Studies of selective laser sintering components with controlled porosity
Abstract of thesis entitled
?TUDIES OF SELECTIVE LASER
SINTERING COMPONENTS WITH
CONTROLLED POROSITY?submitted by
KU Chui Wah, Janny
for the degree of Master of Philosophy
at the University of Hong Kong
in August 2002
Selective Laser Sintering (SLS) is used to fabricate prototypes of single material traditionally. This study focused on inclusion of alcohol and paint on sintered DuraFormTM Polyamide (DF) before and after sintering process, morphology studies of selective laser sintered CastFormTM Polystyrene (CF) and its infiltration behaviour with red wax, and also feasibility of processing biodegradable polymers in SLS. These three areas provide important information for building functional parts by the SLS process.
First, alcohol and paint were used to modify the morphology and mechanical properties of DF parts both before and after the SLS process. The tensile strength of the tensile bars with the treatment of alcohol and paint was studied by means of tensile tests. It was found that alcohol and paint had the effect of weakening the mechanical properties of DF at desired regions when
they were added before the SLS process. However, their effect was milder when they were added after the SLS process.
Secondly, SLS samples with controlled porosity were built from CF and their infiltration characteristics by red wax were studied. The surface and cross-sectional morphologies of the selective laser sintered CF of various energy densities were examined using scanning electron microscopy (SEM) first. Then their average physical densities were measured by density bottle and compared with that of solid material. The results found that the maximum physical density was about 88% of the solid material. The infiltration test showed that the rate of displacement of red wax onto selective laser sintered CF was relatively fast in the first thirty minutes, but started to level off once equilibrium was reached. CF with energy density of 0.0408 J/mm2 gave the best infiltration performance. The mass of red wax that could be infiltrated was also measured, calculated, and compared with the theoretical values. The porosity left after infiltration remained a constant value of 0.13 for CF of various energy densities. The results provided some valuable information about the relationship between porosity and infiltration behaviour of SLS parts which can be exploited when building functional parts which require post-sintering infiltration fully, partially or at selected regions with one or more materials.
Finally, a study was made of the feasibility of processing the three biodegradable polymers, poly(lactide-co-glycolide) [PLG], poly-(L-lactide) [LPLA], and poly-(D,L-lactide) [DLPLA]. It was found that PLG and LPLA could be easily sintered under the Universal M25 Laser Engraving System. PLG
was selected for the study of the degradation characteristics in a buffer solution, which simulates salt solution in human bodies. Loose powder of PLG and two sets of selective laser sintered PLG [selective laser sintered at power rating of 5% (i.e. 1.25 W) & 10% (i.e. 2.5 W)] were immersed in a bag and then immersed in the buffer solution. It was found that when PLG powder and selective laser sintered PLG specimens were immersed in a buffer solution, there was an intake of water first, mainly due to hydrolysis. The specimens then degraded almost completely and gradually lost weight until the dry weights were reached.
Ku Chui Wah, Janny
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:sintering lasers in engineering porosity
Date of Publication:01/01/2003