空间整形飞秒激光加工金属微细槽实验研究 下载: 2373次特邀研究论文
Objective As a typical metal microstructure, the metal microgroove structure is widely used in electronics, communications, aerospace, biomedicine, and other fields. With more applications of metal microgrooves in key parts, higher requirements are put forward on the quality and accuracy of microgrooves. For example, in the micro-heat exchange device, the heat transfer pipe with a rectangular cross-section microgroove array structure has better heat transfer performance than other shapes of the microgroove array structure, and the microgrooves with a width less than 50μm show better heat exchange efficiency. In addition, in the field of biomedicine, rectangular microgroove arrays smaller than 50μm have been proven to have better cell orientation effects than rectangular microgroove arrays of 60μm. The precision manufacturing of microgroove structure often requires high machining accuracy (below 100μm), and the machining edge is free of burrs. Besides, the microgroove structure is often processed on many difficult-to-machine materials with high hardness, toughness, and wear resistance. Traditional metal processing methods, such as traditional cutting, electric discharge machining, and electrochemical machining, are often troubled by insufficient precision or difficult material processing when processing high-precision metal microstructures. Ultrafast laser processing has the advantages of high instantaneous power density, low heat-affected zone, and a wide range of materials that can be processed, and it is playing an increasingly important role in precision processing. Ultrafast laser processing has become an essential processing method, especially for difficult-to-process materials such as ceramic materials, superalloys, and superhard materials. However, due to the uneven light field distribution and shielding effect caused by the processing process, the processed micro groove wall is often accompanied by a certain slope, which affects its application performance. Therefore, reducing the groove wall slope while ensuring accuracy is an urgent problem to be solved. In the present study, we adopt an spatial shaping ultrafast laser processing system, based on the principle of beam shaping, built to modulate the Gaussian beam before focusing on a rectangular flat-top light and explore the influence of spatial shaping light on the microgroove structure and reduction of taper.
Methods In this study, the laboratory's existing femtosecond laser processing experimental system was used to conduct experimental investigations on nickel-based superalloys. The spatial light modulator (SLM) was used to phase-shape the femtosecond laser, and the Gaussian light was shaped into a rectangular flat-top light and the processing experiment of the microgroove was on the nickel-based superalloy. Then, the surface morphology and three-dimensional morphology of the microgrooves processed by the spatial shaping light were analyzed by scanning electron microscope (SEM) and three-dimensional white light interferometer. In the next step, by adjusting the laser parameters, the processing parameters of the microgroove using the spatial shaping light was studied, and the microgroove and through groove with variable width were processed. In addition, the surface morphology and chemical composition of the microgroove were analyzed by SEM and energy dispersive X-ray spectroscopy (EDX). In addition, the effect of femtosecond laser processing on the oxidation of the microgroove was studied by EDX mapping.
Results and Discussion Compared with the Gaussian light, the slope of the microgroove obtained by the spatially shaped light is significantly reduced, and the groove wall profile is straighter. By comparing the effects of different scanning speeds at the same energy, it is found that at a scanning speed of 2000μm/s, as the scanning time increases, the depth of the microgroove gradually increases, and the depth change rate first increases and then decreases. At scanning speeds of 1000μm/s and 500μm/s, the depth of the microgroov gradually increases with the increasing scanning speed, and the depth change rate gradually increases. The analysis shows that with the increase in the scanning speed,the number of pulses deposited in the unit area of the superalloy decreases. After reaching a certain depth, as the processing debris at the bottom of the groove increases, the shielding effect increases, so that the average removed amount of a single pulse is reduced (Fig. 5). As the depth of the microgroove increases, the slope of the groove wall gradually decreases and the minimum slope of the groove wall can reach 1° or less (Fig. 6). In addition, deep grooves with width of 10, 20, and 150μm were processed using spatial shaping light, and the groove wall slope of the deep grooves with a width of 150μm reached 0.63° (Fig. 8 and Fig. 9). The elemental analysis and characterization of the groove wall found that the microgroove wall did not undergo significant oxidation, which should be attributed to the excellent cold working ability of the femtosecond laser (Fig. 10).
