| Skeletons, as important parts of the human body, are responsible for functions of supporting, protecting, hematopoietic, calcium storage, exercise and metabolism. With the arrival of the aging stage of our country, the demand of bone transplantation and repair increases due to the increasing incidence of bone diseases. Therefore, developing the bionic artificial bone suitable for replacing the broken bone in human body is one of the most important methods for bone disease treatments. At present, the composite material of poly lactic acid(PLA)- nanometer hydroxyapatite(n HA) prepared by the fused deposition modeling(FDM) technique has attracted much attention for its unique mechanical properties, biocompatibility of cells, osteoinductivity, biodegradable and advantages for the cells’ growth and reproduction. However, the major challenge of preparing the thermoplastic polymer material of PLA-n HA through FDM technique originates from the easily occurrence of warp phenomena. In addition, the material molding of the ceramic n HA is difficult. Consequently, it is difficult to achieve high printing precision of the PLA-n HA-based bionic artificial bone. Therefore, it is crucial to investigate the FDM process of PLA-n HA and subsequently optimize the processing parameters, which provide effective theoretical basis and experimental guidance for the FDM molding of biomimetic artificial bone.To this end, in this paper the FDM molding process of PLA-n HA is investigated, which aims to improve the molding precision of biomimetic artificial bone. The main work of this paper is:The establishment and analysis of thermodynamic simulation model of FDM molding process. Firstly, the nonlinear transient heat conduction equation and the solving method of thermal coupling stress field on FDM molding process are finalized according to the finite element method(FEM) theory of the temperature field and thermal coupling stress field. Secondly, parameters of material properties, physical simulation model, element type, boundary conditions and loads are chosen based on actual FDM molding process, and simulation models of temperature field and thermal coupling stress field are established by using the "life and death element technology" based on the ANSYS parametric programming language(APDL). Finally, according to the simulation results of FDM molding process to analyze the temperature field distribution, the equivalent force distribution at the end of the forming process, as well as the relationship between characteristics of the node temperature, temperature gradient and equivalent stress with the time change. The simulation results are consistent with the actual forming process, which verifies the correctness of the thermodynamic simulation model.Performing finite element simulations to investigate the influence of printing process parameters on FDM molding process. Firstly, the printing process parameters that influence the molding precision are selected according to the actual FDM molding process. Secondly, thermodynamic simulation models of molding room temperature, nozzle temperature, molding velocity, layer thickness and molding angle are established according to the actual molding process. Finally, the influence of printing process parameters on FDM molding process is studied through the analysis of forming end moment simulation model of temperature field distribution, characteristics of node’s temperature gradient with time change and the forming end time thermal coupling stress field distribution, which provide a theoretical guidance for experimental analysis.Experimental study of FDM molding process. Firstly, the PLA-n HA is prepared by the melt blending technology, and the printing model was designed to facilitate the experimental investigation and measurement. Secondly, the print route for each printing parameter is designed and accomplished according to the actual FDM molding process. The measurement of length, width and thickness of the printed model shows that the experimental results are consistent with the simulation data, which enable the confirmation of the influence of printing process parameters on the FDM printing precision. Subsequently, optimized FDM printing process parameters are obtained based on the simulation and experiment results,which can greatly improve the printing precision. Finally, the three-dimensional model of bionic femoral is established based on the reverse engineering method, which is then used for the FDM printing under the optimized printing process parameters. The printing precision is analyzed by using the 3D scanning technology, and the results show that the average deviation of the bionic femoral is 0.051 mm, which proves the feasibility of PLA-n HA artificial bone transplantation. |
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