Additive manufacturing project Symbionica is rapidly entering its final phase. The project aims to design and build a reconfigurable additive and subtractive manufacturing platform to produce fully customisable smart prostheses for use in the medical technology industry.

This week the Design and Prototyping Group (DPG) at the Advanced Manufacturing Research Centre (AMRC) have published a fascinating new case study reporting on the DPG’s investigation into three methods for correcting CAD models for selective laser melting (SLM) build defects.

SLM can be affected during the additive process by several issues. For example, as the previous layers of the print cool and contract, it can cause the next layer to be pulled in an undesirable direction causing the part to become warped during printing.

Warping and other such additive manufacturing issues can be avoided by modifying CAD to account for known process issues. Using mesh deformation tools developed by ITI in CADfix, the DPG corrected CAD models to reduce SLM build defects.

CADfix was used to import a CT scan of the printed part. This CT scan point cloud was then aligned with the original CAD and compared to locate differences between the physical part and the CAD. These differences show precisely where the part has increased or decreased in size during the SLM process. Using the measured differences as a vector field, a mesh of the original CAD geometry is morphed to the inverse of the CT scan data. This morphed mesh is then used to morph the original CAD model to generate a compensated version of the CAD model. is then passed back into the SLM process for a secondary print. The print of the compensated CAD is re-scanned to confirm that applied compensations to the CAD has reduced the defects in the first printed part.

The original CAD shown in black, the CT scan of the first printed part shown in blue dots, and the updated compensated CAD to be re-printed shown in red.

There are limited options available to predict how much the compensated CAD will correct the result of the SLM process, hence the necessary secondary print to verify the technique.

The experimental process demonstrated in this study has shown that manufacturing defects can be managed successfully in the CAD geometry by implementing these morphed compensation techniques.

To see the study in more detail, it is available to download from the AMRC’s website here: http://www.amrc.co.uk/case-studies/correcting-cad-models-for-slm-build-defects

For more information on the Symbionica project please visit the project website or our project blog or for more details.

Symbionica has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 678144.