Study On The Forming Processes And Properties Of Customized CoCr Alloy Crowns And Fixed Bridges Manufactured By Selective Laser Melting

Selective laser melting(SLM) is a high degree of personalization, high material utilization technology in the field of additive manufacturing(AM). The metal parts with metallurgical bonding, compact texture, good mechanical properties and high precision can be manufactured directly by SLM, which is very applicable to the field of dental restorations with personalized, complicate and digital technical requirements. Since SLM is different from the traditional methods, the forming properties shall vary accordingly, and the crowns and bridges are often thin-walled parts with complex curved surface, their SLM formability is different from the traditional restorations. Research on the feasibility, reliability and security of the application in dental restorations of SLM technology is of great significance. In this study, the Co Cr power is used to manufacture personalized crowns and fixed bridges designed by reverse engineering. The process and property is studied and analysed. The main contents and results are as follows:(1) The process optimization of SLM-made Co Cr alloy crowns and fixed bridge is studied, inclulding the relative density, surface roughness and dimensional accuracy, etc. The orginal optimized parameters obtained by orthogonal test to reach high relative density are P =160W, ? =400mm/s, S =0.08 mm, H =0.025 mm. Further experiments showed that the adhering powder, spatter behavior, contour error, stair effect, spot constraints and other negative phenomena will affect the surface quality of SLM parts. By changing the laying angle of parts and using X-Y inter-layer staggered + contour scan strategy can improve the surface quality, to optimize the beam compensation value can further improve molding accuracy.(2) To evaluate the reliability of SLM-made alloy, the forming properties include the microstructure, mechanical properties, corrosion resistance and metal-ceramic bond strength are studied. Experiments show that SLM-made alloy samples have fine and uniform grain,and have eccellent comprehensive properties. After the ceramic sintering process, the grains of Co Cr alloy grown without orientation, some ? phase transform to ? phase and strengthening ? phase precipitates out. The hardness and tensile strength of it are improved,but the corrosion resistance and elongation decreased slightly, and the average metal-ceramic bonding strength is 36.79 ± 0.49 MPa, all performance are in line with ISO9693 standards. Repeated use of powder inclusions spatter particles will reduce the tensile properties of molded parts, but no significant effect on the metal-ceramic bond performance.Three-point bending tests showed the surface treatmentof polish + sand blast can help to improve the metal-ceramic bond performance.(3) The personalized crowns and fixed bridges are design by three-dimensional digital scanning and CAD methods,and ccording to the geometric characteristics of crowns and fixed bridges, processed the CAD data by smoothing surface, adjusting the placement and adding support structure. The personalized Co Cr alloy crowns and fixed bridges manufactured by optimized SLM molding process parameters acchieve the desired effect, and have good molding precision.