Development of a PGSS system for the production of powder for selective laser sintering

One of the most important additive manufacturing plastic processes is selective laser sintering (SLS). Complex component geometries can be produced directly from the CAD model. A significant factor in the decision for or against the use of SLS is the availability of material. High demands are placed on the laser sintering powder in terms of size distribution, shape, and surface. Therefore, only a few materials have been able to establish themselves on the market so far. The process for producing laser sintering powder researched in this project is the PGSS process ("Particle from Gas Saturated Solutions"). In this process, polymers are plasticised with the help of a twin-screw extruder and applied with supercritical CO2. After the extruder, the plastic-gas mixture is conveyed through a melting pump into a dynamic mixer. Here the mixture is homogenised, and further supercritical CO2 is added. In the subsequent melt cooler, the fluid is mixed again and cooled to pre-expansion temperature before it can be sprayed through a nozzle into the spraying tower. Since the CO2 acts as a blowing agent, the viscosity of the polymer is reduced enormously. At the same time, the pump builds up the necessary pressure to push the polymer-gas mixture through the nozzle and thereby spray it. When the dispersion is sprayed, the supercritical CO2 returns to a purely gaseous state, causing it to expand and thus increase in volume. As a result, the gas dissolves out of the plastic phase and breaks it apart. The resulting particles form a sphere during the fall due to the surface tension of the polymer. At the same time, these spherical particles are strongly cooled and solidified by the Joule-Thomson effect that occurs during the expansion of a gas. The final result should be a laser sintering powder with ideally spherical plastic particles and consequently good flowability.