PDA

View Full Version : Laser Etching Fused Quartz Tubing



Ben Halop
03-21-2013, 2:48 PM
Hi everybody!

So today I am running some tests on etching a Fused Quartz tube. It is similar to borosilicate glass (Pyrex). I would like to achieve the frosted look I get with wine glasses and other glassware, but so far all the etching have come out "clear." The etching is noticeable and looks as the graphic should, but instead of a frosted white-ish color all I have achieved is an etching in roughly the same clear color as the tubing. My results were slightly better running more slowly at 600 DPI rather than my normal goto 400, but still not where I'd like. I am using an Epilog 75 Watt Helix w/ Corel X6 using the rotary attachment for this project.

Any suggestions?

Dan Hintz
03-21-2013, 3:40 PM
Try going lower on the dpi, not higher... and make sure your power is pretty low. Doesn't take much to get glass to fracture.

Ben Halop
03-21-2013, 3:48 PM
Thanks for the response Dan. I just ran a pass using 300 DPI at 100 Speed 100 Power and the etching is even clearer and less defined. Should I drop it down further? My usual setting for other glass is 400 DPI 80 Speed 95 Power

Matt Turner (physics)
03-21-2013, 5:06 PM
Fused quartz/silica has a lower thermal expansion coefficient than borosilicate (about a sixth of that of borosilicate), and a slightly higher thermal conductivity. (These properties make it possible to cut quartz with a laser.) From what I understand, the frosted look achievable on glass is due to the microfractures caused by localized thermal expansion. It's possible you can't achieve these microfractures in quartz with your laser power.

Are you engraving in solid black? I wonder if a dithered grayscale might do a better job of creating more light-scattering surfaces.

Gary Hair
03-21-2013, 6:12 PM
In a word, sandcarving. You may not have that capability but it's truly the only way to get consistent results when engraving glass. People have devised all sorts of methods of improving the laser etching of glass, but, in my opinion, they don't really do much and take more time than sandcarving would take. Just my .02

Dan Hintz
03-21-2013, 8:07 PM
From what I understand, the frosted look achievable on glass is due to the microfractures caused by localized thermal expansion.

Close... the microfractures are actually local stress fractures that happen during the cooling phase.

Good point about the quartz glass, though... didn't put my thinking cap on. Heating should take a bit more power than standard boro, but not much. The lower expansion coefficient, however, could present more of a problem... if you can't stress the glass enough, no fractures, which means no image.

Thinking on it, I'd want to do quartz with a fiber/YAG rather than a CO2, but we work with what we have...

Mike Null
03-21-2013, 9:29 PM
Dan

It has been my opinion that the stress fractures occur during the heating phase when the lasered area expands more rapidly than the unheated area around it. I do not have technical data to verify this view but in my non-techie mind this makes more sense.

Ernie Balch
03-21-2013, 9:47 PM
Dan

It has been my opinion that the stress fractures occur during the heating phase when the lasered area expands more rapidly than the unheated area around it. I do not have technical data to verify this view but in my non-techie mind this makes more sense.


The Laser scribe and break process for LCD panels relies on a cold air jet following the laser. The rapid chilling causes a great deal of stress and cleanly breaks glass sheets. As far as I know the process will not work without the rapid cooling.

Mike Null
03-21-2013, 9:51 PM
Ernie

I understand and completely agree with your point but it is not the same as engraving.

Dan Hintz
03-22-2013, 7:37 AM
Dan

It has been my opinion that the stress fractures occur during the heating phase when the lasered area expands more rapidly than the unheated area around it. I do not have technical data to verify this view but in my non-techie mind this makes more sense.

Several years back when the "glass engraves because of impurities" debate was in full swing, I posted some snippets from a tech paper on glass engraving / cutting. Amongst the snippets was a graph showing the depth to which the 10um wavelength can reach into the glass before being completely absorbed. Along with that, I discussed the mode of fracturing the glass, which is fractures from stress release as the glass cools from localized heating by the laser.

Personally, I could have gone either way (cooling or heating) causing the fractures (but I was certainly against the whole impurities thing), but science says it's the cooling that works, and I would have a harder time deciding how heating itself would cause the cracks anyway. Just as what Ernie posted about the LCD depanelization (for a while they did the same with solar cells, but now I believe they mostly do it was a fiber/YAG laser and trepanning), it's all about heating up a line (these are high-powered lasers) and then hitting it with cold air. The sheets are so thin (<1mm), the crack is easy to propagate.

Mike Null
03-22-2013, 10:02 AM
Dan

Thanks. I had believed it was the expansion because that is the initial change in the material but I can live with cooling doing the job.

