Colloquia

Samenvatting

3D-printing of elastomers is a technology under development where rubber materials are fed into a double screw-extruder and extruded through a nozzle onto a printing bed. The printing bed is capable of controlled movement along the X, Y, and Z axes such that a multilayered object can be printed. The advantage of 3D printing over other production techniques is its ability to rapidly produce complex, customized designs without the need for molds or tooling. This is mainly utilized when prototyping different products. When implementing 3D-printing for the production of elastomeric products, three main challenges are faced. First of all, it turned out to be a challenge to print a geometrical stable product. Furthermore, porosity inside the compounds was observed, lowering the mechanical properties of the printed material. The third challenge was to measure and control the adhesion between the rubber strands. The goal of this study was to understand the influence of the process on the product quality and then to optimize the printing process. To allow for the best printing product quality, both the compound formulation and the process parameters need to be optimized.

The geometrical stability of the printed part was improved by tuning the printing parameters such as screw speed and nozzle distance. Additionally, the velocity along the printing path was estimated and practically optimized considering the die swell to achieve a stable geometry. In order to minimize porosity, both the compound formulation and process parameters such as the chamber temperature, screw design and diameter of the nozzle were varied to study their effect. These were all optimized to achieve the lowest degree of porosity in the compound. Regarding adhesion, the influence of the printing temperature as well as nozzle distance and diameter were investigated using a special designed peel test to measure the interlayer adhesion.

Shown in this study was that co-rotating screws lead to minimal porosity and perform much better than counter-rotating screws. Besides, it was elaborated that changing the compound formulation, chamber temperature and nozzle diameter did not have a significant influence on porosity. The velocity control along the printing path as well as a good combination between screw speed and nozzle distance are key parameters to maintain geometry. Furthermore, a larger interfacial contact area and a higher pressure from the nozzle lead to better adhesion between the layers.