The Study On Selective Laser Melting Forming Process Of Co-Cr Prosthesis And Their Mechanical Characteristics

Selective laser melting is a new type of advanced additive manufacturing technology.Based on the scattering-additive principle, it can melt metal and its alloy powders directly,and form metal parts or moulds with full density, complex shapes and good property. It isparticularly appropriate for the rapid manufacturing of personalized structures applied inthe field of aerospace hard to machine parts, porous structure and bio-manufacturing.However, SLM forming process involves complex physical and chemical behaviors withmultiple affecting factors. Part performance is very different from the traditionaltechnologies, and it is difficult to control.Oriented to the demand of manufacturing prosthesis by SLM and the processoptimization of Co-Cr powder by SLM, applicable study of forming denture implants wasconducted on the basis. As for the fact that the strength and tensile modulus of dense metalparts are higher than that of natual bones leading to the incompatibility of bio-mechanicalproperties, manufacturing porous structures whose shape can be controlled by SLM toreduce their strength and modulus was studied.. The main research content is summarizedas the following three aspects:In the aspect of SLM forming process research: the SLM process of Co-Cr powderwas optimized by single line scanning, single layer scanning and part manufacturingexperiments. The influence discipline of laser power, scan speed, scan interval and layerthickness on part performance was obtained. The optimal process parameters such as laserpower100W, scan speed500mm/s, scan interval0.06mm, layer thickness0.02mm wereobtained, parts with density up to98.6%were manufactured. The microstructure iscolumnar crystal, which is small and uniform with obvious directivity. Grain size alongthe boundary of the molten pool increase obviously. The tensile strength of dense parts is1605.3MPa, offset yield strength is1243.7MPa, compressive strength is2293.8MPa,elongation is7.6%, surface hardness is32.2HRC. Compared with casting parts, SLM partshave higher strength and hardness, lower elongation.In the aspect of forming denture: in order to guarantee the forming process of denture,the cylinder supporting structure was optimized. According to the forming stability, theoptimum supporting structure sizes are as follows: outer diameter is1.0mm, thickness is 0.3mm, support spacing is1.2mm. Applying optimum process and suitable supportingstructure, the denture was successfully manufactured which meet the medical applicationstandard and achieved the clinical application.In the aspect of forming grid structure: the grid structure of repeated unit wasdesigned to reduce the strength of metal parts. Combining the finite element simulationand experimental validation to optimize the grid structure, with the increase of aperture,the compressive strength and elastic modulus decrease, and the variation trend graduallyslows down; When the pore shape is a triangle, square or hexagon, the porosity decreases,compressive strength and elastic modulus increase, and the variation trend of compressivestrength is obviously faster than the elastic modulus. Finally，two kinds of grid structurewere optimized，and their mechanical properties are in accordance with the natural bonds.Through a series of research, the optimum parameters of forming Co-Cr alloy bySLM were obtained, and dentures were formed which are suitable medical application.Grid structure parts were designed and optimized by SLM. The influence of porousparameters on the mechanical property was studied. Finally，two kinds of grid structurewere optimized, which laid a foundation on its clinical application.