[mickmf]

hello all its a few years since i last operated a brake press , i am trying to find a tutorial online that gives me the basics.

main confusion is if i want to form a series of bends in sheet metal is how i work out the folding sequence and relevent bend allowences and backstop positions.

i cannot find any demo software for download to assist in this area , vidios etc are very expensive, here in the uk books on this subject do not seem to exist, have contacted brake press manufactures in the uk but still cannot get much info unless i actualy purchased a brake press.

i am a sheet metal worker but unemployed at the moment most firms want people that can operate a brake press but are not willing to provide any modest instruction in there usage.

thank you

[InspirationTool]

There's a guy on ebay who sells a press brake instructional book. I remember it was fairly cheap and looked pretty good.

-Jeff

[schiada96]

press brake not brake press

[One of Many]

Have you looked into any local trade school courses offered on this subject. They may have books for those courses.

I have seen this book available through Amazon.com. Price is a bit steep, but rare industrial text type of books do not sell by the millions.
Press Brake Technology

I figured I would add this in here too. I worked with the Author of this book and had a couple training classes he taught a few years back. Ben is retired now and it does not suprise me he has put at least a portion of his vast tooling knowledge and experience in print. Ben was one of the premier press brake tooling engineers in the industry for some 40years. Many of the bend tonnage charts you see probaby have Ben's bend data adopted throughout the years.

Press brake tooling fundamentals


There is a wide array of knowledge required to first of all stay safe on these machines and secondarily skilled enough to make accurate parts with little to no scrap materials for trial runs .

Bend allowances are available on charts for rough starting figures to calculate blank sizes. Some guys will use material thickness and/or lower V-die widths to come up with material consumption figures. There are different types of bending procedures(air bending, bottoming and coining) that can alter these estimates, so it becomes experience that will be applied in each condition as required. Variances in upper die nose radius and material spring back also play a role. I sincerely think you need to work with the die combinations on hand to know what to expect first hit, then judge accordingly.

Bending tonnages are based on a combination of the lower V-die width in relation to material thickness. This is also available on charts. With the advances in hydraulic CNC press brakes, the settings can be controlled so that the maximum tonnage for the dies is not exceeded before a position reversal is reached. Not so with the old mechanical eccentric conrod machines that would attempt to move regardless of impending disaster.

The key here is knowing the material and its bend factor and/or if it is bendable at all without fracture or worse. Then selecting the proper dies and tonnage required to fit the machine and die set safely.

Much of this will be machine dependant as to what skills are needed BEFORE you pull the trigger. The methods and tricks of the trade will come as you gain some first hand experience at setting up for the next challenging part. That includes knowing where to start to make consistent parts and what bend(s) can be used off the back gage to maintain tolerances.

Just don't volunteer to chip form 3 tons of 4" plate steel. :nono:

DC

[la_coterie]

I was also a SMW ended up as Workshop manager then jacked it all in to live in France

You say you're a SMW so you will know how to work out the order to fold things. Its over 10 ten years since I used a press brake in anger, well at all actually but experience tells you how to fold it. Its only the sh*tty shape that need a bit of thinking and they don't occur every day.

Now the control - that's a different story. I was instrumental in purchasing a couple of Trumpf press brakes, but b*ggered if I knew how to work them!

If I was still WS manager looking for somebody to hire I'd be looking for somebody who could read a vernier, as you say do bend calcs, and have a fair idea of the order to bend things. Not really bothered about the control cos you'd be lucky to find somebody who's used your type of control before.

If as you say you're a SMW I'm puzzled that you don't have much of a clue on bend calcs and the order of folding?

Anyway as you probably know it's all ball park stuff and if it's that critical you have to use the tried and tested suck it and see method - it all depends on the material, vee size, vee rad, grain and which way the wind is blowing.

In the CNC world most things are either pre punched or lasered so somebody? (hopefully) has done the bend calcs right

Anyway, most shapes that I came across could just be bent from the outside in. Those requiring starting in the middle count as sh*tty shapes and you usually end up punting 0.2mm around the sheet to get it in tolerance.

enjoy - it kills your feet. (think flamingo)

[mickmf]

thanks all i can use a vernier and work out bend allowences etc, what i cannot exactly recall is how one sets up the backstop in relation to fold lines on part to be formed.

seem to recal would measure from center of bottom vee to the back of bottom tool say 50mm,

if i was using material 3mm thick which for example bend allowence /deduction was 4mm wanted first fold 40mm in from stock at 90degrees backstop would be set at 50mm +40mm - 2mm =88mm backstop setting to fold material,

if my next fold was 80mm in from the first fold and reverse direction how i calculate correct back stop distance in relation to the second fold ,not sure if its thickness of material or half bend deduction???

and consequent folds

thank you

[la_coterie]

backstop = inside leg measurement to foldline nothing more complicated.
centre of vee to backstop = inside leg measurement.
above gives reasonable results using vee 8x(ish) thickness

Depends on how accurate you want it. If it was a spotty b*llocks job we'd use a bit of scrap to test fold using as above then adjust as needed.

