Research On Manufacturing Technology Of Micro Thin-walled Parts Based On 3D Printing

Laser Engineered Net Shape(LENS)is one kind of technique which fabricate parts via 3D documents directly without Cutting tools and molds,has broad prospects in the design and manufacture of difficult processing parts,small parts,thin-walled parts and complex shaped parts.However,traditional manufacture techniques are facing ever greater challenges when handling with thin-walled structures due to its unique performance and special processing requirements.Evidently,LENS has competitive edge in processing thin-walled structures,also can simplify the process of thin-walled parts while ensuring processing quality,surface accuracy and microstructure.Nevertheless,the thin-walled cylindrical parts with holes in the wall have been a difficult problem to be solved.At present,most of the literature focuses on the radial inclination of thin-walled rings.Unfortunately,the circumferential inclination formed by the wall holes cannot be used as a reference owing to lacking of mature methods.In this paper,316L stainless steel was severed as the powder material.Using this material as the major work for thin-walled cylindrical manufacturing process to ensure the appearance quality,forming precision,improvement of the microstructure and quality.At the same time,the thin-walled cylinder processing theory was analyzed,the main work and the results are as follows.(1)Firstly,the single-factor,single-layer and single-path experiments was conducted to determine the initial value range of four processing parameters(laser power,scanning speed,powder feeding rate and shielding gas flow rate).Then obtained the interaction among four factors via full factorial test and achieved regression models and regression equation s about shape factor(aspect ratio)and dilution rate.Additionally,I obtained a set of optimal combination of process parameters via analyzing the saliency and residual of the model.Then,the Surface Response Method(SRM)is used to employ the verification test.Based on the original model,the accuracy is improved.Considering the evaluation criteria and interaction,the mathematical models and regression equations with higher accuracy and better performance are obtained.Finally,the original optimal combination of parameters was obtained by the amount of sticky powder,smoothness,other morphological parameters and microstructure observation verification as follows:the laser power is 350W,the scanning speed is 5.5mm/s,the powder feeding rate is 0.8r/min and shielding gas flow rate is 15L/h.(2)Secondly,Single-path and multi-layer test and two different cladding methods(co-directional hot lap and reverse cold lap joint)was carried out to study the effects of Z-axis increase of process parameters.In addition,the optimal Z-axis increase is determined as 0.224mm by measuring the outer diameter,inner diameter and height as well as judgment of flanging,collapse,bending and other undesirable topography quality,also I obtained the actual spot diameter of 1mm.Moreover,the reasons of cracks and top unevenness and flanging phenomenon and the performance of bottom bending were analyzed.Four solutions are proposed,which are as follows:(a)eliminating different inclination angles among the substrate,table and ground,(b)reducing the thermal lens effect,(c)implementing Preheating the substrate to improve system heat dissipation,(d)copping with the initial solution of poor morphology and radial error.Finally,through the observation of microstructure and the measurement of microhardness,the optimum of Z-axis increase and the selection of scanning method were verified.(3)Furthermore,the cause of height error was analyzed,seven kinds of optimization methods were proposed as well as verified that the most effective optimization method is SHL(scan mode optimization × helical scan trajectory optimization × laser power adjustment optimization).The regression model and regression equation of laser power and Z-axis increase were obtained.Semi-closedloop height control was carried out by CCD camera to adjust the laser energy density and laser power for morphology optimization and more accurate topographic features.(4)In the end,the cladding method of thin-walled wall with holes is theoretically designed,also the model of straight wall inclination angle is established.Two scanning methods are designed,which are forward way and backward one.The method of variable parameter processing is studied.By changing the Z-axis increase and the axial inclination to obtain the optimal(ΔY,ΔZ)parameter combination.As a result,the ideal cladding curve of the upper wall of the cladding cylindrical surface was obtained,and the foundation for the later study was laid.