Research On Key Techniques Of Laser Sintering Of PA12/Limestone Composite

Laser sintering, one of excellent additive manufacturing technologies, is expanding to more new application domains because of its layered manufacturing method and wide material selection rang. In order for that process to be competitive and become a strong candidate for new application and adapt to the global sustainable developing trends of high efficiency, energy saving, low carbon and environment friendly, the feedstock needs to be improved. Also, reducing material cost can definitely promote a more extensive development of this technology. Starting with the purposes of reducing the cost, energy consuming and environmental implication of laser sintering polyamidel2 (PA 12), this research developed a new type of sustainable PA12/limestone composite with the advantages of low cost, environmental friendly, energy efficient, good forming accuracy and mechanical strength for Laser Sintering (LS), and it also added a new feedstock to laser sintering fine stone artware and ornament. This material system is composed by commercial PA12 matrix and natural limestone additive.Through material design method, this paper first compared the materials’ properties which are related to laser sintering processing. The embody energy of limestone which is mainly composed by CaCO3 is only 0.6% of the pure PA12’s, and the thermal conductivity is about 10 times higher than PA12’s. Additionally, natural limestone is very cheap and has a low processing CO2 emission which is two orders of magnitude lower than processing PA 12, so it proved the rationality that mixing PA12 matrix with limestone additive as the laser sintering feedstock could serve the purpose of this research. Then different types of powder blends with different mixture ratios were created through alloying limestone and PA 12. Single layer sintering was performed to verify the feasibility of using PA12/limestone composite as the feedstock of LS and determine the maximum mixing ratio of limestone and PA12, which is 1:2, for the greatest degree to reduce costs, energy consuming and CO2 emission. Meanwhile ensuring a good forming ability of the composite material has to be considered. Preliminarily studied the effect of the preheat temperature on the range of laser power selection and curling of sintered area. Morphology observation of PA12/limestone composite was performed. And thermal properties of PA12/limestone composite were studied. Through DSC testing, it studied the effect of limestone additive and its volume of addition on the melting and crystallizing process of PA12 matrix. Sintering widow of PA12/limestone composite was calculated as well. Before sintering experiments, thermal conductivity (which is an important component in understanding and optimizing the processing of laser sintering PA12/limestone) was measured, and it showed the changing law of the PA12/limestone composite’s thermal conductivity with temperature. At last, take the results of DSC testing and thermal conductivity measuring as the theory foundation to interpret the performance of sintered PA12/limestone parts.Discuss the new design for additive manufacturing (DFAM) method brought by additive manufacturing technology altering the mechanical design philosophy of traditional manufacturing technology and based on DFAM method, it designed models of demonstration parts with complicated structure, thin wall, tiny pore, small fit clearance and abundant details for the further verification of formability of PA12/limestone composite.Through experimental design method, a 2 levels 3 factors experiment was designed based on laser power, scanning speed, preheating temperature. Main factors significantly affecting the properties of final sintered PA12/limestone parts were determined, as well as a suitable rang of their value selection for the following research. Demonstration parts and performance testing specimens were fabricated. Mechanical testing shows that sintered PA12/limestone parts’ mechanical properties changing as a function of processing parameters and limestone amount. The optimal processing parameters are investigated. The average tensial strength reaches the minimum tensial strength of solid limestone, and higher than wood-plastic composite and rice husk-plastic composite. By dimensional measurement, the forming accuracy in X, Y, Z directions of sintered PA12/limestone part were investigated, respectively. The mean accuracy of PA12/limestone parts is better than PA 12 parts.Discuss the effect of limestone on the forming performance of PA 12 matrix, and theoretically analyze the enhancement mode of limestone in the PA12/limestone composite, and on top of that, it studied the interaction mechanism and laser sintering bonding mechanism between limestone and PA 12 particles. Combining SEM observation and IR analyzing of PA12/limestone material before and after sintering, it investigated the interfacial boning mechanism between limestone and PA 12 particles as the mechanical interlock. In addition, through SEM it characterized the varying microstructures of PA12/limestone prototypes sintered by different laser power and preheat temperature. It can be further used to analyze and explain the effect of laser power and preheat temperature on the mechanical properties of PA12/limestone parts.The effect of limestone content on the thermal conductivity of PA12/limestone composite was studied. With increasing the limestone content, lots of small limestone particles with high thermal conductivity replaced the air which has very low thermal conductivity in the space amoung PA12 particles, and increased the contact area between particles. So it could improve the thermal conductivity and further forming accuracy of the material system. The research on the effect of limestone content on the density and color of PA12/limestone parts were performed as well. In addition, through SEM, it characterized the microstructures of PA12/limestone part based on varying limestone content and laser power, and studied the changing law, which could explain the effect of limestone content and laser power on the mechanical properties of PA12/limestone part from the microscopic view. At last, through quantitative analysis, it calculated the energy consumption, CO2 emission and costs of PA12/limestone composite and neat PA12, highlighting the advantages of using sustainable PA12/limestone composite as the feedstock of LS. Moreover, it measured the changing of the thermal conductivity with increasing the content of limestone.