脉冲光纤激光诱导氧化硬质合金的温度场分布

利用ABAQUS建立了三维瞬态传热模型,计算了激光诱导下的温度场分布情况,并研究了激光参数对温度场的影响。仿真结果表明,工件最高温度随着单脉冲能量的增大以及扫描速度和光斑直径的减小而增大,热影响区的最大深度和宽度随着单脉冲能量的增大以及扫描速度和光斑直径的减小而增大。研究结果为优选激光诱导氧化硬质合金材料时的激光参数提供了重要依据。     

激光诱导精密沉积铜箔实验

通过改变激光脉冲能量和激光聚焦位置,进行了激光诱导向前转移铜箔的实验,并通过超景深三维显微镜和扫描电子显微镜对基片和约束层上沉积的铜箔进行了观察,探讨了激光脉冲能量和激光聚焦位置对铜沉积效果所产生的影响,在此基础上研究了激光诱导向前转移的机理。研究结果表明,在石英玻璃基片上沉积的铜箔直径最小可达10μm,远小于激光光斑直径;在约束层上也沉积有铜箔,即同时出现了激光诱导向后转移的现象;光脉冲能量增大,石英玻璃上沉积的铜箔逐渐分散,尺寸逐渐增大,而且呈环形分布;通过调节靶材离焦点距离,可以使环形消失,并使沉积尺寸降到激光光斑尺寸以下。最后成功实现了微细阵列的激光诱导沉积。     

激光诱导前向传送中的热分析

针对激光诱导前向传送中牺牲层的热破坏,利用双温方程模型对激光与钛层的电子-晶格系统的作用过程进行分析,结合热传导方程模拟了钛层的纵向温度传递,获得了钛层的温度场。模拟发现激光脉冲能量,光斑直径决定了激光光斑的能量密度,纳米钛层的厚度决定了激光的透光率,三者共同影响钛层最终温度。当脉冲能量为7μJ ,光斑直径为40μm ,钛层厚度为80 nm时,数值计算的微孔尺寸为11.5μm ,与实验的11.77μm基本吻合,说明该数值模型可靠,可用于预测激光诱导前向传送中钛层的破坏。     

激光喷丸诱导镁合金表面微织构的电化学腐蚀性能

利用脉宽为8 ns的Nd:YAG脉冲激光对AZ31B镁合金表面进行激光喷丸处理,研究激光喷丸诱导微织构对AZ31B镁合金耐腐蚀性能的影响,进行表面微织构的形貌分析,测量试样表面的动电位极化曲线。结果表明,激光喷丸产生的微织构周围未出现烧蚀现象,其微凹坑的直径和深度随激光能量的增加而增大,随喷丸次数的增加呈现先增大后趋于饱和趋势。与未处理试样相比,在相同微织构间距下,激光能量为1.0 J、1.5 J、2.0 J时试样的自腐蚀电位分别向正移95 m V、123 m V、151 m V,自腐蚀电流密度分别减少36.48%、50.26%、60.42%;在相同激光能量下,微织构间距为1.0 mm、1.5 mm、2.0 mm试样的自腐蚀电位分别向正移145 m V、134 m V、123 m V,自腐蚀电流密度分别减少50.26%、46.19%、44.34%。研究表明激光喷丸诱导的微织构提高了AZ31B镁合金表面的耐腐蚀性,且激光能量越高,喷丸间距越小,抗腐蚀性能越好。     

环形激光诱导空化泡的数值仿真分析

激光诱导前向转移技术是一种有效的物质传输手段,但在单细胞传送时,存在传送精度低等问题.提出将环形空化泡运用在激光诱导前向转移技术上,进而解决物质传送精度差的问题.利用有限元数值仿真分析方法,探究环形激光诱导环形空化泡的生长溃灭过程.并对其流场中不同方向的速度场进行了分析,发现了环形空化泡膨胀初期对环外部溶液的推动阻隔效应和溃灭后的能量中心汇聚效应均可运用在物质的精确转移技术中.基于响应曲面法,探究激光能量、环形光斑内外径比值、海藻酸钠溶液质量分数对环形空化泡水平和垂直方向最大速率的影响强弱顺序,得出各因素对最大速率的影响强弱顺序由大到小依次为:环形光斑内外径比值、海藻酸钠溶液质量分数、激光能量.其水平和垂直方向最大速率在环形光斑内外径比值为0.7(70μm/100μm)、激光能量60μJ、溶液质量分数为1％时达到最佳值,分别为14.28 m/s和11.82 m/s.     

