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在激光刻蚀铝合金化铣保护胶的工艺研究中,一般需要通过实验手段来获得良好的加工效果,但因刻蚀的微槽结构具有细、长、深等特点,无论是高速相机的同步拍摄, 还是显微镜的离线测量,都只能得到表面微结构的变化情况,而无法获得微槽底部和侧壁的形貌特征。更重要的是,只能得到激光刻蚀过程中微结构的宏观变化规律,而无法准确把握材料内部特征的变化机理,尤其温度场与热应力的变化规律及其对加工过程的影响。在此基础上,本文作者借助COMSOL Multiphysics仿真软件对铝合金化铣保护胶脉冲激光刻型工艺进行热应力耦合理论研究,传热学分析可以直观地展示化铣保护胶在激光辐照作用下的温度场分布情况及变化过程,应力分析可以直观展示激光加工过程中保护胶和铝合金界面处的应力细节,此外,变形几何功能的使用可以动态地显示整个刻型过程中化铣保护胶的形貌演变规律。
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铝合金化铣保护胶激光刻型热应力耦合分析建模中使用到的化铣保护胶材质为AC850,铝合金基体材料材质为2A12,材料对应的厚度如表 1所示。铝合金化铣保护胶激光刻型使用的脉冲激光器为北京热刺激光技术有限公司生产的R40二氧化碳激光器,其输出波长、脉冲宽度、重复频率等参数如表 2所示。
表 1 模拟分析中使用的材料及厚度
Table 1. Thickness of material used in simulation analysis
type material thickness/μm chemcial milling protective glue AC850 400 alumunum alloy substrate 2A12 2000 表 2 脉冲激光器的参数
Table 2. Parameters of the pulsed laser
parameter value wavelength/μm 10.6 pulse width/μs 2~970 repeat frequency/kHz 1~100 duty cycle/% 30~50 focal length/mm 101.6 maximum power /W 300 spot diameter/μm 150 -
微观来看,由于化铣保护胶属于高分子材料,在使用长脉冲激光辐照铝合金化铣保护胶表面时,材料分子吸收大量光热产生分解、气化,直接或间接与空气中的O2发生氧化反应并生成气态物质并逃逸,从而达到激光刻蚀效果。宏观来看,激光刻型时,聚焦区域会达到数千摄氏度的高温,通过叠加激光脉冲,使辐照区域刻型宽度和深度逐渐增加,来实现化铣保护胶的脉冲激光刻型。
本文作者基于COMSOL Multiphysics软件的固体传热、固体力学、变形几何3个模块来实现多物理场耦合仿真计算。固体传热物理场用于计算激光刻蚀过程中随时间和热物理参数改变而变化的温度场,需要考虑到传导传热、对流传热、辐射传热3种传热情况。其中,铝合金化铣保护胶脉冲激光刻型过程中材料表面与空气的换热视为对流换热,对流换热边界条件为:
$ -\boldsymbol{n} q=h\left(T_{\mathrm{ext}}-T\right) $
(1) 式中, h为换热系数, Text为环境温度, T为温度, n为法线上的单位向量, q为激光的热流密度。
激光束热流密度表示为:
$ q=\frac{2 A P}{\pi w^2} \exp \left(\frac{-2 r^2}{w^2}\right) $
(2) 式中, A为材料对激光的吸收率, P为激光功率, w为光斑半径, r为材料表面到光斑中心的距离。
变形几何物理场的加入是为了计算出刻蚀过程中材料在脉冲激光作用下的去除速率,根据材料相变过程中材料的熔化潜热与蒸发潜热推导出材料升华热,则材料的去除速率v可表示为:
$ v=\frac{q}{\rho H} $
(3) 式中, ρ为材料密度, H为材料的升华热。
通过加入固体力学物理场来计算激光刻蚀过程中温度场的实时变化与不同材料属性对热应力场变化规律的影响,对应关系可表示为:
$ \rho \frac{\partial^2 \boldsymbol{u}}{\partial t^2}=\nabla \boldsymbol{\sigma}+\boldsymbol{F}_V $
(4) 式中, u为位移场, $\nabla$为梯度算子, σ为柯西应力张量, FV为单位变形体积上的力。
热应力耦合分析可以反映热温度场和应力场的相互影响过程,根据求解步骤的不同, 分为直接求解法和间接求解法。直接求解法是利用包含温度以及位移自由度的耦合单元,经过一次求解计算同时得到热分析和结构应力分析结果。间接求解法则需要分步进行,首先通过热分析计算出模型的节点温度,将求解的节点温度作为体载荷施加到结构应力分析中,求解出节点应力。由于直接求解法的平衡状态需要同时满足多个准则,复杂的约束条件使得节点自由度较多,并且矩阵方程繁杂,求解效率低。在铝合金化铣保护胶激光刻型热应力耦合分析中,相较于结构响应,热分析的温度对结构分析时应力应变的影响更为显著,因此本文中选择效率较高的间接求解法来实现对铝合金化铣保护胶激光刻型的热应力耦合分析。脉冲激光的刻蚀原理如图 1所示,采用移动高斯热源模拟长脉冲激光与目标材料的相互作用过程。
铝合金化铣保护胶激光刻型热应力耦合分析
Thermal stress coupling analysis on laser engraving of aluminum alloys with protective coatings for chemical milling
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摘要: 激光刻型过程中, 保护胶与铝合金因热物理性能参数不同会导致界面裂纹、保护胶脱落等现象。为了解决这些问题, 基于热应力耦合分析法, 建立了2维多层材料有限元模型, 将脉冲激光以高斯热流密度载荷的形式加载在保护胶表面, 通过计算求解得到铝合金基体的应力分布云图以及在热应力作用下保护胶切口形貌随激光加工参数的演变规律, 对比分析了激光功率、扫描速率、重复频率等加工参数对温度场、应力场、刻蚀形貌与应力位移的影响。结果表明, 功率60 W、扫描速率10 m/min、重复频率100 kHz时, 对温度场、应力场、刻蚀形貌与应力位移的影响最小。该研究对于激光刻型在化学铣切中的实际应用具有参考价值, 为激光刻型的工艺优化提供了方向。Abstract: According to the phenomena of interface cracking and falling off of protective coatings caused by different thermophysical parameters between protective coatings and aluminum alloy in the process of laser engraving, a two-dimensional finite element model of multi layer materials was established based on the thermal stress coupling analysis method. The pulsed laser was loaded on the surface of protective coatings in the form of Gaussian distributed heat flux. The stress distribution nephogram of aluminum alloy matrix and the evolution law of kerf morphology of protective