Laser sintering (sort of)

[JBarche]

Hi,
I got a rather weird idea.
I hat three old DVD burners awaiting the bin but I sourced them for motors etc. as a byrooduct I also saved the laser diodes. Since I am more into modelling (Ships not myself) and things like rapid prototyping and SLS ate pretty useful there there might be some use for them.
It should be possible to use the laser to sinter a plastic powder.
The main problems I would see are:
Power - a 200mW laser shult be able to sufficiently raise the temperature of a 0.25mm diameter area 0.1mm deep when moved at ~1cm/s. (based on an asumed density of 1g/cm3 and a heat capacity of 2J/g*K)
Unfortunately most thermoplastics do nod absorb much red - so I will have to add some carbon black.
later it might als pe possible to coat materials like glassbubbles with that mixture - should giv a much lover density.
Liftime of the diode/cooling- currently I think about monting the laser assembly on a rather large aluminium slide potentially with cooling fins and adding a fan. maybe using a pulsed laser may help as well.

Well these are my very first thoughts
Jens

 

[Bionic-Badger]

You should do more reading on the forum. These kinds of questions have been asked many times before, especially the heatsinking part.

 

[millirad]

Although there are many toxic by-products when burning plastic. Burning PVC releases deadly dioxin as a by product. Highly unrecommended. Welcome to LPF and read the stickies.

 

[Leodahsan]

well if you want a better heat absorption, use IR from the dvd burners. They should give 100mW CW and some members said it go as up to 300mW (with short life). Read more and you should get all your questions answered.

 

[benmwv]

Best for heat absorption is 405nm.

For starters you could try using an sfaw-210. They are like $15 on modwerx.

At about 200mw it would easily melt/fuse black plastic. If your setup works well but you would like to try using different types of plastic or lighter colors like even white you will want to get a 12x. $51 on O-like

As for toxic fume and safety concerns, be sure to put the entire thing in a sealed enclosure with a fan venting through a tube and out the window. Make any viewing windows out of red plastic to block the reflected light.

 

[Leodahsan]

Best for heat absorption is 405nm.

For starters you could try using an sfaw-210. They are like $15 on modwerx.

At about 200mw it would easily melt/fuse black plastic. If your setup works well but you would like to try using different types of plastic or lighter colors like even white you will want to get a 12x. $51 on O-like

As for toxic fume and safety concerns, be sure to put the entire thing in a sealed enclosure with a fan venting through a tube and out the window. Make any viewing windows out of red plastic to block the reflected light.

well, try burning something white or blue with a bluray diode :beer:

I thought that IR would be absorbed by almost any color..
but indeed 405nm has the biggest "punch per photon".

 

[JBarche]

:thanks: for the comments
To some point I agree - IR is used in most commercially used SLS machines. The problem would be to match the wavelength of the laser to the absorbtion of the material - hence the black pigment. AFAIK they use CO2 lasers which seem to match the absorbtion of nylon.
As for the toxic fumes - I wold say that PVC and the like are definitly a no go, I think I will look into acrylics or nylon (mainly used in the professional machines.
On the other hand - the idea with the sintering is that you heat the material to a point where it JUST starts to melt - so in theory unlike burning/cutting there should not be any toxic fumes.
Some sort of enclosure and extraction would still be a good idea.
Jens

 

[Leodahsan]

well, you could TRY with a 445nm diode. They go as far 2.2W and can burn white paper as some members said. Any progress reporting will be appreciated :beer:

 

[benmwv]

well, try burning something white or blue with a bluray diode :beer:

I thought that IR would be absorbed by almost any color..
but indeed 405nm has the biggest "punch per photon".

High end ir, like from a CO2 laser, is definitely better than any other but a 780nm cd diode will barely burn better than a red.

What type of laser needed really depends on the color of what is being burnt. In the realm of diode lasers though, I'm pretty sure blu-ray is the most all-round laser you can get. The beast idea would be to have changeable laser heads, with a 12x in one and a LOC in the other so you can switch them out according to the material being used. There really aren't any diode lasers that are very good with white, mostly because white is white because it doesn't absorb any (visible) colors. Both low end ir and high end uv pretty much count as visible colors.

 

[Leodahsan]

Ohh I understand. I think the best idea then, would be a 445 (or 405 if you prefer) combined via dichros to a double LOC 660nm (combined via PBS).

edit: like this

 

[benmwv]

Yeah, now you have all the color ranges covered and the combined power of the laser would be enough for white.

 

[Leodahsan]

are you going to build it? I may help put you on the right direction if you want.

 

[benmwv]

Who, me?

I have 3 concerns about this.

1. The chassis? The obvious thing to do is to modify a printer, but a printer has like 15-20 "ink applicators" and a laser is only one so if you tried to hook it up to trigger from one of them there would be gaps where there were supposed to be more. I think I seen a video on YouTube of a guys custom flatbed printer that only printed 1 line at a time. That is what we need.

2. The input. Somehow we would have to find a program that will take a 3D model file and take it apart into 1000's of horizontal cross sections and send the to our "printer" as b/w picture files. It will take some searching but there probably is something like this on the Internet somewhere.

3. The material. Finding a source to buy the material probably won't be very hard. The hard part will be figuring out how to apply it in very thin sheets (let's be realistic and say either .5 or 1 mm layers, the .1 stated in the OP probably isn't going to happen). I can't really see a sweeps-by-dropping-powder-as-it-goes bar thing applying such thin layers. The best I can come up with is a bin off to the side of the printing area with a screen in the bottom filled with powder. After a layer has been fused the box holding the model slides over away from the lasers and underneath the bin with the screen on the bottom. Once it is under cell phone vibrator motors mounted to the powder bin turn on for a certain amount of time that we have measured will allow the desired thickness to fall on the model. It then slides back over, gets sintered, and the cycle repeats.

One more thing I just thought of is the the models box will have to move down a little each time so it will stay in the lasers focus. Perhaps if the side of the box stay and only the bottom moves up and down it will work well.

 

[Leodahsan]

well well.. Maybe you could use stepper motors, arduinos with coordinates system, look here...

 

[benmwv]

Yeah well as cool as it would be I don't think I will be able to build this.

I have a large lack of funding.

 

[Leodahsan]

Yeah the biggest problem is the lack of funding. Maybe you could try buying it part by part, and a deal may come in. If you want, start by the laser head; PBS + Dichros.