Creating Multi‑Body STL Files for Multi‑Material 3D Printing

3D printing is revolutionizing design by letting us build complex objects layer by layer, free from traditional spatial constraints. A classic illustration is the “ship in a bottle”—instead of designing a tiny ship that must fit through a bottleneck, we can model the bottle around the ship. The real challenge is making the ship a separate part inside the bottle, so that both the clear bottle and the black ship are printed in a single job. This guide walks you through the proven workflow for producing multi‑body STL files that enable multi‑material 3D printing.

Stage 1: Create Separate Solid Bodies

In this example, we start with a single block that contains the letters “HELLO.” To create independent bodies, we first extrude‑cut the letters and then reuse the same sketch to extrude each letter into the same volume. By disabling the “Merge result” option, we avoid gaps that would require support material and we prevent overlapping geometries. The final part contains eight solid bodies: one for the block and seven for the letters. Adding distinct appearances helps us verify the internal structure.

Stage 2: Use the Save Bodies Command

After modeling, we need separate STL files for each body. If we simply save the part, we receive a single solid STL that prints as a monolithic object—exactly what we want to avoid. The “Save Bodies” feature allows us to export each solid body individually. Using the “Auto‑assign Names” option speeds up the process, but naming the clear block explicitly is essential for the printer’s material workflow.

We then create an assembly from these bodies. The assembly file becomes the source for our STL export.

Stage 3: Export the STL Files

Open the assembly file, choose File → Save As, set the file type to STL (*.stl), and click Options. Here you can fine‑tune the mesh resolution (deviation and angle) for optimal print quality. Crucially, uncheck the “Save all components of an assembly in a single file” box; this keeps each body in its own STL file so that you can assign different materials later.

The preview confirms that eight separate STL files will be generated.

Stage 4: Prepare for Printing in Objet Studio

Import the eight STL files into Objet Studio. Ensure the Assembly checkbox is ticked to access individual parts. Assign VeraClear to the clear block and TangoBlack (FLX9050) to the letters. You can also orient the block to optimize print stability.

Once the material selections are complete, click the Build button. The printer’s software will generate the tool paths and the final print will show a transparent bottle holding a black lettered block, all in one cohesive job.

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Tags: 3D Printing, STL Files, Stratasys