Laser Keyhole Welding with Dual-Beam Control for End Cracking
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Solution Overview
Problem
High-strength metal alloys with high thermal conductivity are prone to cracking at the termination of laser welds, leading to defects and potential catastrophic failure, as existing methods fail to maintain uniform weld cross-sections and are insufficient in preventing cracking.
Innovation Solution
A method involving a focused center beam and a concentric focused annular beam is used for laser welding, where the power of the annular beam is gradually reduced and then maintained, while the center beam power is increased and gradually ramped down, with specific ramp rates to prevent cracking and maintain uniformity, and additional energy is delivered through the keyhole to balance temperatures and control solidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the focused laser beam power is reduced or beam is lifted at weld termination, then cracking is prevented, but weld cross-section uniformity deteriorates
Solution Approach 1:
The laser beam is segmented into two distinct components: a center beam and an annular beam. The center beam maintains a focused spot to preserve weld depth and uniformity, while the annular beam provides broader heating to prevent cracking. This segmentation allows independent control of each beam's power and characteristics to simultaneously achieve uniform weld geometry and prevent termination cracking.
Solution Approach 2:
Different regions of the weld pool receive different heating characteristics: the center beam delivers concentrated energy to maintain keyhole stability and weld penetration, while the annular beam delivers distributed energy to the weld pool edges and heat-affected zone to reduce thermal gradients and prevent cracking. This local quality differentiation resolves the contradiction between maintaining uniformity and preventing cracks.
2Reliability
If a compound laser beam with center and annular beams is used, then crack prevention improves, but device complexity increases
Solution Approach 1:
The annular beam is nested within the center beam, with both beams sharing the same optical path and focusing system. The annular beam's outer diameter is larger than the center beam's diameter, creating a concentric configuration. This nesting allows both beam types to be delivered through a single optical fiber and focused by a single lens, reducing system complexity compared to using separate optical paths.
Solution Approach 2:
The compound laser beam system performs multiple functions simultaneously: the center beam maintains keyhole welding and penetration, while the annular beam prevents cracking and controls heat distribution. This multi-functionality is achieved within a single laser source and optical delivery system, avoiding the need for multiple separate laser systems or complex beam switching mechanisms.
3Stability of the object's composition
If the focused beam moves laterally during power changes, then transition is smooth, but weld width uniformity deteriorates
Solution Approach 1:
The lateral movement of the focused beam is stopped in advance before power changes are initiated. By halting the beam movement prior to adjusting the power levels of the center and annular beams, the system ensures that the weld pool receives consistent energy distribution throughout the power transition, preventing variations in weld width and maintaining geometric uniformity.
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 cracking and maintains a uniform weld cross-section, reducing the risk of defects and ensuring a strong, symmetrical weld without compromising weld speed, precision, or cost, by controlling the power and movement of the laser beams to manage stress and solidification.
Implementation Method 1
a focused beam of laser radiation
Implementation Method 2
Absorbed laser power heats the irradiated material
Implementation Method 3
a focused beam of laser radiation
Implementation Method 4
power densities that are sufficient to vaporize some of the irradiated material
Implementation Method 5
Pressure of the vaporized material on surrounding melted material opens a channel
Implementation Method 6
a focused beam of laser radiation
Implementation Method 7
Absorbed laser power heats the irradiated material, melting material in each part to be joined
Implementation Method 8
a focused beam of laser radiation
Data Source
AI summary
A method for laser keyhole welding is disclosed to weld two pieces together made of a metal alloy. The method independently adjusts power in a focused center beam and power in a concentric focused annular beam. At the termination of a weld, the power of the annular beam is reduced, motion of the focused beams is stopped, the power of the center beam is increased, and the power of both beams is initially ramped down rapidly and then ramped down slowly. Increasing the power of the center beam equalizes the temperature of both pieces prior to solidification and cooling at the termination of the weld. An additional pulse of power may be applied to prevent the formation of defects or to erase any defects.