coatings under the action of thermal stress with different laser processing parameters were obtained by calculation. The effects of laser power, scanning speed, and repetition frequency on temperature field, stress field, engraving morphology, and stress displacement were compared and analyzed, respectively. The results show that when the parameters are selected as power 60 W, scanning speed 10 m/min and repetition frequency 100 kHz, the influence on temperature field, stress field, etching morphology, and stress displacement is minimal. The research of this paper has great reference significance for the practical application of laser engraving in chemical milling, and provides a direction for the process optimization of laser engraving.
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表 1 模拟分析中使用的材料及厚度
Table 1. Thickness of material used in simulation analysis
type material thickness/μm chemcial milling protective glue AC850 400 alumunum alloy substrate 2A12 2000 表 2 脉冲激光器的参数
Table 2. Parameters of the pulsed laser
parameter value wavelength/μm 10.6 pulse width/μs 2~970 repeat frequency/kHz 1~100 duty cycle/% 30~50 focal length/mm 101.6 maximum power /W 300 spot diameter/μm 150 -
[1] 周礼君, 赵晴, 杜楠, 等. TC4钛合金化学铣切槽液调整与再生[J]. 表面技术, 2018, 47(4): 190-195. doi: 10.16490/j.cnki.issn.1001-3660.2018.04.028 ZHOU L J, ZHAO Q, DU N, et al. Adjustment and regeneration of TC4 titanium alloy chemical milling groove fluid[J]. Surface Technology, 2018, 47(4): 190-195(in Chinese). doi: 10.16490/j.cnki.issn.1001-3660.2018.04.028 [2] 刘会军, 乔永莲, 董宇, 等. 芬顿氧化法处理铝合金化铣清洗液的研究[J]. 表面技术, 2017, 46(2): 220-223. doi: 10.16490/j.cnki.issn.1001-3660.2017.02.037 LIU H J, QIAO Y L, DONG Y, et al. Study on treatment of aluminum alloy milling cleaning fluid by fenton oxidation[J]. Surface Technology, 2017, 46(2): 220-223(in Chinese). doi: 10.16490/j.cnki.issn.1001-3660.2017.02.037 [3] 易慧芝, 邓飞跃, 张忠亭. 2197铝锂合金化学铣切工艺研究[J]. 表面技术, 2010, 39(4): 73-76. doi: 10.3969/j.issn.1001-3660.2010.04.022 YI H Zh, DENG F Y, ZHANG Zh T. Research on chemical milling technology of 2197 Al-Li alloy[J]. Surface Technology, 2010, 39(4): 73-76(in Chinese). doi: 10.3969/j.issn.1001-3660.2010.04.022 [4] LI Q S, WANG J H, HU W B. Optimizations of electric current assisted chemical milling condition of 2219 aluminum alloy[J]. Journal of Materials Processing Technology, 2016, 249: 379-385. [5] HOT J, DASQUE A, TOPALOV J, et al. Titanium valorization: From chemical milling baths to air depollution applications[J]. Journal of Cleaner Production, 2020, 249: 119344. doi: 10.1016/j.jclepro.2019.119344 [6] EVANGELOS N, ARISTOMENIS A. FEM modeling and simulation of kerf formation in the nanosecond pulsed laser engraving process[J]. CIRP Journal of Manufacturing Science and Technology, 2021, 35: 236-249. doi: 10.1016/j.cirpj.2021.06.014 [7] 翟兆阳, 梅雪松, 王文君, 等. 碳化硅陶瓷基复合材料激光刻蚀技术研究进展[J]. 中国激光, 2020, 47(6): 600002. ZHAI Zh Y, MEI X S, WANG W J, et al. Research progress of laser etching technology of silicon carbide ceramic matrix composites[J]. Chinese Journal of Lasers, 2020, 47(6): 600002(in Chinese). [8] ZHAI Z Y, WANG W J, ZHAO J, et al. Influence of surface morphology on processing of C/SiC composites via femtosecond laser[J]. Composites, 2017, A102: 117-125. [9] ZHAI Z Y, WEI C, ZHANG Y C, et al. Investigations on the oxidation phenomenon of SiC/SiC fabricated by high repetition frequency femtosecond laser[J]. Applied