| Alumina and zirconia ceramic materials are widely used in clinical practice because of their excellent aesthetics and mechanical properties. The current mainstream processing method is dental CAD/CAM system for cutting molding and this method produces all-ceramic restorations with good performance. But it has limitations such as the high cost and the difficult processing. Selective Laser Melting is an additive manufacturing technology with avoiding the waste of material and can be freely formed. But there are crack problems which seriously affect the material properties.Aim: To analyze the temperature field and the influences of process parameters on the temperature field distribution according to the finite element model of temperature field of Al2O3/Zr O2 ceramic powder in selective laser melting. And the simulation results can be used as a theoretical guidance for SLM experiments and a foundation of getting less crack Al2O3/Zr O2 bulk materials.Methods and Content : In this study, we used ANSYS12.1 Parametric Design Language(APDL), "Element Birth and Death" technology, infrared temperature measurement, scanning electron microscopy(SEM) and microscopic mechanical performance test and research the following content:(1) The numerical simulation model of the temperature field of Al2O3/Zr O2 ceramic in SLM was established by ANSYS and the temperature field was analyzed through this model.(2) We used a colorimetric infrared temperature measurement system to monitor the temperatures of molten pools in SLM. And the temperature measurement results and simulation results were compared to verify the correctness of the temperature field simulation model.(3) We analyzed the influences of process parameters(laser power, scan speed, scan mode and preheat, etc.) on the temperature field distribution, and used the results as SLM theoretical guidance.(4) Multilayer-Al2O3/Zr O2 ceramic bulk material was manufactured under the guidance of numerical simulation results. And we studied mechanical properties and scanning electron microscopy structures of the specimen.Results:(1) Temperature field simulation results show that the maximum temperature of molten pools is stable after a rapid heating process and the temperature overall increases. There are two temperature peaks of the nodes of the first melting layer and the first melting layer is remelted when the second layer is melted. Temperature contours is dense on the areas that are not melted than the areas that are melted.(2) The error of experimental temperature results and simulation results is within 5%. And the specimen surface is continuous and smooth but there are ball phenomenon and cracks and pores when storey is 0.5mm, preheating temperature is 1723 K, laser power is 150 W,scanning speed is 40mm/min and spot diameter is 10 mm.(3) Influences of process parameters on the temperature field distribution are as follow: 1)On the different process parameters, the maximum temperatures of molten pools increase rapidly at first and the temperatures increase slowly or are stable at last. And the temperatures overall increase. 2)When the laser power increases from 100 W to 200 W, the maximum temperature of molten pools and the solid-liquid interface temperature gradient increase. 3)When the scanning speed increases from 5mm/min to 40mm/min, the maximum temperature of molten pools and the solid-liquid interface temperature gradient decrease. 4)Different scanning methods have a little effect on the maximum temperature of molten pools and the solid-liquid interface temperature gradient. 5)The solid-liquid interface temperature gradient is higher when powders are on low preheating temperature or without preheating than the preheating temperature is 2000 K.(4)The process parameters are changed for preparing multilayer-Al2O3/Zr O2 bulk material based on simulation results and specimens are fractional between layers when laser power is low or scanning speed is high. And finally we found that Al2O3/Zr O2 bulk material is good at microscopic structure such as no stratification and no microscopic cracks when storey is 0.5mm, preheating temperature is 2000 K, laser power is 150 W, scanning speed is 10mm/min, spot diameter is 10 mm and scanning mode is reverse scanning method.Conclusion: The influences of process parameters on the temperature field can be fed back through the numerical simulation model of the temperature field which is built by APDL and ?Element Birth and Death? technology. And the SLM experiments show that the method of using the results of numerical simulation as guidance of experiments is feasible.Finally we get the SLM-Al2O3/Zr O2 bulk material which has good performances and this shows that SLM can be used well for oral field. And there are broad prospects for development. |
PDF Full Text Request