Study of the size effects on friction conditions in microextrusion - Part I: microextrusion experiments and analysis
Study of the size effects on friction conditions in microextrusion - Part I: microextrusion experiments and analysis
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DOI：
10.1115/1.2386207
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发表时间：
2007-08-01
影响因子：
4
通讯作者：
Dohda, Kuniaki
中科院分区：
文献类型：
--
作者：
Krishnan, Neil;Cao, Jian;Dohda, Kuniaki
微成形是一个相对较新的制造技术领域，其解决了金属微零件制造中涉及的问题，即，具有至少两个在亚毫米范围内的特征尺寸的金属部件。近年来，产品和技术的小型化趋势对具有极小几何特征和高公差的金属微型零件产生了强烈的需求。传统的成型技术，如挤出，遇到了新的挑战，在微观尺度上，由于“尺寸效应”的影响，往往是占主导地位的，在这个长度尺度。其中一个有趣的因素是摩擦力。这两个同伴的文件调查的摩擦行为和尺寸效应，在第一部分和第二部分中的储能Kolsky棒测试在微挤压过程中观察到的。在这第一篇论文中，一种新的实验装置组成的形成组件和加载阶段已经开发出获得的力-位移响应的黄铜（铜/锌：70/30）制成的销挤压。该实验装置用于挤出具有圆形横截面的销，其最终挤出直径范围从1.33 mm到570 μ m。然后将实验结果与有限元模拟和分析模型进行比较，以量化摩擦行为。结果发现，摩擦条件是不均匀的，并且在均匀材料变形的假设下显示出对微针的尺寸（或大小）的依赖性。这种假设。在第二部分中，摩擦系数将被更直接地测量。第一部分还研究了使用高摩擦/低摩擦模具涂层来改善微挤压中观察到的摩擦学特性的有效性。在微挤压实验中使用了三种不同的挤压模具，所述模具涂覆有具有硅的类金刚石碳（DLC-Si）、氮化铬（CrN）和氮化钛（TiN）。所有涂层在减少摩擦方面都令人满意，相应地，DLC-Si涂层产生最佳结果的挤压力。
Microforming is a relatively new realm of manufacturing technology that addresses the issues involved in the fiabrication of metallic microparts, i.e., metallic parts that have at least two characteristic dimensions in the sub-millimeter range. The recent trend towards miniaturization of products and technology has produced a strong demand for such metallic microparts with extremely small geometric features and high tolerances. Conventional forming technologies, such as extrusion, have encountered new challenges at the microscale due to the influence of "size effccts" that tend to be predominant at this length scale. One of the factors that of interest is friction. The two companion papers investigate the frictional behavior and size effects observed during microextrusion in Part I and in a stored-energy Kolsky bar test in Part II In this first paper, a novel experimental setup consisting of forming assembly and a loading stage has been developed to obtain the force-displacement response for the extrusion of pins made of brass (Cu/Zn: 70/30). This experimental setup is used to extrude pins with a circular cross section that have a final extruded diameter ranging from 1.33 mm down to 570 mu m. The experimental results are then compared to finite-element simulations and analytical models to quantify the frictional behavior It was found that the friction condition was nonuniform and showed a dependence on the dimensions (or size) of the micropin under the assumption of a homogeneous material deformation. Such assumption. will be eliminated in Part II where the friction coefficient is more directly measured. Part I also investigates the validity of using high-strengtly/low-friction die coatings to improve the tribological characteristics observed in micro-extrusion. Three different extrusion dies coated with diamondlike carbon with silicon (DLC-Si), chromium nitride (CrN), and titanium nitride (TiN) were used in the microextrusion experiments. All the coatings worked satisfactorily in reducing the friction and, correspondingly, the extrusion force with the DLC-Si coating producing the best results.