Study On Mechanical Properties Of SLM Formed TC4 New Lumbar Intervertebral Fusion Cage

The rapid development of metal 3D printing technology has made it possible to shape customized lumbar intervertebral fusion cages.Titanium alloy has excellent characteristics such as high specific strength,corrosion resistance,good biocompatibility and low elastic modulus,making it become the mainstream material for lumbar intervertebral fusion cages.In this thesis,a SLM-formed TC4(Ti6Al4V)lumbar intervertebral fusion cage was developed to explore the structural optimization and reasonable processing conditions under the premise of the required mechanical properties of the product.(1)New structural development.The shape was designed with bone-bone window and non-bone window.The internal structure parameters such as lattice unit,specification,porosity and irregularity were analysed and verified by using Solidworks,ANSYS Additive,3-matic softwares,and mechanical testing.A diamond lattice unit having a specification of 0.75 mm × 0.75 mm × 0.75 mm was selected,the porosity was 67.30%,and the irregularity was 40%(2)SLM molding optimization.Processing simulation of single channel molten pool,porosity and porous structure test model using ANSYS Additive,an additive manufacturing software.The processing parameters for the selected new product were laser power 170W and scanning speed 1150mm/s.The simulation results were confirmed by the static mechanical tests on the porous structure,the tensile and shear specimens,and by the CT and SEM micro structural observations(3)Effect of HIP treatment process on the performance of porous structures.CT and SEM techniques were used to analyze the morphology and mechanical tests of the two treatment methods before and after the HIP treatment.The results showed that after the HIP treatment the surface quality of the porous structure was improved,whereas the static mechanical properties were not improved.Therefore,without considering the dynamic fatigue life,the HIP treatment can be omitted to save costs.(4)The mechanical properties of the new product were tested and verified.For the new lumb ar intervertebral fusion cage,static compression,shear and subsidence performance,fatigue compression and shear tests were performied after annealing and heat treatment.The results showed that the axial compression of lumbar intervertebral fusion cage with both bone grafting and non-plant bone window withstood loads of more than 80,000 N without func-tional failure,and the stiffness diference between axial compression-shear test and subsidence test was small.The compression fatigue and shear fatigue of the non-bone window lumbar intervertebral fusion cage completed the prescribed 1.5 million cycles,the compression fatigue of the implanted lumbar intervertebral fusion cage failed at 560,000.cycles,while shear fatigue fracture,occurred before the required cycle period.From the perspective of mechanical properties,it is preliminarily determined that the non-bone window lumbar intervertebral fusion cage of this design is relatively safe nd applicable.