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Thread: 352nm UV laser: will it cut scotch tape?

  1. #21
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    One other consideration here is that you will need to deal with combustion/ablation products from laser cutting. The material that is removed during laser cutting doesn't just "go away", it's converted into other substances including smoke and soot and other particulates and volatiles that like to float around in the air and quite often stick to things like lenses. Plastics, including those in tape and in coated cardboard, tend to produce materials that condense into especially gross and sticky residue. It's also, of course, an air quality issue, and the magnitude of the problem will depend on your throughput. So you'll need to carefully plan to evacuate all of that junk (noting that the draft created by the required ventilation can exacerbate fire risk if you're not careful), and probably plan for regular maintenance to include cleaning any critical surfaces, such as your machine vision lenses and exposed laser optics and any optical sensors, also any surfaces that might transfer that junk to places it shouldn't be. Strategic air/inert gas blast will help, but in this case may wind up mostly blasting the residue onto the contents of the boxes if you're not careful.

    Honestly if your incoming packaging isn't consistent enough that you can deal with it with a mechanical cutting system I have a hard time imagining that a laser is going to be a more reliable solution.

  2. #22
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    Quote Originally Posted by aberry View Post
    One other consideration here is that you will need to deal with combustion/ablation products from laser cutting. The material that is removed during laser cutting doesn't just "go away", it's converted into other substances including smoke and soot and other particulates and volatiles that like to float around in the air and quite often stick to things like lenses. Plastics, including those in tape and in coated cardboard, tend to produce materials that condense into especially gross and sticky residue. It's also, of course, an air quality issue, and the magnitude of the problem will depend on your throughput. So you'll need to carefully plan to evacuate all of that junk (noting that the draft created by the required ventilation can exacerbate fire risk if you're not careful), and probably plan for regular maintenance to include cleaning any critical surfaces, such as your machine vision lenses and exposed laser optics and any optical sensors, also any surfaces that might transfer that junk to places it shouldn't be. Strategic air/inert gas blast will help, but in this case may wind up mostly blasting the residue onto the contents of the boxes if you're not careful.
    You're on point. Dust is a real problem. But it's a problem even without lasers involved and a regular maintenance is a necessity.


    Honestly if your incoming packaging isn't consistent enough that you can deal with it with a mechanical cutting system I have a hard time imagining that a laser is going to be a more reliable solution.
    The hope here is that correcting a laser is easier than a metal blade.

    Sometimes, packages are reinforced with metal braces like this:
    Click image for larger version. 

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    A metal blade hitting one will one or more things at once:

    1. One or more teeth become duller; blade will need to be replaced sooner
    2. Blade may lose a tooth or even explode (not a very frequent event, but it's still happening)
    3. The staple will travel uncontrollably and potentially scrapping goods inside the box.

    This is why most of the existing box openers try to go around the edge instead of trying to cut the seal. This reduces frequency of such events, but does not eliminate them: the outer world is cruel; you always get the worst.

    A laser could potentially either go around the staple or try to cut through (depends on the wavelength and other capabilities).

    Additionally, some packages have irregular shapes. Usually, such cases are handled by humans. Here we try to make a more automated facility, where people will come every day for 3-4 hours, but the rest of the day (20 hours) are "lights off". Therefore we have to handle more of the exceptional cases automatically. It's okay to have tens of packages per day delayed and then handled by a human, but not hundreds or thousands -- after that it's just easier to have people working all day long.

    It's understood that the problem may not have a solution; it's also possible that a solution exists but lasers play no parts of it; we explore more conventional options too. It still makes sense to consider the laser + computer vision approach. At worst, it will be more obvious which issue would be the show stopper.

  3. #23
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    ... as lasers will add a bunch of other (partially unresolvable) problems, my best bet will go back to ceramic blades in a rotating head and/or upped with ultrasonic energy

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  4. #24
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    Quote Originally Posted by fuzzy View Post
    You're on point. Dust is a real problem. But it's a problem even without lasers involved and a regular maintenance is a necessity.
    Sure, there will be debris from mechanical cutting as well, but one of the things I was trying to point is that with combustion/ablation, it's a much more problematic form of debris. Instead of cardboard dust and maybe bits of tape we're talking about very fine particulate, smoke and soot containing potentially carcinogens or other nasty substances, fumes that like to condense into greasy residues on optics (and that can result in destruction of the optics or worse if not dealt with, especially with a high power pulsed laser). Some of that can be ameliorated with the proper cutting parameters, an air blast on exposed critical optics, etc, but all of the ablation products still have to go somewhere. And with no control over the incoming packaging, there's the possibility that a cutting strategy that usually works perfectly well may result in a gooey and/or flaming mess when a package comes in wrapped in some weird type of tape or coated cardboard or whatever that you might not have anticipated.

    Generally, laser processes work best when they can be applied to a very consistent and well controlled problem, which it sounds like you don't really have. Not trying to be discouraging, just trying to clarify some of the challenges this approach entails.

