J-Shaped Laser Lap Weld Joint for Crack-Resistant Auto Frames
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Solution Overview
Problem
Laser lap welding of automobile structural members often results in cracking at the terminal end of the fusion zone, leading to reduced static and fatigue strength due to stress concentration, which is not effectively addressed by existing methods such as protruding lower sheets, oblique laser irradiation, reheating, or elliptical welding.
Innovation Solution
A laser-welded lap joint with a J-shaped weld zone, where the main weld zone length is between 2/3 and 4/5 of the total length, the weld terminal end radius is between 0.5 and 1.5 mm, and the angle is between 3/4π and 2π radians, along with controlled steel sheet thickness and gap sizes, to prevent crack occurrence and propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser lap welding is used to join steel sheets, then welding speed and productivity are improved, but cracking occurs at the terminal end of the fusion zone reducing joint strength
Solution Approach 1:
The terminal end of the weld line is designed with a curved shape having a radius of curvature of 0.5 to 1.5 mm instead of a sharp angle. This curvature distributes the stress concentration that would otherwise occur at the terminal end, preventing crack initiation while maintaining the productivity benefits of laser lap welding
Solution Approach 2:
The weld line shape parameters are specifically controlled: the terminal end curvature radius is set to 0.5-1.5 mm, and the angle of the terminal end is set to 3/4π to 2π radians. These parameter changes optimize the stress distribution to prevent cracking while maintaining welding efficiency
2Reliability
If the lower steel sheet is disposed to protrude to prevent cracking, then crack prevention is improved, but component design flexibility is restricted
Solution Approach 1:
Instead of requiring the lower steel sheet to protrude, the invention uses a curved terminal end weld line shape that achieves crack prevention through geometric optimization. This allows standard component designs to be used without modification while still preventing cracks
Solution Approach 2:
The weld line geometry parameters (curvature radius and terminal angle) are optimized to provide crack prevention functionality without requiring changes to the steel sheet configuration or component design
3Reliability
If oblique laser irradiation is used to prevent cracking, then crack prevention is improved, but welding precision and fusion zone quality deteriorate
Solution Approach 1:
The curved terminal end weld line shape prevents cracking through stress distribution geometry rather than oblique irradiation. This maintains perpendicular laser irradiation, ensuring high manufacturing precision and fusion zone quality while still achieving crack prevention
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
The proposed solution effectively prevents cracking and enhances joint strength by dispersing tensile stress, improving peeling strength, and allowing for more design flexibility in automobile frame components.
Implementation Method 1
a surface of a plurality of lapped steel sheets is irradiated with a laser beam to join the steel sheets together
Implementation Method 2
The portion of the steel sheets irradiated with the laser beam is fused and solidified
Implementation Method 3
The portion of the steel sheets irradiated with the laser beam is fused and solidified, and a fusion zone (weld zone) is thereby formed
Data Source
AI summary
A laser-welded lap joint includes a weld zone formed by joining a plurality of steel sheets one over another together by laser welding. The weld zone has a J shape and includes a main weld zone having a linear weld line shape and a weld terminal end zone having an arcuate or circular weld line shape. The length L1 of the main weld zone is ⅔ or more and ⅘ or less of the full length L of the weld zone represented by formula (1). The radius R of the weld terminal end zone satisfies formula (2). The angle θ of the weld terminal end zone satisfies formula (3). The total size of a gap between the plurality of steel sheets in a lapped portion is 0% or more and 15% or less of the total thickness of the plurality of steel sheets.