laser used in metal 3D printer

I suspect CO2. I think that's mostly what's used for cutting metal & such, because it's easy & powerful.

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www.wescottdesign.com

Well, My NDA expired on the subject from 6 years ago. 400-1000 Watt Co2 in a inert atmosphere. Fiber lasers can be used with some metals.

The trick is not the laser, its the specialized lensing.

Steve

Would it be possible to use a small flame? Much cruder and slower, I suppose, but probably cheaper. Just musing. How small can you make ox-acetylene anyway? Or CO and O2 perhaps to avoid making water.

Cheers

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Syd

I haven't looked at the video. I assume the beam is invisible as CO2 lasers work in the infrared range.

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Rick

Using a small flame, at sub millimeter spot size has some similarities with a plasma or electron beam maybe.

cheers, Jamie

Hi,

I'm interested in hearing about the pulse waveforms driving the laser and the laser pathing. From the video it looks somewhat similar to the pathing used for a filament based 3D printer maybe. Also the lensing, is the tricky part having the lens' redirect the beam down the XY axis or is it the final beam focusing (or both). Maybe a CO2 tube could be mounted vertically on the tool head, and a single focus lens can be used along with Z axis height adjustment to make the optical system simpler at the costof more weight on the tool head.

What metals can fiber lasers work with? Also what is a good source of the metal powder and is it pretty homogenous in grain size/shape? Is there a way to make the powder, it sounds pretty expensive currently.

Thanks for answering any of the above :D

Oh ya where can I find a 400-1000W CO2 tube :)

cheers, Jamie

On the systems I saw, beam positioning was galvanometer scanner based with a F-Theta lens for focal plane correction. The object to be made sat in a tank of argon, and a metal dust tornado" was swirled around the object to be sintered. The lab I was in was making turbine blade prototypes from high temperature materials. As well as other rapid prototypes. These were later annealed in some fashion to become "single Crystal" metals. After SLS, they went into a conventional oven to consolidate the sintering before further treatment. No oxygen is allowed in, for obvious reasons.

I worked in a university laser lab at the time. We were given their castoff s as worn but usable gear when they upgraded to better lasers. It kept us running another two years. Most fun I ever had loading a truck. As a treat( ment) I was given a tour of the SLS labs on site.

Syd, Flame spraying is used for very course deposition, and usually a plasma tor ch running inert gas is the source these days. Flam spraying is usually for placing a hardening layer on a structural object or for building back up w orn spots on a shaft. It is very crude, resolution wise, and the target

Having no idea, I would guess a diode laser. I think you want a really small spot size. A lot of heat in a small volume and something has to melt.

George H.

On a sunny day (Mon, 17 Nov 2014 15:57:39 -0800 (PST)) it happened George Herold wrote in :

There are several high power IR lasers modules on ebay:

small spot size. A lot of heat in a small volume and

Which will not achieve the proper focus size he needs. It has a elliptical beam with horribly different divergence characteristics in the X and Y axis . As do nearly all diode laser arrays.

This is one case where you want a Gaussian or Top Hat beam distribution and a high specific impulse to rapidly fuse the metal dust. While the laser l isted will no doubt heat metal to incandescence, it has the beam properties of a flashlight reflector that has been crushed in a press. Even with cor rection optics, that laser would be a dog for this application.

Your trying to sinter a .004 inch / 100 micron layer of metal. Your spot si ze determines your resolution, the shape of your spot is carried over into the work. To build a uniform structure, you want to sinter that dust as fas t as possible and as uniformly as possible.

That laser is an array of roughly .5 mm wide, 200 micron thick diode chips in a stack. Each chip emits a crude, elliptical beam roughly 15 degrees by

40 degrees wide.

Net result, very poor Etendue at the target.

Oh yeah, you'd fuse metal, but your finished objects would be course and lo ok like crap. For that price you can find a used 100-150 watt industrial l amp pumped YAG laser and start to do it right. Simply because it will have much lower divergence, much better transverse beam shape, and will achieve a much, much smaller spot size.

At 100-200 watts, you'd still be low on power for this process.

Lasers are mainly what I do for a living. Yes, you can sinter thin films of metal with a 200 watt diode array. Can you overcome the heat conduction is sues and fuse quality metal blocks with that laser, not as well as you migh t think.

