Author Topic: Laser cutter to open sealed plastic cases.  (Read 1773 times)

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Offline aargee

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Laser cutter to open sealed plastic cases.
« on: October 06, 2021, 11:11:39 pm »
Hello all,

Maybe an unusual or not wise at all application but.. can you use a laser cutter to open sealed plastic enclosures Read: sealed battery packs.

Currently, I use a 'hot knife method. The battery packs are medical in origin, sealed by plastic welded/glued joints and full of 18650 batteries.
The hot knife method is precarious as trying not to short or cut open batteries requires careful, time-consuming work. I imagine that the laser could be just as precarious if not aligned precisely.

I was wondering if I could use a laser cutter with a profile to suit the shape of the battery pack, to slice through the plastic to open them up.
I imagine having some sort of alignment jig to sit the battery in place and then run the profile.
The reality is that the cut does not need to go completely through, leaving a sliver of plastic is OK, as that can be split apart mechanically to remove.

Or is the whole idea a bit silly?
Not easy, not hard, just need to be incentivised.
 

Offline Kean

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Re: Laser cutter to open sealed plastic cases.
« Reply #1 on: October 07, 2021, 01:23:21 am »
Not silly, but I'd certainly be cautious.  Is it glued or maybe an ultrasonic weld?

First thing to check is the type of plastic (and any glue), and whether it might give off toxic fumes.

Second is that although the laser would follow an accurate and repeatable cutting path, the depth of cut with laser is somewhat uncontrolled and dependant on the material surface.  You'd probably want to keep the laser at a low power and run multiple passes to just weaken the join enough to then manually crack it open.  Personally, I'd probably do this with a jig and program on my benchtop CNC instead, as you can control the depth of cut much better.

The 18650s inside the outer case are likely covered in heatshrink and possibly other protective layers, and inside that is metal case.  So (without seeing the item) I'd guess you'd have to be very unlikely to actually hit something flammable.  The laser could reflect off the metal as well, so it must be behind something that blocks any reflected/scattered laser light to avoid eye damage.

Also keep in mind that you never leave a laser cutter alone when cutting, and always have a suitable (CO2) fire extinguisher handy.
 

Offline thm_w

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Re: Laser cutter to open sealed plastic cases.
« Reply #2 on: October 07, 2021, 09:09:45 pm »
Is there no way to setup your hot knife blade to only cut a certain depth?
 

Offline aargee

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Re: Laser cutter to open sealed plastic cases.
« Reply #3 on: October 08, 2021, 12:12:08 am »
Yes, that's sort of the way I do it now, using a marker rather than a solid guide. But there is no good accessory to control depth - yet. I may have to craft one up.
Not easy, not hard, just need to be incentivised.
 

Offline thm_w

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Re: Laser cutter to open sealed plastic cases.
« Reply #4 on: October 08, 2021, 01:19:41 am »
Yeah make your own, maybe out of PTFE.
Stainless could also work but is a pain to deal with.
 

Offline TimNJ

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Re: Laser cutter to open sealed plastic cases.
« Reply #5 on: October 25, 2021, 02:55:56 pm »
You can open ultrasonically welded plastic cases with an arbor press and a wedge shaped ram, if you have one. This usually cracks the weld quite well, without being too medieval.

If you have a table saw, you can also setup the fence and adjust the blade height to align with the welding line. A little bit more medieval, but not too bad.
 

Offline thinkfat

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Re: Laser cutter to open sealed plastic cases.
« Reply #6 on: October 25, 2021, 03:13:54 pm »
Oscillating saw?
Everybody likes gadgets. Until they try to make them.
 

Offline TimNJ

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Re: Laser cutter to open sealed plastic cases.
« Reply #7 on: October 25, 2021, 04:01:22 pm »
FYI
 

Offline Ziggo

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Re: Laser cutter to open sealed plastic cases.
« Reply #8 on: October 31, 2021, 12:46:18 am »
I agree with TimNJ. I have opened medical devices that were ultrasonically welded in order to replace batteries. By pressing on the correct place, I was able to open them with no marks on the outside at all.
 

Offline Doctorandus_P

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Re: Laser cutter to open sealed plastic cases.
« Reply #9 on: November 15, 2021, 01:59:53 am »
I have also opened some (non medical) wall warts that were ultrasonically welded by hitting them with a hammer in such a way that the weld gets most of the force and this worked remarkably well.

I could even glue the parts together again with only minor visible damage to the box.
Some kind of press to better control the applied force may work even better, but I did not have any available.

A laser cutter may also work, but the results depend a lot on the sort of plastic used. Some will release obnoxious gasses. To get a good result with a laser cutter, focus is pretty important. You can even make use of this. If the laser is out of focus inside the box, then it will produce less damage there.

Another possibility is a circular (table) saw. These are easy to set to a controlled depth to saw (almost) through the enclosure without damaging the internals.
 


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