Diode Laser Fiber Array Solidification Control for Single-Crystal LPBF
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Solution Overview
Problem
Rapid cooling rates in Direct Metal Laser Melting (DMLM) systems lead to cracking of certain alloys and difficulties in achieving desirable grain morphology during additive manufacturing, particularly in forming complex geometries like airfoils for gas turbine engines.
Innovation Solution
A diode laser fiber array is used to emit multiple laser beams onto a powder bed, controlling temperature gradients and solidification velocities to form columnar or single crystal microstructures, allowing for simultaneous melting and precise control of cooling rates to prevent cracking and achieve desired grain structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single high-power laser beam is used to scan the powder bed layer by layer, then the additive manufacturing process can be implemented, but the processing time becomes excessively long (70-100 seconds per layer, days for complete builds)
Solution Approach 1:
The patent divides a single high-power laser beam into multiple lower-power laser beams using a beam splitter or diffractive optical element. These multiple beams are then distributed to scan different regions of the powder bed simultaneously, enabling parallel processing of multiple layers or regions within a layer, thereby significantly reducing total processing time while using commercially available laser sources
Solution Approach 2:
The patent combines multiple lower-power laser beams into a coordinated scanning system that processes multiple areas simultaneously. By merging the functionality of multiple laser sources into a single integrated system controlled by one computer, the patent achieves parallel processing capability without proportionally increasing system complexity or control difficulty
2Productivity
If rapid cooling is used during laser melting, then processing efficiency is improved, but cracking occurs in certain alloys and desirable grain morphology cannot be achieved
Solution Approach 1:
The patent applies different cooling rates to different regions of the melt pool by controlling the scanning pattern and laser parameters locally. Certain regions are cooled rapidly for high productivity, while other regions are cooled more slowly to prevent cracking and achieve desirable grain morphology. This spatial variation in cooling quality allows simultaneous optimization of both productivity and reliability
Solution Approach 2:
The patent uses periodic scanning patterns where the laser beam alternates between rapid scanning (for efficiency) and slower scanning (for quality control). This periodic variation in scanning speed allows the melt pool to experience alternating phases of rapid cooling and controlled cooling, preventing thermal stress accumulation that leads to cracking while maintaining overall high 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
This approach significantly reduces processing time, prevents cracking, and enables the formation of complex geometries with controlled grain structures, improving mechanical properties and reducing post-processing requirements.
Implementation Method 1
A diode laser fiber array is used to emit multiple laser beams onto a powder bed
Implementation Method 2
emitting a plurality of laser beams from selected fibers of a diode laser fiber array corresponding to a pattern of a layer of the article onto a powder bed of the superalloy to form a melt pool
Implementation Method 3
controlling a temperature gradient and a solidification velocity of the melt pool to form the columnar or single crystal microstructure
Implementation Method 4
controlling a temperature gradient and a solidification velocity of the melt pool to form the columnar or single crystal microstructure
Data Source
AI summary
A method of method of forming or repairing a superalloy article having a columnar or equiaxed or directionally solidified or amorphous or single crystal microstructure includes emitting a plurality of laser beams from selected fibers of a diode laser fiber array corresponding to a pattern of a layer of the article onto a powder bed of the superalloy to form a melt pool; and controlling a temperature gradient and a solidification velocity of the melt pool to form the columnar or single crystal microstructure.