Surface Science, 2020, 502: 144131. doi: 10.1016/j.apsusc.2019.144131 [10] LIU C, ZHANG X Z, GAO L, et al. Feasibility of micro-hole machining in fiber laser trepan drilling of 2.5D Cf/SiC composite: Experimental investigation and optimization[J]. Optik, 2021, 242: 167186. doi: 10.1016/j.ijleo.2021.167186 [11] CHEONG H G, CHU C N, KWON K K, et al. Micro-structuring silicon compound ceramics using nanosecond pulsed laser assisted by hydrothermal reaction[J]. Journal of Manufacturing Processes, 2020, 50: 34-46. [12] 李浩宇, 杨峰, 郭嘉伟, 等. 激光清洗的发展现状与前景[J]. 激光技术, 2021, 45(5): 654-661. LI H Y, YANG F, GUO J W, et al. The development status and prospect of laser cleaning[J]. Laser Technology, 2021, 45(5): 654-661(in Chinese). [13] 朱小伟, 胡龙, 杨文峰, 等. 基于CFRP纤维编制网格分块扫描的激光除胶工艺算法[J]. 激光技术, 2021, 45(6): 745-750. ZHU X W, HU L, YANG W F, et al. Laser degumming process algorithm based on block scanning of CFRP fiber woven mesh[J]. Laser Technology, 2021, 45(6): 745-750(in Chinese). [14] KIRILLOV A G, SAKEVICH V N, TROCHIMCZUK R. Automated laser engraving system for the calibration and manufacturing of nonlinear scales for electrical measuring instruments[J]. Proceedings of the Institution of Mechanical Engineers, 2019, E233(4): 849-856. [15] 洪帅, 邹松华, 王帅东, 等. 铝合金表面化铣保护胶层激光刻型的可行性分析[J]. 电镀与涂饰, 2018, 37(24): 1139-1142. HONG Sh, ZOU S H, WANG Sh D, et al. Feasibility analysis of laser engraving on aluminum alloy surface milling protective adhesive layer[J]. Plating and Finishing, 2018, 37(24): 1139-1142(in Chinese). [16] 姚芳萍, 房立金, 李金华, 等. 激光功率对激光熔覆Ni基涂层温度场和应力场的影响[J]. 塑性工程学报, 2021, 28(11): 87-94. YAO F P, FANG L J, LI J H, et al. Effect of laser power on temperature field and stress field of laser cladding Ni-based coatings[J]. Journal of Plastic Engineering, 2021, 28(11): 87-94(in Ch-inese). [17] 刘冬冬. 热障涂层微观形貌的热力行为研究及数值模拟[D]. 成都: 西南交通大学, 2018: 45-56. LIU D D. Thermal behavior study and numerical simulation of thermal barrier coating micro topography[D]. Chengdu: Southwest Jiaotong University, 2018: 45-56(in Chinese). [18] XIE L S, CHEN X Y, YAN H P, et al. Experimental research on the technical parameters of laser engraving[J]. Journal of Physics, 2020, 1646(1): 012091. [19] 吴涛. 基于铁基复合材料激光熔覆多物理场耦合数值仿真[D]. 上海: 华东交通大学, 2020: 21-23. WU T. Numerical simulation of multiphysics coupling based on laser cladding of iron matrix composites[D]. Shanghai: East China Jiaotong University, 2020: 21-23(in Chinese). [20] CHAI Q, FANG C, QIU X L, et al. Modeling of temperature field and profile of Ni60AA formed on cylindrical 316 stainless steel by laser cladding[J]. Surface and Coatings Technology, 2021, 428: 127865. [21] 廖红星, 宋鹏, 周会会, 等. 陶瓷层与界面孔隙率对热障涂层寿命及其失效机制的影响[J]. 复合材料学报, 2016, 33(8): 1785-1793. LIAO H X, SONG P, ZHOU H H, et al. Effects of ceramic layer and interface porosity on the life and failure mechanisms of thermal barrier coatings[J]. Journal of Composite Materials, 2016, 33(8): 1785-1793(in Chinese). [22] RAD M R, FARRAHIA G H, AZADI M, et al. Stress analysis of thermal barrier coating system subjected to out-of-phase thermo-mechanical loadings considering roughness and porosity effect[J]. Surface and Coatings Technology, 2015, 262: 77-86. [23] WANG R J, DUAN W Q, WANG K D, et al. Computational and experimental study on hole evolution and delamination in laser drilling of thermal barrier coated nickel superalloy[J]. Optics and Lasers in Engineering, 2018, 107: 161-175.