本文選題：激光毛化 + 微凹坑��； 參考：《江蘇大學》2017年碩士論文

【摘要】：激光表面織構技術用于改善摩擦副間摩擦學特性,可以對機械零部件表面起到減磨、增壽效果。在眾多表面織構技術中,激光織構技術因其諸多獨特優(yōu)勢得到更加廣泛關注,在軋輥、磁盤、機械密封、模具、刀具、內燃機缸套、軸承等都有應用。但是,目前主要研究更多集中在激光織構中的微凹坑(槽)研究,對毛化(凸體)織構的理論、試驗研究尚缺少系統(tǒng)性、創(chuàng)新性。不同材料、相同材料應用場合存在差異,應用差異導致對工件摩擦副要求不同,因而對毛化形貌、尺寸、毛化點分布規(guī)律都會提出不同要求。鑒于此,本文以金屬塑性成型模具的工程應用為目標,對45鋼、Cr12模具鋼兩種常用材料進行了系統(tǒng)、帶有創(chuàng)新性的激光毛化數(shù)值模擬與試驗研究,并對激光微凹坑加工工藝進行試驗研究。主要研究內容及結論如下。(1)基于激光與金屬物質相互作用機理,利用FLUENT工具軟件建立激光毛化三維數(shù)學模型。探究脈寬、激光功率密度對45鋼、Cr12模具鋼溫度場、流場的影響。結果表明:兩種材料熔池流動方向均是從四周流向中心,形成凸起。45鋼在脈寬500us及其更大脈寬下,熔池中心最高溫度超過沸點,會有材料氣化,該結論得到試驗驗證:脈寬小于500us形成球冠狀,500us及更大脈寬形成凹頂球冠狀。設定功率密度不變,45鋼熔池直徑、深度增加率,隨著脈寬增大均呈現(xiàn)出先大后小變化規(guī)律。通過分析流場、溫度場發(fā)現(xiàn),大溫度梯度可以促進熔池快速生長,溫度梯度變小,熔池生長速率變緩,該結論得到試驗驗證:毛化點直徑、高度增大率從大到小轉折點為脈寬500us。Cr12與45鋼因材料性質不同,導致液體對流存在些微差異,模擬出Cr12熔池深徑比大于45鋼,兩種材料毛化點剖面金相圖驗證了該模擬結果;兩種材料溫度場結合毛化點金相進行分析,從內到外分為氣化區(qū)、熔凝區(qū)、熱影響區(qū)、基材區(qū),并對各區(qū)金相組織、硬度進行檢測分析,毛化點相對基材硬度大幅提高。(2)對毛化形貌進行定量表征。引入推衍參數(shù)凹陷率T、內外徑比Pb。球冠狀T為0;凹頂球冠狀0T0.33;M狀0.33≤T≤1;火山口狀T1,0Pb0.83。并給出各個形貌凸起、凹陷體積近似計算公式,V凸起體現(xiàn)毛化點耐磨性,V外凹、V內凹體現(xiàn)毛化點存儲潤滑油和磨粒的能力。(3)依據(jù)模擬計算給出的結果,采用光纖激光器進行毛化工藝試驗研究。45鋼在選用參數(shù)內,加工出球冠狀,以及因材料氣化并因此誘發(fā)的反沖壓力,加工出凹頂球冠形貌。Cr12因鉻元素沸點較低,且含量較高,因熔池中心材料氣化以及因此誘發(fā)的反沖壓力,在選用參數(shù)內加工出M狀,因等離子體屏蔽作用在選用參數(shù)內加工出凹頂球冠狀。(4)在激光毛化中發(fā)現(xiàn)該激光器在低功率密度1.02*104W/mm2以下打出高質量微凹坑,對該奇怪現(xiàn)象做出初步分析,并對微凹坑加工工藝進行系統(tǒng)探索。(5)探究不同輔助氣體,不同壓力下,毛化形貌及尺寸變化情況。以N_2作為輔助氣體,45鋼在所給加工參數(shù)內,依次出現(xiàn)M狀、凹頂球冠狀、球冠狀;Cr12全部形成凹頂球冠狀。此時兩材料毛化點直徑,相比未加輔助氣體情況下直徑變大,高度變小。以O_2作為輔助氣體,0.05MPa氣壓下,45鋼毛化形貌無規(guī)律可循,Cr12毛化點在M狀和火山口狀中隨機出現(xiàn);0.1MPa下,兩種材料熔池均被吹散,無法形成毛化點。(6)從改變激光吸收率出發(fā),在加工表面涂敷一層水玻璃,探究毛化形貌及尺寸變化規(guī)律。該涂層下,兩種材料毛化形貌高徑比均要大于未涂層時的高徑比。(7)在工件側面加磁鐵,希望加工出偏向一側毛化點。兩種材料作為鐵磁體材料,當溫度超過它們居里溫度成為順磁體,此時磁場無法對液體金屬產(chǎn)生影響,所以毛化形貌無變化。(8)因為活性元素S對熔池對流產(chǎn)生影響,在加工表面涂敷一層直徑5um硫粉進行激光毛化。未出現(xiàn)預想中火山口形貌,發(fā)現(xiàn)形貌成為橢球型,且各個毛化點之間長短軸不一,該現(xiàn)象從試驗上證實了S元素確實對金屬液體對流有影響。
[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.

【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG665

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