Sheet rolling machine with CNC control
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  1. #1
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    Default Sheet rolling machine with CNC control

    Hello, fellow machinists. We have just recently added a sheet rolling machine to our production capacity but we experience problems setting it up without a lot of samples. The parameters which we have access to in programming mode are bend and feed - feed is pretty much straight-forward and doesn't need explaining but "bend" is where things get tricky.
    The machine has a total of 4 shafts - three lower shafts positioned in line and held by two plates in their ends, the plates and shafts can rotate around the longitudinal axis of the machine with the bearings being at the two ends of the center shaft, the upper shaft is centered in line with the lower center shaft and isn't attached to the same plates the lower shafts are and only transmits power. The way that the lower shafts rotate is by being powered by two screws - "bend" zero is when the shafts lay flat. "bend" value is defined by the rotation of the two screws forward of backward depending on the side of the machine you are loading the parts from and the general direction of bending. I established what the "bend" values correspond to degrees of tilt of the lower shafts assembly but do you have any idea to what degrees should we set it up to bend let's say a 3mm sheet to a diameter of 700mm? The unfolded length of the part is 2198mm but what angle should we use to get it done? The machine is nothing similar to a press brake and the machine manufacturer telling me that we have to do it by trial and error make me feel really confused right now Thanks in advance!

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    Due to variables in material composition and residual stress in the sheet metal the exact amount to set the bend for a particular radius / material will vary. Here is where records of previous correct radius/material bends will get you close . . .

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    Quote Originally Posted by Red James View Post
    Here is where records of previous correct radius/material bends will get you close . . .
    Yup. start making a "cheat sheet".

    the matrix should have material, thickness, width to roll, and final dia. needed.

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    Quote Originally Posted by Red James View Post
    Due to variables in material composition and residual stress in the sheet metal the exact amount to set the bend for a particular radius / material will vary. Here is where records of previous correct radius/material bends will get you close . . .
    Exactly why the machine builder refuses to make a technology table for us saying that it won't work anyway.

    Quote Originally Posted by digger doug View Post
    Yup. start making a "cheat sheet".

    the matrix should have material, thickness, width to roll, and final dia. needed.
    That's quite a lot of sheet to cut, bend and then scrap since we can't bend the same part twice as in a manual roll forming machine and the main reason I am looking for a way to calculate a somewhat close "bend" value so I can achieve a close result on the first part and a good result on the second part. The exact bend value isn't described anywhere on cold forming textbooks I have or found probably because most of the rolling machines are still manual and not CNC. Just being unable to find a way or come up with a way to calculate the bend value is driving me nuts.

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    Quote Originally Posted by anht View Post
    Exactly why the machine builder refuses to make a technology table for us saying that it won't work anyway.



    That's quite a lot of sheet to cut, bend and then scrap since we can't bend the same part twice as in a manual roll forming machine and the main reason I am looking for a way to calculate a somewhat close "bend" value so I can achieve a close result on the first part and a good result on the second part. The exact bend value isn't described anywhere on cold forming textbooks I have or found probably because most of the rolling machines are still manual and not CNC. Just being unable to find a way or come up with a way to calculate the bend value is driving me nuts.
    You develop the sheet as you make a job (not as a purpose job using scraps)just like you do presently with the manual machine, after awhile, the chart can be interpolated a bit, estimating values between actual line items, to get close.

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    Thanks, guys. If anyone comes up with something, please let me know. Best regards!

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    My cnc roll bender requires me to scrap 5 pieces of each new material. Set the bender and record the result. Have the first and last close to or beyond your likely extremes. My machine calculates via statistics what any machine setting would most likely result with the material.

    It's been about 20 years since I've done it, but statistical analysis with a graphing calculator would do it.

    Sent from my E6910 using Tapatalk

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    you can get a good start with measuring the arc of the three points of left right and top rolls (offset for material thickness, 1/pi on top roll, 2/3*pi bottom rolls). Your finished part will be 1.016 times larger radius. of course different materials, grains, memory, how you press the roll button, the price of eggs in Alberta all change the 1.016- but it is a really good start. along with your graphs you build over time.

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