Resistance-Welded Fastener for Aluminum-Steel Joining
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Solution Overview
Problem
Current methods for joining aluminum to other materials like steel are inefficient and prone to mechanical weakness and corrosion due to intermetallic compounds, with existing techniques such as self-pierce riveting and friction stir welding requiring high forces and precise alignment, and having long cycle times.
Innovation Solution
A method using electrical resistance welding where a conductive fastener with a higher melting point is inserted through a softened aluminum layer, welded to a steel layer, and the fastener's cap captures the displaced aluminum to form a strong and corrosion-resistant joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If self-pierce riveting is used to join aluminum to steel, then joint strength is improved, but the process requires high forces and causes aluminum cracking
Solution Approach 1:
The invention changes the physical state of the aluminum by heating it to its melting point, transforming it from a solid that resists piercing to a molten state that flows easily. This parameter change (temperature) allows the rivet to pass through without requiring high forces that would crack the aluminum, while still achieving strong joint formation through controlled solidification
Solution Approach 2:
The invention replaces the purely mechanical piercing action with a combined thermal-mechanical process. Instead of relying solely on mechanical force to push the rivet through the aluminum, the process uses thermal energy to soften the material, substituting part of the mechanical work with thermal processing
2Strength
If friction stir welding is used to join aluminum to steel, then joint strength is improved, but cycle time increases to 7-9 seconds
Solution Approach 1:
The invention extracts and eliminates the time-consuming friction stir welding step by using a different approach: heating the aluminum to melting point and allowing it to flow around the rivet during insertion. This removes the need for the complex friction stir process and its associated alignment and execution time
Solution Approach 2:
The invention performs preliminary heating of the aluminum to its melting point before rivet insertion. This preliminary thermal preparation enables the rivet to pass through easily and form the joint in a single rapid operation, eliminating the need for subsequent friction stir welding steps
3Strength
If direct welding is used to join aluminum to steel, then joint strength is improved, but intermetallic compounds form causing corrosion
Solution Approach 1:
The invention introduces a molten aluminum intermediary that fills the space between the steel rivet and the aluminum substrate. This molten aluminum acts as a mediator that bonds to both materials without forming harmful intermetallic compounds, creating a corrosion-resistant joint structure
Solution Approach 2:
The invention utilizes phase transition of aluminum from solid to liquid and back to solid. By melting the aluminum during rivet insertion and allowing it to solidify around the rivet, the process creates a metallurgical bond without the prolonged high-temperature exposure that would form intermetallic compounds
4Ease of manufacture
If conventional riveting is used to join aluminum to steel, then ease of manufacture is improved, but joint strength decreases due to galvanic corrosion
Solution Approach 1:
The invention replaces conventional mechanical riveting with an electrical resistance heating system. Instead of relying on mechanical force alone, the process uses electrical current to heat and melt the aluminum, creating a stronger metallurgical bond while maintaining manufacturing simplicity through automated electrical control
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 enables efficient joining of aluminum to steel with improved mechanical strength and reduced corrosion, accommodating various thicknesses and requiring lower forces and cycle times compared to existing techniques.
Implementation Method 1
applying an electrical potential across the stack, inducing a current to flow through the stack and causing resistive heating, the resistive heating causing a softening of the first material
Implementation Method 2
After the fastener contacts the second material the fastener is welded to the second material
Data Source
AI summary
An apparatus and method for fastening dissimilar metals like steel and aluminum utilizes a steel rivet and a spot welding machine. The rivet and metals are stacked and the heat from the welder's electric current softens the lower melting point aluminum allowing the rivet to penetrate the aluminum and weld to the steel layer. The fastener may be used to join stacks with several layers of different materials and may be used to apply a threaded socket or stud made from steel or titanium to an aluminum or magnesium alloy structure. Layers of non-conductive materials like plastic and ceramics may also be affixed to a conductive layer using the fastener made from a compatible material that extends through a pilot hole.