Two-Pass Laser Welding for Deep Penetration and Smooth Weld Beads
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Solution Overview
Problem
Current laser welding methods fail to achieve large depth of penetration with minimal surface evaporation and surface smoothness, often resulting in limited weld depth and rough surfaces due to high heat affected zones and distortion.
Innovation Solution
A two-pass laser welding method using a high energy, long pulse Nd:YAG laser beam in the first pass with controlled pulse duration and power density below the evaporation threshold, followed by a second pass with a laser beam inclined at 20°-45° from the normal to achieve full depth penetration and surface smoothness, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If high energy and long duration pulses are used to achieve large depth of penetration, then weld depth is improved, but surface evaporation increases
Solution Approach 1:
The patent applies periodic pulsed laser action with specific duty cycles to control the welding process. By using pulses rather than continuous laser beam, the method achieves deep penetration during the pulse duration while allowing cooling intervals that prevent excessive surface evaporation and keyhole formation
Solution Approach 2:
The patent changes key laser parameters including pulse duration, peak power density, and duty cycle to optimize the welding process. By controlling peak power density to be below the evaporation threshold and adjusting pulse duration, the method achieves deep penetration without surface evaporation
2Length of moving object
If peak power density is increased to achieve deep penetration, then weld depth is improved, but surface smoothness deteriorates
Solution Approach 1:
The patent uses periodic pulsed laser action where the laser is activated only during specific intervals. This periodic operation allows deep penetration during pulse duration while maintaining surface smoothness by preventing continuous high-power exposure that would cause evaporation and surface roughening
Solution Approach 2:
The patent optimizes parameter combinations including pulse duration, peak power density, and duty cycle. By controlling peak power density below evaporation threshold and using appropriate pulse durations, the method achieves both deep penetration and surface smoothness
3Length of moving object
If continuous wave laser is used to sustain keyhole, then weld depth is improved, but heat affected zone increases
Solution Approach 1:
The patent replaces continuous wave laser with periodic pulsed laser operation. This allows the laser to deliver energy in controlled intervals, achieving deep penetration during pulses while reducing overall heat input and minimizing the heat affected zone through cooling intervals between pulses
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 allows for deep penetration welding with minimal surface evaporation and heat affected zones, achieving surface smoothness of 5 μm while maintaining low distortion and shrinkage, suitable for various metals and joint types.
Implementation Method 1
delivering a high energy and long pulse solid state Nd: YAG laser beam in first pass on material to be welded
Implementation Method 2
peak power density below the peak power density required for evaporation of a surface to be welded
Implementation Method 3
the laser beam may cause a portion of metal in the interface to volatilize to produce a keyhole bounded by molten metal
Implementation Method 4
peak power density becomes high enough to ablate surface of the welded material
Implementation Method 5
delivering a Nd: YAG laser beam in second pass with welding nozzle inclined at an angle from normal of weld bead... achieving a good surface smoothness in second pass
Data Source
AI summary
An improved laser welding method of materials by means of long pulse and high energy pulses of solid state lasers in such a manner that large depth of penetration with full depth or partial depth of penetration can be achieved with minimum surface evaporation in first pass of laser beam and enhanced surface smoothness having average surface smoothness of 5 mm by second pass of laser beam of lower power density and inclined at a particular inclination.