Overlap Laser Welding Bright Metals Nanosecond Pulses
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Solution Overview
Problem
Laser welding of bright metals and dissimilar metals faces challenges due to high reflectivity, leading to inconsistent welds, over-penetration, and the formation of brittle intermetallic compounds, which are prone to fracture.
Innovation Solution
A method using nanosecond pulsed lasers with controlled pulse widths and fluence to create overlapping melt pools and heat stakes in metals, ensuring distinct and separate distal ends, avoiding intermetallic formation and heat-affected zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high power density laser beams are used to overcome surface reflectivity of bright metals, then laser energy coupling into the metal surface is initiated, but the melt pool grows extremely rapidly and becomes difficult to control, leading to over penetration and unreliable joints
Solution Approach 1:
The patent employs periodic pulsed laser action instead of continuous wave laser. The laser delivers energy in controlled pulses with specific duty cycles, allowing the metal surface to absorb energy incrementally while preventing excessive heat accumulation. This periodic energy delivery enables consistent coupling through reflective surfaces while maintaining control over melt pool formation and preventing over-penetration, thereby improving joint reliability.
Solution Approach 2:
The patent dynamically adjusts laser parameters including pulse width, power density, and scanning speed during the welding process. By making these parameters variable rather than fixed, the system can adapt to changing surface conditions and thermal states, maintaining optimal energy coupling while preventing runaway melt pool growth and ensuring consistent weld quality.
2Reliability
If lower power density is used to avoid over penetration, then over penetration is reduced, but welds become weak or absent due to inconsistent and random coupling of laser beam to metal surface
Solution Approach 1:
The patent systematically optimizes multiple laser parameters simultaneously including pulse width (50-500 ns), power density (10^6-10^8 W/cm²), scanning speed (1-100 mm/s), and pulse frequency (1-100 kHz). By changing these parameters in coordinated combinations rather than adjusting single parameters in isolation, the process achieves both consistent energy coupling through reflective surfaces and sufficient heat input for strong welds, eliminating the trade-off between consistency and strength.
Solution Approach 2:
The patent creates a composite thermal field by combining multiple laser pulses with overlapping heat zones. The cumulative thermal effect from sequentially positioned pulses builds up sufficient heat for strong welds while each individual pulse remains at lower power density to ensure consistent coupling. This composite approach to heat delivery achieves both reliability and strength.
3Ease of manufacture
If conventional laser welding is used on dissimilar metals, then joining is achieved, but intermetallic compounds form at the interface which are brittle and prone to fracture
Solution Approach 1:
The patent uses short pulse widths (50-500 ns) to deliver energy so rapidly that the laser beam skips through or passes through the dissimilar metal interface before significant intermetallic compound formation can occur. This rushed heating process creates welds without allowing the diffusion processes that form brittle intermetallics, thereby maintaining joint fracture resistance while achieving joining capability.
Solution Approach 2:
The patent segments the welding process into discrete pulses rather than continuous heating. This segmentation allows control over the thermal history at the dissimilar metal interface, preventing the prolonged thermal exposure needed for intermetallic formation while still achieving adequate bonding through cumulative heat input from multiple 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
Produces robust, repeatable welds with improved mechanical properties and reduced weaknesses, suitable for bright and dissimilar metals, without intermetallics and heat-affected zones.
Implementation Method 1
providing a laser arranged to emit a laser beam in the form of laser pulses that have pulse widths in the range 1ns to 1000ns
Implementation Method 2
focusing the laser pulses that have the pulse widths in the range 1ns to 1000ns with a spot size and a pulse fluence that cause the formation of a plurality of melt pools
Implementation Method 3
focusing the laser pulses that have the pulse widths in the range 1ns to 1000ns with a spot size and a pulse fluence that cause the formation of a plurality of melt pools in the first metal part
Data Source
Figure 1~4
Figure 5~9
Figure 10~12
AI summary
Apparatus for laser welding a first metal part (1) to a second metal part (2), which apparatus comprises: a laser (3) which emits a laser beam (6) in the form of laser pulses (21), a scanner (4) for moving the laser beam (6) with respect to a metal surface (7) of the first metal part (1), an objective lens (5) which focuses the laser beam (6) onto the metal surface (7), and a controller (12) which controls the scanner (4) such that it moves the laser beam (6) with respect to the metal surface (7) to a plurality of focussed spots (16), characterised in that the apparatus focuses the laser pulses (21) with a spot size (34) and a pulse fluence (36) that causes the formation of a plurality of melt pools (19) in the first metal part (1) and heat stakes (17) in the second metal part (2), each heat stake (17) extends from a different one of the melt pools (19) and has a distal end (101), and the controller (12) spaces the focussed spots (16) apart by a distance (18) that is small enough to cause the melt pools (19) to overlap and that is large enough to ensure the distal ends (101) of the heat stakes (17) are distinct and separate from each other in at least one direction (108).