Rotart Shear cutter into Metal sheet cutting


Thread Starter


Dear all

As I said we are doing a metal sheet cutting machine with Rotart shear which as to cut800mm to 5000 mm

The main problem what we are facing is we are not able to achieve the maximum speed of the machine as the motor is selected by the customer. he selected the motor for 80 cuts/min when it is 800mm, but we are able to achieve only 50 cuts. and our cutting profile is like blade will be on the top and when it reached the material it will come down with synchronous speed and cut it when we are increasing the speed we are getting over voltage trip on the drive.

according to customer this profile is not good and he wants the rotary to move always and accel the speed when it going to cut. looking o this I looking for all your suggestion. which profile will be good customers or ours. Will the shear has to move always or it can stop on the top. right now our accel time and decel time is very less. shear is 340mm and we are having leveler and uncoiler..

What should I have to do. Syn angle is 40 as calculated by customer. Speed of the leveler and shear should be same when it is cutting for synchronization.

Looking forward for your suggestions

With thanks and regards
Edwin Chacko

William Sturm

If you are getting over voltage faults, then you probably do not have enough braking resistors for the drive. If you have no external braking resistors, then you probably need to add some. Your drive vendor should be able to assist with sizing.

Bill Sturm
your customer is correct you should be able to develop a profile for constant motion... you shouldn't decel to a stop... there are motion controllers out there that automatically generate these profiles, and there are third party software packages that can do it... and of course if you're any good... there's doing it the old way... pencil and paper.
I agree that the rotary cutter should not have to stop between cuts. With a decent controller you should be able to alternate smoothly between two speeds -- the synchronous speed for cutting and the indexing speed for the right length.

The synchronous section would match surface speed with the material from, say, "4 o'clock" thru "6 o'clock" to "8 o'clock". The indexing section would pass thru "12 o'clock" back to the "4 o'clock" position at a speed that prepares it for the next synchronous cut at the proper length interval of the material. There does not need to be any stopping between these sections.

Curt Wilson
Delta Tau Data Systems
Thanks for your reply

I too agree for this, but my doubt is if the shear is 314 mm and we have to cut the lengths from 700 mm to 6000 mm. Even in this case it is possible to run the rotary shear in a constant speed. Shear has to wait till material has to come right??

Waiting for your suggestions???

William Sturm

For longer sheets, you just go slower on the backside. You match speed for some angle, say 30 degrees. Then for the other 330 degrees, you slow down to use up enough time for the next speed match. I suppose for really long sheets, it might make sense to stop

Bill Sturm

Peter Nachtwey

The shear will need to wait at the top when the cut length is approximately 2X the shear circumference. At shorter lengths the rotary shear should move without stopping but at the stop it will need to be going faster than the line speed if the cut length is less than the shear circumference ( this case doesn't apply ) and it will need to go slower if the cut length is longer than the shear circumference.

All of this should be obvious. What isn't obvious is the math.

When the shear hits the metal it should not pull or stall the material. That means the horizontal component of the shear motion should match the metal speed to keep from disturbing the reference encoder. Otherwise a feed back condition occurs where the cutting affects the reference encoder which in turn affects the cutting Some people simply match the line speed with the angular velocity but the horizontal components will not match during the whole cut. It will stall at first.

All this makes no difference if your motor is under powered. One should be able to compute the acceleration/torque required at every point in the motion profile.