Plate rolling gurus: Help! CNC programming, repeatability and consistency
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  1. #1
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    Question Plate rolling gurus: Help! CNC programming, repeatability and consistency

    My company bought a new 4-roll CNC plate roller to replace a completely manual, non-digital 3-roll plate roller that's been in service for decades. The old manual roller was used by an experienced craftsman to gradually roll parts to the intended radius. The idea behind the purchase of the CNC machine was to flatten the learning curve for next generation of plate roll operators while benefiting from increased throughput and precision. We use our plate rollers everyday to form parts with very similar geometry, but with varying bending radii, material types and thicknesses, and parts widths. The materials themselves are not exotic: mild steel and 304/316L stainless, with M.T. ranging from 10ga to 1/4 inch. The wide variety of parts -- which are made to order per customer specifications -- means there are hundreds of parts that need to be programmed into the new CNC plate roller.

    We learned pretty quickly that CNC plate rolling is different from other manufacturing processes that use CNC (like cutting or machining) because of the variables of material thickness and hardness. It's impossible to form good parts by simply loading a blank, punching in some numbers and pressing the start button without taking into consideration the inherent variability of the material. But unlike the manual plate roller, where the skilled operator rolls the material gradually to compensate for variable hardness, the CNC plate roller forms parts in one pass. If the part is overbent at the first bending moment it's already too late to avoid rework or the scrap bin. Our company doesn't do mass production, so the computer can't really "learn" the material variability by the many tweaks and adjustments a roll operator would make while rolling hundreds or thousands of the same part.

    We are still rolling test pieces through trial and error to write new programs. Many of the programs we already made produce parts that require rework because the material we are rolling for a job is harder/softer than the material used to write the program. We are hoping for more consistency and repeatability by writing "hard" and "soft" version of all our programs. Yet it's already taken a really long time and literally tons of scrap material to get as far as we have -- and we still have hundreds of parts left to program.

    To any plate rolling gurus out there who have dealt with CNC roll bending and programming:

    • How do I get this machine to crank out good parts sooner and with better consistency?

    • Do you have any tips and tricks for getting better quality and repeatability despite material variability?

    • Do we simply need more patience and diligence and continue with the process we've been following?


    We want to believe that CNC plate rolling will benefit us, but we aren't seeing any benefits yet. I would appreciate any insight you are willing to share. Thank you!

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    Not a guru on them but have set up a few and spent too much time trying to get a good method down. In the end unless you are doing large runs its just not worth it in terms of scrap rate and time to do the job.

    Over time you can get a decent library to give you ballpark to start but it can get to be a very large library. A list needs to include: material type, thickness, diameter, finish on the material, edge finish(shear/laser ect). Even with all that different mill runs can also throw all your numbers right out the window.

    Also over time the bearings will start to wear or loosen up which will mess with all your numbers. Keep in mind some operators will roll hundreds of bad cylinders then go well thats the numbers it called for in the book. I swear the smarter the machine the more stubborn the operator gets. While on that note if you have an employee that likes the machine(makes a big difference) and cares about making good parts then overtime they will get dang good at knowing the quirks and how to adjust it on the fly.

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    I dont have a lot of roller experience especially with CNC, but I do know people that do. A roller is about the same skill level as a press brake. CNC doesnt make the operator great, it is just a digital tape measure.

    I suggest you create a book of numbers that goes like this.

    Rolling 1/4" plate 36" long
    1st roll - From flat - Set both sides at 9.11
    2nd roll- set both sides at 8.52
    3rd roll- set both sides at 8.016
    Check diameter
    Normal finish measurements- 8.003, 7.995, 7.993, 7.982

    Sent from my SM-G960U using Tapatalk

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    I was in a shop that ran an expander as a 2nd op.

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    it will benefit when hundreds of the same lot steel are made, other then that its trial and error sneaking up on it.

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    Thank you all for the great responses. When I started this thread awhile back, I couldn't find it on the forum after. I thought perhaps the moderators removed the post because my questions were so stupid, lol. But I was surprised and delighted to find the thread is still here.

    In the end unless you are doing large runs its just not worth it in terms of scrap rate and time to do the job.
    it will benefit when hundreds of the same lot steel are made, other then that its trial and error sneaking up on it.
    I am reaching the same conclusions. It seems CNC rolling is not fit for purpose in our shop. We maybe form the same part a few dozen times a year, at most. The idea that a less-skilled operator can push a green button and roll a perfect part is not realistic for how we use our plate rollers.

    I suggest you create a book of numbers...
    I have Excel spreadsheets filled with numbers -- and they are epic. Beautiful spreadsheets bursting with so many numbers. The numbers printed on the 10-key pad on my PC keyboard are wearing off from all the data entry into those spreadsheets.

    Even with all that different mill runs can also throw all your numbers right out the window.
    No doubt about it.

    Thanks again everyone for your responses, I truly appreciate it.

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    2020 software (aka bendtech) is a no brainer return on investment with rolling. You still need to sneak up and monkey bend (straighten part by bouncing on it). No table will predict conical (some call it spherical) distortion. cnc is nice for a skilled worker to get 98 or 102 percent there - fast.

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    It all starts with the material
    Ask your material supplier for a material with tighter tolerances on thickness and good consistant formability
    and quality. They are out there

    Peter
    Last edited by Peter from Holland; 07-20-2021 at 08:42 AM.

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    Not CNC, but we would always "pre-brake" each end with the press brake about a foot into the sheet and then just insert in plate rolls, square up, & raise bending roll to radius formed by the press brake. Usually would result in a 1 pass rolling operation.


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