Conclusions In this study, the strategy of spatially shaped femtosecond laser is adopted and the Gaussian beam is formed into a rectangular flat-top beam by the SLM for metal microgroove processing. Compared with the processing result of the Gaussian beam, the slope of the groove wall fabricated by flat-top beam is significantly reduced. In addition, the method has been used to realize the processing of micro-deep grooves ranging from 10μm to 100μm, indicating that the method has a wide range of processing dimensions. Elemental analysis and morphological observation of the deep groove wall section were carried out. No obvious element changes and laser heat-affected zone were found, indicating the excellent processing ability and great application potential of this method.
1 引言
作为一种典型的金属微细结构,金属微细槽结构已被广泛地应用于电子、通信、航空航天、生物医学等领域。随着金属微细槽结构在关键零件上的应用越来越多,对微细槽的质量以及精度等提出了越来越高的要求[1-3]。在微型热交换装置中,具有矩形截面微细槽阵列结构的散热管相比其他形状的微细槽阵列结构具有更好的热传递性能,并且宽度小于50μm的微细槽具有更高的热交换效率[4-5]。此外,在生物医学领域,小于50μm的矩形微细槽阵列被证明比60μm的矩形微细槽阵列具有更好的细胞定向效果[6-8]。微细槽结构精密制造往往需要较高的加工精度(100μm以内),加工边缘无毛刺,且常在许多高硬度、高韧性、高耐磨性的难加工材料上进行加工[9-10]。传统的金属加工方法比如传统切削、电火花加工、电解加工等在加工高精度金属微结构时,常会遇到精度不高或者材料加工难度大等问题,这使得微细槽结构精密制造一直是学术研究的热点[11-17]。国内外研究人员提出了多种加工方法来提高微细槽结构的加工精度和加工质量。南京航空航天大学的齐新新[18]在 100μm厚的不锈钢箔片上实现了平均缝宽为166.65μm、深度为24.34μm的5条微细槽稳定加工。 中国工程物理研究所的尹青峰等[19]通过工艺实验,优选工艺参数,成功地在0.2mm厚的不锈钢薄片上加工出 0.15mm深的微细槽。山东大学的魏志远[20]采用超声振动辅助电解电火花铣削加工工艺,实现了119.2μm宽度的微细槽加工。然而,目前大多数工艺加工的微细槽结构都在百微米量级,对于100μm以内的微细槽结构高质量成型,尤其是50μm以内的微细槽结构精密加工,仍然是当前研究的难点和热点。
超快激光加工具有瞬时功率密度高、热影响区小、可加工材料广泛等优点,在精密加工中发挥着越来越重要的作用[21-24]。尤其是对陶瓷材料、高温合金、超硬材料等难加工材料而言,超快激光加工已经成为一种必不可少的加工手段[25]。目前,超快激光在微小孔精密加工领域的优势已经逐渐得到认可[26]。德国米特韦达大学激光技术学院使用脉宽为220fs,频率为100kHz的飞秒激光器在304不锈钢上加工出直径约10μm,深度达500μm的微孔,微孔锥度为10°[27]。通用原子公司在国家点火装置的钽准直仪中用飞秒激光钻孔,各个孔的直径约为200μm[28]。在微细槽结构的加工方面,超快激光加工也逐渐走进人们的视野。日本芝浦工业大学表面工程设计实验室开发的飞秒激光加工系统,其光斑的最小直径为1μm,可加工出宽度为5~10μm的金属微细槽[29]。Oh等[30]利用激光刻蚀技术在不锈钢表面加工出深宽比为4的微米级微细槽结构。在微细槽的高精度加工方面,超快激光加工表现出巨大的优势。然而,由于加工过程中引起光斑分布不均以及屏蔽效应等[31],加工得到的微细槽槽壁往往会出现一定的斜度,从而影响其应用性能。因此,在保证精度的同时,如何减小槽壁的斜度是迫切需要解决的问题。
基于光束整形原理,本文采用搭建的超快激光空间整形加工系统,将聚焦前的高斯光束调制成矩形平顶光,探索了光束空间整形对于微细槽结构形貌的影响以及锥度的减小情况。以镍基高温合金为例,相较于高斯光束的加工结果,采用矩形平顶光加工的微细槽槽壁斜度明显减小,且随着槽深的逐渐增大,槽壁斜度逐渐减小。此外,采用该方法在加工宽度分别为10, 20, 150μm的深槽的过程中未出现明显的热影响区域,展示了该方法卓越的加工能力和极大应用潜力。
