3D Printing Tips: Powder Behavior and More
Selective Laser Sintering (SLS) is a popular additive manufacturing technique employed for the rapid development of prototypes and the production of functional components in small quantities. This method involves the use of a laser beam to selectively fuse powdered material, effectively binding it together to create a cohesive and solid structure.
The process involves using a laser to selectively fuse specific regions of a powder bed, following the cross-sections generated from a 3D digital model of the required part. After each cross-section is scanned, a new layer of material is added on top, and this sequence continues until the part is complete.
To create these powder layers with precision, it's essential to use a feedstock that can be uniformly distributed by the delivery system and consistently deposited onto the fabrication bed, avoiding any clumps or gaps.
Intermittent flow or the presence of clumps within the bulk material can lead to irregular deposition, negatively affecting the efficiency of the process and the quality of the final product.
Identifying the specific powder characteristics that promote the formation of uniform and repeatable layers allows for optimizing new formulations and finding suitable raw materials. This can be done without incurring the significant financial and time costs associated with compatibility assessments.
This approach also reduces the likelihood of final products not meeting the required specifications.
The Impact of Various Additives
Three Polyoxymethylene (POM) samples were employed in an SLS machine, with two of them incorporating different additives: a pigment and a lubricant. The three formulations displayed unique flow patterns as they were fed from the storage hopper into the machine. This led to differences in the properties and overall quality of the final product.
Despite the application of several traditional characterization methods, they proved incapable of discerning disparities among the samples. Subsequently, an FT4 Powder Rheometer was utilized to assess the three formulations. This advanced testing equipment unveiled evident and consistent distinctions between them, providing valuable insights into their in-process performance.
Dynamic Testing: Fundamental Flow Energy The sample containing the flow additive exhibited a notably higher Basic Flowability Energy (BFE) in comparison to the remaining two samples. This higher BFE signifies that it necessitated greater energy for propelling the FT4 blade through the powder bed.
In this context, a heightened BFE points to a more effective arrangement of particles within the bulk material, indicating that the inclusion of the flow-enhancing additive has led to an improved flowability of the material.
Shear Cell Testing
Minimal variation was noted in the measured Shear Stress values among the samples, suggesting that the Shear Cell testing method may not be the most suitable approach for assessing flow properties in the context of low-stress, dynamic processes commonly found in SLS (Selective Laser Sintering) applications.
The FT4 is a tool that helps us measure and understand how different powders behave. It tells us if they work well in certain situations or not. We found that using only one test, like Shear Cell testing, may not give us all the information we need about how the powder behaves.
Powder flowability is about how well a powder can move the way we want it to in machines. To make things work properly, we need the right match between the powder and the process. Sometimes, a powder can work great in one situation but not in another.
So, we need to use different tests to understand how powders behave, and then we can use this information to figure out how they'll perform in different processes.
Instead of relying on just one test result to understand how a powder behaves in all situations, the FT4 uses many tests to see how the powder responds to different processes and conditions.