Systems and methods for electron beam focusing in electron beam additive manufacturing

Patent metadata

Field	Value
Publication number	US-11837428-B2
Application number	US-202016944836-A
Country	US
Kind code	B2
Filing date	Jul 31, 2020
Priority date	Jul 31, 2020
Publication date	Dec 5, 2023
Grant date	Dec 5, 2023

Abstract

A system for melting, sintering, or heat treating a material is provided. The system includes a cathode, an anode, and a focus coil assembly having a quadrupole magnet. The quadrupole magnet includes four poles and a yoke. The four poles are spaced apart and surround a beam cavity. Each of the four poles includes a pole face proximate the beam cavity and an end opposite the pole face. The first and third poles are aligned along an x-axis and configured to have a first magnetic polarity at their respective pole faces and a second magnetic polarity opposite the first magnetic polarity at their respective ends. The second and fourth poles are aligned along a y-axis and configured to have the second magnetic polarity at their respective pole faces and the first magnetic polarity at their respective ends. The yoke surrounds the poles and is coupled to the poles.

First claim

What is claimed is:

1. A system for melting, sintering, or heat treating a material, said system comprising:
a cathode;
an anode, said cathode and said anode configured to generate an electron beam; and
a focus coil assembly comprising:
a quadrupole magnet comprising:
first, second, third, and fourth poles spaced apart from each other and surrounding a beam cavity through which the electron beam travels, each of said first, second, third, and fourth poles comprising a pole face proximate the beam cavity and an end opposite said pole face, said first and third poles aligned along an x-axis and configured to have a first magnetic polarity at their respective pole faces and a second magnetic polarity opposite the first magnetic polarity at their respective ends, said second and fourth poles aligned along a y-axis and configured to have the second magnetic polarity at their respective pole faces and the first magnetic polarity at their respective ends, wherein the x-axis is perpendicular to the y-axis; and
a yoke surrounding said first, second, third, and fourth poles and coupled to said first, second, third, and fourth poles at said ends of said first, second, third, and fourth poles.

2. The system of claim 1 , wherein said focus coil assembly comprises a first quadrupole magnet, wherein said focus coil assembly further comprises a second quadrupole magnet aligned with said first quadrupole magnet along a z-axis perpendicular to the x-axis and the y-axis, and wherein first, second, third, and fourth poles of said second quadrupole magnet are oriented 90 degrees about the z-axis relative to said first, second, third, and fourth poles of said first quadrupole magnet.

3. The system of claim 2 , wherein an amplitude of current provided to said first quadrupole magnet is in a substantially fixed ratio to an amplitude of current provided to said second quadrupole magnet during operation such that a size of a focal spot of the electron beam on a target remains substantially constant when currents through said first and second quadrupole magnets are changed.

4. The system of claim 2 , wherein said focus coil assembly further comprises a third quadrupole magnet aligned with said first quadrupole magnet along a z-axis perpendicular to the x-axis and the y-axis , wherein said second quadrupole magnet is positioned between said first and third quadrupole magnets, wherein in operation, a first current is provided to said first quadrupole magnet, a second current is provided to said second quadrupole magnet, and a third current is provided to said third quadrupole magnet, wherein magnetic fields generated by the first and third currents have substantially the same magnetic field strength as each other and approximately half of the magnetic field strength of a magnetic field generated by the second current.

5. The system of claim 4 , wherein said third quadrupole magnet is aligned with said first quadrupole magnet along the z-axis, wherein first, second, third, and fourth poles of said third quadrupole magnet are oriented in the same direction about the z-axis relative to said first, second, third, and fourth poles of said first quadrupole magnet.

6. The system of claim 1 , further comprising a control circuit comprising:
an interface configured to receive an electron beam manipulation coil;
a first switching device coupled to a first voltage source and configured to create a first current path with the first voltage source toward the electron beam manipulation coil;
a second switching device coupled to a second voltage source and configured to create a second current path with the second voltage source toward the electron beam manipulation coil; and
a third switching device coupled to a first side of said interface and configured to allow conductance via the first current path and the second current path to said interface when said third switching device is in a closed position, wherein said second and third switching devices are configured to create a third current path with the second voltage source when in respective open positions, the third current path having an opposite polarity with respect to the second current path.

7. The system of claim 1 , wherein each of said pole faces of said first, second, third, and fourth poles is convex.

8. The system of claim 1 , further comprising a shielding surrounding said focus coil assembly.

9. The system of claim 1 , further comprising a metal vacuum tube sized to enclose the beam cavity.

10. The system of claim 9 , further comprising an inverse pulse control configured to abate eddy current.

11. The system of claim 1 , further comprising a stigmator, wherein said focus coil assembly is complemented by said stigmator.

12. The system of claim 11 , wherein said stigmator includes an octupole magnet including two sets of quadrupoles oriented approximately 45 degrees around the z-axis from one another.

13. The system of claim 11 , wherein said quadrupole magnet is a first quadrupole magnet, and wherein said stigmator comprises a second quadrupole magnet oriented approximately 45 degrees about the z-axis relative to said first quadrupole magnet.

14. The system of claim 1 , wherein said quadrupole magnet comprises a first quadrupole magnet, and wherein the system further comprises a deflection coil comprising a second quadrupole magnet configured to generate a dipole magnetic field.

Assignees

• Gen Electric

Inventors

• Price John Scott
• Bai Ye
• Caiafa Antonio
• Neculaes Vasile Bogdan
• Wiedmann Uwe

Classifications

• H01J29/68 Primary

  using permanent magnets only · CPC title

• B29C64/153

  using layers of powder being selectively joined, e.g. by selective laser sintering or melting · CPC title

• B29C64/273

  pulsed; frequency modulated · CPC title

• H01J37/3002

  Details · CPC title

• H01J37/305

  for casting, melting, evaporating, or etching · CPC title