  5. #25
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    Quote Originally Posted by aberry View Post
    Sure, there will be debris from mechanical cutting as well, but one of the things I was trying to point is that with combustion/ablation, it's a much more problematic form of debris. Instead of cardboard dust and maybe bits of tape we're talking about very fine particulate, smoke and soot containing potentially carcinogens or other nasty substances, fumes that like to condense into greasy residues on optics (and that can result in destruction of the optics or worse if not dealt with, especially with a high power pulsed laser). Some of that can be ameliorated with the proper cutting parameters, an air blast on exposed critical optics, etc, but all of the ablation products still have to go somewhere.
    It's a problem, but a second-order one. As everyone agrees in this thread, it's not given that it would even work. And if it does work, then some mitigations about dust / goo buildup may need to be developed. One option is to place a transparent to the laser and optics sheet of plastics or glass between boxes and optics. And then do a daily washdown of the chamber with a pressure washer every day. The exact material for the sheet will depend on the laser wavelength, but it's something that can be addressed.

    And with no control over the incoming packaging, there's the possibility that a cutting strategy that usually works perfectly well may result in a gooey and/or flaming mess when a package comes in wrapped in some weird type of tape or coated cardboard or whatever that you might not have anticipated.

    Generally, laser processes work best when they can be applied to a very consistent and well controlled problem, which it sounds like you don't really have. Not trying to be discouraging, just trying to clarify some of the challenges this approach entails.
    It's understood that some packages will burn / be damaged. Preliminary estimates show that damaging 1 out of 1000 packages is okay-ish, as the costs will be offset by other costs savings.

    But it's going to be quite a challenge to even get it cutting. I was unsure before starting the thread, and I am even less confident after getting 5 expert opinions that the task is much harder than it appears.

    I will still try and I promise to share my progress. Sometimes, even non-successful projects bring interesting or amusing insights.

    I also hope to benefit from the advice provided in this thread.
    Last edited by fuzzy; 05-26-2020 at 11:22.

  6. #26
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    A small update: before I can justify spending a fortune on the 352nm laser, I want to be sure that it would be able to cut transparent scotch tape. So far, it's the most difficult material in the mix.

    Since true UV lasers are expensive, no matter wattage, I had to resort to UV LED light to test if scotch absorbs this wavelength well. I have got a torchlight that is nominally 365nm, but the advhoc results were inconclusive: definitely less bright, but still passes a lot.

    I was unsure, if I got a wrong LED (for instance, it could be 405nm and I would not really notice the difference by eye), or there's some absorption effect on shorter wavelengths, but since LED light is not monochrome, it could be hidden by longer wavelengths of the LED spectrum.

    So, I have got a handle on a Ocean Optics USB2000 spectrometer and measured absorption directly. I also validated that I indeed have a UV LED light that has ~365-370nm peak.
    Below is a graph that shows the difference with and without a scotch tape placed between the light. As it can be seen, the absorption rate is negligible (5% or less). I also confirmed that similar absorption rate is at other places of visible spectrum.

    Click image for larger version. 

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    I will now try to get a shorter-wavelength UV LED light to test if there's anything interesting closer to the target wavelength. It's very unlikely.
    Last edited by fuzzy; 05-31-2020 at 20:27.

  7. #27
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    ... so not worth the hassle

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  8. #28
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    Quote Originally Posted by VDX View Post
    ... so not worth the hassle
    Hi Viktor,

    yeah, nothing suggests that 352nm would be substantially more absorbing than 365nm. But I still want to try, so I bought an LED with the following spectral response:

    Click image for larger version. 

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    This covers the target wavelength, even though it's only half bright at 352nm.

    Once the LED is here, I will do another absorption test and post the results here (unless this begins to feel like a noise - let me know, I can totally keep this boring stuff to myself)

  9. #29
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    I had my luck today and found a scientific paper that discusses micromachining Scotch tape with a laser. Apparently, it's the easiest way to get microfluidic devices to work.

    A variety of commercially available tape products were used to fabricate the microfluidic
    structures including; Scotch® Permanent Double Sided Tape (19.0 mm width and 88.9 μm
    thickness), Scotch ® Gloss Finish MultiTask Tape (19.0 mm width and 50.8 μm thickness),
    Scotch® Shipping Packaging Tape (47.7 mm width and 78.7 μm thickness). These materials
    were chosen because they were commercially available, inexpensive, and nearly ubiquitous in
    modern laboratories. All these tapes laser micromachine well at 266 nm with no melting or
    charring and minimal heat affected zone (HAZ).
    ...
    In order to maintain the reproducibility of the channels' dimensions in the microfluidic
    devices, several parameters in the laser cutting process were kept constant. The output power
    of the laser was set at 1.45 W and was checked continuously to verify stability. The frequency
    of the laser (pulse repetition rate) was set to 25 kHz and the linear speed was 25 cm/s. We
    chose a relatively fast speed in order to minimize thermal effects on the tape during ablation.
    While 266nm lasers are probably still impractically expensive, it gives at least some hope that it is possible to laser cut transparent Scotch tape with a laser and no risk of fire.

  10. #30
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    I really fear your going to have a fire. Your likely to do best with CO2. Organics and polymers absorb much more strongly in that region. Plexi is a good example. That tape is likely black at 10000.

    I think the knife is your best bet. Can you just buy your stuff in bigger packages? The laser your looking at and cnc and camera and fire system is north of 50k and more like 150k plus yearly costs and then you only have one. If you stay cutting heads you can likely have 5 for the same price. Or a crew of high school kids for next to nothing.

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