Overlap Spot Welding With Laser-Hardened HAZ for Martensitic Steel
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Solution Overview
Problem
The existing methods for welding overlapped portions of high-strength steel sheets in automotive structures, particularly those with galvanized coatings, often result in a heat-affected zone (HAZ) that softens, leading to reduced strength and potential fractures during impact, which compromises the structural integrity and safety of automotive parts.
Innovation Solution
A method involving resistance spot welding followed by the emission of a laser beam to form a melted and solidified portion that crosses the nugget and extends into the HAZ, ensuring the depth of this portion is shallower than the galvanized coating, thereby hardening the HAZ and preventing fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If laser beam is emitted to form melted and solidified portion in the HAZ, then the strength of spot-welded portion is enhanced, but the depth control must be precise to avoid damaging the galvanized coating
Solution Approach 1:
The patent uses continuous laser welding to create a melted and solidified portion that extends continuously across the HAZ. This continuous action ensures uniform hardening throughout the softened zone while maintaining consistent depth control
Solution Approach 2:
The patent uses the molten metal itself as an intermediary medium. The laser melts the HAZ material, and as it solidifies, it acts as a self-regulating layer that hardens the zone without requiring external control mechanisms, naturally preventing damage to the galvanized coating
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 enhances the strength of the spot-welded portion, prevents fractures in the HAZ, and allows for the full utilization of high-strength steel properties, improving the impact performance and safety of automotive structures without compromising dimensional accuracy or cosmetic appearance.
Implementation Method 1
emitting a laser beam to form a melted and solidified portion
Implementation Method 2
form a melted and solidified portion crossing an end of the nugget
Implementation Method 3
melted and solidified portion... depth of the melted and solidified portion... shallower than a contacting surface having the hot-dip galvanneal coating or the hot-dip galvanizing coating formed thereon
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3C
AI summary
A method of welding an overlapped portion according to the present invention in which a plurality of steel sheet members are joined at an overlapped portion, and at least one of the plurality of steel sheet members contains martensite, includes: forming a spot-welded portion having a nugget in the overlapped potion; and emitting a laser beam to form a melted and solidified portion crossing an end of the nugget and located between the nugget and a position externally spaced apart from an end of the nugget by not less than 3 mm, this melted and solidified portion being formed in the steel sheet member containing the martensite so as to have a depth of not less than 50% of the thickness of the steel sheet member containing the martensite at a position externally spaced apart from the end of the nugget by 1 mm.