Research On In Situ Machining Process Of Additive And Subtractive Hybrid Manufacturing For 316L Stainless Steel Thin-Walled Parts

Directed energy deposition(DED)technology is one of the important branches in the field of additive manufacturing technology.It uses solid powder as raw material,highpower laser as heat source,and coaxial powder feeding.According to the pre-designed path trajectory,the solid powder undergoes the process of melting and re-solidification,thereby achieving layer-by-layer accumulation.Additive manufacturing technology breaks through the constraints of a series of factors such as fixtures,tools and molds in traditional manufacturing technology,and realizes the high freedom of part design,so it has attracted much attention.Additive-subtractive composite manufacturing technology has become one of the mainstream methods of intelligent,flexible and precision machining of parts.In this paper,316 L stainless steel in-situ additive and subtractive composite manufacturing is taken as the research object.The Hopkinson pressure bar test and cutting test of additive parts,the additive and subtractive composite processing test of straight wall thin-walled parts and square thin-walled parts are carried out.At the same time,the finite element model is established to simulate the Hopkinson pressure bar test,the temperature field of the additive process,the stress field after the additive process,and the laser molten pool morphology of the additive process.The results show that the additive path is an important factor affecting the mechanical properties of the additive parts.The laser path and the scanning speed are the main factors affecting the size of the laser molten pool.The deformation of the straight wall and the frame thin-walled parts increases with the increase of the deposition height,and the two ends of the straight wall thin-walled parts and the corner of the frame thin-walled parts have the largest deformation.Firstly,the theoretical part of additive and subtractive composite manufacturing is studied,the main working principle of additive manufacturing is understood,and the main influence mechanism of process parameters on the forming quality of parts in LMD process is deeply understood.Then combined with the traditional milling introduced the processing principle of additive and subtractive composite manufacturing,summed up some defects and problems in the process of additive manufacturing.In addition,the numerical simulation of the laser molten pool was carried out to further verify the relationship between the laser process parameters and the size of the molten pool.Secondly,the Hopkins pressure bar test and milling test of the additive parts were carried out.The Hopkins pressure bar test was carried out on the samples with different deposition paths.It was found that the deposition path had a great influence on the mechanical properties of the additive parts,and the cross deposition obtained better performance.Orthogonal milling experiments were carried out on the block workpieces manufactured by additive manufacturing.The relationship between cutting force,workpiece surface roughness and milling parameters was characterized,and the optimal milling parameters of additive parts were obtained.Thirdly,the laser rapid forming test of 316 L stainless steel straight wall thin-walled parts and square frame thin-walled parts was carried out by using the additive and subtractive composite manufacturing machine tool.The temperature distribution of the parts and the temperature change of the laser center point in the additive process were recorded by the infrared thermometer.After the additive was completed,the surface of the workpiece was scanned by the laser range finder to obtain the deformation data of the surface of the additive.Finally,the finite element model is established to numerically simulate the temperature distribution,stress distribution and deformation of the test process,and the experimental data are compared with the simulation data.The influence of residual stress on the deformation of 316 L stainless steel thin-walled parts during additive-subtractive composite machining was obtained,which laid a foundation for the subsequent additivesubtractive composite manufacturing of complex parts.