Additive manufacturing has increased in popularity in recent years partly due to the possibilities of producing complex geometries in a rapid manner. Selective laser sintering (SLS) is a type of additive manufacturing technique that utilizes polymer powder and a layer-by-layer technique to build up the desired geometry. The main drawbacks with this technique are related to the reproducibility, mechanical performance and the poor surface finish of printed parts. Surface roughness increase the risk of bacterial adhesion and biofilm formation, which is unbeneficial for parts to be used in the healthcare industry. This thesis investigated the possibility in reducing the surface roughness of SLS printed polyamide 12 with the fully automated post-processing technology PostPro3D. The postprocessing relies on chemical post-processing for smoothening of the parts’ surface. PostPro3D utilizes vaporized solvent which condenses on the printed parts causing the surface to reflow. By this roughness, in terms of unmolten particles, is dissolved and surface pores are sealed. The influence of alternating post-processing parameters; pressure, temperature, time and solvent volume was evaluated with a Design of Experiments (DoE). The roughness reduction was quantified with monitoring the arithmetic mean average roughness (Ra), the ten-point height roughness (Rz) and the average waviness (Wa) using a stylus profilometer and confocal laser scanning microscope (CLSM). The effect of post-processing on mechanical properties was evaluated with tensile testing and the effect on microstructure by scanning electron microscopy (SEM). A comparison was made between post-processed samples and a non-postprocessed reference, as well as between samples post-processed with different degree of aggressivity, with regards to the roughness values, mechanical properties and the microstructure. Results indicated that solvent volume and time had the largest effect in reducing the roughness parameters Ra and Rz, while time had the largest influence in increasing the elongation at break, tensile strength at break and toughness. The post-processing’s effect on waviness and Young’s modulus was less evident. SEM established that complete dissolution of powder particles was not achieved for the tested parameter ranges, but a clear improvement of the surface was observed for all different post-processing conditions, as compared to a non-post-processed specimen. The reduction in roughness by increased solvent volume and time was thought to be due to increased condensation of solvent droplets on the SLS-parts. The increase in mechanical properties was likely related to elimination of crack initiation points at the surface. In general, the mechanical properties experienced a wide spread in the results, this was concluded to be related to differences in intrinsic properties of the printed parts, and highlighted the problems with reproducibility related to the SLS. An optimal roughness of Ra less than 1 µm was not obtained for the tested post-processing conditions, and further parameter optimization is required. / Möjligheten att tillverka komplexa geometrier på ett snabbt sätt, har fått additiv tillverkning att öka i popularitet. Selective laser sintering (SLS) är en typ av additiv tillverkning där polymer pulver sintras samman succesivt lager för lager. Dessa lager bygger tillsammans upp den önskade geometrin. De största nackdelarna med SLS är att de tillverkade delarna har bristande mekaniska egenskaper, har brister i reproducerbarheten samt att ytan har en dålig kvalitet, den är ojämn. Ytojämnheten ökar risken för att bakterier fastnar och ett en biofilm bildas. Då produkten ska användas inom sjukvården, är det viktigt att biofilm bildning undviks. Den här uppsatsen har undersökt möjligheterna att reducera ytojämnheten av SLS-printad polyamid 12 med hjälp av kemisk efterbehandling i PostPro3D. Denna maskin är helt automatisk och åstadkommer ytbehandling genom att förånga lösningsmedel som sedan kondenserar på det SLS-printade materialet. Ytan på materialet löses upp vilket minskar ytojämnheter i form av pulver partiklar samt sluter porer på ytan. Genom att ändra på parametrarna för efterbehandlingen kan graden av aggressivitet påverkas, detta gäller tryck, temperatur, tid och lösningsmedels volym. De optimala parametrarna för att åstadkomma en jämn yta utvärderades med en Design of Experiments (DoE). Reducering av ytojämnhet mättes med hjälp