Micro Weld Pattern Laser Welding for Bright Dissimilar Metals
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Solution Overview
Problem
Laser welding of bright metals like gold, copper, and silver is challenging due to high reflectivity, leading to unreliable joints with high power densities causing over-penetration and weak welds, while lower power densities result in overheating and weak welds, and existing methods are inefficient and complex, especially when welding dissimilar metals.
Innovation Solution
A method using nanosecond fibre lasers emitting in the 1µm wavelength window with pulse energies of around 1mJ to create microwelds with specific spot sizes and pulse fluences, allowing for controlled welding patterns that inhibit intermetallic formation and enhance strength and reliability by flowing one material into a hole in the other without substantial mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high power densities are used to overcome surface reflectivity, then laser coupling into metal surface is initiated, but over penetration occurs resulting in unreliable joints
Solution Approach 1:
The patent employs pulsed laser welding instead of continuous wave welding, using periodic laser pulses with controlled duration and repetition rates. This allows the material to cool between pulses, preventing excessive heat accumulation and over-penetration while still achieving sufficient coupling during the pulse peaks. The pulsed regime enables precise control of energy input to match the narrow absorption window of bright metals.
Solution Approach 2:
The patent dynamically adjusts laser parameters including pulse duration, repetition rate, and peak power during the welding process. By making these parameters variable rather than fixed, the system can adapt to changing material conditions and maintain optimal coupling without exceeding the penetration threshold, thereby resolving the contradiction between initiating welding and preventing over-penetration.
2Manufacturing precision
If lower power densities are used to avoid over penetration, then thermal heat sinking causes overheating of surrounding regions resulting in weak welds
Solution Approach 1:
The pulsed laser regime delivers concentrated energy in short time intervals, creating localized melting and welding zones before heat can diffuse to surrounding areas. The periodic nature of the pulses allows controlled heat accumulation in the weld zone while preventing excessive heat sinking into bulk material, thereby maintaining weld strength without causing overheating of surrounding regions.
Solution Approach 2:
The patent utilizes phase transitions of metal materials during the pulsed laser welding process. The rapid heating during pulses causes localized melting and phase changes that facilitate welding, while the brief pulse duration prevents extensive heat diffusion. This controlled phase transition approach enables strong welds without excessive thermal affect on surrounding material.
3Ease of manufacture
If continuous wave or millisecond pulsed lasers are used, then welding process is simple, but intermetallics form at the weld interface resulting in brittle welds
Solution Approach 1:
By using nanosecond pulsed lasers with high repetition rates, the patent creates a welding process that is both simple to implement and effective at preventing intermetallic formation. The extremely short pulse duration combined with high repetition creates rapid heating and cooling cycles that limit the time available for intermetallic compound formation at the dissimilar metal interface, producing ductile welds without complicating the manufacturing process.
Solution Approach 2:
The patent changes the temporal parameters of laser delivery from continuous or millisecond-scale pulses to nanosecond-scale pulses at high repetition rates. This parameter change fundamentally alters the thermal history of the weld zone, creating conditions that suppress intermetallic formation while maintaining process simplicity. The transformed parameters enable welding of dissimilar metals without the brittleness problems associated with conventional approaches.
4Productivity
If green wavelength lasers (532nm) are used to reduce reflectivity, then welding efficiency increases, but system complexity and cost increase due to frequency doubling requirements
Solution Approach 1:
The patent changes the wavelength parameter from green (532nm) to near-infrared (1064nm or 1030nm), operating at the fundamental frequency of the laser medium rather than requiring frequency doubling. This parameter change maintains adequate welding efficiency for many applications while dramatically simplifying the laser system architecture and reducing costs by eliminating frequency doubling optics and associated control systems.
Solution Approach 2:
Instead of using frequency-doubled green lasers to overcome reflectivity issues, the patent inverts the approach by using fundamental wavelength near-infrared lasers with nanosecond pulsed operation. This inversion of the conventional wavelength choice, combined with pulsed delivery, provides a simpler system that achieves effective welding of bright metals without the complexity of frequency conversion equipment.
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 produces strong, reliable welds with reduced ohmic resistance and increased peel strength, suitable for applications in electronics and electrical engineering, such as batteries and solar cells, with consistent and predictive results across various alloys and metals.
Implementation Method 1
the surface reflectivity is overcome by sufficient laser intensity, a melt of the surface is initiated
Implementation Method 2
The function of the laser beam on a bright material approximates a discreet function with a very narrow operating window from beam hold-off (reflection) and absorption
Implementation Method 3
a key hole is formed in the workpiece, and the key hole is oscillated in a circular motion when forming the weld
Data Source
Figure 1~3
Figure 4~9
Figure 10~14
AI summary
A weld (3) between a first material (1) and a second material (2), the first material (1) being a first metallic material, and the second material (2) being a second metallic material, the weld (3) has a width (4) between 0.5mm and 7mm, the weld (3) comprises at least one microweld (8), the microweld (8) forms a welding pattern (5) defined parallel to a surface (6) of the first material (1), and the microweld (8) has a characteristic feature size (7) of between 20μm and 400um.