Resistance Spot Welding Cooling Asymmetry to Prevent LME Cracking
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Solution Overview
Problem
Existing resistance spot welding methods for high-tensile steel plates coated with zinc fail to adequately inhibit Liquid Metal Embrittlement (LME)-induced cracking, particularly due to insufficient nugget formation sizes across varying steel plate thicknesses.
Innovation Solution
A resistance spot welding method and apparatus that differentially control the cooling rates of high-tensile and low-tensile steel plates by using electrodes with varying contact areas and cooling configurations, ensuring the high-tensile steel plate cools more rapidly than the low-tensile steel plate, thereby reducing tensile stress and inhibiting LME-induced cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resistance spot welding is used on zinc-coated high-tensile steel plates, then nuggets can be formed in certain sizes, but LME-induced cracking occurs due to insufficient cooling rate control
Solution Approach 1:
The patent applies local quality by making the cooling rates different for different steel plates in the weld joint. Specifically, the high-tensile steel plate is cooled at a higher rate than the other steel plate, creating localized differential cooling that prevents LME-induced cracking in the critical high-tensile plate without requiring complex system-wide control
Solution Approach 2:
The patent changes the cooling rate parameter differentially for different steel plates. By controlling the cooling rate of the high-tensile steel plate to be higher than that of the other steel plate, the patent modifies the thermal parameters to reduce tensile stress and prevent cracking, while maintaining relatively simple apparatus structure
2Reliability
If larger nuggets are formed to prevent LME-induced cracking, then crack resistance improves, but welding process complexity increases due to thickness variations
Solution Approach 1:
Instead of adjusting nugget size based on plate thickness, the patent changes the cooling rate parameter to prevent cracking. This approach maintains consistent welding procedures across different thicknesses while achieving crack resistance through differential cooling, thereby maintaining ease of manufacture
3Temperature
If the contact area of electrodes is increased to improve cooling rate, then cooling efficiency improves, but apparatus complexity and cost increase
Solution Approach 1:
The patent applies local quality by making the contact areas of electrodes asymmetric. The first electrode contacting the high-tensile steel plate has a larger contact area than the second electrode contacting the other steel plate, creating localized enhanced cooling where needed without requiring complex symmetric modifications throughout the apparatus
Solution Approach 2:
The patent employs asymmetry in electrode design where the contact areas are intentionally made unequal. This asymmetric configuration naturally produces differential cooling rates with simpler structure compared to symmetric designs that would require additional active control mechanisms
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 inhibits LME-induced cracking in high-tensile steel plates regardless of thickness, while maintaining a relatively simple and cost-effective apparatus structure by ensuring the high-tensile steel plate cools at a higher rate than the low-tensile steel plate during welding.
Implementation Method 1
resistance spot welding
Implementation Method 2
causing a cooling rate of a high-tensile steel plate among the two or more steel plates to be higher than a cooling rate of an other steel plate
Data Source
AI summary
The present disclose provides a method of resistance spot welding that can inhibit Liquid Metal Embrittlement-induced cracking in zinc-coated steel plates irrespective of the plate thicknesses. One aspect of the present disclosure provides a method of resistance spot welding that includes welding a workpiece with a resistance spot welding apparatus. The workpiece includes two or more steel plates in an overlapping state. The two or more steel plates include at least one steel plate coated with zinc. The welding includes causing a cooling rate of a high-tensile steel plate among the two or more steel plates to be higher than a cooling rate of an other steel plate among the two or more steel plates. The high-tensile steel plate has a tensile strength higher than a tensile strength of the other steel plate.