Skip the Mesh, Print from CAD

Until now, additive manufacturing (AM) workflows have relied heavily on intermediary file formats to print CAD files. The two widely used formats are STL and 3MF. Both are triangulated or mesh formats, compromising the accuracy and geometric integrity of the original CAD designs. (For more, read “Bridging CAD to Additive Manufacturing,” April 2020.) But recently, a small but growing number of AM players are laying the groundwork for printing directly from CAD. Skipping the mesh and printing from CAD, some argue, is long overdue. Others point to new methods of displaying and describing geometry as key to this process.

A New Way to Describe Geometry

Bradley Rothenberg, CEO of nTop, wanted to move beyond the typical CAD program’s modeling method, called BREP (boundary representation). It had served the industry well for a long time, but as AM hardware emerged, BREP began to show its limitations. AM offers ways to manufacture complex geometry with lattices and patterns, often compared to membranes, bones, and even alien anatomy. BREP was ideal for representing symmetrical parts with circles, arcs, and lines, but it struggled with the more complex surfaces and topology favored by AM users.

The awkward workaround, still employed today in many areas, was to turn these complex parts into mesh models, by subdividing them into triangular elements. This allows CAD programs to use a mix of BREP and meshes to depict complex geometry, but at a cost. It takes compute power to generate the mesh model and the meshes themselves sometimes come out ill-formed. The more complex the part, the longer it takes. In some cases, the task exceeds the memory capacity of the software, resulting in a crash. With meshing, the file size also grows exponentially, making the model unwieldy to load and edit.

The solution that Rothenberg found was what he called implicit modeling. Most CAD programs license and use the ACIS or Parasolid geometry modeling kernel, both BREP. In a departure from this tradition, nTop would develop and use its proprietary implicit-modeling kernel. “How we represent 3D shapes, in some cases, is thousands of times faster and lighter than a CAD file, and the complexity doesn’t break the system,” says Rothenberg.

Daeho Hong, senior product manager for nTop, says, “With implicit modeling, we can express computational design with mathematical equations and programming logic, so we can do certain things more efficiently, compared to conventional CAD. For example, we can produce lattices and repetitive patterns much faster. Once constructed, we can also individually change the design parameters of those types of structures.”

3D printing hardware usually converts the 3D geometry into motion-input instructions, different for each printing process and hardware. Previously, CAD software programs, including nTop, used intermediary mesh formats to get the printer to understand the geometry. But nTop has figured out a way to bypass the step. “If the 3D printing hardware can understand the original CAD geometry, then meshing is unnecessary,” notes Hong.

Partnerships and Plug-ins

nTop has attracted Autodesk, Materialise, Hexagon, and EOS as partners along the journey. At the Autodesk app store, you can download nTop for Autodesk Fusion, a plug-in that lets you import your Fusion model into nTop and then print directly from CAD. Last year, at the RAPID + TCT 2024 conference, nTop and its partners began demonstrating the new meshless printing workflow.

For more on the nTop plug-in previewed at RAPID + TCT 2024, watch this video.

In the blog post revealing the partnership, Sualp Ozel, an Autodesk product manager, wrote, “The implicit import feature eliminates the need for large mesh files, making it easier to handle highly complex parts. By avoiding the meshing process, nTop users can export their implicit designs and import them directly into Fusion—a task that typically takes mere seconds using the add-in.” (“nTop and Autodesk Fusion Join Forces: Direct Implicit Model Import,” November 2, 2023)

The same feature is now part of Materialise Magics. “The integration of nTop Core’s implicit modeling API with Materialise’s Magics 3D Print Suite and NxG Build Processor allows a seamless exchange of implicit design files between design and manufacturing teams, eliminating the need for meshing and other intermediate steps,” wrote Materialise in its announcement.

CAD-to-Print is Long Overdue

It would be an understatement to say that Harshil Goel, CEO and founder of Dyndrite, has strong feelings about using mesh models for 3D printing. “It’s fundamentally hurtful to me to hear people say you cannot print directly from CAD and you need a mesh file,” he says. “That is so false it hurts my soul as a mathematician.”

He conceded, grudgingly, that in the 1980s and the 1990s when AM was still in its early phase, there were valid reasons for using mesh or tessellated files to print, in part due to the limited computing power of the hardware. “It was a workaround that became the standard,” he says. “It was a step backward from CAD.”

The technical hurdles for printing directly from CAD have long disappeared, but businesses that cater to the mesh-centric AM workflow aren’t ready to let go of the format yet, “because their livelihood revolves around that,” Goel says. His goal, he adds, “is to make printing directly from CAD the standard in the next three to five years.”

In workflows that involve scanning and capturing organic shapes, such as healthcare and visual effects in films and games, mesh models are still important, but in the future, Goel envisions that “mesh models will only have a limited role to play in AM.”

Goel and his team at Dyndrite have developed a geometry kernel (ACE) that allows software and hardware makers to write CAM (print-prepping) software that accepts CAD files. Goel explains, “Dyndrite built an end user app called the Dyndrite LPBF Pro on top of it. Dyndrite LPBF Pro’s use of CAD data has already enabled key end users to print with no supports, better surface finish, homogenous material properties, print three to eight times faster and automate the entire build prep process.”

There are signs that major players in laser powder bed fusion are realizing Dyndrite’s contributions. Dyndrite has signed a partnership with Nikon SLM Solutions and SCANLAB. On the Nikon partnership, Dyndrite wrote, “By integrating Dyndrite’s LPBF (laser powder bed fusion) Pro software, Nikon SLM Solutions’ customers gain access to advanced toolpath strategies that maximize the capabilities of the open-architecture SLM platform.”

On the partnership with SCANLAB, Daniel Reitemeyer, business development manager of SCANLAB, says, “Today’s LPBF machines do not provide the high-resolution data that our hardware control is capable of executing. Dyndrite has the ability to calculate process parameters at extremely high resolutions that can drive our laser control system to its fullest.”

Impossible Objects; Possible Mission

At Dyndrite Developer Conference (DDC) 2021, Len Wagner, chief technology officer of the AM hardware maker Impossible Objects, gave a talk provocatively titled “Let’s Kill STL: aka Direct Printing from CAD.” The key to this strategy, he explained, was to build a Build Server that could accept both mesh and CAD files for printing.

“There’s a lot less steps here, a lot less data to be passing around. It keeps the meta data, keeps the full CAD data. You don’t have to tessellate, and if you do, it’s just as the last step, and doesn’t change the accuracy. We’re doing this at Impossible Objects, and we invite the rest of the industry to do it,” says Wagner.

Explaining the partnership between Dyndrite and Impossible Objects, Dyndrite wrote, “Impossible Objects’ Rules-based Automated Masking Packing and Slicing (on-RAMP) software, powered by Dyndrite, integrates the multi-threaded, GPU-accelerated, Python-based Accelerated Computation Engine from Dyndrite with Impossible Object’s proprietary software to drive its unique CBAM process. The CBAM software powered by Dyndrite delivers an easy to use GUI and automated CAD-to-print workflows” (“Dyndrite and Impossible Objects Showcase End User Software for New High-Speed CBAM 25 Process,” April 2023).

“It is amazing to me what these machines are capable of, and we are just scratching the surface due to the tyranny of the linear mesh approximation of CAD,” says Goel.

More Autodesk Coverage

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