Additive Manufacturing Bridging Layer Shrinkage Control
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Solution Overview
Problem
Powder bed fusion processes, such as selective laser melting and sintering, face significant distortion issues due to shrinkage in bridging areas where separate islands are joined, leading to positional inaccuracies and witness lines.
Innovation Solution
The method involves solidifying separated portions of a bridging layer independently before joining them, allowing for shrinkage, and then connecting them with a joining region located above unsolidified material, with the joining process delayed based on the geometry and material type to minimize distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate islands in a preceding layer are joined together through solidification of a bridging area, then the part is constructed layer-by-layer, but shrinkage of the bridging area distorts the position of islands and creates witness lines
Solution Approach 1:
The bridging area is divided into multiple scan zones (first scan zone and second scan zone) that are solidified in separate passes. The first scan zone solidifies material connecting to one island, while the second scan zone solidifies material connecting to another island. This segmentation allows each zone to shrink independently, reducing overall distortion and preventing witness lines from forming across the entire bridging area.
Solution Approach 2:
The first scan zone is solidified before the second scan zone, establishing a sequential construction approach. By completing the first connection and allowing partial cooling/shrinkage before initiating the second connection, the process accommodates thermal contraction more effectively, reducing distortion of subsequent island positions.
2Productivity
If the laser is maintained on continuously while mirrors move to direct the laser spot along the scan path, then the scanning process is efficient, but thermal loads generated during the build increase
Solution Approach 1:
The laser operation is structured in periodic cycles corresponding to alternating scan zones. The laser is activated for the first scan zone, then deactivated while mirrors reposition for the second scan zone. This periodic on-off pattern reduces cumulative thermal loads compared to continuous laser operation, while maintaining scanning efficiency through optimized mirror movement during laser off-periods.
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 effectively reduces distortion and witness lines by allowing independent shrinkage of separated portions before joining, resulting in more accurate and stable layer formation in additive manufacturing.
Implementation Method 1
A high energy beam is then scanned across areas of the powder layer that correspond to a cross-section of the object being constructed. The high energy beam melts or sinters the powder to form a solidified layer.
Implementation Method 2
Powder bed fusion apparatus produce objects through layer-by-layer solidification of a material, such as a metal powder material, using a high energy beam, such as an electron or laser beam.
Implementation Method 3
In this way, the separated portions are allowed to independently shrink, such as during cooling, before the separated regions are joined together. In this way, distortion of the islands and/or solidified material between the separated portions (a joining region), and consequential witness lines, are avoided.
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
This invention concerns a method of building a workpiece in an additive manufacturing process, in which the workpiece is built through layer-by-layer solidification of material. The method comprises, for a bridging layer (301c) in which an area to be solidified bridges material solidified as separate islands (300c, 300d) in an immediately preceding layer(301b), first, solidifying separated portions (303a, 303b) of the area, each separated portion (303a. 303b) connected with a different one of the islands (300c, 300d) of the preceding layer, and then solidifying material (304) between the separated portions (303a, 303b) to join the separated portions (303a, 303b) together.