| Due to their timely and costly complicated steps and the poor material properties,the conventional manufacturing techniques to processing dental ceramics has been unable to meet the needs of the patients for all-ceramic restorations. Even though the CAD/CAM system could significantly boost the efficiency, it is unable to be fabricated at one step. Therefore this procedure not only makes the operation more complicated, but also costs volume shrinkage which will influence the suitability of restoration edges. Selective Laser Melting(SLM) is an advanced Rapid Manufacturing technology. By the help of CAD/CAM data SLM is toolless and one time produce take shape at once and produce Physical parts of excellent performance which is no more limited by complicated shape. If this kind of advanced technology could be made use of in the field of dental restorations ceramic material, and further processes all-ceramic restoration which conforms to the requirements of the clinical, it will greatly facilitate the production efficiency of restoration so as to reduce the processing cost and meet the demand of all-porcelain restoration.Objective The purpose of this research lies in the research on the relations between Powder raw material — solidification parameters — temperature field environment —forming organization — material performance when Al2O3/Zr O2 ceramic powder is processing in SLM, in order to gain gull density, no crack, internal phase homogeneous SLM-Al2O3/Zr O2 ceramic block material which is beneficial to the future application of SLM technology to Dental ceramic materials processing technology in the field of repair clinical.Method and Contents This research will take advantage of the scanning electron microscope, energy spectrum analysis and XRD diffraction, infrared temperature measurement and microscopic mechanics performance test and so other means.1) In processing of forming phase, the law of growth evolution and its influence factor of the crystalline phase within the organization of Al2O3/Zr O2 duplex ceramic materials.2) Observing the effects caused by preheating temperature on the internal crack of shaped material, and further analyzing extension and growth inhibition mechanism. Based on the infinite element, the analysis of the change rule of temperature field in laser cladding will be carried out so as to optimize various technological parameter.Results1) If the ceramic powder granularity of raw materials is too small, it will cause reunion phenomenon in the powder bed, thus further procures defects and cavity in the inner part of SLM forming ceramic material, while the forms of power exerts no impact on material. Therefore, the requirement of granularity of ceramic power raw material which is processed by SLM is 100μm2) According to the eutectic proportion, in the organization of shaped material by the mixed power, instability of single phase caused by Zr O2 appears, which break though Eutectic cell structure due to Eutectic balanced growth, this structure will produce the decrease of Zr O2 Tetragonal phase in material so as to wield impact on mechanical property of material. Therefore, it is necessary to add more Al2O3 power in the mixed power so as to compensate the loss of aluminium oxide in the process. Experiment shows that the optimal proportion Al2O3:Zr O2 is 62.5wt%:37.5wt%;3) In the case of completely fused, the faster the laser scanning speed, the higher the degree of organization refinement of ceramic material, and the better the performance, but had no significant effect on crystal phase structure of the material4) In the case that the preheating temperature is not enough or is instable, the surface and the internal part will generate a lot of cracks, the generation of the cracks is related with the temperature gradient in the center of molten pool to all a round. Therefore, it is necessary to decrease the temperature gradient, namely, from the preheating temperature to ideal temperature, this temperature gradient should be stable so as to reduce the formation of the internal crack.5) Before fusion, using la ser to implement high speed scanning technology to scan the powder bed back and forth so as to preheat the powder bed, optimized Laser heating parameters is obtained by experiment(laser power is 150 w, scanning speed is 4000 mm/min, preheat 1 min).6) Taking advantage of finite element technology to built SLM forming temperature field model, and simulating the transient state when the laser run into the molten pool and the temperature change when SLM ceramic cladding forming process;7) Designed a kind of powder processing device which could implement in the LFS system multi- layer powder processing, and it could implement multi- layer sintering of SLM ceramic block material, so as to optimize process parameters(laser power 200 w, scanning speed is 100 mm/min, spot 10 mm).8) Using Al2O3/Zr O2 mixed powder(diameter ﹤ 100 μ m, Al2O3:Zr O2=62.5 wt %;37.5 wt %), having spread powder(500 μm thick) laser preheating(laser power 150 w, scanning speed 4000 mm/min, spot diameter 10 mm, preheating time 1 min) and then laser cladding, laser power 200 w, scanning speed is 100 mm/min, spot 10 mm), forming no obvious crack, full density, the organization structure is meticulous, excellent mechanical properties of SLM-Al2O3:Zr O2 ceramic block material.Conclusion Through a series of studies, this paper verifies that the use of Selective Laser Melting SLM to process dental ceramic materials is a novel and feasible machining method, which could greatly shorten the production cycle of the all-ceramic restoration. Although at present there still exist some problems, such as, dust powder remains on surface, low machining accuracy, the further study on the forming performance, improvement of precision and surface properties, SLM technology will lead a new production technology innovation in al-porcelain restoration in dental clinical area. |
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