Refill Friction Stir Spot Welding for Coated Surface Joints
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Solution Overview
Problem
Coating films on welding surfaces of workpieces can lead to a decrease in welding strength when subjected to friction stir spot welding, as they remain in the friction-stirred region and interfere with the welding process.
Innovation Solution
A method and device for friction stir spot welding that includes a coating film removal step using a shoulder member to thermally decompose and remove the coating film before the welding process, preventing its presence in the friction-stirred region and ensuring stronger joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If friction stir spot welding is performed on workpieces with coating films, then the welding process can proceed without additional preparation steps, but the coating film remains in the friction-stirred region causing decreased welding strength
Solution Approach 1:
The patent applies preliminary action by performing coating film removal before the main welding process. The shoulder member is plunged into the workpiece and rotated to thermally decompose and remove the coating film in advance, ensuring the welding surface is clean before the pin member performs the actual welding operation.
Solution Approach 2:
The patent utilizes parameter changes by controlling the temperature through rotational speed and plunging depth of the shoulder member. By adjusting these parameters, the coating film is heated to its thermal decomposition temperature, transforming it from a harmful substance into a removable state without affecting the base metal.
2Manufacturing precision
If the shoulder member is plunged deeper into the workpiece to remove coating film, then coating film removal efficiency improves, but heat input to the workpiece increases potentially affecting welding quality
Solution Approach 1:
The patent applies local quality by concentrating the thermal decomposition action only at the coating film location. The shoulder member is plunged to a specific depth that reaches the coating film but limits excessive heat penetration into the bulk workpiece, achieving localized coating removal while preserving the integrity of the base metal.
Solution Approach 2:
The coating film removal is performed as a preliminary step before welding, allowing controlled heat input at this stage without affecting the subsequent welding quality. The workpiece is prepared in advance with the coating removed, and then the normal welding process proceeds with standard heat input parameters.
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 prevents a decrease in welding strength by removing the coating film, allowing for improved joint integrity and reduced corrosion, with no need for additional equipment beyond the standard friction stir spot welding device.
Implementation Method 1
the coating film may be thermally decomposed by heat generated by rotation of the shoulder member
Implementation Method 2
the coating film may be thermally decomposed by heat generated by rotation of the shoulder member
Data Source
AI summary
A friction stir spot welding method performs friction stir spot welding of a pair of workpieces having a coating film formed on at least one welding surface by using a refill friction stir spot welding device including rotary tools. The method includes removing the coating film by plunging a distal end of the shoulder member into one workpiece up to a position closer to the surface than the welding surface, while rotating the shoulder member as a rotary tool around the axis, and rotating the shoulder member in a state in which the surface of one of the pair of workpieces, with the welding surfaces being overlaid on each other, is pressed by the end face of the clamp member and performing friction stir spot welding of the pair of workpieces after the coating film removal by using the pin member and the shoulder member as rotary tools.