Resistance Spot Welding Control for Stable Nugget Diameter
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Solution Overview
Problem
Existing resistance spot welding methods struggle to consistently achieve a desired nugget diameter and joint strength, especially when disturbances such as current shunting or sheet gaps occur, and are costly and complex to implement, particularly when dealing with high-strength steel sheets.
Innovation Solution
A resistance spot welding method involving test welding to store heat generation data, followed by adaptive control in actual welding, with specific voltage and current ratios to ensure consistent nugget formation and heat treatment, even in the presence of disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resistance spot welding is used with fixed welding parameters, then the process is simple and fast, but the nugget diameter becomes unstable and joint strength decreases when disturbances such as current shunting or sheet gaps occur
Solution Approach 1:
The patent performs preliminary test welding before actual welding to measure the electrical properties (resistance and inductance) of the workpiece. Based on these measurements, the welding parameters (current, time, electrode force) are determined in advance. This preliminary characterization allows the system to adapt to variations in workpiece conditions without requiring complex real-time control during actual welding, thus improving nugget stability while limiting system complexity.
Solution Approach 2:
The patent incorporates feedback by measuring the electrical properties during test welding and using this information to adjust welding parameters. The system measures resistance and inductance, compares them against reference values or thresholds, and modifies the welding current and duration accordingly. This feedback mechanism enables automatic compensation for disturbances like current shunting or sheet gaps, ensuring consistent nugget formation.
2Manufacturing precision
If welding current is increased to compensate for current shunting, then nugget diameter can be maintained, but energy consumption increases and harmful thermal effects worsen
Solution Approach 1:
The patent changes welding parameters (current, time, electrode force) based on measured electrical properties of the workpiece. Instead of using a fixed high current to compensate for all possible disturbances, the system calculates optimal parameters specific to each workpiece configuration. This allows precise nugget diameter control while minimizing energy consumption by applying only the necessary current level required for each welding condition.
Solution Approach 2:
The patent implements dynamic parameter adjustment where welding current and duration are varied according to the measured resistance and inductance values. The system adapts parameters in real-time based on workpiece characteristics, allowing optimal energy utilization. This dynamic approach prevents both under-welding and excessive energy input, achieving precise nugget control with efficient energy use.
3Reliability
If multiple test welds are performed to determine optimal parameters, then welding quality improves, but production time increases and productivity decreases
Solution Approach 1:
The patent performs test welding and electrical property measurement as a preliminary step before actual welding. This preliminary characterization is done once per workpiece batch or configuration, and the resulting parameters are then used for subsequent production welding. This approach ensures high welding quality consistency while limiting the time penalty to only the initial setup phase, not affecting overall production speed.
Solution Approach 2:
The patent implements periodic test welding at predetermined intervals during production runs. Instead of performing test welds before every single welding operation, the system conducts characterization tests periodically (e.g., at the start of a batch or after a set number of welds). This periodic approach maintains welding quality consistency while minimizing the impact on productivity by reducing the frequency of time-consuming test operations.
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 stabilizes nugget diameter and enhances joint strength in high-strength steel sheet combinations, effectively addressing disturbances and improving operational efficiency and yield rates.
Implementation Method 1
Heat generated from the resistance to the flow of the high welding current is used to obtain a spot weld. The spot weld is called a nugget, and results from the overlapping steel sheets melting and solidifying at their contact portion when the current flows through the steel sheets.
Data Source
Figure 1A~1F
Figure 2A~2B
Figure 3A~3B
AI summary
A resistance spot welding method comprises: performing test welding; and performing actual welding after the test welding, wherein in subsequent current passage in the test welding, current passage is performed by constant current control under a condition: 0.5 ≤ Vtp/Vtm ≤ 2.0 when tc < 800 ms; 0.5 - 0.3 × (tc - 800)/800 ≤ Vtp/Vtm ≤ 2.0 - 0.5 × (tc - 800)/800 when 800 ms ≤ tc < 1600 ms; and 0.2 ≤ Vtp/Vtm ≤ 1.5 when tc ≥ 1600 ms, where Vtm is an average value of a voltage between the electrodes in main current passage in the test welding, and Vtp is an average value of a voltage between the electrodes in the subsequent current passage in the test welding, and wherein in main current passage in the actual welding, adaptive control welding is performed, and in subsequent current passage in the actual welding, current passage is performed by constant current control under a condition: 0.8 × Itp ≤ Imp ≤ 1.2 × Itp, where Itp is a current in the subsequent current passage in the test welding, and Imp is a current in the subsequent current passage in the actual welding.