【作者】 单宏宇；

【导师】 周宏；

【作者基本信息】 吉林大学 ， 材料加工工程， 2009， 博士

【摘要】 本文基于工程仿生学理论,以植物叶面及土壤动物体表的非光滑形态、结构及功能为生物原型,利用激光及机械加工技术在45#钢及高速钢模具表面设计并制备出仿生非光滑单元体,单元体和材料表面经生物耦合规律组合,形成类似天然生物体表的仿生非光滑耦合表面,从而实现改善模具表面粘附阻抗性能的目的。考察了单元体特征尺度及非光滑表面润湿性能随制备参数的变化规律,并针对不同制件基体材料,研究了非光滑单元体及其大小、分布和功能对模具表面粘附性能的影响,提出仿生表面粘附阻抗模型。研究表明,仿生非光滑表面上分布的单元体及其所具有的双尺度阶层复合结构能够有效吸附空气,在其表面形成一层稳定的固/气复合界面,降低表面润湿性能,实现亲水材料的表面疏水性转变。同时也能够有效降低与制件粘附界面接触面积,显著提高仿生非光滑耦合模具表面粘附阻抗性能。本文研究范围内,激光制备仿生非光滑耦合模具表面粘附阻抗性能最优,随单元体面积比的提高,模具与制件接触界面间粘附强度显著降低。经磨损及热疲劳试验后,将最优仿生非光滑耦合模具表面形态参数应用于压铸模具型腔。结果表明,仿生非光滑耦合模具表面粘附现象明显降低。可见本研究具有重要的学术价值和应用价值。更多还原

