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Optimierung von additiven Fertigungsprozessen für verbesserte Oberflächen

  • Abteilung 5
  • Metrologie für die Wirtschaft

With the goal of increasing the applicability of additively manufactured components; thin film sensors can be integrated. The sensitivity of thin film sensors in comparison to conventional sensors is one of their many advantages. The surface quality of the substrate material onto which a thin film sensor is microstructured is of importance as it can influence the functional reliability of the sensor. For the surface quality of additively manufactured components to be comparable to those produced by traditional manufacturing processes, certain manufacturing build parameters must be optimised during the Selective Laser Sintering Process (SLS). In this work the material of choice was the polyamide powder. SLS printing parameters include laser power, scanning speed and layer thickness. The laser power parameter and its influence on the resulting surface quality was investigated. Workpieces were built at varied laser powers and the resulting surfaces were characterized. SLS surfaces are usually rough and this necessitates post printing surface treatment. The surface treatment method used was mechanical grinding using Silicon Carbide (SiC) paper. Surface roughness measurements were carried out on the workpieces before and after surface treatment. At lower laser powers work pieces were characterised by very rough surfaces; Ra ≈ 8.5 µm and after surface treatment the surfaces were very porous. Fig. 1 shows a scanning electron microscope (SEM) surface image of a workpiece built at low laser power. Individual polyamide powder particles could be found on the surfaces showing that at least on the top layers the powder was not completely melted and as a result there was no bonding with neighbouring particles. During the mechanical surface treatment these powder particles were easily removed from the surface leaving behind holes and pores as shown in Fig. 2. The surface on which the strain gauge is structured has holes. Fig. 3 shows a comparison of the surface roughness measurements of work pieces built at 18 W laser power and at 24 W laser power. These measurements were carried out on the workpieces directly from the printer before any surface treatment and then after the surface treatment. The main trend that could be observed here is that the higher the laser power during the sintering process the lower the initial Ra value of the surfaces and ultimately the smoother the surfaces are after surface treatment. The initial Ra value for workpieces built at 24 W laser power was 2.63 µm and after surface treatment the Ra value was only 0.19  µm. Higher laser power ensures that the polyamide powder particles completely melt and bond with neighbouring particles leading to less pores and less poorly bonded particles. From the results obtained so far, an initial good surface quality before any surface treatment ensures an overall improved surface quality after surface treatment. This initial good surface quality can be achieved by sintering at higher laser power e.g. 24 W. In future work, tests to investigate the optimum laser power for high quality surfaces in combination with varying of other build parameters will be of interest.

Fig. 1. SEM image of surface of workpiece produced with low laser power

Fig. 2. Thin Film strain gauge sensor on a porous surface

Fig. 3. Surface roughness results for workpieces printed at 18 W and 24 W laser power


Leiter der Presse- und Öffentlichkeitsarbeit

Dr. Dr. Jens Simon

Telefon: (0531) 592-3005


Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig