3D printing using electron beam melting

Hi,

I will take as much info as you are willing or allowed to share about the system, since I don't know much about electron guns its nice to learn from practical examples! For a small scale electron beam melting application, how much power do you think is required for the thermionic source as well as the electron accelerator source? Also the focus and scan coils probably use very little power I am guessing? Basically I am wondering how much overall power is required to do x watts of heating/melting. With a single focus coil and a single deflection coil, would it be possible to generate an electron beam with a 1mm or smaller beamwidth that is capable of melting metals for EBM? Also is the beam focal point set before the part being melted so that electrons cross at a point in space like an optical lens making an image on a scree does? Also for the main structure of the electron gun is this correct:

top: thermionic source produces free electrons with zero net velocity

cathode: small diameter metal circle positioned below thermionic source (not sure about this one)

anode plate with central small hole: electrons accelerate from cathode to anode and some go through the hole forming an electron beam while the rest are absorbed back into the metal anode

focus coil: electron beam from anode hole is focused by a solenoid coil in the same way as a convex lens

XY deflection coil: electron beam angle is changed to aim at desired XY coordinate

Also would it be possibly better to use electrostatic focus/deflection for an EBM application? I have heard that electromagnetic is more linear and more accurate.

Thanks for any additional info, tips etc! I am dreaming of making a bench top electron beam melter 3D printer now :)

cheers, Jamie

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Read that if you have not already seen this material.

The power supply is a cold cathode tube oscillator of a armstrong type of configuration. It operates at 100khz into what is called a pie transformer. This transformer is made of litz wire. The DC supply is variable 0..15kVDC using a 3 phase SCR firing bridge.

Although the tube is capable of 350kwatts, we generally don't exceed

250kW.

The pie transformer is inside a vessel that is pressurized around 90 Lbs of SF6 gas, which is a insulating gas and also makes up as part of the dialectic for the corona rings. These rings sit very close to the wall of the vessel and serve as the capacitors in a cockcroft walton full wave rectifier.

At the end of the stack, there still is a ripple in the rectifiers due to the nature in how it works, this ripple is them used as a 100 kHz source into a step down RF transformer which is used to drive the heater element. There are 2 large stats on the end nose that controls the beam current, which is actually done by setting the heater voltage.

Because our systems do not use a motorized generator down the center to operate the heaters. The main stat is what we called the preset, this is the minimum heater voltage derived from the selected HV voltage at the end of the rectifier stack. The other stat is a variable trim that ramps up in proportion to the increase or more voltage as the process material gets ramp up in speed to maintain dosimetry.

I could go on but I think this is enough to start with.. :)

Jamie