A hybrid Selective Laser Sintering based process for the additive manufacturing of architectured composites

Additive Manufacturing also commonly referred as 3D printing has been given a lot of interest lately. Market is growing exponentially and the aim for obtaining more complex and ready-to use parts is emerging. All the 3D printing processes consist in building a part layer by layer by feeding bulk material. The range of different processes can be divided into sub-categories depending on the type of material, metal or polymer, and their feedstock form.The proposed approach consists in combining two of these technologies, Selective Laser Melting (SLM) and Laminated Object Manufacturing (LOM). SLM relies on fusing a layer ofthe bulk powder on top of a previous one by steering a laser beam that serves as a heat source. On the other hand, LOM builds up a part by bonding and cutting foils on top of the previous one. SLM technology has been chosen as it provides parts with good mechanical strength and a good production throughput. This has lead industrials such as aerospace, automotive or medical to invest in this method where custom and lightweight components are required. The motivation for using a hybrid process to print composites lies in the challenges inherent to SLM. Laser melting of powders requires a high density of energy and leads to extreme temperature gradients between layers. Therefore, printing of dissimilar materials such as polymers and metals would result in degradation of the materials properties. On the other hand, mixing of powders in a single layer can be challenging and requires a post-processing recycling operation. To answer both the challenges of recycling and thermal damaging, the hybrid printing technology relies on using one of the two materials as a foil, while the second material is employed in its powder form. Furthermore, SLM requires to heat up the entire build part to rather high temperatures. As a consequence, printing of materials with different thermal properties results in substantial stresses at interfaces while cooling down.This PhD thesis focuses on proving the feasibility of this novel printing method by addressing the challenges mentioned previously. A custom made hybrid printing prototype has been developed at the Haute Ecole d'Ingenierie et de gestion du canton de Vaud (HEIG-VD) and is presented in this dissertation. A Printed Circuit Board (PCB) has been taken as a case study with the conductor being copper and the dielectric Polyamide 12 (PA12). Copper is reported to have low adhesion properties with polymers, an in-situ laser texturing has been investigated. This texturing has been correlated with laser parameters and adhesion strength. Cohesive failure occurs in polymer while the affected textured copper depth remains compatible with PCB production. The reported processing is two orders of magnitude faster than literature and adhesion improved four times. Simulations will be presented to compare the obtained results with our case study.