Friction Pressure Welding for Strong Dissimilar Material Joints
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Solution Overview
Problem
Conventional friction stir welding processes face issues with inhomogeneous microstructures and reduced mechanical joint performance due to complex material flow and axial stresses, leading to limited bonding strength and shortened tool life, especially when joining high-strength materials.
Innovation Solution
The method involves plunging a non-consumable refractory tool onto a workpiece with axial pressure and rotational motion, generating friction heat that diffuses into the faying joint interface for metallurgical bonding, eliminating complex material flow and relying on heat and pressure for solid-state welding, with control variables like plunge depth, speed, and rotation rate optimized for different materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If friction stir welding is used to join materials, then bonding is achieved through solid-state joining, but complex material flow causes inhomogeneous microstructures and deteriorating mechanical joint performance
Solution Approach 1:
The patent removes the rotating pin tool characteristic of friction stir welding, extracting the source of complex material flow. Instead, a friction pressure welding process is used where a stationary or slowly moving tool applies pressure and friction heat without the intensive stirring action, thereby achieving bonding while avoiding inhomogeneous microstructures caused by complex material flow
Solution Approach 2:
The patent changes the welding parameters from high-speed rotation with intensive stirring to controlled pressure application with friction heat generation. The process parameters are optimized to achieve adequate heat generation and bonding while maintaining microstructure homogeneity, representing a fundamental parameter change from friction stir welding
2Strength
If friction stir welding is used for high strength materials, then bonding is achieved, but large axial stresses result in shortened tool life due to damage and wear
Solution Approach 1:
The patent employs a friction pressure welding tool that can be simpler in construction compared to the robust pin tool required for friction stir welding of high-strength materials. The process generates sufficient heat through friction and pressure without requiring the tool to withstand extreme axial stresses, thereby extending tool life or allowing use of more economical tooling
Solution Approach 2:
The patent replaces the mechanical stirring action with a friction-based heating and pressure application system. This substitution reduces the mechanical stresses on the tool while achieving bonding through diffusion and metallurgical bonding mechanisms, thereby reducing tool wear and damage
3Ease of manufacture
If friction stir spot welding is used, then spot welding is achieved, but limited bonding area results in lower mechanical bonding strength
Solution Approach 1:
The patent merges the advantages of friction heating with pressure application over an extended contact area. By using a tool that applies friction pressure across a larger interface area rather than through a concentrated pin contact, the process achieves both spot welding capability and enhanced bonding strength through increased bonding area
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 approach achieves a strong, large bonding area with minimized microstructure inhomogeneities and enhanced mechanical strength, as demonstrated by higher peak failure loads in lap shear tensile testing, suitable for similar or dissimilar materials and multi-layer stacks, and extends tool life by reducing wear and damage.
Implementation Method 1
The friction heat generated by the interaction between the tool and the top workpiece diffuses into the faying joint interface
Implementation Method 2
The friction heat generated by the interaction between the tool and the top workpiece diffuses into the faying joint interface
Implementation Method 3
Friction heat and applied axial plunge pressure will promote diffusion bonding at the faying joint interface, which consolidates as a solid-state weld
Data Source
AI summary
A method for friction pressure welding a top workpiece to a bottom workpiece is provided. The method includes plunging a non-consumable refractory tool into the top workpiece with axial plunge pressure and rotational motion. The friction heat generated by the interaction between the tool and the top workpiece diffuses into the faying joint interface and into the bottom workpiece. Friction heat and applied axial plunge pressure promote diffusion bonding at the faying joint interface, which consolidates as a solid-state weld. This inventive method is suitable for spot welding or continuous linear welding, and each workpiece can be comprised of similar or dissimilar materials. After the workpieces are joined, the refractory tool is retracted from the top workpiece. Control variables can include plunge depth, force, and rate of rotation, which can be readily optimized for different material combinations for sound joint formation.