Brazed Solid Rotor Rings for Electric Motor Weight Reduction
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Solution Overview
Problem
Existing rotor assembly fabrication techniques for electric motors often compromise between electrical conductivity, weight, material cost, and fabrication complexity, resulting in inferior conductivity and bulky, weighty end rings.
Innovation Solution
A rotor assembly with solid rotor rings fabricated by brazing slugs between the end portions of rotor bars, where the braze joints contact at least 90% of the rotor bar surfaces, using copper for the bars and silver-coated copper slugs, and employing a vacuum furnace or induction brazing for improved electrical and mechanical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional casting or welding processes are used to fabricate end rings, then electrical conductivity between rotor bars is improved, but rotor weight increases due to bulky end rings
Solution Approach 1:
The invention changes the physical state and bonding parameters by using brazing instead of casting or welding. The brazing process uses a lower melting point alloy (bronze or copper) that flows into the gaps between rotor bars and fills voids, creating strong electrical and mechanical bonds without requiring bulky end ring structures. This parameter change in the joining process enables reduced weight while maintaining conductivity.
Solution Approach 2:
The invention uses composite material structure where dissimilar metals (rotor bars made of aluminum or copper, and end rings made of bronze or copper alloy) are joined through brazing. The braze material acts as an intermediate layer that provides both mechanical strength and electrical conductivity, creating a composite structure that optimizes both weight and conductivity properties.
2Productivity
If friction welding or high-speed rotation methods are used to join end rings to rotor bars, then assembly speed is improved, but manufacturing precision decreases due to difficulty in achieving consistent braze joint coverage
Solution Approach 1:
The invention applies preliminary action by pre-heating the rotor assembly before introducing the braze material. This pre-heating ensures that when the bronze or copper end rings are applied, the braze material immediately flows and distributes evenly across all rotor bar surfaces, achieving consistent coverage of at least 90% of the rotor bar circumference. This preliminary thermal preparation eliminates the precision problems associated with friction welding.
Solution Approach 2:
The braze material itself acts as an intermediary that facilitates the joining process. Rather than directly welding metal to metal, the bronze or copper braze material mediates the bond between the end ring and rotor bars, flowing into gaps and voids to ensure complete coverage. This intermediary material enables both high productivity and high precision by simplifying the joining mechanism.
3Ease of manufacture
If end rings are made from multiple individual arc-like pieces, then ease of assembly is improved, but device complexity increases due to multiple components
Solution Approach 1:
The invention merges multiple individual arc-like end ring pieces into a single continuous end ring structure. By brazing the braze material around the entire circumference of the rotor bars, the process creates a unified end ring that maintains the advantages of modular assembly (ease of manufacturing individual sections) while eliminating the complexity of assembling multiple separate components. The continuous braze joint provides both mechanical strength and electrical conductivity across the entire assembly.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a low-weight rotor assembly with enhanced electrical conductivity and mechanical strength, reducing rotor bar-to-rotor bar resistance and weight compared to traditional methods, while allowing for flexible machining and assembly.
Implementation Method 1
heating the first rotor bar/slug assembly to form a first plurality of braze joints; and heating the second rotor bar/slug assembly to form a second plurality of braze joints
Implementation Method 2
employing a vacuum furnace or induction brazing for improved electrical and mechanical characteristics
Implementation Method 3
The solid rotor rings are fabricated by brazing slugs between the end portions of the rotor bars
Data Source
AI summary
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.