Resistance Spot Welding Current Staging for Crack-Resistant Nuggets
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Solution Overview
Problem
Resistance spot welding of surface-treated steel sheets often results in cracking due to liquid metal embrittlement and deformation issues, making it difficult to form a large nugget diameter stably.
Innovation Solution
A two-step energization process is employed, where the first step controls current to minimize deformation and form a base nugget, followed by a second step with increased current and short-term energization patterns to grow the nugget while reducing splashes and deformation, thereby minimizing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high current is applied to form a large nugget diameter, then nugget diameter is improved, but welding deformation and cracking increase
Solution Approach 1:
The welding process is divided into multiple stages with different current levels. The first stage uses high current to rapidly form a large nugget, while the second stage uses lower current to complete the welding without excessive deformation. This temporal segmentation of the welding process allows the nugget to grow to the desired diameter while controlling the total heat input to minimize deformation and cracking.
Solution Approach 2:
The first welding stage performs the critical action of rapidly forming the nugget to the required diameter before significant deformation can occur. By completing the primary nugget formation in advance with high current, the subsequent lower-current stage only needs to complete the welding process, thereby achieving large nugget diameter while controlling overall deformation.
2Manufacturing precision
If welding current is increased to ensure sufficient heat input, then nugget diameter is improved, but liquid metal embrittlement and cracking worsen
Solution Approach 1:
The welding current is segmented into two distinct stages: a first stage with high current to generate sufficient heat for large nugget formation, and a second stage with reduced current to complete welding while minimizing additional heating that would cause liquid metal embrittlement. This temporal segmentation allows achieving the required nugget diameter while controlling total thermal exposure and cracking risk.
Solution Approach 2:
The welding current parameter is dynamically changed during the process - starting with high current in the first stage to ensure sufficient heat input for large nugget diameter, then reducing to lower current in the second stage to minimize further heating and reduce liquid metal embrittlement. This parameter variation allows optimizing both nugget size and cracking resistance.
3Manufacturing precision
If welding time is extended to form larger nugget, then nugget diameter is improved, but welding deformation increases
Solution Approach 1:
The welding time is segmented into two stages with different current levels. The first stage uses high current for a shorter duration to rapidly form the majority of the nugget diameter, while the second stage uses lower current to complete the welding. This temporal segmentation achieves large nugget diameter without the excessive total welding time that would cause significant deformation.
Solution Approach 2:
The critical nugget formation phase is rushed through in the first welding stage using high current, achieving rapid nugget growth to the required diameter before deformation can significantly develop. The second stage then completes the welding process more slowly with lower current, minimizing additional deformation while finalizing the joint.
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 allows for the stable formation of a large nugget diameter while reducing cracking in surface-treated steel sheets during welding, enhancing joint strength and operational efficiency.
Implementation Method 1
The resistance heat generated by the welding current applied is used to obtain a point-like weld 5
Implementation Method 2
the low-melting point metal coated layer on the surface of the steel sheet melts during welding
Data Source
AI summary
A resistance spot welding method in which a high strength zinc-based coated steel sheet used in a sheet set has an equivalent carbon content of 0.20% or more and a tensile strength of 780 MPa or more. The method includes performing a first energization step such that a current value at the end of the energization, a current value Is at the start of the energization, and a thickness of the thinnest steel sheet among steel sheets overlapping each other satisfy specified relationships. The method includes performing a second energization step in which a cooling step of holding a non-energization state for 10 ms or longer and shorter than 160 ms and performing energization at a current value equal to or more than the current value at the end of the first energization step for 20 ms or longer and shorter than 200 ms are repeated.