[makerdoug]

Hey there,

I did some research and found that this should be doable. I went and bought some 1/32" silicone rubber (the red stuff - https://www.mcmaster.com/1460n11-1460N113) which was the recommended material, but I'm having trouble actually cutting through it.

I'm running a 40W laser with a 2.5" focal lens. I'm down to 4mm/s cut speed and it still won't go through at full power. I've fiddled with my focus and I'm pretty sure i have that nailed down. I tried swapping my compressor with a higher PSI air compressor and that didn't make much difference either.

The result I'm getting is that the laser is burning maybe halfway through it then stopping. There appears to be a lot of charred material caught in the cut and so I assume the laser isn't able to cut deeper with the soot there. I don't think I can remove that soot manually (brushing it or wiping it) as it would throw off my positioning and I wouldn't be able to do a second pass on it.

Here's what my test cuts look like: https://i.imgur.com/dgEuyBm.jpg
The couple square that are popped out are ones that nearly cut through but I had to rip in order to remove. The 16 squares on the left are testing various speeds and # of passes, none of them worked. The assorted squares on the right section are various tests of different focal calibration and increase airflow.

I have an 80W tube replacement ready on hand, but I was hoping to finish delivering some gaskets before putting the machine out of commission while I make the swap.

Any ideas on other things I can try or should I just hurry up and swap my tube to get this done?

[grawley]

It is a very, very difficult job. I spent a ton of time, to figure it out.

It comes down to two things. One, you need more laser power and to keep the cut area as cool as possible to reduce charring.

So, grab your 80 watt tube because you need it. Then, try to get your nozzle as close as possible to push the air through so that you can cut quicker.

Your first need to pierce the hole then start cutting. For example, you could make a lead-in line to your squares (where the lead-in is overtop and area outside the enclosed part you do not need because that section get ruined as you pierce because it make a large hole that is thicker than your cut line). To pierce, go to the settings in your software and set the pierce delay to something like 2 seconds.

Once pierced (whether you are laser cutting silicone rubber or thick wood), then the cut speed is faster than the pierce time.

I found that the black, mucky, sticky sides were a hassle to clean, and looked terrible. So, a partial solution was to half-submerge the rubber in water then laser cut. This reduced cleanup, and cleanup was done by rubbing a scrap piece of silicone rubber on the sides, like a pencil eraser--still no fun.

This was one of those jobs you never forget.

So, can a laser be used to do this job properly? Yes, a higher power metal tube laser that possesses the capability to hit a peak power well above the highest continuous wave power is good. I have been told (did not witness it myself) that a Rofin laser at 300 watts (has a peak pulsed power much higher than that), can do the job without charring.

I make that high velocity nozzle product that is retrofitted onto Chinese laser machines so look for it at my site if you want improved cuts on silicone rubber and wood.

[makerdoug]

Those are some pretty impressive cuts. I'll see if I can do the lead-in technique, though I'm on a g.weike with a leetro controller and lasercut 5.3, not sure if that setting is available. I'll have to check when i get into work tomorrow.
Do you think the 80W is necessary if I'm only cutting 1/32" thick material though?

I've never replaced our tube before so I'm not sure how long it will take for me to swap it. If it's possible with the 40W I'd like to do it before committing to X hours/days of downtime.

That quick change nozzle body is pretty tempting but sadly outside my budget right now.

[grawley]

Yes, the delay is available on that model. I own that model and run the same software, and set it up for many customers on their Weike machines, using the same version of the software. It can also be found by searching the word delay within the sysconfig.ini file and changing directly there, though you will see several of them together and in various locations (to cover alternative suppliers for the PCB card), so trial-and-error will get you there.

[makerdoug]

I'll have to give that a go when I get in tomorrow. Thanks for the tip!

Since you happen to have the same setup, do you know how to change the order of cuts in lasercut? I've been frustrated with how it chooses it's starting position (often opposite corner of the laser origin) Perhaps that might help me set up some extra lead in paths too

[grawley]

I'll have to give that a go when I get in tomorrow. Thanks for the tip!

Since you happen to have the same setup, do you know how to change the order of cuts in lasercut? I've been frustrated with how it chooses it's starting position (often opposite corner of the laser origin) Perhaps that might help me set up some extra lead in paths too

We need to thank Universal Laser Systems for taking the time to put together this informative graphic that provides vital information about CO2 laser focus lenses.

In your question to the CNCzone forum, you stated that you ran the job using a 40 watt CO2 laser with a 2 1/2" focus lens on 1/32" silicone rubber. And, the result is that the laser machine has not yet been able to penetrate the material.

From the graphic, we read that the 2 1/2" focal length lens has a laser spot size of 0.005" or five thousandths of an inch. And, the effective cutting thickness is 3/8".

If we ask ourselves, what other lenses can effectively cut 1/32nd of an inch silicone rubber, we read that the 2 inch focal length lens is good because it has an effective cutting thickness of 3/16th of an inch, and also the 1 1/2" lens can do the job, because it can do 3/32nds thick materials.

So, the follow-on question is, what do we gain in laser power for making the switch? The analogy is like pounding a thinner nail into wood with the same size hammer, where the hammer is the 40 watt CO2 glass tube laser.

