Stepped Friction Stir Welding Joint for Burr and Strength Control
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Solution Overview
Problem
Conventional joining technologies face issues with insufficient holding of plastically flowing material during friction-stir-welding of metal members with different thicknesses, leading to low joint strength and excessive burr formation.
Innovation Solution
A joining method involving a rotary tool with a base side pin and a tip side pin, where the taper angle of the base side pin is larger than the tip side pin, and a pin step portion is formed on the outer circumference, allowing for controlled burr formation by adjusting the target angle to maintain the burr thickness between 0 and 130 μm, thereby enhancing joint strength and reducing burrs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional friction-stir-welding is performed on stepped metal members with a standard rotary tool, then the joining process can be completed, but plastically flowing material cannot be sufficiently held down, resulting in excessive burrs and low joint strength
Solution Approach 1:
The rotary tool's pin is segmented into multiple portions with different functions: a large-diameter base portion for holding down material, a smaller intermediate portion for friction stirring, and a tip portion for penetration. This segmentation allows each portion to perform its specific function optimally, preventing burrs while maintaining joint strength
Solution Approach 2:
The invention introduces a new dimensional parameter - the diameter variation along the pin's length (creating a stepped cylindrical geometry). This dimensional change enables the pin to simultaneously achieve material confinement (via the larger base diameter) and effective friction stirring (via the smaller intermediate diameter), resolving the contradiction between holding down material and preventing burrs
2Object-generated harmful factors
If the rotary tool is inclined at a larger angle to hold down material, then burrs are reduced, but undercut portions may form which also reduce joint strength
Solution Approach 1:
The invention changes the geometric parameters of the pin - specifically creating a stepped cylindrical shape with predetermined diameters and lengths for each portion. This parameter change allows the tool to achieve effective material holding down at optimized inclination angles without creating undercuts, as the larger base portion provides sufficient downward force while the smaller intermediate portion maintains proper material flow
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
The method effectively inhibits burr formation and increases joint strength by ensuring the plastically flowing material is held down by the step bottom face of the pin step portion, resulting in improved surface roughness and fatigue strength.
Implementation Method 1
performing friction-stir-welding on the butted portion that is stepped with a rotary tool
Implementation Method 2
friction-stirring is performed with the target angle of the rotary tool kept unchanged and with a plastically flowing material being held down by a step bottom face of the pin step portion
Data Source
AI summary
The invention has a feature of comprising a butting process of forming a stepped butted portion and a joining process of performing friction-stir-welding on the stepped butted portion, wherein the rotary tool includes a base side pin having a taper angle larger than a taper angle of a tip side pin, and a pin step portion in a staircase shape is formed on an outer circumferential face of the base side pin, and wherein in the joining process, a rotation direction and a translation method of the rotary tool are set such that the second metal member is on an advancing side, a target angle by which a rotation axis of the rotary tool is inclined toward the second metal member is set such that a burr formed on a front face of the second metal member after the joining process has a thickness between 0 and 130 μm.