Long-term Properties of Laser Sintered Parts of Polyamide 12 - Influence of Storage Time and Temperature on the Aging Behavior

The key in selective laser sintering (SLS) of polyamide 12 for exceeding the cusp from a prototyping to a serial production technique poses the long-term behavior of such components. The improvement of additive manufacturing technologies is attended by the enlargement of the possible ranges of use. The crucial obstacle for their actual use is the ignorance of the long-term properties and the consequential fact of not given warranty. The aging behavior of polyamide 12 based injection molded parts and powder for the SLS process is largely probed and methods of analysis are well-established. On the basis of several build jobs consisting of vertically build tensile bars, oven storage experiments are realized. Storing for several time periods and temperatures allows a first calculation of the aging behavior in consideration of the building position and process parameters of each bar. First of all the adaptability of two methods of analysis, tensile test und solution viscosimetry, for determining the state of the aging of SLS parts is surveyed. It shows that depending on the used method of analysis the building position of the picked up sample could play a role. Furthermore the influence of the process parameters, the aging processes itself and the necessary storage conditions for the artificial aging of the parts are considered. All in all this article gives a review of the aging mechanisms of oven stored polyamide 12 parts, possible methods of analysis to determinate their state of aging and first results to qualify the adaptability to selective laser sintered parts. In Addition to that a first correlation between mechanical and chemical properties is made. The presented results form a first step for the future to be able to guarantee the requested product quality over its lifetime, but nevertheless other methods of analysis have to be qualified for the determination of the aging behavior of SLS parts.