Resistance Spot Welding Current Staging for Stable Nugget Diameter
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Solution Overview
Problem
Existing resistance spot welding methods fail to consistently achieve a stable nugget diameter and sufficient joint strength, especially when disturbances such as current shunting or sheet gaps occur, and are complex and costly 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 nugget formation and heat treatment, and optimizing the subsequent current passage to prevent surface expulsion and achieve desired heat treatment effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resistance spot welding is performed with fixed welding conditions, then welding process is simple and fast, but nugget diameter becomes unstable due to electrode wear and disturbances like current shunting
Solution Approach 1:
The patent performs test welding before actual welding to measure electrode contact area and calculate appropriate welding current in advance. This preliminary measurement and calculation step allows the system to adapt to electrode wear and material variations, ensuring stable nugget diameter without requiring complex real-time control during actual welding.
Solution Approach 2:
The patent uses measurement data from test welding (electrode contact area, material properties) to calculate and adjust welding current for actual welding. This feedback mechanism ensures that welding parameters are optimized based on actual conditions, compensating for electrode wear and disturbances like current shunting while maintaining process simplicity.
2Manufacturing precision
If welding current is increased to compensate for current shunting and sheet gap, then nugget diameter can be maintained, but joint strength decreases due to surface expulsion
Solution Approach 1:
The patent applies different current levels at different stages: higher current during main current passage for nugget formation, and lower current during subsequent current passage for heat treatment. This localized quality control prevents surface expulsion during the critical heat treatment phase while ensuring adequate nugget formation, thereby maintaining both nugget diameter control and joint strength.
Solution Approach 2:
The patent divides the welding current into two distinct passages: main current passage for nugget formation and subsequent current passage for heat treatment. This segmentation allows optimized current control for each phase, preventing surface expulsion during heat treatment while ensuring proper nugget formation, thus resolving the contradiction between nugget diameter control and joint strength.
3Strength
If subsequent current passage is performed by adaptive control welding, then heat treatment effect is enhanced, but surface expulsion occurs due to excessive current density
Solution Approach 1:
The patent changes the current parameter for subsequent current passage based on test welding results, setting it to 0.5-1.5 times the main current passage current. This parameter adjustment ensures adequate heat treatment effect while preventing excessive current density that would cause surface expulsion, resolving the contradiction between heat treatment effectiveness and surface integrity.
4Reliability
If electrodes are dressed or replaced frequently to maintain contact area, then nugget diameter stability is improved, but productivity decreases
Solution Approach 1:
The patent performs test welding before actual welding to measure the actual electrode contact area and calculate appropriate welding current. This preliminary action compensates for electrode wear effects, allowing consistent nugget diameter to be maintained without frequent electrode dressing or replacement, thus preserving productivity while ensuring quality.
Solution Approach 2:
The patent uses test welding data to feedback-adjust welding current based on actual electrode contact area. This feedback mechanism compensates for electrode wear effects, allowing consistent welding quality to be maintained over extended periods without frequent electrode maintenance, thereby resolving the contradiction between quality consistency and productivity.
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 in continuous welding processes.
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
AI summary
A resistance spot welding method includes: 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 δ Vtp/Vtm δ 2.0 when tc<800 ms; 0.5−0.3·(tc−800)/800 δ Vtp/Vtm δ 2.0−0.5·(tc−800)/800 when 800 ms δ tc<1600 ms; and 0.2 δ Vtp/Vtm δ 1.5 when tc ε 1600 ms, 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 δ Imp δ 1.2·Itp.