基于正交试验设计的45钢激光表面强化工艺优化

利用激光表面重熔强化技术对45钢表面进行重熔处理,以显微硬度和磨损率为考察指标,采用正交试验方法考察激光功率、扫描速度、光斑直径和脉宽4个参数对45钢表面综合性能的影响。结果表明:4个参数对45钢表面综合性能的影响作用由主到次的顺序依次为激光功率、光斑直径、扫描速度、脉宽;最优的激光表面强化工艺参数为激光功率650 W,扫描速度100 mm/min,光斑直径4 mm,脉宽2.4 ms。利用硬度测试仪和摩擦磨损试验机,对采用最优的激光表面强化工艺参数制备的试样的显微硬度和磨损率进行测试,结果表明:采用优化参数制备的试样的激光强化层硬度值分布较为均匀,且硬度值也较高,且与优化前试样相比磨损率明显降低;优化前试样磨损机制为疲劳磨损、磨粒磨损、黏着磨损,优化后试样磨损表面仅有一些微小的划痕,耐磨性能明显改善。     

工艺参数对管材激光弯曲成形影响规律的研究

管材激光弯曲成形是一种柔性金属塑性成形方法。将连续的激光光斑简化为一间歇跳跃的方形匀强面热源,并考虑材料性能参数与温度的相关性,建立了管材激光弯曲成形的热-机耦合有限元工艺仿真模型,对成形过程进行了数值模拟。有限元模拟结果表明:在其他条件不变的情况下,激光弯曲角度随激光功率的增大而增大,两者基本上成线性关系;弯曲角度随扫描速度的升高而减小,随光斑直径的减小而增大,但当光斑直径减小到一定程度后,弯曲角度开始减小;弯曲角度随扫描包角的增大而增大,当扫描包角为180°时,弯曲角度达到最大,弯曲角度随扫描包角的继续增大而减小;扫描次数与弯曲角度间成近似的线性关系,且第一次扫描管材产生的弯曲角度最大。     

车刀表面微孔织构耐磨性能分析

利用激光加工技术在硬质合金刀具表面制备出不同直径大小的微坑结构。通过正交切削Ti6Al4V合金研究有织构和无织构刀具对刀具耐磨损性能和被加工表面粗糙度的影响。结果表明:随着激光功率的增加,微坑直径和坑深呈增大趋势;织构刀具的耐磨损性能优于无织构刀具;织构刀具的被加工表面粗糙度低于无织构刀具;织构刀具微坑直径对刀具耐磨损性能和被加工表面粗糙度的影响存在一个临界值。     

微尺度激光喷丸强化TiN涂层的表面性能

采用直径为300 μm的激光光斑对TiN涂层表面进行微尺度激光喷丸强化处理以进一步提高TiN涂层的表面性能.利用光学轮廓仪和纳米力学测试系统测量了不同激光工艺参数作用下TiN涂层喷丸区域的表面形貌、纳米硬度及弹性模量分布.结果表明,喷丸区域形成的圆锥形凹坑最大深度约为1.2 μm,纳米硬度和弹性模量在喷丸中心处变化最大...     

刀具表面微织构激光加工方法研究与分析

在刀具的表面加工微织构,可显著提升刀具的切削性能,大幅提高刀具耐用度并延长刀具的使用寿命。本文利用脉冲激光在硬质合金(WC-Co,YG8)刀具的表面加工微织构,重点对激光功率、频率、脉冲个数和光斑直径对微坑织构的尺寸、形貌以及激光加工中产生微裂纹的影响进行了系列试验研究。采用波长λ=1064nm、激光功率W=90W、频率f=20Hz、脉冲个数n=20、光斑直径d=500μm的激光参数,在硬质合金刀片300℃预热处理后,用带有4个档位的超声振动辅助手段在刀具表面加工微坑织构。并选用原始激光加工后的硬质合金片和热处理超声振动辅助激光加工后的硬质合金刀片进行比较,试验结果表明,当刀具采用预热处理后,辅以超声振动进行激光加工的方法对控制刀具表面织构尺寸精度、刀具表面形貌的均一稳定和抑制表面微裂纹的产生具有重要意义。     

基底材料对石墨烯膜F-P声压传感器灵敏度的影响分析

文中以多层石墨烯膜为敏感膜片,分别制备了基于P DMS、SU-8、氧化锆的石墨烯膜F-P声压传感器,应用薄膜与基底之间吸附理论,分析了石墨烯膜与基底间吸附能相对于基底材料的杨氏模量成正向变化的趋势,并实验测试了所制备的声压传感器灵敏度.实验结果表明,制备的PDMS和SU-8基底具有较大的表面粗糙度,其虽降低了与石墨烯膜...     

