Resistance Welding Nugget Quality via Transient Resistance Ratio
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Solution Overview
Problem
Existing methods for evaluating spot welding reliability, such as those based on electric resistance differences, lack a sufficient physical basis and are influenced by disturbances like gaps between workpieces and electrode wear, making them unreliable for assessing nugget shape and quality in high-production settings.
Innovation Solution
A resistance welding method that measures the ratio of electric resistance values before and after Joule heating stops, using these ratios to determine the weld state and potentially reheating the welding portion to ensure proper nugget formation, thereby stabilizing the welding process and improving evaluation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If electric resistance difference is used to evaluate weld quality, then evaluation can be performed during welding process, but the evaluation reliability is insufficient due to temperature and shape changes affecting resistance values
Solution Approach 1:
The patent changes the evaluation parameter from absolute resistance difference to resistance ratio (R1/R2). This parameter transformation eliminates the influence of temperature and shape changes on the evaluation, as the ratio of resistance values taken at different times during the welding process reflects the nugget formation state independently of thermal expansion and material softening effects.
Solution Approach 2:
The patent uses transient resistance measurements taken during the welding process itself, rather than relying on post-weld inspection or expensive specialized equipment. The resistance values are measured momentarily during welding and then discarded, providing a simple, low-cost evaluation method that doesn't require persistent monitoring systems.
2Ease of manufacture
If initial resistance value R0 is used as evaluation factor, then measurement is simple, but the value is easily influenced by disturbances such as gaps between workpieces and electrode wear
Solution Approach 1:
The patent performs preliminary measurements of resistance values R1 and R2 during the welding process itself, before the welding is complete. This allows the evaluation to be based on the actual welding conditions and nugget formation process, rather than on initial conditions that may not reflect the final weld quality. The measurements are taken when the welding energy is actively being applied, capturing the true state of the joint formation.
Solution Approach 2:
The patent establishes a feedback mechanism where the resistance ratio R1/R2 is calculated and compared against predetermined thresholds to determine weld quality. This feedback loop allows for real-time evaluation and potential adjustment of welding parameters, ensuring consistent quality while maintaining simple measurement procedures.
3Measurement precision
If resistance values are measured after welding, then accurate post-weld evaluation can be performed, but it is difficult to feed back results to production lines on timely basis
Solution Approach 1:
The patent maintains continuous measurement of resistance values during the entire welding process, rather than stopping to take measurements after welding. This continuous monitoring allows the evaluation to be completed while the welding is still in progress, enabling immediate feedback to the production line without interrupting the welding sequence or requiring post-weld measurement steps.
Solution Approach 2:
The patent performs the evaluation action preliminarily, during the welding process itself, rather than after completion. By calculating the resistance ratio R1/R2 while the welding is ongoing, the system provides advance evaluation results that can be fed back to control subsequent welding operations, maintaining high productivity while achieving accurate evaluation.
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 provides an accurate and reliable evaluation of weld quality by minimizing the impact of temperature and shape changes, allowing for timely feedback and improved nugget formation consistency, preventing defective welds and ensuring uniform nugget sizes.
Implementation Method 1
a power supply unit for supplying heating current to the electrodes for Joule heating a welding portion of the workpieces
Implementation Method 2
a first resistance measuring unit for measuring a first electric resistance value (R1) of the workpieces in a heating state before the heating step ends; a second resistance measuring unit for measuring a second electric resistance value (R2) of the workpieces in residual heat after the heating step ends
Data Source
AI summary
Exemplary embodiments provide a resistance welding method capable of stabilizing quality or improving efficiency of resistance welding such as spot welding. This resistance welding method comprises a calculating step of calculating resistance ratio X of a second electric resistance value R2 of workpieces to be joined in residual heat after Joule heating stops to a first electric resistance value R1 of the workpieces immediately before the Joule heating stops or vice versa (R2/R1 or R1/R2); a determining step of determining whether the resistance ratio X is equal to or greater than a threshold value Xn, and a reheating step of carrying out the Joule heating again when the resistance ratio X is smaller than the threshold value Xn. Thereby at least part of a welding portion is melted and solidified to reliably form a nugget, and a stably resistance-welded member can be provided.