Techniques to Improve MHD Jetting Performance

Patent metadata

Field	Value
Publication number	US-2021379664-A1
Application number	US-201917278050-A
Country	US
Kind code	A1
Filing date	Sep 9, 2019
Priority date	Sep 20, 2018
Publication date	Dec 9, 2021
Grant date	—

Abstract

An improved additive manufacturing system for manufacturing metal parts by magnetohydrodynamic printing liquid metal. A monitoring system including at least one camera capturing light reflected from a strobe light source. Images of the droplets are captured during their jetting and analyzed to determine whether the jetting performance is meeting specifications. A nozzle of the system has a nozzle bottom and a nozzle stem extending outward therefrom on which a meniscus of liquid metal can form. The nozzle is cleaned by bringing a ceramic rod in the vicinity of the nozzle and jetting a bead of metal which is rotated against the nozzle to remove an amount of dross.

First claim

What is claimed:

1 . A method of characterizing droplets of liquid metal during additive manufacture of metal parts using MHD printing of liquid metal, comprising:
directing a strobed light source to a stream of droplets of liquid metal expelled from a discharge orifice of a nozzle by a magnetohydrodynamic force; capturing by at least one camera directed at the stream of droplets a plurality of images of light from the strobed light source reflected from an individual droplet as it traverses a field of view of the camera; and determining from the plurality of images a measured value of at least one physical characteristic of the individual droplet.

2 . The method of claim 1 further comprising the step of comparing the measured value to a desired value of the physical characteristic.

3 . The method of claim 2 further comprising the step of, when a difference between the measured value and the desired value exceeds a predetermined threshold, cleaning the discharge orifice of the nozzle with a cleaning instrument.

4 . The method of claim 2 further comprising the step of, when a difference between the measured value and the desired value exceeds a predetermined threshold, adjusting at least one printing parameter.

5 . The method of claim 4 wherein the printing parameter is an amount of current passed through the liquid metal in the nozzle through a plurality of electrodes.

6 . The method of claim 1 wherein the at least one physical characteristic includes at least one of a size of the individual droplet, a speed of the individual droplet and an angle of the individual droplet relative to an intended angle of ejection.

7 . The method of claim 1 further comprising the step of, for a plurality of individual drops, determining at least one of an exponentially-weighted moving average speed, a standard deviation of speed, an average change in drop-to-drop speed, a difference between highest and lowest speed, and an average angle.

8 . The method of claim 1 wherein the at least one camera is two cameras wherein a first camera has a field of view perpendicular to a field of view of a second camera.

9 . A method of characterizing droplets of liquid metal during additive manufacture of metal parts using MIND printing of liquid metal, comprising:
a strobed light source configured to illuminate a stream of droplets of liquid metal expelled from a discharge orifice of a nozzle by a magnetohydrodynamic force; at least one camera configured to capture a plurality of images of light from the strobed light source reflected off an individual droplet as it traverses a field of view of the camera; and a controller configured to determine from the plurality of images a measured value of least one physical characteristic of the individual droplet.

10 . The system of claim 9 wherein the controller is configured to compare the measured value to a desired value of the physical characteristic.

11 . The system of claim 9 wherein the controller is configured to, when a difference between the measured value and the desired value exceeds a predetermined threshold, cause the discharge orifice of the nozzle to be cleaned.

12 . The system of claim 9 wherein the controller is configured to, when a difference between the measured value and the desired value exceeds a predetermined threshold, adjust at least one printing parameter.

13 . The system of claim 12 wherein the printing parameter is an amount of current passed through the liquid metal in the nozzle by a plurality of electrodes.

14 . The system of claim 9 wherein the physical characteristic is one of a size of the individual droplet, a speed of the individual droplet and an angle of the individual droplet.

15 . The system of claim 9 wherein the controller is configured to, for a plurality of individual drops, determine at least one of an exponentially-weighted moving average speed, a standard deviation of speed, an average change in drop-to-drop speed, a difference between highest and lowest speed, and an average angle.

16 . The system of claim 9 wherein the at least one camera is two cameras wherein a first camera has a field of view at a right angle from a field of view of a second camera.

17 . A method of characterizing droplets of liquid metal during additive manufacture of metal parts using MHD printing of liquid metal, comprising:
directing a strobed light source to a stream of droplets expelled from a discharge orifice of a nozzle via a magnetohydrodynamic force; operating at least one camera directed at the stream of droplets to capture a plurality of images of light from the strobed light source reflected from an individual droplet as it traverses a field of view of the camera; and determining from the plurality of images a measured value of least one physical characteristic of the stream of droplets.

18 . The method of claim 17 further comprising the step of comparing the measured value to a desired value of the physical characteristic.

19 . The method of claim 17 further comprising the step of, when a difference between the measured value and the desired value exceeds a predetermined threshold, cleaning the discharge orifice of the nozzle with a cleaning instrument.

20 . The method of claim 2 further comprising the step of, when a difference between the measured value and the desired value exceeds a predetermined threshold, adjusting at least one printing parameter.

21 . A method of servicing a nozzle of an additive manufacturing system for MI-ID printing liquid metal, comprising the steps of:
positioning the nozzle over a ceramic rod; jetting from the nozzle an amount of liquid metal forming on an upper surface of the ceramic rod a bead of metal; advancing the upper surface of the ceramic rod towards the nozzle until the bead of metal contacts a meniscus of liquid metal at the nozzle and rotating the upper surface of the ceramic rod such that the bead removes an amount of dross from the nozzle; and retreating the upper surface of the ceramic rod away from the nozzle.

22 . The method of claim 21 further comprising the step of when rotating the upper surface of the ceramic rod, moving the ceramic rod laterally with respect to a plane of the nozzle.

23 . The method of claim 22 wherein the step of moving the ceramic rod laterally includes moving the ceramic rod in a predetermined pattern.

24 . The method of claim 23 wherein the predetermined pattern is includes reciprocating laterally in a first direction and moving laterally in a second direction.

25 . The method of claim 21 wherein during the step of rotating the upper surface of the ceramic rod the dross is spun outward from a discharge orifice of the nozzle.

26 . The method of claim 21 wherein the step of rotating the upper surface of the ceramic rod causes the bead of metal to re-wet a portion of the nozzle.

27 . The method of claim 21 wherein the upper surface of the ceramic rod is conical.

28 . The method of claim 21 wherein during the step of advancing and rotating the upper surface of the ceramic rod, jetting additional liquid metal such that the bead is increased in size until at least a portion of the bead solidifies and the bead is ejected away from the upper surface of the ceramic rod.

29 . A method of servicing a nozzle of an additive manufacturing system for MH

Assignees

• Desktop Metal Inc

Inventors

• Gibson Mark Gardner
• Sachs Emanuel Michael
• Bell Julian

Classifications

• B22F12/57

  Metering means · CPC title

• B22F12/38

  Housings, e.g. machine housings · CPC title

• B22F12/17

  to heat the build chamber or platform · CPC title

• B22F12/10

  Auxiliary heating means · CPC title

• B22F10/85

  for controlling or regulating additive manufacturing processes · CPC title