The working principle is very simple. For making a 3D metal printer you need 2 things:
Vacuum
High Voltage
Vacuum:
Electron beam needs vacuum to travel from the electron gun to the working area. If there is air in between, the electrons cannot travel. The needed vacuum is showed in the table above, and depends in the distance between the electron gun and the working area. If the distance is small (few centimeters), you need medium vacuum. If the distance is large (more than 10cm), you need a better vacuum.
Also, if the vacuum is not enough, electrons will collide with air or gas particles and the beam cannot be well focused (the focus spot size will be bigger). We will cover vacuum part in more detail later.
High Voltage:
For generate the electron beam you need high a voltage source. Don't worry, I will explain later how to make one.
The electrons are "extracted" from a hot filament, like a lightbulb hot filament. If you apply a high voltage difference to the hot filament, electrons will be emitted towards to the positive potential.
In this case the voltage used is between 10.000-20.000 volts. If you increase the voltage, electrons have more energy and can melt or sinter the metal powder faster.
2
Vacuum Chamber
Vacuum chamber
Polishing vacuum chamber inner walls
I used my lathe to polish the inner side of the stainless steel tubes
I just realized how long this became. Should I move it to an FAQ or some other place?
Did you consider electro-polishing? Compared to the other things that you do it is not very technically challenging and it has a huge effect on the surface area.
Also are you planing on heating the chamber for bake-out?
Will you back fill with nitrogen? That will greatly reduce the pump down time.
Are you worried about the metal powder shifting during pump down?
Even with your baffle, oil contamination of the vacuum chamber is inevitable. Are you concerned that oil contamination will effect how smoothly the powder move? Can you heat the powder to drive off all of the oil?
I'm not familiar with the operation of actuators in vacuum. What type of actuators will you use? Do they need to be baked?
If you don't have another source you can get high vacuum electrical feedthroughs from the magnetron tube in discarded microwave ovens. I have dozens of magnetron tubes that I have been saving for the feedthroughs if you want some.
You can also get 6000VDC power supplies from old microwave ovens. The last stage is a voltage doubler maybe you could double is again. I don't know how smooth it is and if you can vary it. I know they are typically rated at 1000W of microwave power but I don't know if that means that the power supply puts out all of that, more or less.
Can we use the high voltage beam steering electronics from an old CRT and add a higher power filament?
Are you worried about the powder getting in the mechanism that move the powder build platform etc.?
Sorry for so many questions. I really like to project and want to know more.
Agustin Cruz
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I just realized how long this became. Should I move it to an FAQ or some other place?
Did you consider electro-polishing? Compared to the other things that you do it is not very technically challenging and it has a huge effect on the surface area.
Also are you planing on heating the chamber for bake-out?
Will you back fill with nitrogen? That will greatly reduce the pump down time.
Are you worried about the metal powder shifting during pump down?
Even with your baffle, oil contamination of the vacuum chamber is inevitable. Are you concerned that oil contamination will effect how smoothly the powder move? Can you heat the powder to drive off all of the oil?
I'm not familiar with the operation of actuators in vacuum. What type of actuators will you use? Do they need to be baked?
If you don't have another source you can get high vacuum electrical feedthroughs from the magnetron tube in discarded microwave ovens. I have dozens of magnetron tubes that I have been saving for the feedthroughs if you want some.
You can also get 6000VDC power supplies from old microwave ovens. The last stage is a voltage doubler maybe you could double is again. I don't know how smooth it is and if you can vary it. I know they are typically rated at 1000W of microwave power but I don't know if that means that the power supply puts out all of that, more or less.
Can we use the high voltage beam steering electronics from an old CRT and add a higher power filament?
Are you worried about the powder getting in the mechanism that move the powder build platform etc.?
Sorry for so many questions. I really like to project and want to know more.
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