Hybrid manufacturing
Enabling flexible first-time-right production, hybrid 3D manufacturing methods can transform the production of smart systems that integrate electronic functions in structural parts. Hybrid digital manufacturing creates one integral production chain by combining additive manufacturing (3D printing) with assembly and 3D integration of electronic parts, and in-line quality monitoring. Major opportunities can be found in flexible and cost-effective production of smart systems, for example, enabling customized electronics for new lighting and automotive products.
Reden conducted modeling studies on 3D-printed and integrated electronics products to extract design rules for additive manufacturing, in order to make the printing process predictable and controllable. This work was part of the Hyb-Man (Hybrid 3D Manufacturing of Smart Systems) project. Hyb-Man was a European RD&I project funded by Penta, a Eureka cluster devoted to supporting collaborative projects in micro- and nanoelectronics enabled systems and applications. The project consortium comprised partners from Germany and the Netherlands, including Philips Lighting (now Signify), Eindhoven University of Technology, Fraunhofer, TNO, Robert Bosch and Reden.
Transient, anisotropic and multi-scale
The biggest challenge we encountered in the analysis of the 3D-printed structures was due to the nature of the printing process, which involves high temperatures for melting the (plastic) material before it can be deposited in the so-called melt pool. Therefore, thermal transients occur in and around this melt pool during cooling down and solidification of the printed material. These processes have a long, respectively short time scale, and give rise to significant residual stresses and unwanted deformations during the process.
In addition, the material exhibits anisotropic behavior, structurally as well as thermally, while the micro-scale geometry created by the printing sequence influences the macro-structural behavior of the object being printed. Consequently, the thermal, mechanical and thermo-mechanical models developed to describe the 3D-printing process have to account for its transient, anisotropic and multi-scale nature.
Two-step approach
The 3D integration of electronics complicated matters even further. Hence, the need for analytical methods that enable the prediction of the performance of hybrid 3D-printed objects. We set out to develop such methods and adopted a two-step approach in our simulation studies, first focusing on the analysis of the printing process and then on the analysis of the resulting product.
The process analysis included the determination of the optimal printing path to be followed, the various process parameters, and the properties of the building material used, such as ABS (acrylonitrile butadiene styrene). The analysis was aimed at the prediction of the thermal field, residual stresses, micro geometry, and macro material behavior.
Using the predictions from this process analysis, the product analysis could be performed. This concerned location-dependent material behavior, resulting geometry and stiffness, and residual stresses. Combining these outcomes with various manufacturing and loading cases, predictions of the thermal field, the stress/strain field and the failure behavior of printed parts could be generated.
Computational efficiency
Another challenge we had to address was computational efficiency. 3D printing is a layer-wise process that creates a product that becomes bigger and bigger until it is finished. As the printing process progresses, simulating the transient behavior in detail for the complete product in the making would become increasingly computationally intensive. Therefore, we developed a method that uses a very fine mesh near the melt pool, while at greater distances a coarser mesh can be applied with lumped modelling, which works with material properties averaged over a larger volume.
Special attention was required for managing all the mesh elements involved in the simulation. At the actual printing spot, material is added, so new elements have to be activated in a smooth manner such that discontinuities are avoided. At the same time, elements that have reached a sufficient distance to the melt pool, have to be integrated into larger, lumped elements in such a way that their properties represent the combined elements properly.
Validation and demonstration
After extensive simulations we performed experimental validation. To that end, we studied the temporal and spatial temperature distribution in test samples due to the heat injected by the printing process as well as electrical heating by the integrated electronics, even to the point where locally material could melt. This yielded satisfactory agreement with the simulation results. All in all, it demonstrated that we managed to capture the physics of hybrid 3D manufacturing in a computationally efficient manner and succeeded in producing effective design rules for the additive manufacturing of hybrid electronics.
