Hybrid Laser Scanner for Precise Powder Bed Beam Steering
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Solution Overview
Problem
Existing selective laser melting (SLM) and selective laser sintering (SLS) additive manufacturing technologies face challenges in achieving precise control over laser beam scanning, leading to thermal loads that cause warping and curling of parts, particularly due to the limited dynamic response of galvanometers and absorption issues with electro-optic and acousto-optic scanners when using high-power laser beams.
Innovation Solution
A scanner system combining galvanometers with piezoelectric, voice coil, or normal stress actuators to enhance the dynamic response and directionality of the laser beam, allowing for rapid changes in direction and reduced absorption, enabling sharper scanning paths and finer details by 'hopping' the laser beam across the powder bed, while maintaining high power handling capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If galvanometers are used to steer the laser beam, then the system can achieve reasonable scanning capability, but the dynamic response is limited causing divergence from desired scan paths
Solution Approach 1:
The patent combines galvanometers with piezoelectric actuators to create a hybrid scanning system. The galvanometer provides the primary scanning motion while the piezoelectric actuator adds high-speed corrective motion to compensate for the galvanometer's limited dynamic response, thereby achieving both reasonable scanning capability and high scan path accuracy.
Solution Approach 2:
The patent replaces part of the mechanical galvanometer system with a piezoelectric actuator system that offers faster response characteristics. The piezoelectric actuator uses electro-mechanical conversion rather than purely mechanical rotation, enabling rapid adjustments to the laser beam path that compensate for galvanometer lag.
2Speed
If electro-optic or acousto-optic scanners are used, then rapid scanning is achieved, but absorption of high-power laser beams occurs causing heating
Solution Approach 1:
The patent replaces electro-optic or acousto-optic scanners with a mechanical/piezoelectric hybrid scanning system. This substitution eliminates the absorption and heating problems inherent in electro-optic and acousto-optic materials while maintaining fast scanning capability through the piezoelectric actuator's rapid response.
Solution Approach 2:
The patent introduces a piezoelectric actuator as an intermediary device between the laser source and the scanning mirrors. This intermediary provides the fast response needed for rapid scanning without directly absorbing the high-power laser beam, thereby avoiding the heating issues that plague electro-optic and acousto-optic scanners.
3Productivity
If continuous mode laser operation is used, then build time is reduced, but melt pool control is poor leading to less detailed solidification lines
Solution Approach 1:
The patent applies dynamic scanning strategies where the scanning speed and laser power are continuously adjusted during the building process. The system transitions between continuous and pulsed modes, and modifies scan paths in real-time to optimize both build speed and melt pool control for different regions of the part being manufactured.
Solution Approach 2:
The patent employs periodic pulsed laser operation interspersed with continuous scanning. By strategically placing pulsed exposures at critical locations (such as border scans) and using continuous mode for bulk material deposition, the system achieves both high productivity and precise solidification line detail where needed.
4Manufacturing precision
If pulsed mode laser operation is used with traditional scanners, then solidification line accuracy is improved, but build time increases significantly
Solution Approach 1:
The patent applies pulsed laser operation selectively rather than universally - using pulsed mode only where high precision is required (such as border scans and critical features) while employing continuous mode for the majority of the build volume. This partial application of pulsed action maintains solidification line accuracy where needed without sacrificing overall build speed.
Solution Approach 2:
The patent dynamically switches between pulsed and continuous laser modes based on the current scanning location and part geometry. The system uses real-time control to transition between operating modes, applying pulsed operation only when and where it is necessary for accuracy, thereby minimizing the time penalty associated with pulsed mode operation.
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 solution allows for more accurate and efficient scanning strategies, reducing thermal loads and improving part accuracy, while minimizing build time and maintaining high power laser compatibility, thus enhancing the precision and quality of additive manufacturing processes.
Implementation Method 1
The scanner comprises a piezoelectric actuator configured to change the direction of the laser beam in response to an applied voltage
Implementation Method 2
A laser beam is then scanned across areas of the powder layer that correspond to a cross-section of the object being constructed. The laser beam melts or sinters the powder to form a solidified layer.
Data Source
Figure 1
Figure 2
Figure 3a
AI summary
An additive manufacturing apparatus comprising a scanner (110) for directing a laser beam (118) on to layers of flowable material (104) to selectively solidify the material to form an object (103) in a layer-by-layer manner. The scanner comprises an optical component (106a, 106b) operable under the control of a first actuator (121a, 121b) to reflect the laser beam (118) over a first range of angles in a first dimension and the or a further optical component (106c) operable under the control of a second actuator (120a, 120b) to reflect the laser beam (118) over a second range of angles in the first dimension, wherein the second actuator (120a, 120b) provides a faster dynamic response but a smaller range of movement of the laser beam (118) than the first actuator (121a, 121b).