Resistance Weld Fastener for Dissimilar Metal Joining
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for joining dissimilar metals, such as aluminum and steel, face challenges due to intermetallic compounds that reduce mechanical strength and corrosion resistance, and existing fastening techniques like friction stir spot welding and riveting are either inefficient or require precise alignment and additional costs.
Innovation Solution
A method using electrical resistance welding with a conductive fastener having a higher melting point than the layers being joined, which induces resistive heating to form a molten weld zone between the layers, ensuring strong and corrosion-resistant joints by retaining the fastener within the weld zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If direct welding between aluminum and steel is employed, then joint strength is improved, but intermetallics are generated which negatively affect mechanical strength and corrosion resistance
Solution Approach 1:
The patent introduces a copper-based intermediate layer between aluminum and steel components. This intermediary layer facilitates metallurgical bonding while preventing direct contact between aluminum and steel, thereby avoiding the formation of harmful intermetallic compounds. The copper layer acts as a buffer that enables joint strength improvement without compromising corrosion resistance.
Solution Approach 2:
The invention creates a composite joint structure consisting of multiple material layers (aluminum, copper intermediate layer, and steel). This composite approach combines the advantages of each material: aluminum provides lightweight properties, copper enables ductile bonding and prevents intermetallic formation, and steel provides structural strength. The composite structure achieves both high joint strength and corrosion resistance.
2Strength
If friction stir spot welding is used to join aluminum to steel, then joint properties are improved, but the process requires very precise alignment and fit-up
Solution Approach 1:
The patent replaces the mechanically intensive friction stir spot welding process with an electrical resistance welding process using a copper-based fastener. This substitution eliminates the need for precise mechanical alignment and fit-up requirements, as the electrical resistance welding process is more tolerant of positioning variations while still achieving strong joints.
3Strength
If self-pierce riveting is used to join high strength aluminum to steel, then fastening is achieved, but the aluminum can crack during the riveting process
Solution Approach 1:
The invention changes the material parameter of the fastener from aluminum (in traditional SPR) to copper-based material. This parameter change allows the fastener to undergo plastic deformation during insertion without causing cracking in the high-strength aluminum workpiece. The copper fastener's lower strength and higher ductility enable it to absorb the deformation energy, preserving the integrity of the aluminum component.
4Strength
If flow drill screws are used to join aluminum to steel, then fastening is achieved, but alignment with a pilot hole is required which complicates assembly and adds cost
Solution Approach 1:
The patent extracts and eliminates the pilot hole requirement from the fastening process. The copper-based resistance weld fastener can be directly applied without pre-drilling or alignment features, simplifying the assembly process and reducing manufacturing steps. This removes the complexity associated with pilot hole alignment while maintaining fastening capability.
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 effectively joins dissimilar metals with improved mechanical strength and corrosion resistance, reducing the need for precise alignment and minimizing additional costs, while maintaining the integrity of the metal surfaces.
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 layer
Implementation Method 2
urging the fastener into the softened first layer toward the second layer forming a molten weld zone that extends to and includes at least a portion of the second layer
Data Source
AI summary
An apparatus and method for fastening layers of non-ferrous alloys, like aluminum, magnesium and copper utilizes a steel fastener and a spot welding machine. The fastener and metals are stacked and the heat from the welder's electric current softens the lower melting point aluminum allowing the fastener to penetrate the aluminum. A weld zone between the fastener and the various layers creates an internal weld. The fastener has a rough shaft that is coated by the molten weld zone and is hard to withdraw on solidification. Layers of non-conductive materials like plastics and ceramics may also be affixed to a conductive layer using a fastener made from a compatible material that extends through a pilot hole and welds to or penetrates a conductive layer. The fastener may have projections that initially reduce contact area with the stack.