The capability of ECDM in creating effective microchannel on the PDMS

Today, polydimethylsiloxane (PDMS) is widely used in medical and industrial applications. Lithographic processes are commonly used to create microchannels in PDMS, which have encountered several limitations such as high fabrication time and cost. In this study, the effect of tool characteristics (distance, geometry and diameter) and electrolyte properties (temperature and type) on the surface quality, surface roughness and dimensional accuracy of the created microchannel on PDMS through electrochemical discharge machining (ECDM) are investigated for the first time. The results stated the capability of ECDM in the formation of channels with the similar quality of created channels by lithography. In addition, it has been declared that increasing the tool/workpiece distance would lead to an increase in the surface roughness as well as deteriorated surface quality of the grooves due to the longer traveled distance by the particles and the subsequent energy increase by colliding the workpiece surface. According to the obtained results, increasing the mentioned distance from 20 μm to 150 μm was followed by a 356% increase in the surface roughness. Moreover, by the utilization of grooved tools instead of simple ones, thicker gas film would be formed at the vicinity of the tool, and consequently, intensified stray sparks and the resultant increased material removal area would be achieved. Furthermore, rising the electrolyte temperature from 25 °C to 65 °C led to an increase in surface roughness from 0.109 to 0.140 μm. Additionally, respective reductions of 33% and 3% in surface roughness and microchannel width were attained by 20% reduction in the tool diameter.     

液压支架激光熔覆不锈钢合金涂层的实验研究

采用激光熔覆技术在硅锰钢样件表面制备了不锈钢涂层,用SEM和能谱仪分析了基体与熔覆层界面以及熔覆层之间的微观组织及成分,开展了试样弯折和冲击强度测试实验。结果表明:在激光功率为6kW、扫描速度为8mm/s、光斑直径为5mm、搭接率30%的工艺条件下,基体与熔覆层界面以及熔覆层之间出现小亮带,形成冶金结合;熔覆方向垂直于观察面的覆层形貌呈蜂窝状,熔覆方向与观察面平行的覆层形貌呈竖直条状;在功率6kW、扫描速度16mm/s、光斑直径5mm、搭接率30%时,熔覆层与基体以及熔覆层之间会产生夹渣;熔覆层具有较好的韧性和冲击强度,熔覆后的试样的冲击强度提高了7.7%。     

一种可控曲面光栅的研制

提出了一种制作曲面变间距光栅的方法。首先在平面基片上制作光栅,然后通过一种高分子材料(PDMS)作为载体将光栅转移到曲面上,而事先涂在曲面上的混合溶胶-凝胶取代了传统的光刻胶,使得光栅的制作效率大大提高。采用这种方法在曲率半径为100 mm的凹球面基底上制作了平均线密度为80 l/mm的光栅,并用环境扫描电镜以及数字图像处理法检测了光栅的线密度分布。检测结果表明:光栅质量好,条纹清楚,衍射效率也没有降低。所制曲面光栅具有平面光栅和透镜两种光学器件的功能,可用曲面变间距光栅一种光学元件取代透镜和平面光栅两种光学元件,简化了光路,提高了制作效率,降低了成本。     

The lubricant retaining effect of micro-dimples on the sliding surface of PDMS

The frictional behavior of elastomers is characterized by compliance of asperities, special surface chemistry, and wetting properties. The objective of this paper is to investigate the coupled influence of surface texture and wettability on the lubrication of an elastomer contact. Patterns of micro-dimples were fabricated on disks of a polymer material, PDMS. An oxygen plasma treatment was used to hydrophilize the disk surfaces. Friction tests of the disks sliding against a spherical pin of PDMS were carried out. The experimental results indicate that the effect of surface texture is different for PDMS with different wetting properties.     

WC颗粒增强镍基涂层改善制动盘组织与磨损性能

为提高汽车制动盘耐磨和高温氧化性能,延长其使用寿命,采用激光熔覆技术在中碳钢表面制备了以WC颗粒为增强相的Ni基复合涂层.借助SEM和XRD等表征手段对制动盘表面涂层进行了组织和物相分析,利用维氏硬度计测试了制动盘表面涂层截面显微硬度分布,通过摩擦磨损实验研究了制动盘表面涂层的磨损性能.研究表明,制动盘表面涂层主要由γ-（Ni,Fe）固溶体、均匀分布WC颗粒和碳化物抗磨损相组成.涂层平均显微硬度HV0.2670,显微硬度值波动较小较为平稳,证明涂层组织比较均匀.在多种强化效果共同作用下,制动盘表面涂层的磨损量与基材相比明显减小,仅为基材的20％,抗磨损性能显著提高.     

