Laser Welding of Coated Sheets Without Spatter or Porosity
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Solution Overview
Problem
Laser welding coated workpieces, such as zinc-coated steel sheets, often results in defects like spatter and porosity due to the sudden evaporation of coating materials at high temperatures, which can distort the weld seam and reduce quality.
Innovation Solution
A method involving two laser beams is used, where the first beam melts the upper workpiece partially while leaving a web of non-melted material, and the second beam welds the workpieces together, minimizing coating material introduction into the melt pool by evaporating it laterally and avoiding vapor capillary distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the workpieces are positioned one on top of the other for laser welding, then the welding speed can be increased and the process simplified, but coating material evaporates into the melt pool causing spatter and porosity defects
Solution Approach 1:
The patent divides the laser welding process into two separate method steps: a first method step for coating evaporation and a second method step for welding. This segmentation allows each step to be optimized independently, preventing coating material from contaminating the melt pool while maintaining high welding speeds
Solution Approach 2:
The first method step performs preliminary action by evaporating the coating material before the actual welding process. This preliminary coating removal creates a clean surface for welding in the second step, preventing spatter and porosity defects
2Device complexity
If the same laser beam is used for both coating evaporation and welding at different speeds, then the process complexity is reduced, but the total processing time increases significantly
Solution Approach 1:
The patent employs two laser beams that can each perform multiple functions. The first laser beam can evaporate coating and potentially weld, while the second laser beam can weld through the depleted coating region. This multi-functionality allows flexible process optimization without requiring additional specialized equipment
Solution Approach 2:
The two laser beams operate in a continuous sequence without interruption between coating evaporation and welding. The first laser beam evaporates the coating and the second laser beam immediately follows to weld, eliminating idle time and maintaining continuous productive action throughout the process
3Manufacturing precision
If the workpieces are positioned spaced apart to avoid coating evaporation into the weld, then spatter and porosity are reduced, but complex positioning preparation is required and surface indentations occur
Solution Approach 1:
The patent extracts the harmful coating material from the welding zone by evaporating it in the first method step before welding occurs. This removal of the problematic coating layer eliminates the source of spatter and porosity defects without requiring the workpieces to be positioned apart or requiring complex positioning preparations
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 achieves a high-quality weld seam with reduced defects and allows for faster processing by enabling higher advancement speeds and avoiding spatter formation, ensuring a strong and reliable connection between the workpieces.
Implementation Method 1
the coating of the workpieces on their facing sides at least partially evaporating along a depletion trace
Implementation Method 2
the first laser beam melts the material of the upper workpiece, so that a web of non-melted material of the upper workpiece remaining
Implementation Method 3
the material of the two workpieces being melted within the depletion trace, as a result of which the workpieces are welded to one another
Data Source
AI summary
A method for laser welding two coated workpieces includes positioning an upper workpiece and a lower workpiece on top of each other and passing a first laser beam over the upper and lower workpieces from a side of the upper workpiece so as to at least partially evaporate the respective coating of each of the workpieces on their facing sides along a depletion trace. A second laser beam is passed over the workpieces from the side of the upper workpiece so as to melt a material of the two workpieces within the depletion trace, and thereby weld the workpieces to one another. In the first laser passing, the first laser beam melts the material of the upper workpiece, so that a web of non-melted material of the upper workpiece remaining between the melted material of the upper workpiece and the facing side of the upper workpiece.