【Abstract】 Due to the physical adsorption, interface reaction, mould shrinkage etc., adhesion may occur between moulds and parts during the demoulding process. As a result, parts are difficult to be removed when they adhere to the mould cores or cavities, especially for the parts with thin walls, deep cavities or high-quality required surfaces. Moreover, adhesion will make the parts have white blemishes, cracks, deformations or even broken when large demoulding loads are applied. Although mould releasing agent can effectively decrease the adhesion, more assistant work should be done before production. Correspondingly, the continuous-running efficiency is decreased. Therefore, it is necessary and urgent to investigate the adhesion mechanism of mould/part contact surface and find a way to make a novel mould with remarkable anti-adhesion performance for increasing the production efficiency and prolonging the service life of mould.Through the process of evolution for hundreds of millions of years, the shapes and structures of organism surfaces present the maximum adaptability to the natural environment. In this paper, the anti-adhesion surfaces of some animals and plants, such as dung beetle, earthworm, lotus and rice were imitated as the organism archetypes and the coupling effect of multiple functions and scales of the surfaces of natural lives was studied in order to give a new idea for solving the adhesion problem effectively. 45# medium carbon steel and high speed steel were chosen as the base materials. Mimicking the non-smooth morphologies and structures of the surfaces of natural lives, biomimetic non-smooth units were designed and fabricated on the surfaces of steel moulds by laser processing, machining and laser associating with machining processing, respectively. The purpose was to create non-smooth mould surfaces with excellent anti-adhesion performance, which is similar as the characteristic of the surfaces of natural lives. The structures of non-smooth units and adhesion resistant property of non-smooth samples processed by laser using various parameters were studied. The influences of the unit shape, dimension, distribution and their coupling characteristics on the anti-adhesion properties of 45# steel and high speed steel moulds against metal, high polymer and clay were investigated. In addition, the changes in mould surface roughness using various laser current, defocusing amount, frequency and laser pulse width were examined. Moreover, the model of the anti-adhesion mechanism of biomimetic non-smooth surfaces was presented. Based on the above experimental tests, the biomimetic non-smooth coupling technique was applied to the practical moulds for casting oil pump bonnets. The results are as follows:(1) The coupling effect of multiple functions and scales of anti-adhesion body surfaces of natural lives, such as dung beetle, earthworm, lotus and rice was investigated. Based on the comparability theory and optimum design, for geometrical non-smooth units, with the same or different structures and dimensions, are regularly or randomly distributed on the mould surfaces to form continuously geometrical biomimetic non-smooth coupling surfaces. Mimicking the anti-adhesion surfaces of nature lives, the model of characteristic parameters of non-smooth units and biomimetic non-smooth coupling surfaces was established.(2) Based on the model of biomimetic surface and practical running conditions, biomimetic non-smooth coupling surface, which was composed of several biomimetic non-smooth units as regular distribution on the metal mould surface were designed and fabricated by laser processing and machining technique, in order to reduce the adhesion between moulds and parts.(3) The laser processing parameters have significant effect on the structure of biomimetic non-smooth unit. With the same defocusing amount, the influences of laser processing parameters on the depth and width of non-smooth unit are as follows: the current intensity> pulse width> frequency> scanning velocity. The surface roughness increases with the increase of current intensity and frequency but decreases with the increase of pulse width. A lot of micro- or nano-scale units with different morphologies distribute in the area around biomimetic non-smooth units due to the selectivity ablation by laser processing since there are surface imbalances (including the imbalance of chemical compositions and phase differences in different areas on the surface) and the segregation of impurity atomic on the substrate. The two-scale structure, consists of the large remelted concave unit and several micro- or nano-scale units around it, is called dual non-smooth structure.(4) The adhesion forces of the designed samples with non-smooth surfaces are lower than those of the samples with smooth surfaces. Compared with the smooth moulds, the biomimetic moulds have a beneficial effect on decreasing the adhesion to metal and polymer parts, whose adhesion forces reduce 15.4% and 52.7%, respectively. The factors affecting the adhesion resistance of moulds with the biomimetic non-smooth surfaces include the non-smooth unit width, unit distance, unit distribution, the area ratio of the non-smooth unit to the testing sample (SN/S) and physical and chemical structures of parts. The apertures formed between the non-smooth units and the melting parts, resulting from the biomimetic non-smooth unit effect, make the contact area of the sample/part couples decrease and the negative atmospheric pressure reduce during the demoulding process. That is the main reason of enhancing the adhesion resistance of moulds with biomimetic surfaces.(5) The influences of non-smooth unit width, unit distribution, the area ratio of the non-smooth unit to the testing sample (SN/S), and the factor of external environment with moisture content and the load, on the adhesion between biomimetic non-smooth coupling surfaces and clay parts were investigated. The results indicate that the non-smooth surfaces processed by biomimetic coupling processing have an advantageous effect on improving the anti-adhesion behavior against clay. Compared with the smooth ones, the adhesion forces of moulds with non-smooth units against clay decrease 47.3%. The effect of biomimetic non-smooth unit can breach the formation of the continuous water film and counteracts a portion of negative air pressure, which reduces the influence of capillary negative adsorption and negative air pressure. Consequently, the non-smooth surfaces of biomimetic samples have an excellent effect on reducing adhesion against clay.(6) The anti-adhesion mechanism of biomimetic non-smooth coupling surfaces is as follows: On the one hand, owing to the individual adhesion resistance of biomimetic non-smooth units, the soakage of liquid parts on the areas of non-smooth unit is effectively blocked. Thereby, the air is entrapped into the non-smooth units so that the solid/gas composite surfaces are formed between moulds and parts and the surface energies decrease. As a result, the influences of contact area of the sample/part couples and the negative atmospheric pressure are reduced during de-moulding process, whereas the stress source of the interface of sample/part couples is enlarged. On the other hand, the coupling effect of multiple functions, scales and layers of biomimetic non-smooth units increases the effect of individual adhesion resistance of biomimetic non-smooth unit by the geometric series, and makes the biomimetic non-smooth surfaces have an excellent anti-adhesion property.(7) The samples with biomimetic non-smooth units have better wear and thermal fatigue resistance than those of the smooth ones. Afterwards, the biomimetic non-smooth coupling technique was applied to practical moulds for casting oil pump bonnets. The results indicate that moulds with biomimetic coupling non-smooth surfaces have better anti-adhesion property than the smooth moulds. Furthermore, the wear and thermal fatigue resistance of moulds is improved, thus, the service lives of moulds are prolonged.To sum up, the application of biomimetic non-smooth coupling process keeps the intrinsic compositions and capabilities of base materials. Meanwhile, it provides the mould surfaces with special functional properties, such as wear, thermal fatigue and adhesion resistance, which prolongs the service lives of moulds, economizes resources and reduces production costs. Therefore, the new type moulds with biomimetic non-smooth coupling surfaces have widely application foreground, remarkable economic and societal benefits.更多还原