av aritmetisk genomsnittlig ojämnhet (Ra), tio-punkts höjd ojämnhet (Rz) och medel-vågighet (Wa), med nålprofilometer och konfokal mikroskop. Efterbehandlingens påverkan på de mekaniska egenskaperna utvärderades i ett dragprov, medan mikrostrukturen undersöktes med svepelektronmikroskop (SEM). Ytjämnheten, de mekaniska egenskaperna och mikrostrukturen jämfördes mellan icke behandlade prover och ytbehandlade prover, med varierad grad av aggressivitet. Resultaten indikerade att tid och volym hade störst effekt på Ra och Rz, medan tid hade störst positiv inverkan på töjning, styrka och seghet. Effekten på styvheten (E-modulen) och vågigheten (Wa) var mindre uppenbar, och någon tydlig påverkan kunde inte observeras. SEM-analys visade att fullständig upplösning av partiklar på ytan inte sker för de testade behandlingarna, men en tydlig förbättring kunde ses vid jämförelse av ett obehandlat prov och ett behandlat prov. Den ökade ytjämnheten för längre tid och högre volym tros bero på en ökad kondensering av lösningsmedel på ytan under efterbehandlingen. Ökningen i mekaniska egenskaperna är troligtvis relaterade till eliminering av kritiska defekter på ytan. Generellt visade de mekaniska egenskaper en stor spridning i resultaten, detta tros bero på inneboende egenskaper i provstavarna. Denna slutsats understryker den bristande reproducerbarheten för SLS-printning. En optimal ytjämnhet antas vara ett Ra värde under 1 µm, denna ytjämnhet har inte uppnåtts med de testade efterbehandlingsparameter värdena, därför krävs ytterligare parameter optimering för att nå optimal efterbehandling.

Additive manufacturing (AM) is an attractive way to shorten development time, reduce product weight and allow the manufacturing of more complex products than by conventional manufacturing processes. The problem arises when the previous traditional manufacturing requirements need to be fulfilled by AM as well as the volume production capability. This investigation is done together with Ericsson to evaluate the possibilities of the different AM technologies, post-processing methods and silver coating processes to guarantee the specifications of radiofrequency (RF) filters. Here, minimal RF signal insertion losses are targeted. Since insertion losses are dependent on surface roughness, surface smoothness is sought as well. Ericsson simulation software uses correction factors to account for surface roughness, however there are some inconsistencies between the simulated and actual surface roughness that is allowed in the parts. In AM parts, surface roughness is not easy to control since it depends on parameters related to feedstock, process and machine properties. Commonly, most AM components do not comply with requirements of lower surface roughness values. Therefore, parts need to be smoothened before silver plated; this step is necessary to ensure the electrical conductivity in this specific application. These finishing processes add costs to the final product and increase time to market. Firstly, a comprehensive study was carried out to better understand the landscape of AM technologies, postprocessing and silver coating methods. Secondly, the different processes are assessed with the help of selection matrices, considering the products requirements. The components to print are two RF filters with different shapes and dimensions but similar requirements. The CAD design is modified depending on each AM process and directly affects the results. Afterwards, the design of an experimental plan is carried out; the number of samples of each part comparing AM technologies, feedstock, different suppliers (3D printing and post-processing) is obtained. Due to budget and time restrictions, the parts were printed using Multi Jet Fusion and Selective Laser Melting processes. After printing, tolerances and surface roughness were measured. This thesis results in the selection of suitable AM technologies and post-processing methods for RF filters. For MJF printed cavities at 0˚, 30˚ and 90˚ orientation, the best results for this application are obtained at 30˚ providing a good balance between sharp detail and smooth surfaces. In the case of SLM, waveguides are printed at 0˚ and 30˚. 30˚ waveguides present lower surface roughness values than the 0˚ ones as inner support material is needed at 0˚ orientation. SLM cavities were printed at 30˚ in seek of asymmetry between faces, resulting in higher surface roughness in the downfacing face.