Steve

On a sunny day (Tue, 18 Nov 2014 05:41:44 -0800 (PST)) it happened " snipped-for-privacy@EnergyNull.com" wrote in :

Hey, but I liked it :-) Just a bit too dangerous to order one and play with it.

in a tank of argon, and a metal dust tornado" was swirled around the object to be sintered.

in some fashion to become "single Crystal" metals. After SLS, they went into a conventional oven to consolidate the sintering before further treatment.

No oxygen is allowed in, for obvious reasons.

us running another two years. Most fun I ever had loading a truck. As a treat(ment) I was given a tour of the SLS labs on site.

for placing a hardening layer on a structural object or for building back up worn spots on a shaft. It is very crude, resolution wise, and the target

Hi,

Sounds pretty interesting, also I was wondering if it would be possible to couple a CO2 laser (200Watt to 1kW) to an optical fiber bundle and then a focusing lens?

cheers, Jamie

Co2 is at 10.6 Microns right in the middle of a silica adsorption band. This means a expensive, exotic "Chalcogenide" fiber needs to be used. You can can get a pretty nice used BWM for the probable price of a piece of that fiber.

ND:YAG at 1.06 Microns on the other hand goes through high power silica fibers.

Jamie, Start with Jeff Hecht's book "The Laser Guidebook" and Silfvast's Book "Laser Fundamentals" before you go down this beam path.

The learning curve is extremely steep and the simplest mistakes are very expensive with high power lasers.

Steve

There's bright visible light, but it's not clear to me whether it's the laser, the incandescence of the metal, or if the laser has a spotter light on it.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

Hi,

Thanks, I recall hearing from previous discussions on here that glass is opaque to CO2 laser wavelengths. I was also wondering about a relatively cheap CO2 40Watt laser tube like this one:

Could the output laser beam from something like that be focused down to a small enough spot that it would melt metal powder? If so I guess as was mentioned already the bonding to the layer below might be the reason a cheap 3D metal printer can't be made with these tubes, otherwise it could be good for really high resolution small metal parts. Maybe the concept of a "heated bed" common in plastic filament

3D printers could be used to keep the small (ie 1cm x 1cm) work area hot enough to make the layers bond easier.

cheers, Jamie

Your lens would need to be quartz or perhaps a plastic that is transparent to IR. In chemistry we used quartz cuvettes to hold samples for spectrophotometry... although I think that was for UV. I guess the opaqueness of glass depends on the frequency of IR as we did use glass test tubes for some IR work... I think. Heck, that was some 40+ years ago.

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Rick

lenses for CO2 laser are afaict made of Zinc selenide

I can't see how a 40W CO2 laser would be nearly enough for welding, that is what is used at the lower end in laser cutters that can only just cut something like 6mm plastic or wood

-Lasse

The issue is mostly 3-D heat conduction away from the hot spot. A semi-infinite chunk of metal effectively drops half the delta-T across a thickness equal to the spot diameter, so for a given delta-T you need a power level of the order of

P >~ deltaT*alpha*diameter

where alpha is the thermal conductivity. For metal this is typically

100 W/m/K, so for a 50-micron spot (which is doing pretty well with a CO2 laser) and a 700 K delta-T, you need about

P ~ 700K * 100W/m/K * 5e-5 m = 3.5 W.

So if you wrote slowly enough, you ought to be able to use that 40-W laser. How slowly? To heat up a 100-micron cube would take

E = (0.01 cm)**3 * 1.7 kJ/cm**3 = 1.7 mJ, so your writing speed would be on the order of 2000 resolution elements per second, i.e. 0.005 cm *

2000 or 10 cm/s, which is pretty slow.

These numbers are probably within a factor of 3, so you really have to have more laser power than that for a practical instrument.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Hi,

Thanks, that is cool, I guess the simplest way to do it is mount a

40watt tube vertically right to a small CNC machine (or beefy 3D printer) spindle/tool holder, and then use a single focus lens, and adjust the vertical height to get the desired (tiny) spot size.

A 40Watt CO2 laser tube is about 70cm long, but I think it could still be put in a custom tool holder and weight balanced for good XY motion.

A quick search found these focus lens for CO2 lasers:

Here is one:

"18mm ZnSe Focus Lens for CO2 10600nm 10.6um Laser Engraver/Cutter FL:1.5" 38.1mm"

Would a single lens like one of these be able to get down to a 50 micron spot size from one of these cheap ebay 40watt laser tubes?

40Watt CO2 laser

I already have a 3D printer and a small CNC so just would need to figure out which one to put a laser on :D

cheers, Jamie