Method of fabricating a rotor assembly for an electric motor
A rotor assembly and a method for fabricating the same are provided in which a solid rotor ring is formed at either end of a stack of laminated discs, the solid rotor rings yielding improved electrical and mechanical characteristics in a low weight assembly. The solid rotor rings are fabricated by brazing slugs between the end portions of the rotor bars, the braze joints contacting a large percentage (at least 90 %) of the rotor bar end portions.
1. A method of fabricating a rotor assembly for an electric motor, the method comprising the steps of:
inserting a plurality of rotor bars into a corresponding plurality of slots within a stack of laminated discs, wherein a first portion of each of said plurality of rotor bars extends away from a first end surface of said stack of laminated discs, and wherein a second portion of each of said plurality of rotor bars extends away from a second end surface of said stack of laminated discs;
inserting a first plurality of slugs between corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars to form a first rotor bar/slug assembly, wherein each slug of said first plurality of slugs is separate and independent from all other slugs of said first plurality of slugs, wherein each of said first plurality of slugs is sized so that a first and a second slug contact surface contacts at least 90% of said corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars, and wherein said first and second slug contact surfaces of said first plurality of slugs are completely coated with a brazing material;
inserting a second plurality of slugs between corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars to form a second rotor bar/slug assembly, wherein each slug of said second plurality of slugs is separate and independent from all other slugs of said second plurality of slugs, wherein each of said second plurality of slugs is sized so that a first and a second slug contact surface contacts at least 90% of said corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars, and wherein said first and second slug contact surfaces of said second plurality are completely coated with said brazing material;
heating said first rotor bar/slug assembly to form a first plurality of braze joints between said first and second slug contact surfaces of said first plurality of slugs and corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars;
heating said second rotor bar/slug assembly to form a second plurality of braze joints between said first and second slug contact surfaces of said second plurality of slugs and corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars;
machining said first rotor bar/slug assembly to remove a first circumferential edge portion of said first rotor bar/slug assembly, wherein said first circumferential edge portion is comprised of a region of each of said first plurality of slugs and a region of said first portion of said plurality of rotor bars, wherein said first circumferential edge portion is located at an outermost end region of said first rotor bar/slug assembly;
machining said second rotor bar/slug assembly to remove a second circumferential edge portion of said second rotor bar/slug assembly, wherein said second circumferential edge portion is comprised of a region of each of said second plurality of slugs and a region of said second portion of said plurality of rotor bars, wherein said second circumferential edge portion is located at an outermost end region of said second rotor bar/slug assembly;
fitting a first containment ring over said first rotor bar/slug assembly, wherein said first containment ring is positioned on said first rotor bar/slug assembly at a location corresponding to said outermost end region of said first rotor bar/slug assembly where said first circumferential edge portion was removed via said step of machining said first rotor/bar slug assembly; and
fitting a second containment ring over said second rotor bar/slug assembly, wherein said second containment ring is positioned on said second rotor bar/slug assembly at a location corresponding to said outermost end region of said second rotor bar/slug assembly where said second circumferential edge portion was removed via said step of machining said second rotor/bar slug assembly.
2. The method of claim 1 , wherein said steps of heating said first and second rotor bar/slug assemblies are performed simultaneously.
3. The method of claim 1 , further comprising the steps of:
fabricating said plurality of rotor bars from a copper material;
fabricating said first plurality of slugs from said copper material;
fabricating said second plurality of slugs from said copper material; and
selecting silver as said brazing material.
4. The method of claim 1 , further comprising the steps of:
fabricating said plurality of rotor bars from a copper material;
fabricating said first plurality of slugs from said copper material;
coating said first plurality of slugs with silver;
fabricating said second plurality of slugs from said copper material; and
coating said second plurality of slugs with silver.
5. The method of claim 1 , wherein each of said first plurality of slugs is sized so that said first and second slug contact surfaces contact at least 95% of said corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars, and wherein each of said second plurality of slugs is sized so that said first and second slug contact surfaces contact at least 95% of said corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars.
6. The method of claim 1 , wherein each of said first plurality of slugs is sized so that said first and second slug contact surfaces contact at least 99% of said corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars, and wherein each of said second plurality of slugs is sized so that said first and second slug contact surfaces contact at least 99% of said corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars.
7. The method of claim 1 , wherein each of said first plurality of slugs is sized so that said first and second slug contact surfaces contact all of said corresponding adjacent rotor bar surfaces of said first portion of said plurality of rotor bars, and wherein each of said second plurality of slugs is sized so that said first and second slug contact surfaces contact all of said corresponding adjacent rotor bar surfaces of said second portion of said plurality of rotor bars.
8. The method of claim 1 , wherein said steps of heating said first and second rotor bar/slug assemblies are performed in a vacuum furnace.
9. The method of claim 1 , wherein said steps of heating said first and second rotor bar/slug assemblies are performed using an induction brazing system.
10. The method of claim 1 , further comprising the steps of:
wrapping at least one loop of a first wire around said first rotor bar/slug assembly prior to said step of heating said first rotor bar/slug assembly, wherein said at least one loop of said first wire insures that said first plurality of slugs remain in place during said heating step; and
wrapping at least one loop of a second wire around said second rotor bar/slug assembly prior to said step of heating said second rotor bar/slug assembly, wherein said at least one loop of said second wire insures that said second plurality of slugs remain in place during said heating step.