颗粒尺寸及组合对SLS碳化硅预制体精度的影响

采用热法包覆方法制备了不同颗粒组合的碳化硅陶瓷粉末,并利用选区激光烧结(SLS)工艺制备了碳化硅陶瓷预制体,研究了颗粒尺寸及组合对激光烧结陶瓷预制体成形精度的影响规律。结果表明：颗粒尺寸及组合对激光烧结陶瓷预制体成形精度的影响显著,预制体翘曲量随颗粒尺寸的增大而减小,表面粗糙度和尺寸误差均随颗粒尺寸的增大而增大;相对于单一颗粒,由双尺寸颗粒组合制备的预制体的翘曲量减小了11%~50%,表面粗糙度Ra值减小了12%~20%,尺寸误差减小了38%~79.6%。     

磁流体辅助抛光工件表面粗糙度研究

给出了磁流体辅助抛光的机理,以及依据Preston方程建立的磁流体辅助抛光的数学模型。并通过实验详细研究了磁流体辅助抛光后工件的抛光区形状,以及抛光区内表面粗糙度情况。最终加工出了表面粗糙度为0.76 nm(rms值)的光学元件,其高频表面粗糙度达到0.471 nm(rms值),满足了对一定短波段光学研究的要求。结果表明:磁流体辅助抛光可以用于对光学元件进行超光滑加工;在磁流体辅助抛光过程中,较大粒度的磁流体抛光液有利于工件表面粗糙度快速降低,较小粒度的磁流体抛光液可以获得更加光滑的光学表面。     

Fabrication of PDMS micro through-holes for electrochemical micromachining

Surface texture has played a fundamental role in the development of many advanced fields. Through mask electrochemical micromachining (TMEMM) is a feasible alternative for fabricating surface textures. In this paper, polydimethylsiloxane (PDMS) is firstly employed as a mask in TMEMM due to its chemical resistance, low cost, flexibility and high moulding capability. A simple method for fabricating PDMS micro through-holes is proposed. A vacuum-aided process was introduced to fill a PDMS gel into an SU-8 mould, and the PDMS gel was solidified in an oven. Then, the cured PDMS micro through-holes were peeled off of the SU-8 mould. PDMS micro holes with a minimum diameter of 50 μm and a thickness of 200 μm were obtained. Furthermore, the PDMS micro through-holes were then used as a mask to prepare a micro dimple array by TMEMM. Experiments were conducted to verify the feasibility of the proposed approach, and the effect of applied voltage and machining time on the diameter and depth of the micro dimple was investigated. Finally, an array of micro dimples 109 μm in diameter and 9.7 μm deep was successfully fabricated by using PDMS.     

Investigation of laser and process parameters for Selective Laser Erosion

The process of Selective Laser Erosion (SLE) was investigated to study the effects of different process and laser parameters on the process outputs such as surface quality and erosion rate. The SLE process is a direct method to remove material in a layer-by-layer fashion due to high energy densities provided by the laser beam. In addition to its direct use as a subtractive manufacturing method, SLE may be used in combination with layer-additive techniques such as Selective Laser Melting (SLM). Such combination mainly makes sense when both processes can be performed with the same laser. However, one of the major problems involved in SLE process is the high number of the laser and process parameters (laser power, pulse frequency, scan speed, scan spacing, ambient atmosphere, etc.) and the complexity of the relations between them which has not yet been investigated completely.This paper presents an overview of the laser erosion process with nano-second Nd:YAG laser pulses and the results of several single-factor experiments that were carried out to determine the influence of the major parameters on the depth of erosion per layer and surface roughness. Additionally, the relations between the parameters are studied to investigate the interactions between them. The results from single-factor experiments showed that some relations were highly governed by the power intensity of the laser beam and also that cross interactions between the parameters play an important role on the output characteristics. The paper explains how multiple parameters (spot size, pulse frequency, scan speed, scan spacing) can be combined to define two indirectly controlled geometrical parameters, namely the scan and pulse overlap factors. Those two parameters allow calculating the number of hits of the laser beam on a same location on the workpiece possible which is the first step in physical modeling the topography of the surface left behind.