Investigation of orange peel phenomenon related to powder deterioration and relevant process parameters

• Main Author: Abid, Mahmud
• Published: Cardiff University 2009
• Subjects: 666
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584575

PA3200 is a material developed by EOS GmbH and is a mixture of PA2200 polyamide powder and glass beads. PA3200 is used to produce sintered parts via a rapid prototyping process known as Selective Laser Sintering (SLS) or simply Laser Sintering (LS). This thesis reports on an experimental investigation based upon a commercially available LS machine (a Sinterstation 2500 HiQ from 3D Systems Inc) into how heat and the glass content affect the material. The main aim of the research was to determine the ranges of process parameters and ratios of glass/polyamide and used/virgin materials needed to produce good quality parts, i.e. parts that are dense and geometrically accurate and do not display a rough orange-peel-like surface. The thesis presents the design of experiments, the experimental procedure adopted and the results of the tests conducted. The latter included assessments of the thermal and flow properties of the material via Differential Scanning Calorimetry (DSC) and Melt Flow Rate (MFR) measurements, a study of the crystallisation behaviour of powder using gel permeation chromatography (GPC) to evaluate changes in molecular weights and visual examination of the microstructure of the sintered parts via optical microscopy. The experimental work involved controlling parameters such as the laser power, laser speed, scan spacing, layer thickness and part bed temperature. The results obtained confirm that the melt viscosity of the material increases with the glass content and decreases with temperature. Also, as expected, exposing the material to elevated temperatures causes it to deteriorate and increasing the proportion of recycled material (that has been exposed to high temperatures) adds to the risk of producing parts with an orange-peel like surface. The thesis derives empirically-based recommendations for the minimum MFR value, the maximum glass/polyamide mass ratio and the maximum recycled/virgin materials ratio to ensure the production of parts not affected by the orange peel problem.