Research On The Forming Properties Of PA12 And The Process Analysis Of Porous Scaffold Based On Selective Laser Sintering

Selective laser sintering(SLS)is one of the fastest and most promising technologies in rapid prototyping manufacturing.It has many advantages,such as wide forming material and no support.However,due to the characteristics of "layer by layer sintering",the SLS process is prone to warpage,shrinkage and poor mechanical properties.Reasonable process parameters are the key to obtain high precision and high quality SLS parts.At the same time,the porous scaffold SLS forming process with both mechanical and biological activity has become a hot spot in the field of bone defect treatment.Therefore,in view of the excellent mechanical properties and the most widely used PA12 powder,the effect of process parameters on the accuracy and mechanical properties of SLS parts is discussed.At the same time,the porous scaffold was prepared by adding hydroxyapatite(HA)powder with good biological properties in PA12 powder,and the effect of process parameters on the forming and compression strength of the porous scaffold was studied,which provided a solution for the bone defect disease.The specific content and research results of this paper are as follows:(1)Analysis of SLS process parameters based on single factor experiment.The pure PA12 powder has confirmed that the process parameters suitable for SLS are 170 C of preheating temperature,the thickness of substrate 12 mm,and the single layer thickness 0.1mm,and the experiment shows that the printing direction has great influence on the mechanical properties of the parts,and the axial ratio along the XY axis is better than that of the Z axis.(2)Numerical model and influencing factors analysis of PA12 product density based on SLS technology.Based on the response surface method,the nonlinear model between SLS part density ρ and three technological parameters(laser power P,scanning distance d,scanning rate v)is established.The accuracy test and model optimization are carried out by variance analysis,and the influence of P,d and v on the density ρ of the workpiece is analyzed.The results are as follows: with the increase of P,the density of SLS parts increases first and then decreases,and the laser power P has a great influence on the precision of the parts.The low value of P leads to the poor printing effect,and the excessive value of P leads to the warpage easily.ρ decreases with the increase of d,ρ decreases with the increase of v value,and the interaction between d and v is obvious.(3)The optimization design of the process parameters of SLS parts of PA12.With precision and density as the evaluation index,the optimization interval of three factors such as laser power P,scanning distance D,scanning rate V is set,and P=27.5W,d=0.1mm,v=1500mm/s are the optimal technological parameters combination of PA12 parts by SLS process,and the optimized parameters are verified experimentally.(4)PA12/HA porous scaffold design and process parameters influence analysis.First,the PA12/HA powder thermal analysis results show that the porous scaffolds can be prepared with the same technological parameters as pure PA12 powder.Then,the effect of different HA content,pore shape and porosity on the compressive strength of porous scaffold is studied based on the orthogonal test.The results were as follows: the factors affecting the compressive strength of scaffolds are arranged in order of significance,porosity,porosity and HA content.With the increase of porosity,the compressive strength of scaffolds decreased and the trend of decline increased.The compressive strength of porous scaffolds with circular holes is obviously stronger than that of the other two kinds of passes.With the increase of HA content,the compressive strength of scaffolds increased slightly.