【作者】 刘占瑞；

【导师】 李长河；

【作者基本信息】 青岛理工大学 ， 机械制造及自动化， 2010， 硕士

【摘要】 磨削加工过程中,磨削比能高,故磨削区的温度较高。当温度超过某一临界值时,就会引起零件表面的热损伤(表面氧化、烧伤、残余应力和裂纹),使其抗磨损性能下降,抗疲劳性差,从而降低使用寿命和可靠性。另外,磨削周期内工件的积累温升,会导致工件尺寸精度、形状精度误差以及砂轮寿命急剧下降。所以,有效控制磨削区的温度,防止工件表面的热损伤,是研究磨削机理和提高磨削表面完整性的重要课题。传统的磨削加工过程中,通常采用浇注磨削液的方式,来降低磨削温度。由于砂轮的高速旋转,在其周围形成“气障层”阻碍磨削液进入磨削区,真正有效进入磨削区的磨削液很少,大量的磨削液只能对工件基体起到冷却降温的作用。同时造成严重的浪费和污染,难以适应现代绿色制造的生产加工潮流。近几年人们提出了绿色磨削加工——微量润滑(minimum quantity lubricant,简称MQL)。它是将微量的润滑油充分雾化后形成微米级汽雾,借助高速流体冲破“气障层”,有效进入磨削区。微量润滑能够起到较好的润滑功效,但是其冷却作用差。由强化换热理论可知,固体的导热能力远远大于液体和气体。在微量润滑介质中添加入固体颗粒,可以显著的增加流体介质的导热系数,提高对流传热能力,从而弥补微量润滑冷却能力不足的缺陷。本论文将纳米固体颗粒添加入到润滑流体介质中制得纳米流体,然后采用高压射流方式,为氧化锆陶瓷的精密磨削加工提供润滑和冷却。主要内容包括:一、详细阐述了纳米流体强化换热的机理。重点介绍纳米流体的制备、组成要素;纳米流体热传导系数的测量实验研究和影响因素的分析。二、将纳米流体作为MQL磨削加工陶瓷的冷却介质进行实验研究。研究主要内容:磨削力、磨削力比和磨削温度,进一步分析材料去除机理。三、研究磨削热传递。针对纳米射流微量润滑的陶瓷磨削加工进行有限元仿真,计算磨削区的热量分配。四、表面完整性评价。根据磨削条件的变化,对陶瓷表面完整性的影响因素进行分析,对表面可控性磨削进行预测。更多还原

【Abstract】 The grinding process generates an extremely high input of energy per unit volume of material removed. Virtually all this energy is converted to heat, which can cause high temperatures and thermal damage to the workpiece such as workpiece burn, phase transformations, undesirable residual tensile stresses, cracks, reduced fatigue strength, and thermal distortion and inaccuracies.In addition, the high grinding temperature rise will lead to the dimensional and shap accuracy of workpiece and dramatically life of wheel.Therefore,how to control the high grinding temperature and workpiece burning is very important.There is an important issue to study the theory of grinding and improve the integrity of workpiece.In traditional grinding usually use a large number of grinding fluids to control the grinding temperature.But a little grinding fluids can enter grinding zone for air flow layer around the high speed grinding wheel.So plentiful grinding fluids only can cool the substrate of workpiece,and then make a lot of pollution and waste.Environmental protection and the need for cost-reduction have all promoted the development of new environmentally conscious machining processes.Recent years,the minimum quantity lubricant(MQL) is a green machining way . The use of MQL is of great significance in conjunction between large cutting fluids application and dry machining. It can reduce the amount of frictional heat generation and provide some cooling in the tool-workpiece interface and hence keep the workpiece temperatures lower than those in a completely dry machining. Experimental results showed that MQL provided effective lubrication but insufficient workpiece cooling with conventional abrasive wheels. The recent development of nanofluids provides alterative cutting fluids which can be used in MQL grinding. The advanced heat transfer and tribological properties of these nanofluids can provide better cooling and lubricating in the MQL grinding process, and make it production-feasible.The main contents of this paper is MQL grinding of zirconia using nanofluids as the heat transfer medium.The following is the main content of the article:1. The research of heat transfer enhancement by nanofluids jet lubrication.It presents formation and characterization of nanofluids. The methods of nanofluids synthesis are introduced and several different types of nanofluids are formulated. The method used how to measure the thermal conductivity of nanofluids.2. It presents the experimental work of MQL grinding using conventional abrasive wheels. Both water based and oil based nanofluids were employed in MQL grinding and the performance was evaluated in terms of grinding force, G-ratio, and surface roughness, etc.3. There focuses on heat transfer in grinding. Based on thefinite element method,the temperature field of ceramics grinding conditions are modeled and analyzed.Temperature experiments of zirconia is researched under different grinding conditions and verified the finite element results above.4. The evaluation of the surface integrity in grinding.The microscopic photos can display the quality of grinding surface in all conditions.The parts of zirconia grinding will control the quality of surface after analysising.更多还原