光纤激光复合织构形貌的数值模拟与试验研究

发布时间：2018-05-15 15:49

本文选题：激光毛化 + 微凹坑　；参考：《江苏大学》2017年硕士论文

【摘要】：激光表面织构技术用于改善摩擦副间摩擦学特性,可以对机械零部件表面起到减磨、增寿效果。在众多表面织构技术中,激光织构技术因其诸多独特优势得到更加广泛关注,在轧辊、磁盘、机械密封、模具、刀具、内燃机缸套、轴承等都有应用。但是,目前主要研究更多集中在激光织构中的微凹坑(槽)研究,对毛化(凸体)织构的理论、试验研究尚缺少系统性、创新性。不同材料、相同材料应用场合存在差异,应用差异导致对工件摩擦副要求不同,因而对毛化形貌、尺寸、毛化点分布规律都会提出不同要求。鉴于此,本文以金属塑性成型模具的工程应用为目标,对45钢、Cr12模具钢两种常用材料进行了系统、带有创新性的激光毛化数值模拟与试验研究,并对激光微凹坑加工工艺进行试验研究。主要研究内容及结论如下。(1)基于激光与金属物质相互作用机理,利用FLUENT工具软件建立激光毛化三维数学模型。探究脉宽、激光功率密度对45钢、Cr12模具钢温度场、流场的影响。结果表明:两种材料熔池流动方向均是从四周流向中心,形成凸起。45钢在脉宽500us及其更大脉宽下,熔池中心最高温度超过沸点,会有材料气化,该结论得到试验验证:脉宽小于500us形成球冠状,500us及更大脉宽形成凹顶球冠状。设定功率密度不变,45钢熔池直径、深度增加率,随着脉宽增大均呈现出先大后小变化规律。通过分析流场、温度场发现,大温度梯度可以促进熔池快速生长,温度梯度变小,熔池生长速率变缓,该结论得到试验验证:毛化点直径、高度增大率从大到小转折点为脉宽500us。Cr12与45钢因材料性质不同,导致液体对流存在些微差异,模拟出Cr12熔池深径比大于45钢,两种材料毛化点剖面金相图验证了该模拟结果;两种材料温度场结合毛化点金相进行分析,从内到外分为气化区、熔凝区、热影响区、基材区,并对各区金相组织、硬度进行检测分析,毛化点相对基材硬度大幅提高。(2)对毛化形貌进行定量表征。引入推衍参数凹陷率T、内外径比Pb。球冠状T为0;凹顶球冠状0T0.33;M状0.33≤T≤1;火山口状T1,0Pb0.83。并给出各个形貌凸起、凹陷体积近似计算公式,V凸起体现毛化点耐磨性,V外凹、V内凹体现毛化点存储润滑油和磨粒的能力。(3)依据模拟计算给出的结果,采用光纤激光器进行毛化工艺试验研究。45钢在选用参数内,加工出球冠状,以及因材料气化并因此诱发的反冲压力,加工出凹顶球冠形貌。Cr12因铬元素沸点较低,且含量较高,因熔池中心材料气化以及因此诱发的反冲压力,在选用参数内加工出M状,因等离子体屏蔽作用在选用参数内加工出凹顶球冠状。(4)在激光毛化中发现该激光器在低功率密度1.02*104W/mm2以下打出高质量微凹坑,对该奇怪现象做出初步分析,并对微凹坑加工工艺进行系统探索。(5)探究不同辅助气体,不同压力下,毛化形貌及尺寸变化情况。以N_2作为辅助气体,45钢在所给加工参数内,依次出现M状、凹顶球冠状、球冠状;Cr12全部形成凹顶球冠状。此时两材料毛化点直径,相比未加辅助气体情况下直径变大,高度变小。以O_2作为辅助气体,0.05MPa气压下,45钢毛化形貌无规律可循,Cr12毛化点在M状和火山口状中随机出现;0.1MPa下,两种材料熔池均被吹散,无法形成毛化点。(6)从改变激光吸收率出发,在加工表面涂敷一层水玻璃,探究毛化形貌及尺寸变化规律。该涂层下,两种材料毛化形貌高径比均要大于未涂层时的高径比。(7)在工件侧面加磁铁,希望加工出偏向一侧毛化点。两种材料作为铁磁体材料,当温度超过它们居里温度成为顺磁体,此时磁场无法对液体金属产生影响,所以毛化形貌无变化。(8)因为活性元素S对熔池对流产生影响,在加工表面涂敷一层直径5um硫粉进行激光毛化。未出现预想中火山口形貌,发现形貌成为椭球型,且各个毛化点之间长短轴不一,该现象从试验上证实了S元素确实对金属液体对流有影响。
[Abstract]:Laser surface texture is used to improve the tribological characteristics of friction pairs, which can reduce the wear and prolong the life of mechanical parts. In many surface texture technologies, laser texture technology has been paid more attention to many unique advantages, such as roll, disk, mechanical seal, die, tool, cylinder liner, bearing and so on. But at present, the main research is mainly focused on the micro pits (grooves) in the laser texture. The theory of the texturing (convex) texture is not systematic and innovative. There are differences in the application situation of different materials and the same materials, and the application difference leads to the different requirements for the friction and friction of the workpiece, thus the distribution of hair morphology, size and hair point distribution The law will put forward different requirements. In view of this, this paper aims at the engineering application of the metal plastic molding mold, and carries out a systematic system of two common materials for 45 steel and Cr12 die steel, with innovative laser hairy numerical simulation and experimental research, and the experimental study of laser micro pits processing. The main contents and conclusions are as follows. (1) based on the interaction mechanism of laser and metal material, the three-dimensional mathematical model of laser hairy is established by using FLUENT tool software. The influence of pulse width and laser power density on temperature field and flow field of 45 steel and die steel is investigated. The results show that the flow direction of the two kinds of molten pool is from four directions to the center, forming a convex.45 steel in the pulse width of 500us and its application. Under the larger pulse width, the maximum temperature of the pool center exceeds the boiling point, and there will be material gasification. The conclusion is proved that the pulse width is less than 500us and the coronal coronal of the ball is formed, and the 500us and the larger pulse width form the coronal coronal of the concave top. The set power density is constant, the diameter of the molten pool and the depth increase rate of the 45 steel, with the increase of the pulse width, all present the small change law. The flow field and temperature field