Press brake talk

[Portable Welder]

I really need a Press Brake, My goal is to bend 10' of 1/4"

A power leaf brake or ( apron brake) gives a capacity for the length.

A hydraulic press brake is based off tonnage per ft. x what the opening of the bottom die is. For 1/4" plate on a 2" bottom die requires 15.4 Ton per ft.

What I'm trying to understand when it comes to mechanical press brakes is you have 2 different tonnage charts.

Mid stroke and bottom stroke tonnage.

Based on what I have found is you need 225 ton on a mechanical press brake to bend 10' of 1/4" with a 2" bottom die.

So what press brake should I get and what advantages does a press brake have verses a leaf brake.

[Tryagn5]

voltage....

When i looked at presses the biggest issue i found was voltage. I could not afford a new one, so used was the only option, almost everyone i found was 460, or 575 3 phase. I could not power any of the presses which i found, so i gave up on the idea. I did find used presses very cheap, if i could move them.
Kevin

[MMW]

A mechanical brake is powered by a large flywheel. As the flywheel makes one revolution the upper die or punch makes one complete stroke, down then up. Picture the linkage at 12 o'clock & the upper die at the top of it's stroke. Now at mid stroke the linkage on the flywheel is at somewhere between 2 & 4 o'clock. It has less power or tonnage here. Then at bottom stroke, between 4 & 6 o'clock it has the most power or tonnage. Picture you standing below a large wheel at the 6 o'clock position & you are trying to stop it from turning. If you are pushing on it at the 3 o'clock position you have more mechanical force to slow it than if you were pushing on it at the 5 o'clock position. I hope this makes sense to you.

The resistance of the plate being bent has more effect of pushback on the flywheel at mid stroke than it does at bottom stroke.

If you can afford it buy a hydraulic brake. Much easier to be accurate on. You don't need one with all the bells & whistles either. A basic hydraulic brake with numerous dies can do almost anything in a job shop.

[MMW]

So what press brake should I get and what advantages does a press brake have verses a leaf brake.


You can change out top & bottom dies to different shapes. Radius dies, step dies, etc. You can also use it for straightening & flattening plates & bars. A press brake is much more versatile than an apron or leaf brake.

[Tryagn5]

So what press brake should I get and what advantages does a press brake have verses a leaf brake.


You can change out top & bottom dies to different shapes. Radius dies, step dies, etc. You can also use it for straightening & flattening plates & bars. A press brake is much more versatile than an apron or leaf brake.

All very true, also i have always been told a press brake is far safer, has bettar accuracy, and is more user friendly. I have only used a hydraulic press brake myself.
Kevin

[Portable Welder]

Trygn5, If I find the motor voltage cannot be changed then theres always the option of a transformer or just buying a new motor.

Unfortunately, I do have to take the motor HP in to account since I only have single phase power and will use a phase converter to power it.

MMW, Your example was perfect at 3 o'clock you have less power and max power is at 5-6 o'clock so its the tonnage at 3 o'clock that has to be big enough to bend 10' of 1/4" plate that I really need to be concerned about more than the max tonnage of the press brake.
Let me know if this is correct

[elvis]

For this application can you use a vfd instead of a phase converter? And just run it on full power? The motor is just running a big hydraulic pump, right?

[MMW]

Yes you need to have enough tonnage at mid stroke to bend what you want to. You also need extra tonnage so don't buy at the limit. The charts are just guide lines. Some plates are harder than others, bending with the grain vs. against it, bending stainless requires approx. 1.5 times that of steel. All examples of why you want a bigger machine than you think you need.

You can also cheat by using a wider opening on the bottom die. A 2.5" opening will not make much difference in the bend radius but does make a difference in tonnage needed.

Also with a mechanical brake you can "hammer" the plate. Not recommended but you just keep slamming the ram down on the pc. which if right at the limit will bend it a little each time it hits until you finally get the bend you want. By getting the flywheel at top dead center or even a little before you get all that momentum when it contacts the plate. Kinda scary on a big pc.

I was told that on any plate, the first 30 degrees or so of bend requires the most tonnage.

