Betrachtung zur Pulvernutzungsdauer beim Laser-Sintern und Einfluss der Prozessführung auf die Entstehung von Ausschussbauteilen

Abstract

When using nylon powders for laser sintering, material aging appears depending on the time the material is stored under temperature in the building chamber. The use of aged powder can lead to the occurrence of the so called orange peel effect, if the powder is not refreshed sufficiently. This results normally in defective parts. Origin of the material aging is post-polymerization. In the last years MVR-measurement has been established for the laser sintering process to characterize the material aging. However, the correlation of powder age, parts’ properties and the influence of different process parameters has not been analyzed in detail, yet. Therefore, materials with different aging levels were used in this study. The aging levels range from virgin powder to defective powder. These powders were processed on an EOS Formiga P100 to analyze the powder properties, the processing conditions and the parts’ properties for different parameter settings. The Hausner-ratio was used to determine the flow properties of the powder, while MVR-value should characterize the material’s aging level. The packing density of the powder bed was used to analyze the quality of powder spreading. In a second step, different parts’ properties were considered to evaluate the resulting quality of the parts as a function of aging. These were the mechanical properties, the part’s density and the surface finish. Fill and outline laser power as well as fill scan spacing were used as possible influencing factors on the appearance of the orange peel effect and the descend of parts’ properties caused by material aging. Aim of the research done was to correlate the time at which defective parts occurs with the used process parameters