Friction Stir Spot Welding Temperature Control via Speed and Plunge Depth
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Solution Overview
Problem
Conventional friction stir spot welding methods face challenges in accurately controlling the welding temperature, leading to either excessive heat causing material brittleness or inadequate joint strength due to insufficient heat, and the tool temperature often deviates from the welding temperature, reducing accuracy.
Innovation Solution
A friction stir spot welding device with a controller that adjusts the tool's rotational speed and plunge depth in a predetermined pattern to maintain the welding temperature within a set range, ensuring the tool temperature accurately reflects the welding temperature, thereby controlling the welding process effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the plunge depth of the tool is increased to obtain strength, then the joint strength is improved, but the welding temperature becomes excessively high causing material brittleness
Solution Approach 1:
The patent applies periodic action by making the tool move periodically in the planar direction during friction stir spot welding. This periodic motion prevents the welding temperature from rising monotonously, allowing the material to be stirred adequately without exceeding the transformation temperature and causing brittleness. The periodic movement creates cycles of heating and cooling that maintain temperature within an optimal range while still achieving sufficient material plasticization for strong joints.
Solution Approach 2:
The patent implements dynamics by transitioning from a static tool position to a dynamic periodic motion in the planar direction. This dynamic approach allows the tool to remain effectively at the welding position while introducing controlled movement that regulates temperature rise. The dynamic motion enables the system to achieve both adequate stirring (requiring depth) and temperature control (requiring movement), resolving the contradiction between joint strength and welding temperature.
2Temperature
If the plunge depth of the tool is reduced to lower welding temperature, then material transformation and quenching are prevented, but the fluidity of plasticized material is reduced and adequate welded spot is not formed
Solution Approach 1:
The patent applies continuity of useful action by maintaining continuous frictional heating through periodic tool motion. Even though the tool moves periodically, the continuous nature of the frictional contact ensures that heat is generated continuously, keeping the material in a plasticized state with sufficient fluidity. This continuous heating action allows adequate welded spot formation without requiring excessive plunge depth that would cause overheating.
3Device complexity
If the tool stays at a specified position during spot welding, then the welding process is simple, but the welding temperature is significantly increased
Solution Approach 1:
The patent applies periodic action by introducing simple periodic motion in the planar direction while maintaining the tool's position at the welding spot. This periodic movement is sufficient to control temperature rise without complicating the overall welding process. The motion pattern is straightforward and easy to implement, preserving process simplicity while effectively managing welding temperature.
4Device complexity
If control is based on tool temperature, then the control system is simple, but accuracy of welding temperature is reduced due to deviation from actual welding temperature
Solution Approach 1:
The patent applies feedback by using the tool temperature as a control parameter with periodic motion to indirectly control the welding temperature. The periodic motion creates a predictable temperature pattern where the tool temperature correlates with the welding temperature. By adjusting the periodic motion parameters based on tool temperature feedback, the system achieves accurate control of the actual welding temperature without requiring direct measurement at the weld zone.
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 approach allows for precise control of the welding temperature, preventing material transformation and achieving a high-quality weld with improved joint strength and reduced brittleness, while maintaining the tool at an optimal temperature.
Implementation Method 1
a tool having a projection at a tip end is rotated and plunged into lapped portions of the plate members, to soften the lapped portions by friction heat
Implementation Method 2
the tool is plunged into the lapped portions while rotating the tool, to perform friction stir spot welding
Implementation Method 3
the controller controls the rotation driving unit so that a rotational speed of the tool is set to a value which is equal to or lower than a predetermined rotational speed at which a temperature of the tool is regarded as being equal to a welding temperature
Data Source
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AI summary
During friction stir spot welding, a controller executes a temperature holding control in which the controller controls a rotation driving unit so that a rotational speed of a tool is set to a value which is equal to or lower than a predetermined rotational speed at which a temperature of the tool is regarded as being equal to a welding temperature of lapped portions, and in which the controller controls a displacement driving unit to increase and reduce a welding pressure or plunge depth of the tool so that the temperature of the tool is held in a predetermined set range.