Laser Keyhole Welding with Dual-Beam Control for Crack-Free Termination
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Solution Overview
Problem
High-strength metals and metal alloys are prone to cracking at the termination of a laser weld, which can lead to catastrophic failure due to residual stress and thermal or mechanical stress, and existing solutions are insufficient for these materials.
Innovation Solution
A method involving a focused laser beam with a concentric annular beam is used, where the annular beam is ramped down to zero power and the center beam is ramped up and then down in a controlled manner to reduce the melt zone and keyhole dimensions, minimizing residual stress and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rapid power ramp down or beam lift is used at weld termination, then termination defects are reduced for many materials, but high-strength alloys and metals with high thermal conductivity remain prone to cracking
Solution Approach 1:
The laser beam is segmented into a center beam and an annular beam that can be independently controlled. The annular beam is ramped down first while the center beam is ramped up, creating a staged power reduction process that prevents cracking in difficult-to-weld materials while maintaining compatibility with other materials.
Solution Approach 2:
The patent changes the power parameters of the center and annular beams in a specific sequence and ratio. The annular beam power is reduced while the center beam power is increased, with the ratio of center to annular beam power being controlled to prevent cracking. This dynamic parameter adjustment resolves the contradiction between reliability and material adaptability.
2Strength
If keyhole welding is used to achieve narrow and deep weld profiles, then weld strength is improved, but stable keyhole maintenance in hot dynamic melt pools becomes difficult
Solution Approach 1:
The laser beam is divided into center and annular components that can be independently controlled. The annular beam maintains the keyhole while the center beam fills the melt pool, separating the keyhole maintenance function from the melting function to improve both strength and operational ease.
Solution Approach 2:
Different regions of the beam profile serve different functions: the annular beam region maintains the keyhole channel while the center beam region provides intensive heating for melting. This local differentiation of beam function achieves stable keyhole welding with improved ease of operation.
3Productivity
If conventional single beam laser welding is used to maintain weld speed and precision, then productivity is maintained, but cracking occurs at weld termination due to residual stress
Solution Approach 1:
The laser beam is segmented into center and annular components with independent power control. This allows the annular beam to be ramped down first to reduce residual stress, while the center beam continues to provide heating, maintaining weld speed and precision while preventing termination cracking.
Solution Approach 2:
The annular beam is ramped down before the center beam during weld termination. This preliminary action reduces the overall power and residual stress in the melt pool before the final power reduction, preventing cracking while maintaining productivity.
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
The method effectively prevents cracking and defects at the weld termination by controlling the cooling rate and annealing the solidified material, maintaining the advantages of weld speed, precision, and cost of contemporary laser welding.
Implementation Method 1
Conduction welding occurs at lower laser powers and lower power densities. Absorbed laser power heats the irradiated material, melting material in each part to be joined, which flows, mixes, and then solidifies.
Implementation Method 2
Keyhole welding occurs at higher laser powers and higher power densities that are sufficient to vaporize some of the irradiated material. Pressure of the vaporized material on surrounding melted material opens a channel through the melted material
Implementation Method 3
In laser welding, a focused laser beam locates each weld spot or seam precisely, while minimizing collateral heating.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
A method for laser keyhole welding of metal alloys is disclosed. 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 in the center beam is initially ramped up and then ramped down, while the power in the annular beam is ramped down. Increasing the power in the center beam enables a controlled and prolonged contraction of the keyhole and melt pool, thereby preventing undesirable cracking.