2 实验原理
2.1 实验装置及原理
利用本课题组现有的飞秒激光加工实验系统进行实验探究,采用空间光调制器(SLM)对飞秒激光进行相位整形。本实验采用钛-蓝宝石激光器,出射的飞秒激光波长为800nm,脉宽为50fs,频率为1kHz。SLM的型号为holoeye-PLUTO-NIR-01,像素面积为8μm×8μm,刷新率为60Hz。加工实验是在恒定温度(20 ℃)下进行的。样品固定于六轴平移台表面,通过计算机程序实现样品的运动控制,飞秒激光入射到SLM的液晶表面,经过相位整形后射出,再经过4f系统和物镜聚焦后对样品表面进行加工。
图 1. 基于SLM的飞秒激光空间整形光路装置图
Fig. 1. Optical path device diagram of femtosecond laser spatial-shaping based on SLM
图 2. 矩形平顶光的仿真示意图与灰度图。(a) 矩形光斑仿真示意图;(b)利用迭代算法得到的灰度图
Fig. 2. Simulation diagram of rectangular flat-top beam and grayscale image. (a) Simulation diagram of a rectangular spot; (b) grayscale image obtained by an iterative algorithm
2.2 矩形光斑的实际光强分布及显微镜下观测结果
通过程序将灰度图加载至SLM后,采用光束质量分析仪对SLM整形后聚焦得到的矩形平顶光斑进行实时测量,测量结果如
图 3. 整形后的光斑表征及脉冲打点表征。(a)光束质量分析仪测得的矩形平顶光光斑分布; (b) 20个脉冲下的高温合金表面加工形貌;(c) 100个脉冲下的高温合金表面加工形貌;(d) 500个脉冲下的高温合金表面加工形貌
Fig. 3. Characterization of light spot and pulse dot after shaping. (a) Light spot distribution of rectangular flat-top light measured by a beam quality profiler; (b) morphological image of surface with 20 pulses flat-top light ablation; (c) morphological image of surface with 100 pulses flat-top light ablation; (d) morphological image of surface with 500 pulses flat-top light ablation
3 实验结果与分析
为了对比高斯光与矩形平顶光的加工质量,采用焦点线扫的方式,以相同的扫描速度(500μm/s)和扫描次数在高温合金表面进行微细槽加工实验。合金为镍基高温合金,牌号为gh2135。白光干涉仪的型号为ZYGONexView。采用高斯光进行微细槽加工时,用10×物镜进行聚焦,脉冲能量为20μJ,以500μm/s的扫描速度进行线扫加工。通过增加扫描次数的方式来增加微细槽深度,得到的微细槽阵列如
图 4. 采用高斯光和平顶光加工的微细槽阵列对比。 (a)采用高斯光加工的微细槽阵列形貌;(b) 采用平顶光加工的微细槽阵列形貌;(c) 采用高斯光扫描100次加工的单个微细槽截面轮廓;(d)采用平顶光扫描100次加工的单个微细槽截面轮廓;(e)微细槽阵列的深度与斜度的变化关系
Fig. 4. Comparison of microgroove array processed by Gaussian beam and flat-top beam. (a) SEM image of microgroove array fabricated by Gaussian beam; (b) SEM image of microgroove array fabricated by flat-top beam; (c) cross-sectional profile of a single microgroove (100 scanning times) fabricated by Gaussian beam; (d) cross-sectional profile of a single microgroove (100 scanning times) fabricated by flat-top beam; (e) relationship between the depth and the slope of the microgroove arrays
