Stitch-Welding Galvanized Steel Flanges to Control Zinc Outgassing
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Solution Overview
Problem
Existing methods for laser welding of metal sheets, particularly in car body construction, face challenges such as insufficient seam quality due to zinc outgassing, limited connection cross-section, and difficulty in reproducing welding depth, especially with galvanized steel, which can result in defective welds that appear perfect on the surface but are actually flawed, and require complex seam tracking systems and additional materials to achieve adequate strength.
Innovation Solution
The method involves using a beam influencing device to dynamically control the laser beam's focus, power, and speed during the welding process, including preheating, step welding, and post-treatment to optimize degassing and microstructure formation, allowing for adjustable line energy and connection depths, and enabling the production of high-strength welds with minimized thermal softening of the metal sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If I-welds or fillet welds are used to weld galvanized steel sheets, then the welding process can be performed, but zinc outgassing occurs during welding leading to insufficient seam quality, weld defects, and difficulty in reproducing penetration depth
Solution Approach 1:
The patent applies preliminary action by pre-heating the workpiece before welding to control zinc outgassing. The laser beam is used to locally heat the galvanized steel sheets in advance, allowing controlled evaporation of zinc before the actual welding process begins. This preliminary thermal treatment reduces harmful zinc outgassing during welding and improves seam quality by preventing zinc vapor interference with the weld pool.
2Ease of manufacture
If the weld cross-section is limited by the top sheet thickness, then the welding process is simpler, but filler materials are required to enlarge the joining area and larger flange dimensions are needed
Solution Approach 1:
The patent applies dimensionality change by transitioning from conventional surface welding to end-face welding. Instead of welding along the surface of the sheets, the laser beam welds the end faces of the sheets perpendicular to the sheet plane. This dimensional change allows the weld cross-section to extend through the entire thickness of the sheets, enlarging the joining area without requiring filler materials or larger flange dimensions.
3Device complexity
If the laser spot positioning accuracy is insufficient relative to the lap joint, then the welding process is simpler, but complex weld guidance systems are necessary
Solution Approach 1:
The patent applies self-service by using the laser beam itself to create a visible trace or mark on the workpiece during positioning. The laser beam temporarily marks the intended weld path on the sheet material, allowing operators to visually verify and adjust the positioning accuracy. This self-marking capability eliminates the need for complex external weld guidance systems while ensuring precise laser spot positioning for end-face welding.
4Strength
If the entire end face of the flange is melted to achieve desired weld pool volume, then weld strength is improved, but tight tolerances on flange overhang difference are required and significant tooling expenditure is necessary
Solution Approach 1:
The patent applies local quality by concentrating the laser energy on specific localized areas of the end face rather than melting the entire end face uniformly. The laser beam creates discrete weld points or short weld segments at strategically selected locations on the end face. This localized welding approach achieves sufficient weld strength without requiring tight tolerances on overall flange overhang dimensions, reducing tooling expenditure while maintaining weld quality.
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 ensures reproducible high seam quality, increased connection strength, and reduced material stress, improving crash behavior and allowing for more efficient processing with reduced material usage, while enabling non-destructive verification of weld quality.
Implementation Method 1
end-face welding of sheet metal flanges with the aid of a laser beam
Implementation Method 2
The laser beam is used to locally heat and melt the sheet metal surfaces at the flange end faces
Implementation Method 3
due to the zinc outgassing that occurs during welding
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method with which stitch welds (5) can be produced on the front faces of metal sheets (preferably on flanges) by means of laser welding. To produce the stitch weld seam, the following steps are cyclically repeated: preheating the parts (1, 2) to be joined in an area in front of the stitch weld seam to be produced; producing a short stitch weld section (7) with relatively low resulting welding speed; and producing a section without a stitch weld, whereby an intervening space (9) is formed between neighbouring stitch weld sections (7). The ratio of the lengths (6, 8) of intervening spaces (9) and of stitch weld sections (7) is selected in such a way that de-gasification is achieved to such an extent that a high quality of the stitch weld seam (5) is achieved. The method is particularly suitable for producing welded joints between galvanised, heat-treated steel sheets of the type frequently used in vehicle/body construction.