 but can be done with a 12mm if a tighter radius is required. But it’s depends on what tools your supplier has top tool makes a difference to your folds aswel . A hemming tool will give a really sharp bend where as a straight tool will increase the radius .

 

[Hitch]

What tolerance are you putting on it...? Thats the key...


And think about how they will be folded... a folded channel, to make a drawer, the width could be the critical dimension here, but backstops would be used from two opposite sides for folding, this relys on your blank size being accurate, or the overall width (uncontroled) could end up large or small which will play havoc with drawer runners...

You could backstop from one edge, then from the first fold, so the bottom width is then controlled... downside there is if your blank size is not spot on, one side will be higher than the other- the drawer would hang wonky.



Generally, working on internal sizes will give an acceptable result on thinner material 2/3mm with a 1mm or so rad top, working on a 8xt die...
Start getting up to 6mm internal rads and suitable dies and you have too much material if you do it like that.
If you work on internal sizes, and they use a super tight punch and die (silly on aluminium) it my come out too small, especially if theres multiple folds in one piece.
If they specialise in this type of work, they may even have the luxury of numerous radius tools or even anti crack top tooling.

Minimum internal of 8mm sounds big, even on 6mm, unless you specifically wanted that radius inside i'd tend to use a smaller radius.

I wouldn't bother doing test pieces in an edwards folder, and then doing laser cut drawings to form he parts on a pressbrake. You wont get the sme result.


If I had £1 for every laser cut conponent ive thrown in the bin over the years because its been the wrong size once folded because the bend allowance have been wrong, i'd buy the beers all night!

 

[hotponyshoes]

My own tolerances are for the interior dimensions and are not that critical, I can add 5mm happily enough.

The runners mount to the outer dimensions and should have a gap of between 0.2 and 0.5mm between the drawer and the carcase which gives me a tolerance of .4 to 1mm so I would be aiming to work to about 0.7mm .
Widest drawer would be 1250mm so to keep things accurate enough I would get the sheets laser cut and have locating tabs on the sides going into the front/rear panels to provide the dimensional accuracy.
It does mean I need to work out the bend allowance into the drawing to get the parts cut though.