在一定的激光脉冲频率下,扫描速度会影响沉积的脉冲数量,进而影响材料的去除速率。为了分析扫描速度对矩形平顶光加工微细槽的影响,在相同的脉冲能量(100μJ)下,分别采用2000,1000,500μm/s的扫描速度,在高温合金表面进行微细槽阵列加工。在特定的扫描速度下,通过增加扫描次数来改变微细槽的深度,进而得到不同扫描速度下深度不同的微细槽阵列。对上述3个扫描速度下的微细槽阵列三维形貌和微细槽截面轮廓进行对比,结果如
表 1. 现有激光加工微细槽情况小结
Table 1. Summary of existing laser microgroove processing
|
图 5. 矩形平顶光在不同扫描速度下加工的微细槽对比
Fig. 5. Comparison of microgrooves fabricated by flat-top beam at different scanning speeds
此外,研究了不同激光能量下以及不同扫描速度下的微细槽深度和微细槽壁斜度的变化规律。从
图 6. 不同脉冲能量下微细槽深度和微细槽壁斜度的变化情况。(a)微细槽深度随扫描次数的变化情况;(b) 微细槽壁斜度随深度和扫描次数的变化情况
Fig. 6. Variation of depth and slope of microgrooves under different pulse energies. (a) Depth of microgrooves changed with scanning times; (b) slope of microgrooves changed with microgroove depth and scanning times
为了证明空间整形的矩形平顶光束在微细槽加工领域的应用潜力,采用逐行扫描加工的方式进行变宽度微细槽阵列加工实验。在100μJ的脉冲能量下,控制扫描速度为1000μm/s,扫描次数为40次,扫描间距为5μm。通过逐渐增大扫描宽度的方式来控制微细槽的深度,实现了槽宽从10μm到60μm的变宽度微细槽加工,得到的微细槽阵列的表面形貌如
图 7. 采用空间整形光束加工的变宽度微细槽阵列。(a)变宽度微细槽阵列的表面形貌图; (b)微细槽阵列截面轮廓图
Fig. 7. Microgroove arrays with variable width processed by spatially shaped beam. (a) Surface morphology of the microgroove array; (b) cross-sectional profile of microgroove array
激光加工已经作为一项比较成熟的技术广泛地应用于微细槽结构的加工中(
为了探究激光烧蚀过程对槽壁的影响,对
图 8. 加工宽度为10μm和20μm的微细槽形貌图
Fig. 8. Topographies of microgrooves with width of 10μm and 20μm
图 9. 宽度为150μm的微细槽形貌图。(a) SEM图;(b)白光干涉三维图;(c)横截面轮廓图
Fig. 9. Topography of microgroove with width of 150μm. (a) SEM image; (b) three-dimensional white light interference image; (c) cross-sectional profile view
图 10. 微细槽侧壁边缘元素分布及信号强度变化。(a)微细槽侧壁截面的SEM形貌图;(b)元素信号强度的横向分布;(c) O元素在横向面的分布;(d) Ni元素在横向面的分布;(e) Fe元素在横向面的分布
Fig. 10. Distribution and intensity changes of elements at the processing edge of microgroove. (a) SEM image of the microgroove side wall section; (b) transverse distribution of element intensity; (c) distribution of O element in the transverse plane; (d) distribution of Ni element in the transverse plane; (e) distribution of Fe element in the transverse plane
4 结论
本研究采用空间整形飞秒激光加工的方法,利用SLM将高斯光束整形成矩形平顶光束后进行金属微细槽加工,相较于高斯光束的加工结果,利用矩形平顶光斑加工的槽壁斜度显著减小。采用该方法实现了10μm量级到100μm量级的微细深槽加工,表明该方法具有较宽的加工尺度范围。对深槽槽壁截面进行元素分析和形貌观察,未发现元素含量明显变化的区域和明显的激光热影响区,说明该方法具有卓越的加工能力和极大的应用潜力。
[1] 王云峰, 张天润, 张文武, 等. 复杂曲面零件表层微槽激光加工技术研究[J]. 电加工与模具, 2018( S1): 43- 46.
