Aging behavior of polyamide 12 during Selective laser melting process - Influence on mechanical properties

Selective laser melting is a well-established manufacturing technique in prototype construction. In recent years a tendency to rapid manufacturing applications and the production of ready to use components with this technology can be observed. If components made by laser melting are desired to be applied in technical series products, their achievable properties play a major role. The high process temperatures in combination with long build times during laser melting process lead to chemical and physical aging mechanisms on the polymeric feed material. The unmolten partcake material, which acts as a supporting structure, can be removed after each building process and reused for further processes. To achieve part properties which endure the necessary mechanical loads, refreshing of partcake powder with 30 up to 50 % by weight virgin material is necessary. However, constant refreshing strategies will lead to varying component properties due to an undefined aging state of the basic partcake material. Therefore, a fundamental understanding of the correlation between the feed material aging state and resulting mechanical properties is alienable. This paper deals with the analysis of the relationship between the aging state of the feed material focused on rheological behavior, mechanical part properties and deformation behavior. Therefore, polyamide 12 powder is used for at least five processing cycles without refreshing. Before and after each build process, bulk and material characteristics like bulk density, hausner ratio, viscosity number, melt volume rate and average molecular weight were determined. Tensile tests were conducted in order to study the mechanical material and deformation behavior. Finally, mechanical behavior as a function of feed material can be evaluated. On this basis, powder life cycles in dependency of mechanical properties can be derived.