Case Study: Speckle Size Validation for Printing

NOTES:

• This case study was built for spg_v5
• This case study follows the Giant Brain Aneurysm case
• The following guide was developed and has only been tested for Houdini 17
• The following guide expects user familiarity with Houdini

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Introduction

When dealing with embedded geometries in Houdini, it is easy to lose a sense of dimensionality. While Houdini allows users to create infinitesimal objects, manufacturing technologies have size limitations. To test the model manufacturing feasibility, without committing the printer to the material and time of the actual part, a new validation section has been added to the spg_v5 network.

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Process

0. Open spg_v5.hipnc using any Houdini 17 version

   1. The spg network has been set to update manually
      • We highly recommend that this option is conserved by the user
      • Certain operations in the network can highjack the computer's RAM (depending on the input model)

1. Convert Speckels into Voxel-based Volumes

2. Subtract Volumes
   • Using VDB Combine, subtract the voxel-based base geometry (in this case the aneurysm model) and the voxel-based speckles

3. Slice Viewer
   • Using the Volume Slice and Merge nodes, the validation network allows users to visualize cross-sections of the combined voxel-based volumes, for the purpose of inspecting the ratio/proportion between speckles and model thickness (thickness of the aneurysm wall)

NOTE:

• Visual inspection may be enough for some users, rendering the rest of the guide as optional
• However, the need for further resizing of the model outside of Houdini (i.e. scale changes within the printer's slicer) would benefit from the fabrication of a slice or section of the final model
• The remaining steps of this guide discuss the fabrication of said slice or segment

4. Cut Slice or Segment
   • Using the Switch node, the user can select the best slice for fabrication
   • Using the Box node, the user uses the slice as a reference to fabricate a thin box
   • Using the Transform node, the user can resize said box to cut as much of the model as needed

5. Cut and Remesh
   • Using the Boolean node, the program cuts the model using the cut box/plane/slice
   • Two Boolean nodes are used, one for the speckles and one for the base model (in this case, the aneurysm)
   • Using the Remesh node, create an adaptive mesh for both models

NOTE:

• The resultant mesh from the Boolean operation may not be proper for slicing and 3D printing
• Using the Remesh is highly recommended

6. Export Surface Files

7. Visualizing in Printer Slicer

   • Printer slicers like GrabCAD Print can give the user some preview of the print, but do not necessarily advice the user on the effects of scaling the object
   • For demonstration, three copies of the exported slices were printed (100%, 75%, and 50% scale)

6. Printed Slices
   • Successful printing of small features heavily relies on the printer's resolution