Wang YF, Zhang TR, Zhang WW, et al. Study on laser processing technology of surface micro grooves for complex surface parts[J]. Electromachining & Mould, 2018( S1): 43- 46.
[2] 王俊杰, 郭钟宁, 何俊峰, 等. 微细超声辅助高速微槽铣削加工工艺研究[J]. 组合机床与自动化加工技术, 2020( 5): 119- 123.
Wang JJ, Guo ZN, He JF, et al. Research on micro-ultrasonic-assisted high-speed microgroove milling process[J]. Modular Machine Tool & Automatic Manufacturing Technique, 2020( 5): 119- 123.
[3] 史杨, 许兵, 吴东, 等. 飞秒激光直写技术制备功能化微流控芯片研究进展[J]. 中国激光, 2019, 46(10): 1000001.
[4] Ternet F, Louahlia-Gualous H, Le Masson S. Impact of microgroove shape on flat miniature heat pipe efficiency[J]. Entropy, 2018, 20(1): 44.
[5] Ghajar M, Darabi J. Evaporative heat transfer analysis of a micro loop heat pipe with rectangular grooves[J]. International Journal of Thermal Sciences, 2014, 79: 51-59.
[7] Fu G, Soboyejo W O. Cell/surface interactions of human osteo-sarcoma (HOS) cells and micro-patterned polydimelthylsiloxane (PDMS) surfaces[J]. Materials Science and Engineering C, 2009, 29(6): 2011-2018.
[8] Ren L, Zhou X W, Nasiri R, et al. Combined effects of electric stimulation and microgrooves in cardiac tissue-on-a-chip for drug screening[J]. Small Methods, 2020, 4(10): 2000438.
[9] 李伟国, 周欢伟, 李克天. 在单点金刚石机床上用刨削加工微槽的方法[J]. 机电工程技术, 2018, 47(10): 7-10,86.
[10] 李元成, 张晓兵, 毛忠, 等. 紫外纳秒激光加工316L不锈钢微槽尺寸和形貌控制研究[J]. 应用激光, 2019, 39(6): 994-1001.
[11] Kuo C L, Huang J D. Fabrication of series-pattern micro-disk electrode and its application in machining micro-slit of less than 10μm[J]. International Journal of Machine Tools and Manufacture, 2004, 44(5): 545-553.
[12] Lauwers B, Oosterling H, Vanderauwera W. Development of an operations evaluation system for sinking EDM[J]. CIRP Annals, 2010, 59(1): 223-226.
[14] Ya C. Internal laser writing of high-aspect-ratio microfluidic structures in silicate glasses for lab-on-a-chip applications[J]. Micromachines, 2017, 8(2): 59.
[15] Wang W, Zhu D, Qu N S, et al. Electrochemical drilling with vacuum extraction of electrolyte[J]. Journal of Materials Processing Technology, 2010, 210(2): 238-244.
[16] 李飘庭, 傅波, 荆奇, 等. 电极丝前置式射流电解加工铣削微槽试验研究[J]. 新技术新工艺, 2020( 4): 67- 74.
Li PT, FuB, JingQ, et al. Experimental research on milling micro-groove by wire-proposed electrochemical jet machining[J]. New Technology & New Process, 2020( 4): 67- 74.
[17] 李增强, 赵佩杰, 宋雨轩, 等. 微磨料水射流加工技术研究现状[J]. 纳米技术与精密工程, 2016, 14(2): 134-144.
[18] 齐新新. 柔性金属箔群槽微细电解加工技术研究[D]. 南京: 南京航空航天大学, 2018.
Qi XX. Research on electrochemical machining of microgrooves in flexible metal sheet[D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2018.
[19] 尹青峰, 李盛年, 盛友萍, 等. 薄片工件的微细铣削加工[J]. 制造技术与机床, 2015( 9): 115- 117.
Yin QF, Li SN, Sheng YP, et al. Micro milling of sheet parts[J]. Manufacturing Technology & Machine Tool, 2015( 9): 115- 117.
[20] 魏志远. 超声振动辅助微细电解电火花加工技术研究[D]. 济南: 山东大学, 2019.
