【作者】 王黎；

【导师】 史玉升； 魏青松；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2012， 博士

【摘要】 选择性激光熔化成形技术（Selective Laser Melting, SLM）是快速原型及制造（Rapid Prototyping&Manufacturing, RP&M）领域最具发展潜力的技术之一。该技术利用高能束激光直接熔化金属粉末，可成形近全致密的高性能金属零件。由于可成形传统加工方法无法加工或多部件拼装的复杂结构，因此在航空航天、个性化生物制造及复杂模具镶块等方面具有广阔的应用前景。但是SLM成形影响因素众多，成形零件的精确控形与控性存在较大难度。为此，本文重点研究SLM成形零件的表面质量、尺寸精度及力学性能，并在SLM成形复杂模具上进行初步研究。主要内容包括如下几个方面：（1）研究了SLM成形零件的表面粗糙度。通过系列实验，研究了单熔化道尺寸特征，引用形状系数F来评价熔化道的形状。揭示了SLM工艺参数及扫描策略对单道、单层表面粗糙度的影响规律。研究表明，熔化道表面粗糙度随着扫描速度的提高而降低，随着激光功率的提高先降后升。激光沿一个方向扫描一次的表面粗糙度最大，用两倍间距扫描一次，再用正常间距扫描第二次后的成形表面粗糙度最小。研究了成形角度（成形零件侧面与工作平面的角度）、激光功率密度及加工层厚等多因素对零件侧面表面粗糙度的影响规律。结果表明，在成形角度小于60°时，随着成形角度的增加，表面粗糙度呈大幅降低的趋势。在成形角度大于60°，随着角度的增加，表面粗糙度有所降低，但是变化并不明显。（2）研究了SLM成形零件的尺寸精度。研究了SLM成形精细零件的加工性，设计了尺寸从0.1-0.45mm厚的薄壁件，分析加工误差。结果显示，由于激光光斑的尺寸接近0.1mm，壁厚越小，其相对误差越大。壁厚为0.1mm的零件，其相对误差接近99%。当壁厚增加到0.4mm时，其相对误差只有0.1%。研究了不同工艺参数时XY平面及Z轴的成形精度的影响因素，工作平面不同位置的零件的尺寸误差。利用三维测量工具对成形零件的三维尺寸进行测量，并对比模型进行分析。测试结果表明，SLM成形金属零件在Z轴方向存在收缩情况，但其高度方向相对误差在1%以内。激光熔化粉末后形成致密金属层，由于粉末体松装密度较低，导致熔化后的层厚出现明显降低，该现象经过累积，对Z轴的精度有一定影响，粉末松装密度越高，铺粉层厚越小，影响越小。（3）研究了SLM成形零件的致密度。利用田口分析方法，分析了SLM工艺参数对零件致密度的影响规律。结果显示，在影响SLM成形致密度的三个因素中，成形速度影响最大，占43.98%，激光功率影响其次，占34.61%，扫描间距影响较小，仅为19.81%。说明了扫描速度对成形致密度的影响最大，超过扫描间距的2倍。研究了成形平面的不同区域内SLM零件的致密度变化。在不同区域内零件的致密度表现出一定差异，离平面中心位置近的致密度最高。（4）研究了SLM成形零件的力学性能。通过成形不同倾斜角度的零件研究了零件的延伸特性变化规律。结果发现，熔化道搭接处，即熔池边界为性能弱区，是降低SLM零件延伸率的重要因素。熔池边界的空间拓扑导致SLM零件的拉伸特性产生明显的各向异性。通过热处理消除熔池边界，可大大提高SLM成形件的延伸性能，并减小各向异性特征。研究了不同粉末粒径分布对成形性能的影响。研究发现，平均粒径为26.36μm的粉末成形性能较好，松装密度大（松装密度为0.56）的粉末成形致密度高，为99.1%。（5）研究了SLM技术成形模具的初步应用。利用SLM方法成形随形冷却流道模具。模拟和试验表明，SLM成形的随形冷却流道模具，其冷却效率和冷却均匀性优于传统直流道。综上所述，本文着重研究了SLM成形零件的表面粗糙度、尺寸精度及力学性能，为SLM成形实用零件提供了指导。并在模具应用方面进行了一定的探讨，为SLM成形零件的工程应用奠定了基础。更多还原

