Upstroke press brakes - Reccomendations?

[PhoenixMetal]

I am considering buying an upstroke (Amada) press brake for my shop and wanted to see if anybody had any experience using these.

I am used to normal downstroke brakes where the bed and backgauge is stationary and the ram comes down from above. With an upstroke brake, the bed and backgauge move up to meet the stationary top ram.

It seems to me like an upstroke brake would be less accurate because it would be more difficult for the operator to consistently hold the workpiece against the backgauge while the whole thing is in motion. On the other hand, this is how Amada makes their machines, and in my opinion, Amada is pretty much as good as it gets when it comes for metalforming machinery. So there must be something good about it.

Does anybody have any experience with upforming press brakes?

[gridley51]

I`ve got a couple of 35 ton upstrokers.Don`t have any bother holding the work in contact with the backgauge but as they`re only 35 ton they`re mainly used for bracket work so the parts are not big.Both good machines,one`s a Promecam and the others a Haco.
Mark.

[douglasco]

I ran a nice trumpf cnc brake for about a year. I can't imagine why anyone would buy an upstroke unless it was really cheap or they didn't care about precision and weren't going to be using it constantly. But thats just my opinion, i am very curious about this too. I actually started a thread asking the same question a few days ago.

[gridley51]

Douglasco,we ran tens of thousands of brackets a week on upstroking pressbrakes,for many years.Material was mainly 0.200" mild steel and tolerances between bends was usually 0.004" max.For to say that an upstroker isn`t accurate proves that you know nothing about the subject.We also had downstrokers and they were no more accurate than the upstrokers.

[douglasco]

No, I've never ran one, thats why i too was asking questions. The most my boss would stand for was usually .002". There were many of the thinner parts that the way you held the part and let it lift off your fingers made all the difference in the world on holding tolerances. Its just like anything else, the more repetitions you did the better you got at it, but the first ones were never as good as the 100th. I'm sure you could do it in an upstroke too, i just think it would take longer to get good at. And it always starts over, at least to some slight degree, for every different part you do. But i do realize for the majority of parts being made this is overkill.

Another concern i would have is safety. I would bet the percentage of injuries caused from upstroke is higher then down.

[gridley51]

"Another concern i would have is safety. I would bet the percentage of injuries caused from upstroke is higher then down."

Actually a downstroker is a more dangerous machine,as the blade can drop through gravity if anything fails.
UK rules are that the guard stops the operator reaching the beam while the press goes through the first part of the stroke,the beam stops 1/4"/6mm above the job and the guard switches off.The operator can then move into the guard area and hold the job against the stop while the beam completes the bend.
Ok he can still trap his fingers between the top tool and the job,if,for example he is doing a double bend such as a channel shape but,that applies equally to downstrokers and upstrokers.
I personally have no preference either way for up or downstroke unless I am bending large plates when the downstroker would be first choice as the plate does not move until the bend starts and it is then clamped in position between the tools.
I suppose for small pieces when working with the fingers close to the tooling the upstroker is better as the initial movement of the beam and job upwards tends to focus your mind before any bending movement and possible finger trapping takes place.
As for 0.002" tolerance that is only possible on very thin or precision rolled plate.Once you get up to 1/8"-1/4" plate the allowable tolerance on thickness far exceeds 0.002" and this makes it very difficult to hold a tight tolerance on large batches.The only way to achieve it is to mic every plate and put them into batches according to thickness.You would struggle to take ten tons of 1/4" HR plate,shear it into say 6" x 8" blanks and put one 90 degree bend in them all and hold 0.015" on the distance of the bend from any one end.