Resistance Spot Weld Evaluation for Liquid Metal Embrittlement Cracking
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Solution Overview
Problem
Conventional methods for evaluating susceptibility to liquid metal embrittlement (LME) cracking in resistance spot welded steel sheets suffer from low reproducibility and lack quantitative accuracy, particularly due to biases in welding current path and variations in deformation stress and strain.
Innovation Solution
A method involving resistance spot welding without a sheet gap or electrode inclination angle, followed by controlled application of bending or tensile strain to the welded portion, and subsequent observation for LME cracking, allowing for quantitative evaluation of susceptibility based on strain and temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sheet gap or electrode inclination angle is used to promote LME cracking occurrence, then LME cracking frequency increases, but welding current path becomes biased and nugget shape deviates from preferred form
Solution Approach 1:
The patent extracts and removes the sheet gap and electrode inclination angle from the evaluation method, using instead a standard resistance spot welding configuration without these deviations. This eliminates the bias in welding current path and nugget shape deviation while maintaining the ability to evaluate LME cracking susceptibility through controlled strain application.
Solution Approach 2:
Instead of using sheet gap or electrode inclination to promote LME cracking, the patent inverts the approach by using standard welding conditions and applying controlled strain to the welded portion. This reverses the conventional method's logic while achieving the same evaluation goal more accurately.
2Reliability
If sheet gap is increased to promote LME cracking, then deformation stress and strain increase, but contact between steel sheets at LME cracking site is hindered
Solution Approach 1:
The patent removes the sheet gap from the evaluation setup, using instead standard contact welding conditions. This maintains proper contact between steel sheets at the LME cracking site while still enabling LME cracking evaluation through controlled strain application during or after welding.
3Reliability
If conventional evaluation methods are used, then LME cracking can be observed, but quantitative evaluation of susceptibility is not achieved
Solution Approach 1:
The patent introduces a feedback mechanism by applying controlled strain to the welded portion and observing whether LME cracking occurs, then using this information to quantitatively evaluate susceptibility. The method establishes a relationship between applied strain, temperature, and LME cracking occurrence to provide numerical susceptibility values rather than qualitative observations.
Solution Approach 2:
The patent changes the evaluation parameters from simple presence/absence observation to controlled strain application with specific magnitude and timing, combined with temperature measurement. This enables quantitative determination of susceptibility by identifying the strain and temperature conditions that trigger LME cracking.
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 enables highly accurate and quantitative evaluation of LME cracking susceptibility, providing a reliable assessment of the critical strain and temperature conditions for LME cracking occurrence.
Implementation Method 1
Joule heating generated at this time melts and solidifies the inside of the sheet combination, forming a nugget of weld metal and joining the sheet combination.
Implementation Method 2
applying bending strain or tensile strain controlled to a defined amount of strain to a welded portion
Implementation Method 3
observing the welded portion to ascertain the presence or absence of LME cracking
Data Source
AI summary
A method for evaluating susceptibility to liquid metal embrittlement cracking in a resistance spot welded portion of a steel sheet that enables highly accurate and quantitative evaluation is provided. The method includes: overlapping a first steel sheet and a second steel sheet, one or both of which are galvanized steel sheets, without an intervening gap to obtain a sheet combination, sandwiching the sheet combination between a pair of electrodes, and applying current and pressure via the electrodes to perform resistance spot welding; applying to a welded portion of the second steel sheet at the same time as or after the end of the current application; then observing the welded portion of the second steel sheet to ascertain the presence or absence of liquid metal embrittlement cracking; and evaluating susceptibility to liquid metal embrittlement cracking in the welded portion based on the observation result.