Resistance Spot Welding Hold Time for Electrode Misalignment Cracks
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Solution Overview
Problem
Resistance spot welding methods fail to effectively inhibit cracking in welds, particularly in surface-treated steel sheets, due to limitations in alloying element content, high welding current settings, and axis misalignment issues, which restrict their applicability to various steel grades and increase the complexity of implementation in automotive assembly.
Innovation Solution
The method adjusts the electrode force retaining time based on the axis misalignment amount between electrodes, ensuring that the relationship 2·D·(t·T/(F·d))1/2≤H is maintained, where D is the axis misalignment, t is the total sheet thickness, T is the tensile strength, F is the electrode force, and d is the electrode tip diameter, to prevent cracking by controlling the temperature and stress at the weld.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high welding current is used to achieve joining, then welding speed and productivity are improved, but cracking in the weld increases due to liquid metal embrittlement
Solution Approach 1:
The welding process is divided into two distinct phases: a first welding current phase for nugget formation and a second welding current phase for crack prevention. This segmentation allows each phase to be optimized independently - the first phase uses high current for productivity while the second phase uses controlled current to prevent liquid metal embrittlement, thus resolving the contradiction between welding speed and weld quality
Solution Approach 2:
The first welding current is applied preliminarily to form a sound nugget before the second welding current is applied. By establishing a proper nugget structure first, the subsequent second current phase can effectively prevent cracking without compromising the already-formed weld, thereby maintaining both high productivity and weld reliability
2Reliability
If specific alloying element ranges are imposed on steel sheets to prevent cracking, then weld reliability is improved, but the versatility and adaptability to various steel grades are reduced
Solution Approach 1:
Instead of changing the material composition (alloying elements), the invention changes the process parameters (welding current phases, holding time, electrode force) to prevent cracking. This allows the same welding method to be applied to various steel grades without imposing restrictions on alloying element content, thus maintaining both weld reliability and versatility across different steel types
Solution Approach 2:
The invention replaces the chemical approach (controlling alloying elements) with a mechanical/process approach (controlled current application and holding time). By substituting material composition control with process parameter control, the method achieves crack prevention without limiting the range of applicable steel grades
3Device complexity
If axis misalignment between electrodes is not corrected, then device complexity is reduced, but manufacturing precision and weld quality deteriorate due to increased cracking
Solution Approach 1:
The welding process itself compensates for axis misalignment through the controlled second welding current phase and extended holding time. The process parameters are adjusted to account for misalignment effects, allowing the system to maintain weld quality without adding complex alignment mechanisms, thus resolving the contradiction between device simplicity and manufacturing precision
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 approach effectively reduces cracking in welds regardless of steel grade, improving the reliability and productivity of resistance spot welding by optimizing the holding time in accordance with axis misalignment, thereby preventing liquid metal embrittlement and ensuring a stable weld formation.
Implementation Method 1
a high welding current is passed therethrough for a short time to achieve joining. A spot weld 5 is obtained by utilizing resistive heat generated by the passage of the high welding current
Implementation Method 2
the molten low melting point metal penetrates the grain boundaries of the base material of the surface-treated steel sheet, which decreases the grain boundary strength, and this causes cracking in the weld
Data Source
AI summary
Provided is a resistance spot welding method that inhibits, in accordance with the degree of axis misalignment between electrodes, the occurrence of cracking in a weld regardless of the steel grade. In resistance spot welding methods according to the present invention, H (ms) is an electrode force retaining time after completion of current passage, D (mm) is an amount of axis misalignment between the electrodes, t (mm) is a total sum of sheet thicknesses of a plurality of overlapping steel sheets, T (MPa) is a tensile strength of a steel sheet having a highest tensile strength among the plurality of steel sheets, F (N) is an electrode force, and d (mm) is a tip diameter of one electrode of the pair of electrodes that has a smaller tip diameter. The electrode force retaining time H is specified to be a predetermined value or greater.