SculptPrint employs voxels. A voxel is a cube of space. Voxels are not a new technology. Since computing began, representing 3D space as an indexed array has been an obvious idea. However, the computing power in terms of memory and processing needed to compute 3D arrays of significant size has only recently become widely available and affordable. SculptPrint uses parallel processing from graphics processing units from nVidia to process billions of voxels quickly and efficiently.
The three types of 3D models supported by SculptPrint are shown above. These include boundary representation (b-rep) models, triangle mesh models, and voxels. SculptPrint supports import and display of b-rep and triangle mesh models in order to voxelize them to the SculptPrint voxel format. A quick explanation of b-rep and triangle mesh models will help in explaining voxels.
B-rep models are a collection of 3D surfaces and curves with connections between the surfaces and curves tracked by a data structure. The surfaces can be simple shapes such as planes or cylinder as well as more exotic shapes such as b-splines or NURBS. Computer-aided design packages primarily use b-rep models. B-rep models are the best for tracking precise geometry such as bolt patterns. SculptPrint supports importing these types of models and allows the user to access the precise geometry during tasks when the b-rep model is the best choice of representation.
Triangle meshes are a collection of triangles. Most 3D graphics is performed using triangle meshes. Often b-rep modeling software will necessarily need to generate a triangle mesh through a process called tessellation in order to display the model on a computer screen.
Triangle meshes are also the most popular form of 3D model for 3D printing. However, interest in using voxels for 3D printing is on the rise. A few examples are below:
SculptPrint converts imported B-rep and triangle mesh models into voxels through a process called voxelization. Voxelization is one of many operations in SculptPrint that use the GPU. Both b-rep and triangle mesh models only capture the boundary between full and empty space, but voxels allow each cube to carry information about whether the cube of space is inside or outside.
Voxels can also be assigned additional information such as density, distance from the surface, or a physical property such as temperature or pressure.
SculptPrint renders voxels using nVidia's CUDA technology directly. The need for an additional triangle mesh is not necessary. In the image above, one can see the smooth voxels and then a small red sample of voxels displayed in the lower left. The model is composed of billions of voxels.
All Three in SculptPrint
SculptPrint primarily uses voxels but allows all three types of 3D models to be used together. In the image above a part to be manufactured has all three types of models listed, b-rep, mesh, and voxel. The concept is similar to a 2D image modeling package such as Adobe Photoshop. A 2D image might be composed of vector graphics layers and raster graphics layers. The vector graphics layers are analogous to the b-rep and triangle mesh models. The raster graphics layers are pixels and are analogous to the voxels. SculptPrint's approach is to allow the user to use the "right tool for the right job" in terms of 3D model representation.
Last month, Georgia Tech students used SculptPrint to produce a complete centrifugal compressor. A housing for the impeller featured in the last blog post was sculptprinted on an Okuma Multus B-300 5-axis millturn machine. SculptPrint features supporting boring operations were used extensively to produce the inner diameter geometry of the housing.
The voxel model of the compressor housing in the SculptPrint software is shown below.
The millturn machine allows a mixture of turning and milling pass to produce the asymmetric geometry of the housing.
A boring pass on the inner diameter is shown below.
A milling pass to produce the asymmetric outlet port geometry is shown next.
A turning pass as modeled in SculptPrint is shown below.
A collision free milling pass on the inner diameter modeled in SculptPrint is shown next.
Finally, the test rig for the assembled compressor is shown. The compressors was tested up to around 2800 rpm with good results.
Georgia Tech students used SculptPrint to generate CNC paths for a turbocharger impeller. The impeller was produced on an Okuma Multus B-300 5-axis millturn machine. The tool paths were automatically assigned collision free orientations using SculptPrint’s access map technology. The students are also working on a housing for the impeller to complete the turbocharger.
The part modeled in SculptPrint using voxel modeling and access map technology shown below.
The image above show the “Candle Holder” geometry produced at Georgia Tech on their Mazak VCU 500 5-axis mill. The aluminum part has difficult to access spirals. SculptPrint’s advanced GPU technologies such as voxel modeling and access maps made producing this shape possible.
The image of the voxel model in SculptPrint is shown below.
In April of 2016, SculptPrint was featured at nVidia’s GPU Technology Conference. Demos of the software were given in our booth as well as in nVidia’s Design and Manufacturing section of their booth. The slides from the talk given at the conference are now available on nVidia’s website and can be found here.