Friction-Stir Joining Tool Reciprocation for Coated Workpiece Defects
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Solution Overview
Problem
Friction-stir joining methods often result in fatigue cracks and joining defects at the origin when dealing with plated or coated workpieces, particularly due to the difficulty in dispersing hard platings and coatings.
Innovation Solution
A friction-stir joining method where the joining tool is reciprocated between the start and turning-back points, with the tool moving backward to scratch off and disperse softened platings and coatings into molten metal, ensuring effective dispersion and preventing interface fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the joining tool is positioned at the joining start point and moved forward directly to the joining finish point, then the joining process is simple and efficient, but fatigue cracks develop at the joining start point and joining defects occur at weld origins in plated or coated workpieces
Solution Approach 1:
The joining tool performs a preliminary backward movement from the joining start point to a turning-back point before the actual forward joining process. This preliminary action prepares the interface by scratching off and dispersing platings and coatings, eliminating the harmful factors that would otherwise cause joining defects and fatigue cracks at the start point.
Solution Approach 2:
Instead of moving only forward from the start point, the joining tool first moves backward to a turning-back point, then turns around and moves forward. This inverted sequence of operations allows the tool to prepare the interface by scratching and dispersing coatings before the main joining process, thereby preventing defects at the joining origin.
2Reliability
If the joining tool is reciprocated backward and forward to disperse platings and coatings, then joining quality improves and interface fractures are prevented, but the joining process time increases
Solution Approach 1:
The joining tool performs a partial backward movement only to a turning-back point (not the full length of the joining line) before returning forward. This partial reciprocation is sufficient to scratch off and disperse platings and coatings at the critical joining start region, achieving the necessary preparation without excessive time consumption that would result from full-length reciprocation.
3Productivity
If the turning-back point is positioned closer to the joining start point, then the reciprocation distance is reduced and productivity improves, but the dispersion of platings and coatings becomes insufficient
Solution Approach 1:
The position of the turning-back point is optimized as a critical parameter, set at a specific distance (0.75-1.5 times the pin diameter) from the joining start point. This parameter optimization ensures that the reciprocation action extends far enough to effectively scratch off and disperse platings and coatings, while keeping the reciprocation distance minimal for productivity.
4Manufacturing precision
If the predetermined distance is larger than 1.5 times the pin diameter, then the dispersion of platings and coatings is more thorough, but the turning-back portion that must be cut off increases and yields deteriorate
Solution Approach 1:
The predetermined distance is optimized within a specific range (0.75-1.5 times the pin diameter) to balance dispersion quality and material yield. The upper limit of 1.5 times ensures thorough scratching and dispersing of coatings while minimizing the length of the turning-back portion that must be cut off, thereby maintaining high material yield.
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 achieves sound joining of plated or coated workpieces by dispersing platings and coatings into molten metal, reducing interface fractures and improving tensile strength consistency.
Implementation Method 1
a joining tool rotating at a high speed is brought into contact with workpieces or objects to join or weld together the same with resulting friction heat
Implementation Method 2
partial platings and coatings softened and scratched off by a first travel backward of the pin portion
Implementation Method 3
whirled up and dispersed in molten metal by a second travel forward of the pin portion
Data Source
AI summary
Disclosed is a friction-stir joining method for joining a first member, having a base metal covered with a substance different from the base metal, with a second member with the second member placed on the first member by moving a joining tool along a joining line having thereon a joining start point and a joining finish point. The method includes steps of: inserting the joining tool into the second member at the joining start point; moving the joining tool a predetermined distance along the joining line in a direction opposite the joining finish point; causing the joining tool to turn back at a turning-back point spaced the predetermined distance from the joining start point; moving the joining tool along the joining line to the joining finish point past the joining start point; and pulling the joining tool out from the second member at the joining finish point.