Refill Friction Stir Spot Welding for Protective-Layer Joint Strength
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Solution Overview
Problem
Friction stir spot welding methods fail to maintain joint strength when workpieces with protective layers are joined, as the protective layer components distribute unevenly, leading to crack formation and reduced joint strength.
Innovation Solution
A refined friction stir spot welding method using a rotary tool with a cylindrical shoulder and columnar pin, where the shoulder is plunged 1 mm deeper into the workpieces to concentrate the protective layer components in the central portion of the stirred area during backfilling, and the surface pressure in the backfilling process is set to 90-175 MPa to prevent crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If refill friction stir spot welding is performed on workpieces with a protective layer, then the joint strength is reduced, but the welding process can still be completed
Solution Approach 1:
The invention applies local quality by creating a concentrated distribution of protective layer components specifically in the central portion of the stirred portion, rather than uniform distribution. This localized concentration in the center away from the periphery prevents crack formation at critical stress points while maintaining the beneficial protective layer material in the joint
Solution Approach 2:
The invention changes the distribution parameter of protective layer components through controlled plunging depth (1 mm or more into the second workpiece) and backfilling pressure (90-175 MPa), transforming the protective layer from a harmful distributed element into a beneficial concentrated element in the joint center
2Strength
If the shoulder is plunged deeper into the workpieces to concentrate protective layer components centrally, then crack formation is prevented, but the plunging depth increases by 1 mm or more
Solution Approach 1:
The invention optimizes the plunging depth parameter to 1 mm or more into the second workpiece, which is sufficient to achieve central concentration of protective layer components without excessive depth. This parameter optimization balances the need for crack prevention with minimal additional plunging depth
3Strength
If the surface pressure during backfilling is set to 90-175 MPa to prevent crack formation, then joint strength is improved, but the process requires precise pressure control
Solution Approach 1:
The invention defines a specific pressure range of 90-175 MPa for the backfilling process, which concentrates protective layer components centrally and prevents crack formation. This parameter specification provides clear control targets for manufacturing while achieving the desired joint quality
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 effectively suppresses the lowering of joint strength by concentrating the protective layer components centrally, preventing crack formation and enhancing the overall strength of the joint.
Implementation Method 1
a rotary tool is plunged into workpieces that are stacked together. At the time, frictional heat is generated, which softens part of the workpieces
Implementation Method 2
frictional heat is generated, which softens part of the workpieces
Implementation Method 3
a component of the protective layer flows into an inside of the shoulder together with other stirred materials
Implementation Method 4
performing a backfilling process of pushing the stirred materials that have flowed into the inside of the shoulder in the plunging process out of the shoulder by the pin while rotating the rotary tool
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A friction stir spot welding method according to one aspect of the present invention includes: performing a plunging process of moving a shoulder (28) toward a second workpiece (102) from a first workpiece (101) side while rotating a rotary tool to plunge the shoulder into the first and second workpieces; and performing a backfilling process of pushing stirred materials that have flowed into an inside of the shoulder in the plunging process out of the shoulder and backfilling a plunging hole with the stirred materials, the plunging hole being formed by the plunging of the shoulder. In the plunging process, the shoulder is plunged to a position that is shifted from a boundary between the first workpiece and the second workpiece to the second workpiece side by 1 mm or more, such that a component of a protective layer (104) is concentrated in a central portion of a stirred portion (105) when the backfilling process is completed.