Refill Friction Stir Spot Welding for Coated Joint Strength
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Solution Overview
Problem
The presence of coating films on welding surfaces of workpieces can lead to a decrease in welding strength when using refill friction stir spot welding, as the films may remain in the friction-stirred region, affecting the joint's integrity.
Innovation Solution
A method and device for friction stir spot welding that includes a coating film removal step using heat generated by a shoulder member to decompose and remove the coating film before the welding process, ensuring it does not remain in the friction-stirred region, thereby preventing a decrease in welding strength.
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 operation. The shoulder member is plunged into the workpiece to decompose and remove the coating film in advance, ensuring the welding surface is clean before the pin member performs friction stir spot welding. This preliminary preparation step prevents the coating film from interfering with the welding process while maintaining overall process efficiency.
Solution Approach 2:
The patent converts the harmful effect of the coating film into a beneficial process feature. By utilizing the friction heat generated during the welding process to decompose and remove the coating film, the previously harmful coating becomes a controlled element that can be eliminated through the welding operation itself. The heat that would otherwise be wasted is now used to serve the dual purpose of heating for welding and decomposition of the coating film.
2Reliability
If the shoulder member plunges deeper into the workpiece to remove the coating film, then the coating film removal effectiveness increases, but the risk of damaging the workpiece or creating excessive heat increases
Solution Approach 1:
The patent applies local quality by concentrating the coating film removal action at the specific location where the coating film exists on the workpiece surface. The shoulder member is plunged only to the extent necessary to remove the coating film from the friction-stirred region, not throughout the entire workpiece thickness. This localized approach ensures effective coating removal while minimizing the risk of workpiece damage and excessive heat generation in non-critical areas.
Solution Approach 2:
The patent utilizes parameter changes by controlling the plunge depth, rotation speed, and dwelling time of the shoulder member to optimize coating film removal. By adjusting these parameters, the process achieves effective coating decomposition at controlled temperatures that prevent workpiece damage. The parameters are carefully selected to decompose the coating film without causing excessive heat accumulation or structural damage to the base material.
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, ensuring a stronger joint by eliminating the film from the friction-stirred region, which enhances the bonding process and maintains the coating's functional properties like corrosion resistance.
Implementation Method 1
decompose the coating film by heating the coating film to a temperature equal to or more than the thermal decomposition temperature by using the heat generated by the rotation of the shoulder member
Implementation Method 2
removing the coating film by plunging a distal end of the shoulder member into the one workpiece up to a position closer to the surface of the one workpiece than the at least one of the welding surfaces
Implementation Method 3
rotating the shoulder member in a state in which the surface of the one workpiece, with the welding surfaces being overlaid on each other, is pressed by the end face of the clamp member
Implementation Method 4
performing friction stir spot welding of the pair of workpieces after the coating film removal step by using the pin member and the shoulder member
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(e)
AI summary
A friction stir spot welding method is a method of performing 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 a coating film removal step of 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 a welding step of performing friction stir spot welding of the pair of workpieces after the coating film removal step by using the pin member and the shoulder member as rotary tools.