Feature first published in the January/February 2022 issue of 3D ADEPT Mag. Interviews, roles and industrial examples reflect that period.
One of the most fundamental steps in a product development process is the modelling, which entails creating 3D models of objects. Here is the thing, some designers believe that CAD is the only way forward – completely removing mesh workflows from the file preparation process while others think that MESH is slightly faster. The first step in building consensus is to clarify the importance of CAD & MESH – individually.
CAD (computer-aided design) describes computer-supported design activities and tools. A mesh is a discrete representation of geometry, rather than a competing design process. A surface mesh uses vertices, edges and faces; a volume mesh also contains cells, for example for simulation. Autodesk’s mesh documentation illustrates the surface representation. The useful distinction is therefore between representations and tasks, not two mutually exclusive workflows.
When it comes to 3D printing, both concepts can be used in a file preparation workflow. “Commonly CAD starts with sketching and then using subtractive tools to build 2.5D or 3D designs. Meshing starts with existing CAD, breaking CAD into fine elements to run mathematical calculations for different types of simulations”, Jaideep Bangal, Design and Manufacturing – Global Technical Team, Altair Engineering states.
This describes a common engineering workflow, not every modelling route. CAD tools also use additive geometric operations, and meshes can originate from scanning, sculpting or other modelling methods rather than a pre-existing CAD model.
Meshing for print preparation and meshing for simulation serve different purposes. Tessellating a surface into triangles can produce an STL representation; a finite-element model can instead use surface or volume elements selected for the analysis. These representations and their quality requirements are not interchangeable.
Speaking of file preparation, Altair’s expert states: “engineers commonly use STL, CAD, 3mf etc file formats to prepare designs for 3D printers. They still need a mechanism to convert this data into printer specific format, which can be exported by these tools or printers”.
Here, “CAD” names a broad category, not one file format; native CAD files and exchange formats such as STEP serve different workflows. An STL stores triangular geometry, whereas 3MF can carry additional manufacturing information. Supported data still depend on the receiving software.
Applications of CAD and meshes
Meshes can serve different purposes including reverse engineering, dimensional analysis and 3D printing – which is the angle we focus on.
In reverse engineering, a scanned mesh can help reconstruct a CAD model when the original design is unavailable. In dimensional inspection, comparison with reference geometry can reveal deviations. For printing, a mesh may be transferred through formats such as STL or 3MF, but it still needs suitable validation, orientation, build preparation and slicing for the target process. Importing a geometric file does not, by itself, make a part ready to manufacture.
CAD on the other hand, can serve a different range of objectives: design creation, design modification, manufacturing or digital inventory. Be it for design creation or design modification, there are a wide range of suite-specific CAD that provide a variety of tools that will enable designers to create models from scratch, including prototypes, tooling, and much more – on the other hand, to modify the designs based on desired requirements.
As Bangal notes, “almost every engineering company has some sort of CAD capabilities, engineers save their design work using PLM systems along with various design iterations during the product development process. On the contrary, CAE experts create mesh files from CAD provided by design engineers for simulations. They clean up CAD, prepare models, generate the mesh, and analyse performance using simulation solutions.”
That being said, the various objectives that may lead to the use of CAD or Mesh are also the ones that help differentiate their unique advantage: “CAD is built upon geometry, which is enabling engineers to modify their designs quickly, even from neutral CAD file formats. But it also creates geometry nuances that might make it unusable for simulations”, Bangal comments. “Unless engineers are using meshless technology such as Altair® SimSolid®, all simulation solutions create finite element models from CAD for performance analysis or to prepare the model for manufacturing, that’s mesh”, he lays emphasis on, taking the example of Altair’s products.
The quoted comparison concerns Altair’s engineering workflow. Finite-element analysis is not the only form of simulation: other numerical methods exist, and the required discretisation depends on the problem and solver.
A key focus on workflows for file preparation
CAD tools commonly offer mesh export for print preparation, including STL, while some workflows accept native or neutral CAD geometry directly. However, reality reveals that, “both CAD and mesh are important depending on when it is used and who uses it. Typically, CAD comes first followed by mesh during the product development workflow. Design engineers prefer to work in a CAD environment while simulation experts use mesh. If CAD is king, mesh is kingmaker!” So, what should we tell to design engineers who continuously compare both in order to decide which one they should go for?
Bangal recommends hybrid workflows that combine editable CAD geometry with mesh-based operations where useful. Materialise likewise presents both representations as complementary within file preparation; the choice depends on the operation rather than a universal ranking of one above the other.
“For example, CAD is known for its impressive capabilities while editing parts because it’s of a higher resolution than mesh. It will be seamless to go from design optimization software to file preparation with Magics and complete tasks such as enhancing parts, creating fillets, and adding holes. However, there are also clear benefits when using mesh while preparing parts for 3D printing. It’s crucial to complete certain steps with mesh, especially during build preparation and for applications with organic textures. It is also very powerful for operations where you want to ignore the complexity of designs, such as the wrapping of a complete engine assembly. Mesh contains all the information about the inside and outside of 3D models necessary to slice parts and begin 3D printing”, the 3D printing company explains.
The comparison is Materialise’s product explanation. Geometric accuracy depends on CAD tolerances and mesh resolution; CAD is not universally “higher resolution” in every sense. A complete mesh also does not contain every machine setting or material parameter needed to print safely and successfully.
In December 2021, Materialise announced CAD workflows using Siemens Parasolid for Magics 26, planned for 2022. This was the development discussed in the original January/February feature, rather than evidence that all versions of Magics already provided the same workflow.
Bangal describes the intended benefit of this approach as “combining the benefits of an easy alteration of parametric CAD and the flexibility of Polynurbs descriptions, to address the organic shapes resulting from topology optimization, as they are often found in designs for 3D printing.”
For a historical software demonstration, Materialise provides the “What’s New in Magics 26” webinar replay. It concerns that release, not a current product comparison.
Featured image: lightweight bicycle-frame demonstrator. Image: Altair.
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