Wei ZY. Study on ultrasonic vibration assisted micro electrochemical discharge machining technology[D]. Jinan: Shandong University, 2019.
[21] 赵亮亮. 基于电子状态调控的飞秒激光加工高深宽比结构的实验研究[D]. 北京: 北京理工大学, 2015: 8- 17.
Zhao LL. Experimental studies on fabrication of high-aspect-ratio microgrooves by femtosecond laser based on electron dynamics control[D]. Beijing: Beijing Institute of Technology, 2015: 8- 17.
[22] 宋雨欣, 银恺, 董欣然. 飞秒激光加工ZnS晶体沟槽形貌及其疏水性能研究[J]. 应用激光, 2017, 37(3): 398-402.
[23] Jiang L, Wang A D, Li B, et al. Electrons dynamics control by shaping femtosecond laser pulses in micro/nanofabrication: modeling, method, measurement and application[J]. Light: Science & Applications, 2018, 7(2): 17134.
[24] Ma Z C, Zhang Y L, Han B, et al. Femtosecond-laser direct writing of metallic micro/nanostructures: from fabrication strategies to future applications[J]. Small Methods, 2018, 2(7): 1700413.
[25] 魏超, 马玉平, 韩源, 等. 飞秒激光加工超硬材料的研究进展[J]. 激光与光电子学进展, 2019, 56(19): 190003.
[26] 郭敏超, 王明娣, 张胜江, 等. FR-4覆铜板飞秒激光微孔加工工艺研究[J]. 中国激光, 2020, 47(12): 1202008.
[28] Laser micro-machining[EB/OL]. [2020-08-20].https://www.ga.com/manufacturing-and-fabrication/ laser-micro-machining.
[29] AizawaT, InoharaT. Pico- and femtosecond laser micromachining for surface texturing micromachining[M]. Tokyo: Intech Open, 2019: 4- 15.
[30] Oh K H, Park J B, Cho S I, et al. Investigation of sidewall roughness of the microgrooves manufactured with laser-induced etching technique[J]. Applied Surface Science, 2009, 255(24): 9835-9839.
[31] Kerse C, Kalaycıoĝlu H, Elahi P, et al. Ablation-cooled material removal with ultrafast bursts of pulses[J]. Nature, 2016, 537(7618): 84-88.
[32] Fasasi A Y, Mwenifumbo S, Rahbar N, et al. Nano-second UV laser processed micro-grooves on Ti6Al4V for biomedical applications[J]. Materials Science and Engineering: C, 2009, 29(1): 5-13.
[33] Ketabi M, Deporter D. The effects of laser microgrooves on hard and soft tissue attachment to implant collar surfaces: a literature review and interpretation[J]. The International Journal of Periodontics & Restorative Dentistry, 2013, 33(6): e145-e152.
[35] Liu Y Y, Liu L L, Deng J X, et al. Fabrication of micro-scale textured grooves on green ZrO2 ceramics by pulsed laser ablation[J]. Ceramics International, 2017, 43(8): 6519-6531.
[36] Kikuchi T, Sakairi M, Takahashi H, et al. Fabrication of micropores and grooves on aluminum by laser irradiation and electrochemical technique[J]. Journal of the Electrochemical Society, 2001, 148(11): C740-C745.
[37] Takayama N, Asaka S, Yan J W. Nanosecond pulsed laser irradiation of sapphire for developing microstructures with deep V-shaped grooves[J]. Precision Engineering, 2018, 52: 440-450.
Article Outline
梁密生, 李欣, 王猛猛, 原永玖, 陈孝喆, 许晨阳, 左佩. 空间整形飞秒激光加工金属微细槽实验研究[J]. 中国激光, 2021, 48(2): 0202003. Misheng Liang, Xin Li, Mengmeng Wang, Yongjiu Yuan, Xiaozhe Chen, Chenyang Xu, Pei Zuo. Spatially-Shaped Femtosecond Laser Manufacturing of Microgrooves in Metals[J]. Chinese Journal of Lasers, 2021, 48(2): 0202003.