Cut piece 100mm wide measure - fold 90 deg BS=50 measure o/a dims - add up - take of 2x thickness difference between start flat sheet and your number now is bend allowance - sod all those silly calcs ;-)

Second fold pretend the first ain't there same rules as at top above - don't forget retract and delay if stop gonna move in... that can make a mess..

[Al_The_Man]

press brake not brake press

Actually I think it is always misspelled, shouldn't it be BREAK? :devious:
Al.

[mickmf]

thanks all not sure what inside leg measurement refers too ???

if i wanted fold to be 40 mm in from edge of stock ,and finished flange height 20mm (outside dimention) set backstop 60mm -2 thicknesses say stock 2 mm backstop setting from middle of vee 58mm which would be center of fold.??


thank you

[schiada96]

1/3ir + mt x 1.295 is the bend deduction formula for a 90 degree bend.

[la_coterie]

hi Schiada96

Depends what material and what size Vee and what shape punch and what way the wind blows.

What I'm basically saying is that you can get a rough size from calcs which are normally good enough. but if you want it spot on test with a piece of the sheet you're goning to use

Our favourite for sheet - i.e, 3mm & less inside dims added up - works for us on mild steel in 8x mt Vee

[la_coterie]

Ok so you're not a SMW but you want to be,

I don't know anybody thast calls the sheet "stock" you must be a machinist

OK post #6
centre of vee to back of vee you say hypothetically 50mm just think about it draw it out. You want a 40mm fold, you say 40mm in from stock? I presume you mean 40mm in from edge so thats 40mm inside? assuming the vee is less than 80mm you can fold it (normal around 25mm) Think where does the punch fall? (top tool) in the centre of the vee. So logically the backstop will be set 40mm back

In reality backstops are tuned to give inside leg dims which words fairly well on the thinner stuff as I said if in doubt use a bit of scrap to test

So you're descibing a Zed section, first fold 40mm inside (43mm overall). Height of Zed 86mm overall
Fold 1 BS = 40mm

Fold 2 BS = 83mm retract + pause before return to 40mm

It don't matter which way the fold goes for bend calcs

we are of course talking CNC stuff here.

Maybe they call sheet stock in your neck of the woods, then keep on calling it that, but then you'd be a stock metal worker

Simply, backstop zero = centre of vee

[schiada96]

hi Schiada96

Depends what material and what size Vee and what shape punch and what way the wind blows.

What I'm basically saying is that you can get a rough size from calcs which are normally good enough. but if you want it spot on test with a piece of the sheet you're goning to use

Our favourite for sheet - i.e, 3mm & less inside dims added up - works for us on mild steel in 8x mt Vee

The formula is north american avations. You make the material form to the inside radius you want not what it wants. I have found this formula to be best and consistent to within .002.
Jeff

[la_coterie]

Aircraft sheet metal now that's further up the food chain and your material is better quality

[bob mascaro]

i agree .. i get so tired of aaarguing with people over microns ..lol .In sheetmetal the thickness varis more than bend allowances not to mention coinage are concerned .
Its bend dedution and twice the metal thickness is the answer. Bob ie the solidworks guy with 20+ yrs fab exp.

[la_coterie]

Cor more than year since this was last aired!

Strange that the originator of the question hasn't posted any more, maybe he was a troll. Not the most obvious thing to start an agrument on though.

Yeah Bob, I agree. how big is a micron anyway

If you need it that acurate the design must be crap, or go and machine it out of a lump of solid!

I dunno what your sheet tolerances are across the pond, I guess the same as UK +/- 10%

You know sheetmetalworkers are miracle workers really

[schiada96]

i agree .. i get so tired of aaarguing with people over microns ..lol .In sheetmetal the thickness varis more than bend allowances not to mention coinage are concerned .
Its bend dedution and twice the metal thickness is the answer. Bob ie the solidworks guy with 20+ yrs fab exp.

Beg to differ but your formula will be wrong with a insde radius of .03 by about 1/16 on .125 thick material. Tell me what solidworks comes up with for .125 thick material on with a inside radius of .75.
And if your material thickness is varies that much please find a new suppiler. You are talking about thickness variences of .100?

[bob mascaro]

see thats what im talking about lol. and by the way what kind of repeatability do u expec to get with a 3/4'' radi on 11 guage ,surley u dont expect to hold that flange length anywhere near std. tolerances unless its only a few feet long? try stamping or coining maybe.

[bob mascaro]

the formula is for right angle 90 degree bends u have to go into bend allowances for more acute or obtuse bends

[bob mascaro]

actually its called a brake because it has a brake just like a car or at least the old ones did (conventional) . there was a fly wheel that actuated the ram
some peeps called it a clutch so we could also call it a clutch press if we wanted to . Even the hydraulic press have whats called a brake valve