【Abstract】 Selective Laser Melting is one of the most potential Rapid Prototyping andManufacturing technologies. By using a high-energy laser to melt metal powder directly, itcan manufacture metal parts which are formed in nearly full density and havehigh-performance. This technology can manufacture complex structures which areimpossible for traditional methods to make or need to assemble multi–components, so ithas a Broad application prospect in the fields such as aerospace manufacturing,personalized biomanufacturing and complex mold inserts manufacturing. But influencedby many factors，the precise control of shape and control of the forming part are mostdifficult. This paper focuses on the surface quality, dimensional accuracy and mechanicalproperties of SLM forming part; the manufacture of complex molds has also beenresearched. The main content of research in the paper is as following:(1) Surface quality of the SLMed parts. Through a series of experiments, dimensionalcharacteristic of single melting Road is analyzed with shape factor F evaluating themelting road. Meanwhile the paper also exposes how SLM process parameters andscanning strategies influence the surface roughness of single-channel and single-layer. Theresults show that with the improvement of the scanning speed, surface roughness of theroad is reduced, which is first down then up when laser power increases. Single scan in thesame direction has the worst surface quality, while with twice the spacing scan first, thenthe normal scan, surface roughness is the least. This paper also illustrates how the factorssuch as manufacturing angle, laser power density and processing thickness influence thesurface roughness on the parts’ side face. The results show that when manufacturing angleis less than60°, the surface roughness tends to decrease significantly with the increase ofthe angle; while, when the angle is more than60°, it decreases a little, but not obvious,with the increase of the angle.(2) Dimensional accuracy of SLMed parts. A research in the property of manufactureprecision parts has been done. In order to analyze processing errors, a series of0.1-0.45mm thickness parts have been made. The research shows that when the laser beam spot size close to0.1mm, relative error increases with the decreasing of its wall thickness.The relative error of the part which just has a thickness of0.1mm is close to99%. Therelative error is just0.1%when the thickness rises to0.4mm. The paper researches howthe parameters influence the forming precision on the XY plane and the Z-axis, and errorof the parts in different positions of the working plane. Measured in terms of thethree-dimensional size and compared with the model, metal parts have a shrinkage inZ-axis direction with a relative error of less than1%. Laser melt powders will form adense metal layer, due to low density of the powder, thickness of the layer decreasesdramatically after the melting. With accumulation of the error, accuracy of the Z axis willbe affected to some degree. The higher the density of the power and the lower thethickness of power, the smaller this impact will be.(3) Density of SLMed parts. This paper analyzes how the SLMed process parametersinfluence the density through Taguchi analysis method. The results show that, among thethree factors which influence SLMed forming density, forming speed has the greatestimpact, accounting for43.98%; laser power is next, for34.61%; the impacts of scanspacing is very small, just about19.81%. So the forming speed is much more importantthan scanning spacing, which should be optimized in the first place. The paper researchesthe change of the density in different areas, indicating that density is different in differentarea, the center position of the plane being with a higher density.(4) Mechanical properties of SLMed parts. This paper researches the variation of theextension properties of different parts by manufacturing the parts of the different tiltangles. The results show that lap joints of melting road, also called boundary of weldingpool is the obvious weak performance area, which is the important factor to reduce theelongation of the SLM Part; the space topology of the boundary brings out a significantanisotropy of the parts’ tensile properties. By using heat treatment to eliminate theboundary pool, the extended performance will be improved and anisotropy will be reduced.This paper analyzes how powder particle size distribution influences the formability. Theresults show that an average smaller particle size of26.36μm powder has a betterperformance and the higher bulk density of the powder (0.56) has a high density about (5)Preliminary application of manufacturing mold by SLM. This paper researches howthe SLM technology apply to the manufacture of complex parts by manufacturing customcooling channels for molds. The test proves that both cooling rate and cooling uniformityare better than traditional ones.All in all, this paper has focused on the research of the surface roughness, dimensionalaccuracy and mechanical properties of SLM forming part, and provided guidance formanufacturing practical SLM parts. It also explores the mold application and throws somelight on the market of SLM manufacturing parts.更多还原