What's new
What's new

Press brake servo motor system

SShep71

Cast Iron
Joined
Sep 17, 2014
Location
San Diego, Ca
I have an old Chicago-Dreis 12 ton mechanical press brake that has been beat down and repaired by some of the "finest in the chain of the species". I have tried to bring it back to life but there is just SO MUCH wrong with it that it does not seem feasible at this point. I have been kicking around the idea of converting it to hydraulic, but by the time I built cylinders, sourced a pump, built a tank and cooler, and furnished the valving it would be a hell of a project. Only to yield a hydraulic system (not that there is anything wrong with that). I started to look at other options and I came across servo press brake systems. I knew they existed, I just never considered one for this application. I am curious about the configuration of the servos that are used, most of the information I can find depicts a perpendicular drive system (servo motor at 90deg to the ball screw centerline), I was thinking about a linear drive system (ball screw inline with the motor) however I haven't found much to support the idea. I know the math to calculate the size of the servo needed should be pretty straight forward, I am just not there yet as I wanted to get feedback before I started to put the go gears in motion here. Does anyone have experience with the servo systems involved? I was hoping to get some feedback (pros/cons if you will) about the system, the size of the servos involved, and other general aspects of the design. The press brake I have is a 36" wide Chicago Dreis & Krump 131. I want to keep it a 36" brake and be able to bend 1/8" at 36". So my specs would be 80000psi tensile, 1.5" die opening, .125 radius, so somewhere around 7TPF of bend. There would obviously have to be some big improvements to the structure of the machine, but for now I am going to focus on the servo system.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
An old job had a 4' 40 ton press brake with a servo connected to the screws through a 1:2 or 1:3 timing belt. The cost of the ballscrews outweighs the cost of surplus hydraulics, without even considering the cost of the servos.

The cheapest press brake you can make that doesn't suck is a servo driven leadscrew that carries the ram, and then a hydraulic cylinder that pushes or pulls the leadscrews a fixed displacement.

The control logic would be to back off the hydraulics by stroke + safety margin by timing the valves. The leadscrews rapid travel the ram to above the material, and the hydraulics drive it home against a hard stop. The position of the ram on the screw determines the ultimate depth.

I was going to make a 6' 50 ton brake using 2 5" diameter hydraulic cylinders which pulled on two 2"-4 acme screws driven by nema 34 steppers. We ended up growing and buying a brake, but I have the hydraulics and will probably make it into a nice shop press some time. My particular approach use rotary divider valves, but you can use resynchronizing cylinders or a mechanical torsion beam or chain balance setup.
 

Bondo

Hot Rolled
Joined
May 14, 2011
Location
Bridgeton NJ
That seems like a lot of work to just get a 12 ton machine.

I would just look at replacing the whole thing. Get something like 35 ton for the same price as spending it on rebuilding that old one.

Sent from my SM-G960U using Tapatalk
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
So how are you planning to increase the frame capacity from 12 tons to 21 tons and why?

I took my entire 65 ton verson apart, rebuilt some of it and updated the screw feed to a servo setup before putting it to work. It was pretty straightforward.
 

SShep71

Cast Iron
Joined
Sep 17, 2014
Location
San Diego, Ca
Strostkovy: The setup you described is slightly similar to what is there currently. There are lead screws that adjust the lower die with respect to the bottom of the stroke (dwell) of the mechanical throw. I figured there was going to be a large difference in the cost because of the requirement for precision ball screws with a fine pitch, yet are capable of the tonnage over the distance. As I have been looking into this further, I think that I may go with a hydraulic setup. Originally I was going to try to use a Centroid controller for a mill or lathe to just control the Z axis stroke. That way in theory (the way I have been looking at it) I can just program a rapid in Z (lathe or mill) to just above the piece to be bent, slowly feed down into the piece creating the bend, then rapid back out. I have no idea if it would be possible, but I figured I would at least give it some thought/time for due diligence.


Bondo: The machine is a 12ton setup now as a mechanical brake, I was hoping to wind up with something along the lines of a 25 ton press by the end of it after all the modifications to the frame and the actual mechanical system. I looked at the cost of a replacement to step up to a 25 0r 30 ton setup and the price is not high. The issue is that I cannot find anything that is small, I don't need a 6' brake for anything. This small 36" brake is shallow and has done most of what I need it to do. I just like to keep things condensed in size, as I am out of room in my shop.


Garwood: The existing frame is 5/8" or 1/2" steel plate, I was going to reinforce the frame to achieve the increased tonnage capacity plus a significant safety margin. I have done work similar to this in the past, I did some modeling and analysis in Solidworks and by adding some plate to the sides as well as some additional bracing I can easily achieve what I need it to do. I was actually thinking of using this project as an introductory project for my Youtube channel. IF I ever get to that point. I have another idea for this machine that I have been pushing around for quite some time, but I will keep that one under wraps for now.
 








 
Top