This article describes the density parts fabricated on the Studio System. A pdf of this article is available for download.
Four factors impact the density of Studio System parts:
1) Infill line spacing
2) Shell thickness
3) Toolpath-based macroporosity
4) MIM-based microporosity
This article will:
- Explain the concepts of infill, shell thickness, toolpath based macroporosity, and MIM-based microporosity
- Describe the impact of each factor on part density
As an extrusion-based process, BMD enables the fabrication of parts with closed-cell infill—a fully-enclosed, internal lattice structure is printed within the part. With the exception of very small geometries, all Studio System parts are printed with closed-cell infill. Printing with infill reduces fabrication time and material usage, both of which reduce the cost of the part. Infill also reduces the weight of a part while maintaining the design-intent of the part surfaces.
Impact of infill on density
The overall density of a part will correspond to the density of the printed infill— 45% dense at default print settings. In Fabricate, users can adjust the distance between lines of infill in order to increase or decrease part density.
The part shell can be thought of like the shell of an egg: it is the exterior surfaces of the part. Together, the printed walls, bottom layers, and top layers make up the part shell. Depending on Fabricate settings, parts printed with the Studio System feature a 1.2 - 2.4mm thick shell.
The impact of shell thickness on part density will depend on part geometry. When printing small parts, the solid shell accounts for a large percentage of the part’s volume, minimizing the effect of infill. As a result, the density of small parts will be higher than the density of large parts.
Example: large part
Example: small part
The Studio printer extrudes a bead of material through the opening of the print head nozzle. The round beads are extruded line by line in the horizontal plane and then layer by layer in the vertical plane. Due to the round shape of the extruded bead and the path of the print head, some geometries or features may have small voids of material, referred to as ‘toolpath-based macro-porosity.’ In the final sintered part, these small voids appear as larger “pores.” This type of porosity is inherent to all FFF printing processes.
Impact of toolpath-based macro-porosity on density
Desktop Metal employs advanced toolpath algorithms and extrusion techniques to minimize the occurrence and severity of toolpath-based pores. The volume of these pores will vary by geometry, but they constitute roughly 2-4% of the volume of the part.
MIM-based micro-porosity refers to the tiny pores (15-25 micron) scattered randomly throughout the printed material. These pores are indicative of high quality sintering of metal particles from the metal powder and binder feedstock.
Impact of MIM-based micro-porosity on density
Desktop Metal’s Studio furnace sinters parts under vacuum, leading to high-density sintered material. The micro-pores indicative of high quality sintering typically constitute 1-3% of volume of the solid areas of BMD parts (consistent with 97-99% density).