Friction Stir Welding Surface Tool for Nuclear Fuel
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Solution Overview
Problem
Existing methods for creating linear welded connections between flat workpieces, such as those used in Al-U/Mo-Al sandwich nuclear fuel elements, face challenges of high thermal energy input leading to structural changes and material mixing, which are undesirable for maintaining material properties and separating different materials.
Innovation Solution
A method where the friction tool's contact area with the second workpiece is limited to its surface away from the first workpiece, minimizing thermal energy input and preventing material mixing, using a friction tool that rotates on the surface of the second workpiece without penetrating, and applying controlled pressure and heat to form a welded connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding processes are used to create linear welded connections between flat workpieces, then a firm bond is achieved, but high thermal energy input causes structural changes and material property degradation
Solution Approach 1:
The patent replaces thermal welding processes with a mechanical friction-based process. A friction tool with a friction surface is pressed against the workpieces and moved relative to them, generating friction heat locally at the contact interface. This mechanical system substitutes conventional thermal energy input methods, concentrating heat generation exactly where needed for bonding while minimizing overall thermal energy input to the workpieces.
Solution Approach 2:
The patent changes the fundamental parameter of heat generation from external thermal energy input to internal friction-based heat generation. By controlling the friction force, contact pressure, and relative motion speed, the process generates heat precisely at the interface where bonding is required, rather than heating the entire workpiece volume as in conventional welding. This parameter change enables localized heating that avoids structural changes in the bulk material.
2Strength
If high thermal energy input is applied to create a welded connection, then a firm bond is achieved, but the workpieces expand unevenly and no longer lie flat against one another
Solution Approach 1:
The patent applies heating locally only at the friction contact interface rather than uniformly across the entire workpiece. The friction tool generates heat concentrated in a small region where the friction surface contacts the workpieces, while the rest of the workpieces remain at ambient temperature. This local quality approach prevents uneven thermal expansion across the workpiece surfaces, maintaining their flatness and ability to lie flush against one another.
Solution Approach 2:
By replacing conventional thermal welding with mechanical friction-based bonding, the process avoids the widespread thermal effects that cause distortion. The mechanical friction process confines energy input to the immediate contact zone, preventing the thermal gradients that lead to uneven expansion and loss of flatness in conventional welding processes.
3Object-affected harmful factors
If diffusion welding is used to avoid high punctiform energy input, then structural changes are reduced, but thermal energy input is still required which can cause structural changes in alloys with low transformation temperatures
Solution Approach 1:
The patent substitutes thermal diffusion welding with a mechanical friction-based process. Instead of heating the workpieces to high temperatures to induce diffusion bonding, the process uses mechanical friction between the friction tool and workpieces to generate heat locally at the interface. This substitution eliminates the need for sustained high-temperature heating that causes structural changes in temperature-sensitive alloys.
Solution Approach 2:
The patent fundamentally changes the energy input parameter from thermal energy (diffusion welding) to mechanical energy (friction process). The friction tool converts mechanical energy to localized heat through friction, achieving bonding without requiring the sustained high-temperature conditions of diffusion welding. This parameter change enables bonding of temperature-sensitive materials that would undergo unwanted structural changes during diffusion welding.
4Strength
If a rotating pin penetrates both workpieces in friction stir welding, then punctiform connections are made, but materials of different workpieces are mixed which is undesirable for maintaining material separation
Solution Approach 1:
The patent extracts the friction tool from the workpiece volume, keeping it entirely on the surface. Unlike penetrating pins that go through both workpieces and mix materials, the friction tool with its friction surface remains in contact only with the outer surfaces. This extraction principle ensures that materials of different workpieces remain separated while still achieving strong surface connections through friction-based bonding.
Solution Approach 2:
Instead of penetrating into the workpieces to create connections (conventional friction stir welding), the patent inverts the approach by having the friction tool contact only the outer surfaces. The friction surface is pressed against the workpieces and generates heat and bonding at the surface interface, reversing the conventional penetration approach. This inversion prevents material mixing while maintaining connection strength.
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 reduces thermal energy input to prevent structural changes and material mixing, ensuring a stable connection with minimal material alteration, suitable for applications requiring low heat and clean separation of materials, like nuclear fuel elements.
Implementation Method 1
a friction tool (1) which can be driven in rotation about an axis of rotation (3) with a friction surface (4), wherein the friction surface (4) is designed in such a way that when the friction tool (1) rests on the second workpiece (11) and is set in rotation, the contact area between the friction surface (4) and the second workpiece (11) runs completely in the surface of the second workpiece (11) which faces away from the first workpiece (10)
Data Source
Figure 1
Figure 2~3
Figure 4~5b
AI summary
The method involves preparing the two workpieces in a stack (9) and placing the second workpiece on top of the first and setting up a friction tool (1) with its friction surface (4) on the top of the second workpiece remote from the first workpiece. The friction tool is then rotated to produce the welded connection whereby the friction surface rubs on the surface of the second workpiece remote from the first workpiece and the contact area between friction face and second workpiece is kept entirely within this surface area. The first workpiece bears against a heating element by its surface remote from the second workpiece. Independent claim describes device with rotational friction tool with friction surface placed on top surface of workpiece and a predetermined pressure applied by same to workpieces perpendicular to the workpiece plane. A laser can be provided.