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Thread: Least expensive way to drive 8W 915nm laser diode

  1. #11
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    ... I'm driving 975nm-diodelasers with 9Watts or 25Watts @9Amps and TTL-switching through a MOSFET with a group of LM317 / LM350 / LM338 configured as current regulators and running parallel to sum the curent.

    It's a simple circuit - you can find some infos in my lasercutter-WiKi: http://www.reprap.org/wiki/Laser_Cutter_Notes

    I've made this Wiki some years ago then with 5Watt-diodes running with 5Amps max, but you can replace the LM317 (until 1.5Amps, continuous current 1A) by LM350 (until 3Amps) or LM338 (until 5Amps) to receive more current per chip.

    My actual driver has two LM317 and three LM338 configured to 1A+1A+2A+2A+2.5A, which i can switch together in any combination for predefined max current from 1A to 8.5A for different diodes or running the 'big' diodes with lower current than the max. spec of the diode says (what will enhance the lifetime until 'forever').

    The 'finetunig' is made with TTL-level (0-5V) through an opto-coupler and PWM-switching the MOSFET, that drives the current through the LM's and the laserdiode.

    Recently I've found an analog circuit with a LT1215 OP, that can drive the same LM-configuration with analog voltage level until 1MHz clocking rates! and will solder and test this in the next weeks ...

    Viktor

  2. #12
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    Quote Originally Posted by swamidog View Post
    it should appear. give it another try. i've bought from badip in the past and he's been very responsive.
    I second the above. I know for sure that he is very very busy these days, as i also contacted him for drivers and it took him 3-4 days to come back to me.
    But things worked out well

    I do seem to recall the idea to tie all 4 channels together as a good one, but let's wait for Thomas to come back to this.
    "its called character briggs..."

  3. #13
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    I've sent the message again last night (had the text saved on my computer), and still can't see anything in my sent items

    Not in a hurry, so I don't mind waiting. I'm using the time to read about SLS, specifically researching about aluminum powder SLM (Selective Laser Melting)

  4. #14
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    ... aluminium powder is a bit tricky, even with inert gas shielding - better use brass powder or common sintering powder what's composed from - Fe89% Cu8% Pb3%

    I have some kg dark brown lignin powder, what's a natural thermoplast extracted from wood dust ... and made some tests with black mineral microspheres and dark plastic dust without inert gas.

    With the IR-diodes you need dark powders or you have to mix shiny materials with dark thermoplastic pigments or carbon to get enough energy absorbed ...

    Viktor

  5. #15
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    I'd definitely prefer to work with plastics, but haven't been able to find a "cheap" source of powdered plastic (sub 100 micron particles).

    Bronze wouldn't be much easier to work with as its melting point is about 300C more than aluminum and without some gas shielding it would too oxidize (granted it wouldn't combust like aluminum).

    The only reason why I'm looking into aluminum sintering is because the powder is widely available. Otherwise, plastic would be my first choice.

  6. #16
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    ... you can try with grinding down some black thermoplastics like POM or ABS (maybe you have to cool it while grinding) and sieve the dust for selection.

    But best methode would be jetting a stream of molten plastic on a fast rotating disk, so it will be spreaded into micro-droplets and while falling down they'll solidify to perfect uniform micro-spheres ...

    Viktor

  7. #17
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    Quote Originally Posted by VDX View Post
    ... you can try with grinding down some black thermoplastics like POM or ABS (maybe you have to cool it while grinding) and sieve the dust for selection.

    But best methode would be jetting a stream of molten plastic on a fast rotating disk, so it will be spreaded into micro-droplets and while falling down they'll solidify to perfect uniform micro-spheres ...

    Viktor
    Trying to make my own powder is too complicated and probably too expensive to justify the effort.

    Just did a search on alibaba.com (for some reason I hadn't thought about searching there until your comment!), and found a supplier in china for powder plastic that is advertised specifically for SLS uses (http://www.alibaba.com/product-free/...ter_rapid.html), but their minimum order quantity is 30kg, which is A LOT. I'll try to contact them tonight to see if I can get them to sell me a couple of kilograms and get more info about pricing.

    An 8W laser will be much faster working on plastic than on metal powder, not to mention a much simpler workflow as it won't need gas shielding (just good ventilation).

  8. #18
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    ... the linked powder is white, so not really usable with the IR-diode - try to get some dark coloured powder or thermoplastic pigment colour to try with it pure or to mix with the white powder.

    Another material interesting for first tests could be dark red or brown clay powder, used in cosmetics ...

    Viktor

  9. #19
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    Quote Originally Posted by VDX View Post
    ... the linked powder is white, so not really usable with the IR-diode - try to get some dark coloured powder or thermoplastic pigment colour to try with it pure or to mix with the white powder.

    Another material interesting for first tests could be dark red or brown clay powder, used in cosmetics ...

    Viktor
    You wouldn't happen to be the same VDX on the reprap forums, would you?

    I read the discussions about SLS on the reprap forums. There were a couple of SLS printer technicians in the thread linked above who said the most important thing for SLS is preheating the material. This prevents the printed object from curling and minimizes the power needed to melt the plastic while increasing the printing speed.

    Preheating is also getting me to think if 8W is really needed. Wonder how fast/slow would the 700mw 405nm bluray diodes be with a preheated pwoder to say 160-180C? Still waiting to hear back from the chinese supplier of the powder about pricing and characteristics. Also sent an email to these guys but haven't heard anything back yet. Also need to think about how to pre-heat the powder and what to make the powder box and Z-axis platform from.

    Still, the powder color isn't really an issue as coloring pigments are widely available (my availability scale is ebay. If its widely available there, its easy to get).

  10. #20
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    Quote Originally Posted by IraqiGeek View Post
    You wouldn't happen to be the same VDX on the reprap forums, would you?
    ... the world isn't really big, is she? --- yes, that's me too ;-)

    Heating will reduce the needed amount of laser energy or enhance the max. possible speeds ... but it's a big chunk more of work, so not really essential for testing different powders for their SLS-usability.

    Another option is to use two lasers - one with a spot of maybe 2mm diameter will preheat the surface without melting it ... the other with 0.1mm pointing in the center of this hot-spot will melt the dust ...

    Mixing white/translucent powder with dark pigments will give some funny results with laser-melting - depending on the energy density, the fused material will change the colour because the absorbing pigment particles will start to vaporize, while transferring heat to the surrounding white particles. So you can start with dark powder and receive slightly coloured translucent objects ... maybe usefull for art or some special effects, like clear windows in opaque parts?

    405nm @700mW and preheating could be enough for melting the uncoloured powder - but could be hard to achieve a melting spot in the size of the laser focus, the transmission/duiffusion between the particles is depending on the optical characteristics of the plastic in respect to the wavelength.

    And there is something more special with lasers melting powders ...

    Viktor
    Last edited by VDX; 12-12-2012 at 05:42.

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