微观选择性激光熔化技术发展的现状及未来展望 - 图文 

Author name et al. / Engineering 2(2016) xxx–xxx17表5?各种喷砂条件对表面光洁度的影响对比Substrate materialTi implantsYellow-gold alloysInitial conditionSLMSLM

Abrasive blasting mediaCorundum

Corundum sand, glass beadsRoughness, Ra or Sa (μm)Initial3.312.9Final0.94.2Reduction (%)7267Ref.[122][132]HSS, coated carbidesMilling/ turning/ drillingCeramic beadsWC-Co

EDMSiCTiN/Al2O3/TiCN coatingsCVDCorundumY-TZP

Milling

Y-TZP particles

HSS: high-speed steel; CVD: chemical vapor deposition; NA: not available.该技术大幅度降低了SLM试样的表面粗糙度（48 h的处理时间内从13.3 μm到0.2 μm）。尽管该技术具有良好的表面处理性能和工艺简单性，但缺点是耗费时间长。为了从前文讨论的可用技术库中识别出适用于微观SLM组件的表面处理工艺，必须考虑许多因素，包括制造特征的初始粗糙度、零件尺寸、几何形状、最小特征尺寸分辨率、工艺复杂性、周期时间等。微观SLM组件的尺寸通常为毫米级，而最小特征分辨率却在几微米的范围内（表1）。表4中列出了用于微观SLM组件的技术的合格性。尽管整体研磨技术可以获得良好的表面光洁度，但可能会在此过程中损害微尺度特征。用计算机数控技术（CNC）加工微观SLM零件是可行的，但复杂几何条件下的微加工和刀具路径控制是难点。特别是，薄壁的精密加工以及内部和高深宽比特征的精密加工非常困难且耗时。CHE和ECP通常要求表面平整，并要沿着边缘侵蚀材料，这可能会导致微小零件的尺寸误差较大。磨料喷砂通常用于整饰许多行业（如牙科和珠宝）的微小零件，所以可能是一种理想的选择。微磨料喷砂是一系列医疗应用中最常用的表面处理之一，例如用微磨料喷砂可获得支持骨整合的牙种植体所需的表面光洁度[122,131,138–140]。Kennedy等[124]在高速钢（HSS）和涂层碳化物上使用陶瓷珠进行微喷丸处理，表面粗糙度降低60%，最细的表面Ra为0.4 μm。激光抛光是另一种合适的选择，尽管重熔引起的热应力可能导致部件变形，尤其残余的热应力对薄弱部分的冲击很大。混合制造系统将AM与减法或其他辅助系统集成在一起，以提高机器系统的生产率和定制性能[141–143]。AM中的混合系统把激光熔覆头（在LMD的情况下）安装在铣床的z 轴上，然后集成激光系统和CNC铣床[143]。总的来说，系统设计应该以最少的后处理来提高结构的构建性能、精度和表面光洁度。在粉末床熔融添加剂制造（PBF-AM）的情况下，除了Sodick OPM250E和Matsuura LUMEX Avance-25 [144]之外，很少有混合10.460[124]1.30.746[123]0.180.0950[134]NS

1.7

NA

[131]

