Influence of degradation behavior of polyamide 12 powders in laser sintering process on produced parts

Abstract

Additive manufacturing technologies, such as selective laser melting of polymers enable manufacturing of complex parts without tools and forms. Due to high temperature during processing, a degradation of the used plastic powder occurs. The unmolded material in the building chamber, the so-called partcake, can be removed from the finished component after building and reused for another process. To realize reproducible part properties refreshing of partcake powder is necessary. This paper presents results on the investigations of degradation behavior of polyamide 12 powder during selective laser melting process. The influence of different ambient conditions, e.g. ambient air, nitrogen and vacuum, is investigated in a model experiment. Oven aged polymer powders were analyzed with regard to their process relevant material properties. Considered material properties are phase transition temperatures, melting viscosity or molecular weight. The results of the investigations show, that the influence of high process temperatures on used material can be reduced using other ambient conditions. Process relevant material properties are minor affected by storage under vacuum. In addition to that the influence of different ambient conditions as well as a material pretreatment on the degradation behavior of sls materials, e.g. exclusion of intermolecular located oxygen, is analyzed. To correlate these results of the model experiment with real manufacturing process laser sintering experiments are done. PA12 powder is used for several building processes with refreshing. Produced specimens and resulting partcake powder are analyzed and correlated to the results of model experiment. Correlating effects, regarding process relevant material properties as well as aging influenced mechanical properties of specimens can be detected.

Surface modification of the laser sintering standard powder polyamide 12 by plasma treatments

“…However, the problem of the unmelted particles increases when the treated powder is subjected to melting conditions replicating those of laser sintering. The LS technique failed to fuse all the particles from the nontreated powders (see Figure d) especially with aged powder (recovered powder) which was thermally degraded during subsequent LS processes …”

Modelling of the aging behavior of polyamide 12 powder during laser melting process

“…Whereas storage periods over 64 hours lead to an increase of the molecular weight due to chain scission [10,11]. Furthermore previous investigations dealt with the influence of the amount of building cycles on thermal and rheological material properties [12]. The rheological behavior has the highest change in the first building processes and reaches a stable level afterwards [12].…”

“…Furthermore previous investigations dealt with the influence of the amount of building cycles on thermal and rheological material properties [12]. The rheological behavior has the highest change in the first building processes and reaches a stable level afterwards [12]. Gornet [13] also dealt with the influence of the amount of processing cycles on thermal, rheological and mechanical material properties.…”

Preparation and characterization of novel PA6/SiO2 composite microsphere applied for selective laser sintering

“…In addition, the use of PA12 powders often creates unsatisfactory mechanical properties. The thermal stability of the material is decreased under strong irradiation with UV or long-term UV exposure, which makes both powder and sintered products prone to yellowing [17,18]. Therefore, the development of new high-performance and low-cost polymer powders is urgent.…”