show that the large temperature gradient can promote the rapid growth of the molten pool, the temperature gradient becomes smaller and the growth rate of the molten pool slows down. The conclusion is proved that the diameter of the hairy point, the height increase rate from the large to the small turning point is 500us.Cr12 and 45 steel because of the different properties of the material, resulting in some micro difference in liquid convection and simulating the Cr12 melting. The depth diameter ratio of the tank is greater than 45 steel, and the simulation results are verified by the gold phase diagram of the two material hairy points. The temperature field of the two materials is analyzed in combination with the gold phase of the hairy point. It is divided into the gasification area, the melting zone, the heat affected zone, the substrate area, and the hardness of the metallographic structure in each area, and the hardness of the hairy points is greatly improved. (2) A quantitative characterization of hairy morphology was made with the introduction of T, the inner and outer diameter ratio of Pb. ball coronal T was 0, the coronal 0T0.33 of concave top ball, M like 0.33 or less T less than 1, the crater like T1,0Pb0.83. and the approximate calculation formula of various morphologies and sags, the wear resistance of the hairy point, the V outer concave, and the V inner concave to store the lubricating oil and abrasive grains. (3) according to the results given by the simulation calculation, the fiber laser is used in the hairy process test to study the.45 steel in the selected parameters, the processing out of the ball coronal, and the recoil pressure caused by the material gasification and thus induced by the material. The shape of the crown shape of the concave top ball is.Cr12 because the chromium element has a lower boiling point, and the content is higher, and it is gasified by the central material of the molten pool. In the selected parameter, the M shape was processed in the selected parameters. (4) it was found that the laser produced the high quality micro pits under the low power density of 1.02*104W/mm2 in the laser hairy, and made a preliminary analysis of the strange phenomenon and the processing technology of the micro pits. System exploration. (5) explore different auxiliary gases, under different pressure, hair morphology and size changes. With N_2 as auxiliary gas, 45 steel in the processing parameters, in turn, appear M, concave top coronal, spherical coronal, Cr12 all form a concave top ball coronal. At this time, the diameter of the two material hairy point, compared with the diameter without auxiliary gas under the condition of the diameter. With O_2 as auxiliary gas, under 0.05MPa pressure, the hairy morphology of 45 steel can be irregular, and Cr12 hairy points appear randomly in M and crater shape. Under 0.1MPa, two kinds of materials are blown away and can not form hairy points. (6) from the change of laser absorption, a layer of glass is applied to the machined surface to explore hairy morphology. Under this coating, the height to diameter ratio of the two materials should be greater than that of the non coating. (7) a magnet on the side of the workpiece is added to the side of the workpiece. It is hoped to produce a partial hairy point. Two materials are used as ferromagnets, and when the temperature exceeds their Curie temperature, the magnetic field can not affect the liquid metal at this time. There is no change in hairy morphology. (8) because the active element S affects the convection in the molten pool, a layer of 5um sulfur powder is coated on the machined surface to be laser hairy. There is no preconceived crater morphology, and the morphology becomes ellipsoid, and the long and short axis of each hairy point is different. This phenomenon confirms that the S element does to the metal liquid from the experiment. Convection has an impact.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

【参考文献】