Coaxial Dual-Laser Melt Pool Cooling Control in Powder Bed DMLM
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Solution Overview
Problem
Direct Metal Laser Melting (DMLM) processes face challenges in controlling cooling rates of melt pools, leading to internal part stress and cracking, particularly in nickel base superalloys used in airfoils, due to high temperature gradients and fast cooling rates, which are difficult to manage with conventional two-laser configurations.
Innovation Solution
A method involving a first laser beam to form a melt pool and a second coaxially aligned laser beam that is laterally offset to control the cooling rate, using a reflector and beam combiner to direct and tilt the second laser beam, creating a controlled thermal zone that heats without melting, thereby reducing cooling rates and stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high-power laser is used to rapidly melt and fuse metal powder layers, then manufacturing productivity and build speed are improved, but extremely high temperature gradients and fast cooling rates occur leading to internal part stress and cracking
Solution Approach 1:
A second laser is positioned to preheat the powder bed and build platform in the region ahead of the primary laser melt pool. This preliminary heating action reduces the thermal gradient when the primary laser rapidly melts and solidifies the metal powder, preventing stress accumulation and cracking while maintaining high build speeds
Solution Approach 2:
The second laser acts as an intermediary thermal management tool between the primary laser and the material. It creates a controlled thermal field that mediates the extreme temperature changes caused by the primary laser, reducing thermal stress and preventing defects without interfering with the primary melting process
2Reliability
If a second laser is used in proximity to the melt pool to alter the cooling rate, then part integrity is improved, but device complexity and system cost increase due to requiring two independent sets of optics and scanners
Solution Approach 1:
The patent combines the functions of two separate lasers into a single integrated optical system. Both the primary laser for melting and the second laser for thermal control are directed through a shared scanner and optics assembly, eliminating the need for two independent optical systems and their coordination complexities
Solution Approach 2:
The single optical system is designed to perform multiple functions: it directs the primary laser for rapid melting, positions the second laser for preheating and thermal gradient control, and can potentially switch between different operational modes. This multi-functional approach reduces system complexity while maintaining the benefits of dual-laser processing
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 controlled cooling rates, reducing part stress and cracking, enabling crack-free fabrication of complex geometries like airfoils with reduced system costs and improved mechanical properties by dynamically altering the cooling pattern around the melt pool.
Implementation Method 1
a first laser beam to form a melt pool
Implementation Method 2
the second laser beam heats but does not melt powder within the focus spot
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A method of controlling the cooling rate of a melt pool of a powder bed includes directing a first laser beam (5) on the powder bed to form a melt pool; coaxially aligning a second laser beam (7) with the first laser beam (5), and laterally offsetting a focus spot of the second laser beam (7) with respect to the melt pool, wherein the second laser beam (7) heats but does not melt powder within the focus spot.