Methods for quantifying the stable sintering region in laser sintered polyamide‐12

Abstract

Manufacturing complex parts by the laser sintering process requires a minimum amount of energy input for consolidation of polymer particles to occur; however too much energy can result in a decline in mechanical properties. This decrease is thought to be the result of polymer chain degradation. A stable sintering region (SSR) has been proposed to describe the optimum temperature range for successful laser sintering. This article will aim to quantify the SSR for polyamide‐12 by using thermogravimetric analysis (TGA) to provide a framework for identifying key laser sintering processing parameters. Weight loss with respect to temperature is the main measurement output of the TGA procedure. However, the precise temperature and thermal history of a material is difficult to quantify during the laser sintering process; instead an energy input approach has been developed. A degradation energy was calculated from the TGA data and was used in conjunction with a laser sintering formula called energy melt ratio to prescribe build parameters for laser sintered parts. The mechanical properties of these parts illustrated the effect of degradation at various levels of energy input. Implications for this work include optimizing the material selection process for polymer laser sintering materials beyond polyamide‐12. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Predicting processing parameters in high temperature laser sintering (HT-LS) from powder properties

“…The upper limit is the temperature at which the 1% weight loss degradation occurs during a TGA experiment that is carried out from room temperature to HT at a heating rate of 10 ˚C x min -1 . This method clearly does not take into account the crystallisation effect present in semi-crystalline polymers such as PA based powders or PAEK materials and therefore according to Vasquez et al [9] can be used for more types of polymers. The authors showed that PA 12 presents a stable sintering region at 120˚C, with lower limit at 200˚C and upper limit at 320˚C.…”

“…With this intent, Vasquez et al [9] defined the EMR for material degradation (EMR D ) (Eq.5) in the LS process using the volumetric energy density for degradation (ED vol,D ), the volume energy required to melt the powder material (E m ) and theoretical energy of degradation (per unit volume) (E D ).…”

“…The stable sintering region is a concept introduced by Vasquez et al [9] to study established and new potential LS materials in the region above their melting points and below their degradation temperatures. It aims to predict the temperature interval that leads to thermal degradation of the material in order to avoid it, during a LS building operation, especially during the laser exposure.…”

“…The Energy Melt Ratio (EMR) is a numerical parameter introduced by Starr et al [19] and later investigated by Vasquez et al [9], used to study the relationship between LS manufacturing parameters and mechanical properties of laser sintered PA specimens. The parameter describes the ratio between the energy applied in LS (ED vol ) and the energy required to melt a unit volume of a given material (E m ) (Eq.4).…”

“…More recently, Vasquez et al [9] reported on the investigation of a parameter called Energy Melt Ratio (EMR), where material characteristics obtained by thermal analysis, gel permeation chromatography and thermo-gravimetrical analyses are used to predict the ideal LS processing parameters. "Ideal parameters" indicated those building settings that prevented material degradation during the laser consolidation while reaching the highest mechanical properties in the parts.…”