Friction Stir Spot Welding Depth for Stronger Thermoplastic Joints
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Solution Overview
Problem
Friction stir spot welding methods for thermoplastic resin members often result in insufficient welding strength due to inadequate plunging depth settings, leading to stress concentration and fractures around the faying surface.
Innovation Solution
A friction stir spot welding method using a double-acting tool with a pin and shoulder, where the plunging depth is adjusted based on the thickness of the members to ensure the shoulder penetrates both layers, maintaining the stress concentrating part away from the boundary, thereby improving welding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the plunging depth is set around the welding surface between members (similar to metal welding), then the welding process is simple, but the welding strength is insufficient for thermoplastic resin members
Solution Approach 1:
The invention changes the plunging depth parameter from the conventional shallow depth (around the welding surface) to a deep depth (penetrating through the first member and reaching at least the middle of the second member). This parameter change fundamentally alters the welding mechanism for thermoplastic resin members, enabling the stirred weld to anchor into the second member and achieve sufficient welding strength while maintaining process simplicity.
2Strength
If the plunging depth is increased to penetrate through members, then the welding strength is improved, but the stress concentrating part may form at the boundary causing fractures
Solution Approach 1:
The invention converts the potentially harmful stress concentration at the boundary into a beneficial anchoring effect. By penetrating the tool through the first member and reaching at least the middle of the second member, the stirred weld creates a mechanical anchor that prevents fracture propagation. The stress concentrating part is positioned within the welded region rather than at the boundary, transforming what would be a weakness into a strength-enhancing feature.
3Area of stationary object
If the tool penetrates deeply into both members, then the bonding area is increased, but the complexity of controlling plunging depth increases
Solution Approach 1:
The invention employs a self-regulating plunging mechanism where the tool automatically penetrates through the first member and reaches at least the middle of the second member based on the material properties and stack-up configuration. The process inherently controls the plunging depth through the friction stir mechanism and material flow characteristics, eliminating the need for complex active control systems while maximizing the bonding area between members.
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 enhances welding strength by maintaining the stress concentrating part away from the boundary, reducing fractures and improving the bonding between thermoplastic resin members.
Implementation Method 1
friction stir spot welding includes: plunging a tool which is rotating into an overlapping part of the two members to be spot welded to perform friction stir
Data Source
AI summary
A double-acting tool for friction stir spot welding is used to weld a first member and a second member each formed of a thermoplastic resin molding by friction stir spot welding. An overlapping part of the first member and the second member is formed, and the tool is disposed against the overlapping part while rotating a pin and a shoulder about a rotation axis. The shoulder is plunged into the overlapping part to start friction stir. The plunging is continued until the shoulder penetrates the first member, and penetrates the second member or reaches a depth corresponding to a first thickness t1 or lager. Subsequently, the overlapping part is backfilled with a resin material overflowed due to the plunging.