High-resolution digitalisation for components’ shape accuracy

Designing (or scanning) and converting the component’s CAD model into a universal STL file is the first step towards Selective Laser Melting (SLM) of metal components. AM machines universally read STL files. To accurately reflect the geometry and complexity of the specimen without artifacts such as faceting, the conversion from CAD to STL files must be carried out with suitable resolution for a fine balance between parts' shape accuracy and convenient digital processing time.

The STL file (Standard Tessellation Standard) converts the original CAD file into a mesh of tiny triangles laid over the surfaces defined by the CAD model. The STL file simplifies the complex mathematical description of the solid surface geometry into a form that is easily and universally readable by SLM machines. The surface geometry is broken down (tessellated) into a series of logically small triangles known as facets. Each facet is described by the triangle and its perpendicular direction.

The size and number of facets (triangles) determine the accuracy of the surfaces. A mesh with large triangles will create a small STL file and produce a prototype with visible facets. A mesh with triangles the size of the material layer thickness (~20/80um range) will produce an accurate prototype. A smaller triangular mesh will increase the STL file size and require longer digital processing times (subsequent repairs, slicing,…)  without added prototype accuracy.

A triangle is by definition flat and planar. When original 3D models exhibit curvatures or apertures, error and/or deviations from the initial geometry occur. The deviation can be reduced by using small triangles (down to a practical limit). If the triangles are too small, the file size increases in line with the number of facets (triangles) required. Most CAD software offer suitable settings to output STL files displaying a balance between file size and part resolution and accuracy. However, it is worth not to rely on the default parameters in order to avoid cleaning (post-machining) the facets.

In SolidWorks, the option to refine these resolution settings is accessible when the file is saved as an STL dataset.

When saving the file as an STL extension, go into 'option' to optimise the resolution and size of your output file.