Magnetohydrodynamic deposition rate control for metal manufacturing
Devices, systems, and methods are directed to applying magnetohydrodynamic forces to liquid metal to eject liquid metal along a controlled pattern, such as a controlled three-dimensional pattern as part of additive manufacturing of an object. An electric current delivered to produce the magnetohydrodynamic forces can be controlled between a pulsed electric current and a direct electric current to change the rate of liquid metal ejection from a nozzle. For example, the electric current can be switched between a pulsed electric current and a direct electric current based at least in part on a position of the nozzle along the controlled pattern, providing accuracy of liquid metal deposition along portions of the pattern having more detail and providing speed of liquid metal deposition along portions of the pattern having less detail.
1. A method of additive manufacturing, the method comprising:
providing a liquid metal in a fluid chamber at least partially defined by a housing, the fluid chamber having an inlet region and a discharge region;
directing a magnetic field through the housing;
moving the discharge region in a controlled pattern; and
delivering electric current between electrodes defining at least a portion of a firing chamber within the fluid chamber between the inlet region and the discharge region, the electric current intersecting the magnetic field in the liquid metal in the firing chamber to eject liquid metal from the discharge region; and
wherein the step of delivering electric current includes delivering current in pulses sufficient to eject a series of droplets of the liquid metal over a first portion of the controlled pattern, and delivering current sufficient to eject a constant stream of the liquid metal over a second portion of the controlled pattern, to form an object.
2. The method of claim 1 , wherein the controlled pattern is a three-dimensional pattern and the object is a three-dimensional object.
3. The method of claim 1 , wherein the first portion of the controlled pattern includes a boundary of the object being formed.
4. The method of claim 1 , wherein the second portion of the controlled pattern is within a boundary of the object being formed.
5. The method of claim 1 , wherein the current pulses are delivered at a frequency that is less than a resonance frequency of the liquid metal in the fluid chamber.
6. The method of claim 1 , wherein a frequency of the pulses is controlled according to the speed of movement of the discharge region to achieve a desired mass flow rate of the liquid metal.
7. The method of claim 1 , wherein the current is delivered at pulses at a first frequency to define at least a portion of a boundary of the object being formed and at a second frequency to define at least a portion of the area internal to the boundary of the object being formed, wherein the first frequency is different from the second frequency.
8. The method of claim 1 , wherein a frequency of the pulses is less than about 5 kHz at a maximum speed of movement of the discharge region.
9. The method of claim 1 , wherein the ejection of the constant stream of liquid metal results in a higher mass flow rate than the ejection of the series of droplets.