To do this mathematically, we examine the area of a circle, in order to figure out the proportional increase in power. So, like you said that you got half way through the silicone rubber with the 2 1/2" lens. So, how much more power, proportionally do you think you need--because you may need to invest in a new lens in order to succeed in completing the job--and you need to have confidence that the lens has a sufficient increase proportionally in order to plunk down the money.

Further, you need to make the decision whether it is worthwhile to invest in the lens, or simply swap the laser tube and power supply and do a beam alignment (could be a few hours).

The diameter of the current lens (2 1/2") is 0.005. So, the formula for area is 1/4 x pi x d, so in this case its 1/4 x 3.141 x 0.005 = 0.0039
The diameter of the 2 inch focal length lens is roughly 0.003, so the math is 1/4 x 3.141 x 0.003 = 0.00235, so we'll call it 0.0024

Proportionally, first lens divided by second lens is 0.0039/0.0024 = 1.61. In other words, 1.61 times more powerful, or for 40 watts x 1.61 = 64 watts.
In other words, the better choice is to swap to the 80 watt tube, rather than purchase a two inch focal length lens because it is more effective to cut through the material.

The diameter of the 1 1/2" focal length lenses spot size is 0.002. The area is 1/4 x 3.141 x 0.002 = 0.00157, so we'll round that to 0.0016

Proportionally, the first lens divided by the third lens is 0.0039 / .0016 = 2.4 time more powerful, or for a 40 watt laser, then 40 watts x 2.4 = 96 watts.
So, in this case, you get more power with the 1 1 /2" lens than swapping in the 80 watt laser tube.

That said, the air flow does effect the cut quality in a significant way, though largely ignored in lower power CO2 lasers, it is paramount when using a CO2 laser for metal cutting as shown by the PRC Laser company chart section below.



A major benefit of the focus assembly that I make, is that the nozzle distance to the material can be adjusted, without changing the distance from the lens to the material. The nozzle that comes with my setup has a 1mm diameter orifice, where your current setup has about a quarter inch opening. And, the Chinese laser focus head only permits adjusting the lens and its nozzle as a single piece. In my Mahoney setup, the focus lens is stationary, the the nozzle held by the nozzle tube is lowered independently so that you can adjust to get the optimal stand-off distance for best quality. I put together the graphic below to show the invisible air waves that come out of the nozzle during cutting, to show how they change with regard to stand-off distance and nozzle orifice diameter--comes with a 0.0040 diameter and spare drills to drill it larger if you prefer. In summary, laser cutting quality for silicone rubber is greatly improved with focused, fast, assist air when cutting.

[shang]

Precautions during cutting:

When cutting silicone rubber, it is easy to catch fire. Be sure to blow. Prevent contamination of focus lenses. There is smoke on the suction fan. For more details, please contact us at the official website https://www.leapion.com

[makerdoug]

@grawley That first image you linked seems broken. Was that in response to my question on lasercut choosing sequence of cuts?

Okay, I'm starting to get some results now.

I was able to find the lead-in delay setting and have that set to 1 second, 2 was a bit longer than it took to pierce through. My cut speed is stupidly slow though, 2mm/s and it takes two passes. If I go 1mm/s it burns up more and gives me an ugly cut, if I go 3mm/s I need 3 or more passes.

I am attempting to cut 0.8mm holes in this rubber and in the process I'm finding that my kerf is 0.8mm @__@. I have to undersize my holes down to 0.4mm diameter to get the correct size. (I made an error earlier, my lens is actually 2" but this kerf seems rather large given the dot size you mentioned earlier, no?). I also observed I was getting some wierd edge effects on the bottom side of the rubber wherever it was touching the metal grid of the honeycomb bed. I put a piece of MDF under it which gave me more consistent edges but it doubled my kerf somehow. I suppose maybe just nowhere for the energy/air to disappate?

> I found that the black, mucky, sticky sides were a hassle to clean, and looked terrible. So, a partial solution was to half-submerge the rubber in water then laser cut.

I might try a water tray next if I can find a throwaway baking sheet or something flat. Though the material is so thin, it wouldn't be a lot of water.

I was able to skip using the higher psi compressor (thank god, it's so noisy) and have gone back to my little air pump (idk what it's actual output is but it seems to be fine now) The difference in pressure didn't seem to affect it much so I would probably defer to your comments on the hole size at the tip where the air is coming out from being a larger factor than the PSI behind it.

With what i have right now I think just swapping my tube out would be the best bet to making this go faster. The pieces I'm cutting take about 10 min per set and I have to make 100 sets, that's a lot more time than I anticipated.
I already have the tube available, it's just dealing with the downtime to swap it and being able to deliver the pieces in a reasonable time frame. I think now that I have dialed it in to the point where it's cutting it's better to just let the job run even if it takes 16 hours.

[makerdoug]

Here's a photo album of the tests so far. https://photos.app.goo.gl/SUcb9F2txqGK5XJt7

The last thing I had was inconsistent hole sizes across my piece, I suspect the MDF i put underneath is affecting airflow or heat disappation. I'll probably try a metal sheet next.

[makerdoug]

Damn, the metal sheet did worse. I think a solid sheet of anything underneath doesn't allow the holes to punch through properly and with the metal it's compounded with heat dissipation. The holes on the backside only have the pierce hole.

I also had more buckling and because the sheet deformed the cuts were no longer accurate.

I added two more photos to the album with the piece right after it's cut. You can see charred material is buckling/stringing out of the cut line.