Reply by Lasse Langwadt Christensen November 20, 20142014-11-20
Den fredag den 21. november 2014 00.13.49 UTC+1 skrev Jamie M:
> On 11/19/2014 6:58 PM, sroberts6328@gmail.com wrote: > > Here is a detailed thesis on the matter > > > > http://etheses.whiterose.ac.uk/378/1/uk_bl_ethos_400851.pdf > > > > At lower laser powers a copper doped stainless steel powder is the material of choice. The copper aids in bonding the steel particles. > > This still needs fusing in a furnace. > > > > Steve > > > > Hi, > > Have you ever come across a wire feed laser welder? I was thinking > something like a MIG welder, but using a laser instead of the electrical > arc. If the wire feed was small enough diameter something like this > could be used for 3D printing too. > > cheers, > Jamie
http://youtu.be/b5Xi1LfeJdw -Lasse
Reply by Jamie M November 20, 20142014-11-20
On 11/19/2014 6:58 PM, sroberts6328@gmail.com wrote:
> Here is a detailed thesis on the matter > > http://etheses.whiterose.ac.uk/378/1/uk_bl_ethos_400851.pdf > > At lower laser powers a copper doped stainless steel powder is the material of choice. The copper aids in bonding the steel particles.
This still needs fusing in a furnace.
> > Steve >
Hi, Have you ever come across a wire feed laser welder? I was thinking something like a MIG welder, but using a laser instead of the electrical arc. If the wire feed was small enough diameter something like this could be used for 3D printing too. cheers, Jamie
Reply by Jamie M November 20, 20142014-11-20
On 11/19/2014 6:58 PM, sroberts6328@gmail.com wrote:
> Here is a detailed thesis on the matter > > http://etheses.whiterose.ac.uk/378/1/uk_bl_ethos_400851.pdf > > At lower laser powers a copper doped stainless steel powder is the material of choice. The copper aids in bonding the steel particles.
This still needs fusing in a furnace.
> > Steve >
Thanks! :)
Reply by Jamie M November 20, 20142014-11-20
On 11/19/2014 6:15 PM, sroberts6328@gmail.com wrote:
> Also check to see if the Co2 will run vertically before you buy it. Some cheap tubes do have a thermal gradient issue. Has to
do with convective gas flow patterns in the tube.
> > I'll be shocked if you get good structural strength at 40 watts. > > > Phil's numbers strike me as highly optimistic. I can barely cut thin steel shim stock at 40 watts on a professional laser cutter,
with assist gas. I would not even try to weld it.
> > Steve
Hi, Thanks for the info about the thermal gradient issue, I guess this could cause overheating near the top of the tube.. Also what is your cutting beam diameter approx at 40watts? Do you ever have problems with metal splatter onto the optical components? Phil's example used a 50micron focus beam diameter, about 0.002", is your shim stock about that thickness too? What do you think you could cut without the assist gas? I think that thickness might be the high end of what powder thickness could be welded. I came up with a simple idea for a metal powder leveler that is just a fixed horizontal bar attached to the spindle/toolholder axis, and at a fixed height so that it always levels the metal powder to the exact height of laser beam focus, this way when the Z stage goes up to melt the next layer of metal, the levelling bar also goes up the same amount and levels the powder, which there is an excess pile of. cheers, Jamie
>
Reply by November 19, 20142014-11-19
Here is a detailed thesis on the matter

http://etheses.whiterose.ac.uk/378/1/uk_bl_ethos_400851.pdf

At lower laser powers a copper doped stainless steel powder is the material of choice. The copper aids in bonding the steel particles. This still needs fusing in a furnace.

Steve 
Reply by November 19, 20142014-11-19
Also check to see if the Co2 will run vertically before you buy it. Some cheap tubes do have a thermal gradient issue. Has to do with convective gas flow patterns in the tube.

I'll be shocked if you get good structural strength at 40 watts. 


Phil's numbers strike me as highly optimistic. I can barely cut thin steel shim stock  at 40 watts on a professional laser cutter, with assist gas. I would not even try to weld it.

Steve
Reply by Jamie M November 19, 20142014-11-19
On 11/19/2014 8:16 AM, Phil Hobbs wrote:
> On 11/19/2014 03:19 AM, Jamie M wrote: >> On 11/18/2014 2:44 PM, sroberts6328@gmail.com wrote: >>> 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 an >> >> >> 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: >> >> http://www.ebay.com/itm/151058818267 >> >> 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 >> >> > 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.
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: http://stores.ebay.com/CNCOLETECH/_i.html?_nkw=lens Here is one: http://www.ebay.com/itm/18mm-ZnSe-Focus-Lens-CO2-10600nm-10-6um-Laser-Engraver-Cutter-FL-1-5-38-1mm-/151123324956 "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 http://www.ebay.com/itm/151058818267 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
> > Cheers > > Phil Hobbs > >
Reply by Phil Hobbs November 19, 20142014-11-19
On 11/19/2014 03:19 AM, Jamie M wrote:
> On 11/18/2014 2:44 PM, sroberts6328@gmail.com wrote: >> 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 an > > > 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: > > http://www.ebay.com/itm/151058818267 > > 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 > >
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
Reply by Lasse Langwadt Christensen November 19, 20142014-11-19
Den onsdag den 19. november 2014 09.55.40 UTC+1 skrev rickman:
> On 11/19/2014 3:19 AM, Jamie M wrote: > > On 11/18/2014 2:44 PM, sroberts6328@gmail.com wrote: > >> 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 an > > > > > > 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: > > > > http://www.ebay.com/itm/151058818267 > > > > 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. > > 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. >
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
Reply by rickman November 19, 20142014-11-19
On 11/19/2014 3:19 AM, Jamie M wrote:
> On 11/18/2014 2:44 PM, sroberts6328@gmail.com wrote: >> 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 an > > > 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: > > http://www.ebay.com/itm/151058818267 > > 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.
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. -- Rick