Study On Surface Quality And Forming Accuracy Of Ti6Al4V Titanium Alloy Formed By Selective Laser Melting

Ti-6Al-4V,one of the most important titanium alloys for industrial applications,is widely used in aerospace,marine engineering,automotive,energy,chemical and biomedical fields.However,traditional manufacturing methods are unable to process complex structural Ti-6Al-4V parts.Selective laser melting(SLM),as an advanced manufacturing technology,manufactures parts by accumulating material layer by layer.Compared with traditional manufacturing technology,SLM technology has the advantages of shortened production cycle time,high material utilization rate,and strong personalization,etc.It breaks through the limitations of tools,molds and fixtures,and can form complex titanium alloy structural parts that cannot be processed by traditional manufacturing methods.Due to the rapid melting and solidification of the processed material during the SLM forming process,SLM formed specimens have problems such as low surface quality and large geometric accuracy errors.In this paper,we analyze the melting and solidification mechanism of SLM titanium alloy melt pool and the interaction mechanism between adjacent melt channels,investigate the influence of SLM process parameters on the surface quality of formed parts,study the influencing factors of geometric accuracy of formed parts of titanium alloy Ti-6Al-4V,and propose a geometric accuracy improvement strategy based on the model modification of formed parts.The geometric accuracy improvement strategy based on the model modification of formed parts is proposed.The main research contents are as follows:(1)Analysis of melt pool dynamics and part warpage during SLM titanium alloy forming process.With the change of laser input energy,the melt pool size,solution fluidity,melt pool stability and forming ambient temperature change.Based on the melt pool analysis,a reasonable lap ratio can balance the forming quality and forming efficiency.The analysis and theoretical calculation of the warpage phenomenon based on the non-uniformity of the cooling of the part show that the total warpage is closely related to the size of the part.(2)Study on the surface quality of SLM titanium alloy parts.The influence of laser power,spot spacing and exposure time on the surface shape and roughness of the part was investigated.Based on the analysis of the measured data,it was concluded that the surface micro features and line roughness of the fabricated parts showed significant directional changes,and their directionality was highly correlated with the laser scanning path.The spheroidization and lap defects are more likely to appear at low laser power;the parts made by high laser power and long exposure time have flat surface morphology and fewer surface defects,but are prone to melt and powder sputtering.(3)Study on the forming accuracy of SLM titanium alloy parts.The influence of SLM process parameters on the accuracy of the parts was investigated,revealing that the residual stress generated by the cooling shrinkage of the parts is the main factor of the forming error.The combined effect of temperature difference between the upper and lower part of the same forming layer,substrate and heat transfer causes the deformation of the upper part of the same forming layer to be larger than that of the lower part,resulting in warpage defects in the part.(4)Optimization study of forming accuracy of SLM titanium alloy parts.The non-linear relationship between conical deformation and forming height is established,and the size of the part is designed to be pre-compensated,and the overall equivalent force only increases slightly after optimization.