Resistance Spot Welding of Galvanized Sheets With Two-Stage Nugget Control
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Solution Overview
Problem
Resistance spot welding of galvanized steel sheets is prone to cracking due to liquid metal embrittlement, especially when the thickness ratio of the surface layer steel sheet is large or disturbances occur, and existing methods struggle to secure a stable nugget diameter while avoiding cracking.
Innovation Solution
Control the shoulder angles of the steel sheets and divide the current passing process into two stages to form and enlarge an intermediate nugget, minimizing deformation and cracking, while ensuring a desired nugget diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If resistance spot welding is applied to galvanized steel sheets with large thickness ratios, then manufacturing efficiency is maintained, but cracking occurs due to liquid metal embrittlement
Solution Approach 1:
The welding process is divided into multiple stages with different current values. The first stage uses a higher current value to quickly form an initial nugget, while the second stage uses a lower current value to grow the nugget to the target diameter. This segmentation allows control over the welding process to prevent liquid metal embrittlement cracking while maintaining manufacturing efficiency.
Solution Approach 2:
The welding process employs periodic current application with distinct phases. By alternating between higher current (first stage) and lower current (second stage), the method creates a controlled thermal cycle that prevents excessive heat input and liquid metal embrittlement while ensuring complete welding. This periodic action resolves the contradiction between speed and reliability.
2Productivity
If high current is used to form large nugget quickly, then productivity increases, but deformation and cracking increase
Solution Approach 1:
The welding process is divided into two stages: first stage with higher current for rapid nugget formation, and second stage with lower current for precise nugget growth to target diameter. This segmentation enables both high productivity and precise control, resolving the contradiction between welding speed and nugget diameter control.
Solution Approach 2:
The current value is dynamically adjusted during the welding process. The system transitions from a higher current state (first stage) to a lower current state (second stage), allowing the process to adapt to different phases of nugget formation. This dynamic adjustment optimizes both productivity and precision.
3Manufacturing precision
If multi-stage current with three or more stages is used, then nugget diameter control improves, but device complexity increases
Solution Approach 1:
The invention extracts and eliminates the unnecessary intermediate stage from multi-stage welding processes. By using only two stages (first stage with higher current, second stage with lower current), the method achieves sufficient nugget diameter control while reducing device complexity and process overhead compared to three or more stages.
Solution Approach 2:
The invention applies different current values locally to different phases of the welding process. The first stage uses higher current locally for rapid heating, while the second stage uses lower current locally for controlled growth. This localized quality approach achieves precise nugget control with minimal process complexity.
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 effectively suppresses cracking and maintains a stable nugget diameter, suitable for galvanized steel sheets, even with large thickness ratios or disturbances, enhancing joint strength and corrosion resistance.
Implementation Method 1
a point-like welded portion is obtained by using resistance heat generated by the welding current
Implementation Method 2
the nugget 5 is the portion that melts and solidifies at the contact point of the overlapped steel sheets when the electric current flows through the steel sheets
Implementation Method 3
Pressure is applied from the welding electrodes 3, 4 from above and below while a welding current is passed between the welding electrodes 3, 4
Data Source
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AI summary
Provided is a welded joint for which cracking of the welded portion is suppressed and nugget diameter is a desired size, even when at least one of the surface layer steel sheets of a sheet combination is a galvanized steel sheet and the thickness ratio of a surface layer steel sheet is large or a disturbance has a large effect. At least one of Expressions (1) or (2) is satisfied for a shoulder angle a of the first steel sheet of the sheet combination and a shoulder angle b of the nth steel sheet of the sheet combination.