[Portable Welder]

Elvis, I didn't want to use a VF converter because they only run one machine where as a rotary phase converter can run multiple machines.
The phase converter people tell me I will get full power.

MMW, I was talking to a salesmen about mechanical press brakes and he told me to make sure it has a air clutch - Brake for Air bending, I'm not sure exactly what air bending means.

[JSFAB]

Big problem with a mechanical brake is they have to make a full stroke, every time. With a hydraulic brake, you can stand off to the side, using a protractor, get your bend perfect if you want a one-time bend of 87 3/4 degrees (just picking a number out of the air). Once it gets to where you want, just manipulate the limit switches and reverse it. Can't do that with a mechanical brake, I can still remember having to climb up in back and manually spinning the flywheel backwards, just to get a mechanical brake to the point we could reverse the stroke.

If you set the limit too deep on a mechanical brake, you either split the work (or the bottom die), or else jam it. Again, have to climb up in back and manually spin the flywheel backwards until you can get it to cycle without it destroying something.

Mechanical brake is great for production work, you want to make hundreds or thousands of similar hits. Fabrication work? No, go for the hydraulic brake.

I understand there are now some hybrid mechanical/hydraulic brakes out there now, for the last twenty years or so at least. I know nothing about these.

[DetroitRob]

Hydraulic vs Mechanical

A shop I used to work at bought a used mechanical brake.... Great big old machine that saw production use in WWII.. I put all new controls on it, and it got the job done. But it was scary as heck bending large plate, having to use the foot pedal clutch and being next to it when it hit. I would give anything to never have to use it again! On smaller stuff we had a tendency to use the adjusting motor to drive the die down and never even spun the flywheels But one of the guys tried to bend some 1/8" plate and it was not adjusted right... when the die struck it jammed and we almost tipped it over with a 4' pipe wrench on the adjusting shaft lifting it with a 10 Ton crane to break the machine free.

[MMW]

Buy a hydraulic brake. You won't be sorry.

Air bending just means you are not die forming/pressing the shape. Let's say you are bending a plate 45*. Your bottom & top die is most likely a little over 90*. You just push on the plate until it is 45* plus your allowance for spring back. So in effect the bend itself is "in the air" & never touches the dies. This requires less tonnage than press forming which the die set is the exact shape of the bend & you actually press it until it contacts all areas of the die set. Requires more tonnage because you can't have any spring back.

A clutch on a mechanical brake lets you slip it so you have some control over the ram making the stroke. If you didn't have a cutch when you hit the pedal it would just make one complete stroke without any control of the speed. This lets you be able to bend a pc. as JS was talking about. One pc., creeping up on the degrees you want. Almost impossible to do at max tonnage because you are losing tonnage by slipping the clutch & loosing the inertia of the flywheel. Still more difficult than a hydraulic brake.

[Bodybagger]

An excellent source of information on press brakes published by Cincinnati:

http://www.e-ci.com/storage/pdfs/Pre...20Brochure.pdf

[Tryagn5]

An excellent source of information on press brakes published by Cincinnati:

http://www.e-ci.com/storage/pdfs/Pre...20Brochure.pdf

excellant info. Wonder what a brake press like pictured in the pdf costs! Also curious to power requirements and concrete floor thickness needed. That press did not look to light!

[MMW]

This is a picture of the brake I learned on & used for a long time. Bought new it's a mid 80s Cincinnati 230 ton, 12 ft. bed, 10 ft. between uprights. It was the largest brake we could get without cutting a hole in the floor for the front apron. It's a basic hydraulic unit. 3 phase 460/480v, not sure of the amps but had 10ga wire to power it so wouldn't have been much. This floor was about 4 or 5" thick.

I loved this machine & wish it didn't get sold when the co. went under. Pic is from late 2009 as we were cleaning out & liquidating the shop. I had hoped to take the business over some day but such is life. Bad economy hit us hard. An equally nice Cincinnatti 10 ft. x 1/4" shear was sold with it as a pair for $62,000 with a lot of dies. You can see a die rack in the pic. This was full of dies As well as a whole box of shorts. Also note the 1-ton gantry which is a must for large pcs. If I only had the room & the foresight of where I would be today.