系统可用，尽管PBF-AM之后的组件的表面质量一直存在问题[128]。虽然在粉末床AM加工过程中，精密加工已经改善了许多，但是还没有开发出包括加成和减成加工的混合系统来制造微尺度的金属材料。与表4中列出的精密加工工艺相比，激光重熔或激光抛光与微SLM集成来开发混合系统似乎是最可行选择。可以在现有SLM系统中使用相同的激光源或不同的激光源。尽管如此，应该承认每种精密加工技术都有其自身的优点和局限性，而选择一种理想的表面处理工艺取决于SLM制造零件的初始条件和精加工要求。因此，应改进SLM技术的能力以制造具有精细表面光洁度的特征，以便消除对任何二次加工的需要。6. 潜在应用微观AM（特别是微观SLM）已经应用于多个领域的精密器件和元件的制造中。微流体装置可应用于细胞生物学、生物医学科学和临床诊断领域[145]。本文尝试了直接型AM的微流体装置，但发现该方法的生产率远低于典型的注射成型工艺[146,147]。制造微流体装置的最常用技术是喷射模塑法和热压成型[148,149]。这些技术需要主模具或工具插件把特征复制到基板上。用于微流体的主模具通常由光刻、电镀和模塑（LIGA）及类似LIGA的工艺[150,151]制造出来。然而，这些技术受到材料和设计的限制。用电铸镍来制造金属母模也是一种方法，但制造出来的模具硬度不够[152,153]，微型模具的强度还需要改进。精密的制造金属微型模具的AM技术可以提高工具寿命，从而提高生产率。相同的技术可用于生产高深宽比的微结构，这种微结构越来越多地应用于MEMS [154]。Roy等[44]使用微型SLS工艺来制造电气互连实体和电介质，用于组装集成电路（IC）组件。两个柔性基板是通过在预制的迹线上印刷银电极和银连接体桥接的[16]。18Author name et al. / Engineering 2(2016) xxx–xxx微观AM也可以应用于牙科领域。目前，除了最常见的立体光刻和数字光投影（DLP）之外，SLM和SLS也用于牙科[155,156]。牙桥和牙冠、牙种植体、局部义齿和模型铸件都是微观AM在牙科行业中的一些潜在应用。在过去十年中，珠宝行业一直在尝试使用AM加工珠宝。这个领域正在不断发展，因为几乎所有主要的AM设备制造商都不断加大使用AM来加工贵金属：如金、铂和钯合金的力度[157]。AM除了一些常见的优势，如近净成形制造，减少材料浪费，以及加快小批量的整体工艺周期速度外，微观AM制造薄壁、花丝、网状物的能力，还有轻巧的部件可以增强设计的自由度和美感，是吸引珠宝行业的特定因素。珠宝制造商的多项研究[158,159]强调，尽管目前局限性仍然存在，但是SLM将与传统铸造共存，以节约成本和实现设计的多功能性。Hirt等[16]设想可以将设备和传感器直接印刷应用到航空、汽车、医疗和光学行业的现有技术上。微米级或纳米级分辨率的部件有助于实现可控的微结构。利用微结构的精确控制来改善AM制造部件的机械强度和摩擦学性能。7. 结论本文系统地回顾了SLM技术在金属材料上实现微尺度特征的应用。微观SLM与传统SLM的区别在于三个因素：激光光斑尺寸、粉末颗粒尺寸和层厚度。微观SLM的现有研究成功证明了在不同材料上（包括聚合物、陶瓷和金属）制作具有微观分辨率特征的可行性。目前的微观SLM系统的最小特征分辨率为15 μm，最小表面粗糙度为1 μm，最大部件密度为99.3%。考虑到该领域的学术研究有限，让人惊叹的是，市场上已经出现了一些商业化的微观SLM系统。商业系统可达到的最小光斑尺寸和层厚度分别为20 μm和1 μm。现有文献的一个主要限制是，没有一项工作试图研究制造零件的物理性质和微观结构，这使得跨尺度比较SLM工艺变得困难。为了发展微观SLM技术，SLM系统还需要进一步的修改，如调整光学系统，粉末重涂和粉末的分配和成形阶段的驱动。目前限制获得薄且均匀的粉末层的因素主要是粉末特性和粉末重涂系统。文献表明，目前的粉末重涂方法主要是通过刀片或滚轮进行的，并不适合处理细粉末。本文综述了几种可能的干粉滴涂方法在粉末床AM系统中的可行性。在已经实施和测试的AM系统中，人们采用了振动和静电的粉末分配方法。静电技术在涂层循环时间方面似乎是最有希望的。微观SLM的有效策略是整合所有子系统：如粉末分配、收集和粉末筛分，并建立一个闭环反馈系统。本文还研究了SLM部件表面处理技术。虽然大多数工艺可以实现小于1 μm的表面粗糙度，但是选择一个理想的微观SLM工艺要基于许多因素，包括零件几何形状、特征分辨率和精加工要求。文献表明，喷砂是目前微零件常用的精加工技术。在混合处理的方法中，激光抛光作为微观SLM的二次精加工技术似乎比其他技术更实用。不限于SLM/SLS，制约微AM应用的常见因素有：粉末粒径有限，由于金属中的高散热导致加热区的限制较低，分辨率控制困难，表面粗糙，粉末处理能力不理想以及取模困难[14,16]。这些因素表明有必要开发新的系统，使用新型的方法来进行粉末配置和部件的后期处理。微观SLM未来方向应侧重于两个方面：与设备有关的因素和与工艺有关的因素。应设计一种系统来处理纳米级且易于聚集的金属粉末。重点应放在开发一种创新性的粉末重涂系统，该系统可以实现亚微米级厚度的均匀粉末层，同时不会影响重涂速度。关于工艺知识，需要更多的研究来了解纳米级粉末颗粒与激光束之间的相互作用。由于目前研究数量有限，需要进一步了解微SLM制造的部件的微观结构和力学性能。考虑到具有优良性能的金属微粒在精密工程、生物医学、牙科和珠宝等各个领域的应用日益广泛， SLM的进一步改进将扩大它本身甚至AM的应用领域。AcknowledgementsThe authors would like to acknowledge financial sup-port from the Science and Engineering Research Council, Agency for Science, Technology and Research (A*STAR), Singapore (142 68 00088).Compliance with ethics guidelinesBalasubramanian Nagarajan, Zhiheng Hu, Xu Song, Wei Zhai, and Jun Wei declare that they have no conflict of Author name et al. / Engineering 2(2016) xxx–xxx19interest or financial conflicts to disclose.References [1] Qin Y, Brockett A, Ma Y, Razali A, Zhao J, Harrison C, et al. 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