Laser Welding Galvanized Steel Sheets Zigzag Pattern
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Solution Overview
Problem
Laser welding of galvanized steel sheets with an improper gap between them leads to the formation of explosive pores, pin holes, and breakage at the welding portion due to zinc vapor generation, resulting in interfacial fractures during tensile tests.
Innovation Solution
A method of laser welding that involves a stitch welding step followed by a pattern welding step, where a laser beam is irradiated along the welding portion with a zigzag pattern to form a molten pool, ensuring a sufficient gap for zinc vapor discharge and preventing pin holes and burn-through by securing sufficient molten width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a predetermined gap is maintained between galvanized steel sheets for zinc vapor discharge, then explosive pores are prevented, but welding complexity increases due to requiring precise gap control
Solution Approach 1:
The welding process is divided into two distinct steps: stitch welding to form a molten slot, and pattern welding to form the final molten pool. This segmentation allows each step to address specific requirements - the stitch welding creates a controlled molten slot that facilitates zinc vapor discharge, while the pattern welding completes the weld with proper penetration, thereby maintaining welding quality without requiring precise gap control throughout the entire process
Solution Approach 2:
The stitch welding step is performed as a preliminary action before the main pattern welding. This preliminary action creates the molten slot that serves as a pathway for zinc vapor discharge during the subsequent pattern welding, preventing explosive pores formation in advance and enabling the main welding process to proceed without strict gap control requirements
2Productivity
If laser beam is focused to a small focal region for keyhole welding, then welding speed increases, but pin holes and burn-through occur when gap is large
Solution Approach 1:
The welding process is divided into two distinct steps: stitch welding to form a molten slot, and pattern welding to form the final molten pool. This segmentation allows each step to address specific requirements - the stitch welding creates a controlled molten slot that facilitates zinc vapor discharge, while the pattern welding completes the weld with proper penetration, thereby maintaining welding quality without requiring precise gap control throughout the entire process
Solution Approach 2:
The stitch welding step performs a partial welding action that creates a molten slot without completing the full weld. This partial action prepares the welding zone by creating a pathway for vapor discharge and pre-heating the material, allowing the subsequent pattern welding to proceed with higher energy density without causing burn-through or pin holes even when gaps are present
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 effectively prevents pin holes and burn-through, securing sufficient molten width and improving welding quality, even with large gaps between steel sheets, thereby enhancing tensile and shear strength and maintaining the integrity of the welding portion.
Implementation Method 1
a laser beam is irradiated along the welding portion with a zigzag pattern to form a molten pool
Implementation Method 2
an heat expansion portion is formed at the lower steel sheet along the welding portion by thermal conduction
Implementation Method 3
explosive pores are formed at the welding portion W due to zinc gas generated by evaporation of zinc layer 13
Data Source
AI summary
A method of laser welding where two steel sheets are welded by a laser beam after the two steel sheets are overlapped with a predetermined gap is disclosed.The method includes: a stitch welding step where a laser beam of focal region is irradiated along a welding portion of the upper steel sheet and the lower steel sheet such that a molten slot is formed at the upper steel sheet along the welding portion and an heat expansion portion is formed at the lower steel sheet along the welding portion by thermal conduction; and a pattern welding step where the laser beam of focal region is irradiated along the welding portion with a predetermined pattern such that an edge of the molten slot formed at the upper steel sheet is melted together with the heat expansion portion of the lower steel sheet so as to form a molten pool.