Reactive Metal Foil Joining for Copper Conductors
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Solution Overview
Problem
There is a need for a method to form strong, low electrical resistance welds between copper workpieces with minimal deformation and heat generation, suitable for use in electric motor stators, while avoiding degradation of polymeric wire insulation.
Innovation Solution
A metallurgical reaction joining process using a thin layer of reactive metal or alloy, such as copper-phosphorus or copper-phosphorus-tin-silicon, is applied between copper workpieces to clean surfaces and form a solid-state weld at reduced temperatures, minimizing heat exposure and preserving insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding methods are used to join copper conductors, then strong welds can be formed, but excessive heat is generated causing degradation of polymeric wire insulation
Solution Approach 1:
A reactive metal interlayer is introduced between the copper conductor surfaces to facilitate welding at lower temperatures. This interlayer mediates the joining process by reacting with copper to form a eutectic alloy that melts at a lower temperature than pure copper, enabling weld formation without exposing the polymeric insulation to excessive heat
Solution Approach 2:
The welding process changes the temperature parameter by utilizing the eutectic reaction temperature (lower than copper melting point) instead of conventional high-temperature copper-to-copper welding. This parameter change allows weld formation at reduced temperatures that do not degrade the polymeric wire insulation
2Strength
If high temperature welding is used to form copper-to-copper joints, then strong welds are achieved, but deformation of the workpieces increases
Solution Approach 1:
The process changes the temperature parameter from conventional high-temperature copper welding to lower-temperature eutectic reaction welding. This temperature reduction prevents excessive thermal expansion and deformation of the copper workpieces while still achieving strong welds through the metallurgical reaction
3Ease of manufacture
If traditional welding processes are applied to copper conductors in motor stators, then joints can be formed, but the process requires excessive heat affecting nearby insulation
Solution Approach 1:
The reactive metal interlayer serves as a mediator that enables joining at lower temperatures. It reacts with the copper surfaces to form a eutectic alloy system with a lower melting point, allowing the welding process to proceed at temperatures that do not affect the polymeric insulation of nearby conductors in the motor stator
4Temperature
If reactive metal foil is used between copper surfaces, then low temperature welding is achieved, but the foil placement and configuration becomes complex
Solution Approach 1:
The reactive metal foil is designed to perform multiple functions: it cleans the copper surfaces through reaction, forms the eutectic alloy for low-temperature melting, and facilitates weld formation. This multi-functionality simplifies the overall process despite the foil placement requirement, as the foil replaces multiple separate operations
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
This method produces strong, low-electrical-resistivity copper-to-copper welds with minimal heat impact, effectively joining multiple copper conductor pairs in electric motor stators without degrading polymeric insulation.
Implementation Method 1
a thin layer of a reactive metal or alloy is placed between the facing surfaces of the copper workpieces and is used to clean the surfaces to allow intimate contact over broad areas and the formation of a solid-state weld
Implementation Method 2
a layer on each workpiece surface is eliminated through a combination of dissolution of a portion of the copper workpieces and expulsion of the reacted metal under pressure
Implementation Method 3
The liquid phase must have a solidus temperature that is lower than the melting point of the workpiece metal
Implementation Method 4
Copper has a melting point of 1084° C. while copper-7 wt. % phosphorus alloy has a melting temperature of 710° C.
Implementation Method 5
The process is conducted by placing a thin (for example, 50 to 250 microns thick) piece of the reactive metal between facing surfaces of the copper workpieces to be joined. The sandwich joint is then compressed and heated to a temperature well above the solidus temperature of the metal/reactive metal alloy system
Data Source
AI summary
Copper conductor members or other copper-based workpieces are welded using a suitable copper alloy material that is reactive with the joining surfaces of the copper members. The reactive metal material may be applied as a thin metal foil strip between assembled facing joining surfaces. The members are pressed together against the reactive material and electrical resistance heated in forming the weld. Practices are adapted for forming many such welds in the pairs of facing ends of conductor bars or wires assembled, for example, in slots in a stator for a vehicle traction motor. Practices are disclosed for shaping and automated placement of suitably sized and shaped foils of reactive metal. Practices are also disclosed for use of a resistance welding tool in aligning and heating the many pairs of conductors to be welded.