Dissimilar Metal Butt Joining With Friction Tool Overlap Control
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Solution Overview
Problem
Existing methods for butt-joining thin plates made of dissimilar metals with different melting points, such as copper and aluminum, often result in low joining strength due to the formation of thick intermetallic compound layers and require precise positioning and high flatness, making them difficult to apply effectively, especially for thin-plate members.
Innovation Solution
A method using frictional heat to butt-join dissimilar metals by overlapping and pressurizing the end portions with a rotating joining tool having a protruding portion, where the tool's tip end is not in contact with the first member, and utilizing a recessed portion on a backing plate to manage the melted material, resulting in a sloped joint surface with a thin intermetallic compound layer and increased joining area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If welding or brazing is used to join dissimilar metals, then the joining process is simple, but thick intermetallic compound layers are generated resulting in low joining strength
Solution Approach 1:
The invention changes the fundamental joining parameters from thermal processes (welding/brazing) to solid-phase friction stir joining. By controlling rotation speed, feed rate, and tool pressure, the process achieves strong joints without forming thick intermetallic compounds, resolving the contradiction between process simplicity and joint strength
Solution Approach 2:
The invention utilizes phase transition of the base metal from solid to softened state through frictional heating, then back to solid upon cooling. This phase transition enables material flow and mixing without melting, preventing thick intermetallic layer formation while maintaining joining strength
2Strength
If friction stir joining is used with the rotating tool inserted into the low-melting-point metal, then the intermetallic compound layer thickness is reduced, but small pieces of high-melting-point metal are dispersed in the low-melting-point metal causing variable joining strength and electrical resistance
Solution Approach 1:
The invention inverts the conventional friction stir joining approach by inserting the tool into the high-melting-point metal instead of the low-melting-point metal. This inversion prevents high-melting-point metal fragments from dispersing into the low-melting-point metal, ensuring consistent joining strength and electrical resistance
Solution Approach 2:
The stirring pin acts as an intermediary that facilitates material flow and mixing in a controlled manner. By rotating within the high-melting-point metal and dragging the low-melting-point metal, it creates a homogeneous joint structure without fragment dispersion, improving reliability
3Strength
If the stirring pin is brought into close contact with the butt end face of the high-melting-point metal by 0.1 mm, then satisfactory joining is obtained without dispersing high-melting-point metal, but high flatness and positioning accuracy are required making it difficult to apply to thin-plate members
Solution Approach 1:
The invention performs preliminary action by overlapping the end faces of the thin plates before joining. This pre-positioning eliminates the need for precise 0.1 mm contact positioning, making the process suitable for thin-plate members while maintaining joining strength
Solution Approach 2:
The invention transitions from precise linear positioning (0.1 mm contact) to area-based overlapping. By utilizing the overlapping area dimension, the process accommodates thin-plate members without requiring high positioning accuracy or flatness
4Shape
If the end portions of thin plates are overlapped and pressurized by a rotating joining tool, then the low-melting-point metal is softened and deformed, but the high-melting-point metal cannot be sufficiently deformed due to larger deformation stress resulting in thin joining and insufficient joining strength
Solution Approach 1:
The invention changes the deformation parameters by inserting the tool into the high-melting-point metal and controlling the feed rate and pressure. This ensures both high-melting-point and low-melting-point metals are sufficiently deformed and mixed, achieving strong joints
Solution Approach 2:
The invention introduces dynamic control of the joining process by adjusting rotation speed, feed rate, and tool pressure in coordination. This dynamic adjustment ensures balanced deformation of dissimilar metals with different flow stresses, improving joining 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 achieves a sufficient joining strength and reduced electrical resistance by forming a sloped joint surface with a thin intermetallic compound layer, increasing the joining area and preventing material displacement, thus enhancing the structural integrity and electrical properties of the joint.
Implementation Method 1
the thin plate made of the low-melting-point metal is softened and deformed by frictional heat generated between the joining tool and the thin plate made of the low-melting-point metal
Implementation Method 2
the overlapped portion is pressurized by a rotating joining tool to obtain a butt-joint
Data Source
AI summary
A method for joining dissimilar metals according to the embodiment is a method for butt-joining, using frictional heat, a first member having a plate shape and containing first metal and a second member having a plate shape and containing second metal having a melting point higher than that of the first metal. The method for joining dissimilar metals includes: overlapping an end portion of the second member on an end portion of the first member; and pressurizing the second member toward the first member by bringing a rotating joining tool having a protruding portion at a tip end into contact with an overlapping portion of the second member with the first member. When the second member is pressurized toward the first member, the tip end of the rotating joining tool is not in contact with the first member.