Ben Halop
03-22-2013, 12:34 PM
Thanks for all the responses guys! I ran a few more tests yesterday varying the DPI and power, and while I was able to achieve a deeper, textured engraving on the quartz I wasn't able to get the frosted look I was going for yet. A little too high power and it would cause the stress fractures you mentioned Dan.


Fused quartz/silica has a lower thermal expansion coefficient than borosilicate (about a sixth of that of borosilicate), and a slightly higher thermal conductivity. (These properties make it possible to cut quartz with a laser.) From what I understand, the frosted look achievable on glass is due to the microfractures caused by localized thermal expansion. It's possible you can't achieve these microfractures in quartz with your laser power.

Are you engraving in solid black? I wonder if a dithered grayscale might do a better job of creating more light-scattering surfaces.
Yes I have been engraving in solid black with the Stucki dithering setting. While I have some experience using the grayscale to achieve shading on wood and anodized aluminum, I am unsure as to how this could be applied to the quartz tubing to give a frosted look. Would you mind going into a little more detail on this?


Close... the microfractures are actually local stress fractures that happen during the cooling phase.

Good point about the quartz glass, though... didn't put my thinking cap on. Heating should take a bit more power than standard boro, but not much. The lower expansion coefficient, however, could present more of a problem... if you can't stress the glass enough, no fractures, which means no image.

Thinking on it, I'd want to do quartz with a fiber/YAG rather than a CO2, but we work with what we have...
Believe me if I had the funds I would own each and every type of machinery I could haha. I need to find a way to sell the idea of a YAG laser to my company so they'll foot the bill. At one time I was looking into cutting carbon fiber and engraving stronger materials not just marking them, but they wouldn't go for it then. What I really need right now (besides the quartz engraving) is a way to engrave bare brass, copper, stainless steel, and titanium but thats a whole other monster.


Ernie

I understand and completely agree with your point but it is not the same as engraving.
Yes I do not wish to cut the tubing, as it is already sized, flame-polished and annealed to their desired specs.


In a word, sandcarving. You may not have that capability but it's truly the only way to get consistent results when engraving glass. People have devised all sorts of methods of improving the laser etching of glass, but, in my opinion, they don't really do much and take more time than sandcarving would take. Just my .02
How much roughly would it take to get started sandcarving in $$? Keep in mind that I'm starting with none of the equipment, though I may be able to get my hands on a cabinet and we already have compressed air running throughout my shop and available outside.

Ben Halop
03-22-2013, 12:36 PM
Oh and luckily for this project, of the three accounts I am etching the quartz tubing for the one that will be due the soonest actually preferred the clear engraved look to the frosted so thats a plus. But the other two projects coming right after are still desiring the frost.

Dan Hintz
03-22-2013, 1:06 PM
Yes I have been engraving in solid black with the Stucki dithering setting. While I have some experience using the grayscale to achieve shading on wood and anodized aluminum, I am unsure as to how this could be applied to the quartz tubing to give a frosted look.

Ah... some of us have been doing this so long, we tend to forget not everyone knows "the tricks". You typically don't want to engrave substrates like glass with solid black. You want to do something like 70%... and on a side note, at 100% black, dithering (like Stucki) is pointless. You can't dither a solid color.

A solid color actually re-engraves a spot you just engraved (particularly at higher dpi), or close enough to it, that you end up blowing away the nicely fractured surface. This leads to the nearly clear / smooth surface you're describing. You want a low dpi where the dots don't overlap (like 250dpi... you may get away with 300dpi in some circumstances), and just enough power to cause the glass to fracture. The contrast comes from the fractured surface reflecting/refracting light in a random direction, so you want as much of that randomness as you can get.

Ben Halop
03-22-2013, 1:42 PM
Ah... some of us have been doing this so long, we tend to forget not everyone knows "the tricks". You typically don't want to engrave substrates like glass with solid black. You want to do something like 70%... and on a side note, at 100% black, dithering (like Stucki) is pointless. You can't dither a solid color.

A solid color actually re-engraves a spot you just engraved (particularly at higher dpi), or close enough to it, that you end up blowing away the nicely fractured surface. This leads to the nearly clear / smooth surface you're describing. You want a low dpi where the dots don't overlap (like 250dpi... you may get away with 300dpi in some circumstances), and just enough power to cause the glass to fracture. The contrast comes from the fractured surface reflecting/refracting light in a random direction, so you want as much of that randomness as you can get.
Yup, even though I've been working with this laser for a couple years now I still consider myself a beginner. I will run some tests with the lighter % today. I really had no idea and feel like I've been doing this wrong the entire time now. I will have to run tests on both the quartz and the wine glasses which are my norm. Always looking to make my work look better ya know.

Matt Turner (physics)
03-22-2013, 1:57 PM
Somewhat relevant: http://www.synrad.com/synradinside/pdfs/Glassmarkingmethods.pdf