Thermal conductivity of glass/talc filled Polyamide 12 as function of tapping level
Résumé
Selective laser sintering is a layer-by-layer process that allows complex shapes to be processed but
requires specific properties for the powder used to build the final object. The advantages of free
crucible processing and freedom of design makes this process interesting for several applications.
Despite the large number of SLS printer available in the market, a deep understanding of the physical
phenomena of this process is still lacking, due to the number of parameters involved, directly
influencing the final part’s properties through the microstructure. In this work, glass beads or talc were
added to Polyamide 12 (PA 12) matrix in order to evaluate these filler’s influence on powder bed. We
started with PA 12 and glass beads (PA90/GB10 in wt%) untill 70/30 wt%, with a 5 wt% increment. As
SLS operates with CO2 laser working at 10.6μm to melt powders, it is fundamental to investigate how
heat will be conducted through the different sintered layer. Various parameters can influence thermal
conductivity of filled Polyamide 12 powder bed such as particle shape, aspect ratio, chemical
composition, presence of impurities and also the packing of the particles from powder bed. Hence,
porosity is such an important parameter as air inside is highly insulating the material and reduces its
thermal conductivity by convection between pores. This convection is also governed by the pores size.
(Rayleigh criterion) Several experiments were carried out in order to evaluate the thermal conductivity
as a function of porosity which highly depends on how particles are settled, thus how the powder bed
is tapped. These results were obtained using a hot wire conductivity meter from Neotim which can
give thermal conductivity through a powder bed. To determine samples porosity, we used a powder
tester which returned powder densities for different tapping levels. As we are working with filled
polyamide 12 matrix, a huge drop of flowability has to be considered upon addition of filler which
can cause issues during the process. Changes of processing parameters could be required due to
significant modifications of the thermal behavior resulting from the presence of fillers.