Implicit Modeling for Additive Manufacturing

What Is Implicit Modeling?

Implicit modeling is a way of representing a geometric shape using equations. Data about the geometry is stored in a signed distance field, essentially a grid; each point of data in this grid indicates how far that point is from a boundary. Rather than a literal representation of the surfaces of a shape, implicit modeling is more of a “recipe” for the geometry.

How Does Implicit Modeling Differ from Explicit Modeling?

In explicit modeling methods used by most CAD systems, shapes are modeled by explicitly describing their boundaries — in other words, the vertices, edges and faces that define the surface of the shape. Geometries are typically represented either with boundary representation (B-rep) solid models or a triangle mesh.

For many parts, explicit surface modeling poses no particular challenge. However, for the complex parts that additive manufacturing can produce, software based on explicit modeling can get bogged down in processing. If there are many surfaces to represent, this translates into large file sizes and difficulty in making changes as well as in saving and sharing files.

What Are the Benefits of Implicit Modeling?

Compared to explicit modeling methods, implicit modeling can lead to faster processing of design changes and smaller file sizes. Because implicit modeling is based on equations rather than discrete data, the strategy makes it easy to scale up designs or make modifications without slowing down the software.

Implicit modeling may allow designers to overcome previous constraints imposed by CAD software, enabling faster processing of complex structures such as gyroid lattices, as well as the use of new kinds of shapes. This modeling technique can more easily enable opportunities such as metamaterials and material property gradients based on geometry.

What Are the Drawbacks of Implicit Modeling?

When used to recreate objects from the physical world, implicit modeling may be less accurate than explicit modeling. The model’s outcome depends on the inputs and skill of the designer.

Implicit modeling is perhaps better suited to developing new designs, where support for design complexity and flexibility in iteration is more important.

How Does Implicit Modeling Help Additive Manufacturing?

While explicit modeling is well-suited to subtractive operations based on surfaces such as CNC machining, implicit modeling can be a more efficient choice for representing the complex infill structures and other features that additive manufacturing makes possible. Implicit modeling is especially effective for designing parts that include many surfaces, such as heat exchangers, filters and bioreactors.

Implicit modeling avoids the file size challenges of explicit modeling by avoiding the need to literally represent every surface on a part. Its method of using equations to describe geometry, rather than B-rep or mesh models, makes it faster and easier to execute design files, and results in smaller, more portable file sizes. In some cases switching from explicit to implicit modeling can result in time savings on the scale of days to alter or save a design file.

Can Implicit Models Be 3D Printed?

In many cases designs that have been developed with implicit modeling tools are exported as STL files to create explicit representations for 3D printing. It is also possible to export sliced models including stacks of images for digital light processing (DLP) and other light-based 3D printing processes, as well as hatch patterns.

While exporting implicit models to explicit formats is common, some tools also make it possible to print the implicit model without such conversion. Some platforms can even stream implicitly modeled geometry directly to the 3D printer, providing the representation data piece by piece, just as it is needed for printing. With this method, the implicit model is not converted into explicit data, but directly translated into the physical part.

Can Implicit Modeling Be Combined with Other Strategies?

Yes! “Hybrid modeling” that combines implicit strategies with explicit modeling can be useful for parts that include both simple and complex surfaces. In this example from Oqton, B-rep is used to model the intake of a heat exchanger, while implicit modeling was applied to the interior lattices. 

What Software Uses Implicit Modeling?

Design programs and software including implicit modeling capability include Altair Inspire, Autodesk Fusion 360, Metafold (platform and API), nTop, Oqton 3DXpert, Rhino through various Grasshopper plugins, and Siemens NX.

What Other Ways Can Implicit Modeling Be Used?

Outside of manufacturing, implicit modeling is also being used to produce visual effects; to represent natural features in geology and mining; to model organs and blood vessels in medicine; and in quantum mechanics research, among other applications.