DMLS newbie questions

After seeing the solar sinter by Markus Kayser I thought that maybe selective sintering is easier than I previously thought and I want to build a direct metal sinter machine eventually, I had a few brainstorming ideas but I am not sure if they will work at all, so before doing stupid things I am going to ask more knowledgeable people on the forum.

You can replace the laser with a fresnel lens powered by the sun, the focus will not be a perfect spot of a few microns, so what about putting a diaphragm of a material with a high melting point near the focus? Maybe like an iris of a photographic machine or just a disc with a hole of 0.5 mm in the middle. Will it give a more precise focus spot? Will I have problems of diffraction? Will it still melt the metal?

Using a big lens will still help even with a diaphragm near the focus, cause the small spot of a big lens reduced with a diaphragm will still have more energy than a small lens spot reduced with a diaphragm, right?


For the atmosphere you can use a glove box or just glass panels sealed with silicone to contain it, right?

If I will put water into it to test for any leakage, does it mean that if it contains water it will contain a gas too?

I see that the argon in a gas cylinder is expensive and I see that the machines used to generate nitrogen locally exist but they look really big and expensive like this [www.terrauniversal.com]

Does anyone know the prices?

What about burning some charcoal powder or maybe a candle inside the box? Will it burn the oxygen and raise the pressure inside? (Since CO2 is heavier than O I think that there will be more gas and so more pressure, is this right?). It will be easy to burn cause I have this big fresnel lens inside the chamber that can ignite it. Will it generate weird gasses that I am not aware of? Will I explode?


And for steel maybe you don't need controlled atmosphere but you can mix charcoal powder with steel powder in air in the correct percentages and it will not oxidize when the focus is over it, is this even remotely right?

Edited 2 time(s). Last edit at 07/04/2011 02:40AM by Autarkyboy.

... a big lens with diaphragma in the spot will melt the material, if enough energy goes through the hole - when the diaphragma is close to the surface, the resulting melting bubble will be slightly bigger than the hole, so should work.

But for me all the fussing with solar concentrators and trajectory feeding is bigger trouble than buying a cheap CO2 laser tube or high power diode laser.

I have some fibercoupled IR-diodes with 975nm and 5, 9 or 25Watts of power.

Comercial available fibercoupled 9Watt-diodes will cost something around 300 Euros per piece ... or 200 Euros when bought in quantities of 5 or more ...

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> Will I have problems of diffraction?

Diffraction is an edge effect -- as light passes an edge, it diffracts. The higher the ratio of edge to area, the worse the issue becomes. Diffractionwise, you're better off using a larger iris further from the focus.. but that may not give the best results. Worst case, experiment.

> For the atmosphere you can use a glove box or just
> glass panels sealed with silicone..
>
> I see that the argon in a gas cylinder is
> expensive ..
>
> What about burning some charcoal powder or maybe a
> candle inside the box? ..

The idea is to eliminate reactive gasses from the sintering environment, and then to keep them out.

Argon is a noble gas, so its nonreactive, won't decompose at high temperature, is of compartively high molecular weight, is comparitively cheap, and perhaps most importantly to an experimenter such as yourself, isn't toxic and will stay that way no matter what you do to it. The only risk you face with the Argon is suffocation.. which is easily avoided by not breathing too much of it. Start with it and, once you get things working, then play with substituting gasses.

> And for steel maybe you don't need controlled
> atmosphere but you can mix charcoal powder..

This won't work, not for steel anyway. Steel is an alloy of iron and carbon. Melt it in the presense of carbon, or in an atmosphere that will react with the carbon, and you'll change the ratio and thereby the properties of the steel.


Or you could learn on an easier material than metal.. like wax. A powdered wax printer could be interesting Or perhaps sugar. Sintered 3D-printed sugar creations? Could be yummy

Sintered 3D-printed sugar creations? Could be yummy
really funny idea.
But for those kinds of low melt point things , heat transform have to be considered