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Investigation of liquid nitrogen lubrication effect in cryogenic machining.

机译：低温加工中液氮润滑效果的研究。

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摘要

This thesis focuses on the investigation of the lubrication mechanism of liquid nitrogen (LN2), namely, on how and why the friction behavior is changed between the chip and the tool with the presence of LN2 in machining. Lubrication evidences are collected through the studies on the change on cutting forces, tool wear, chip microstructure, and frictional coefficient. A new application method of penetrating LN2 to the main cutting spot was introduced in machining using modified chipbreaker to reduce contact area on chip-tool interface and normal stress in the sliding zone on the tool.; Possible mechanisms for LN2 are mainly focused on friction and wear behavior by material properties at low temperature and LN2 hydraulic effect. Using LN2 injection to form a physical barrier or thin lubrication film between two bodies, it may be possible to reduce friction.; The results of 3D cutting force measurements indicated that the strengthened workpiece material at low temperature increased the cutting force component in cryogenic machining, but resulting in a lower frictional force component due to the reduced feed force.; In addition, tool life tests were performed and showed that machining with LN2 has less tool wear than emulsion cooling. And increased shear angle and decreased thickness of the secondary deformation zone and chip thickness observed from chip microstructure provide another evidence that the tool-chip friction is reduced in LN2 assisted machining.; Three mathematical models, that is, projection, vector, and geometry methods, were formulated to convert the 3D forces measured in tool-in-use coordinate system for oblique cutting into the normal and frictional force components on the tool rake face, and then to evaluate the apparent friction coefficient. It was found that the apparent friction coefficient on the tool-chip interface was considerably reduced in cryogenic machining, even compared to conventional machining by emulsion.; In addition, the frictional behavior for sliding contact was simulated under the same normal loading and surface speed as those in actual machining. Effective lubrication behavior of LN2 has been revealed from sliding friction test. It is found that the cryogenic lubrication has shown a better performance also in the pure sliding friction testing for both a titanium alloy and low carbon steel.; To verify proposed LN2 mechanisms and distinguish them, idealized disk-flat contact test were performed. From the testing results, LN2 lubrication effect by low temperature was dependent on material pairs. (Abstract shortened by UMI.)
机译：本文主要研究液氮（LN2）的润滑机理，即在加工过程中在存在LN2的情况下切屑与刀具之间的摩擦行为如何以及为何发生变化。通过对切削力，刀具磨损，切屑微结构和摩擦系数变化的研究，收集了润滑证据。在采用改进的断屑槽的加工中引入了一种将LN2穿透到主切削点的新应用方法，以减少切屑与刀具界面的接触面积以及刀具滑动区域中的法向应力。 LN2的可能机制主要集中在低温下的材料特性和LN2水力效应引起的摩擦和磨损行为。使用LN2注入在两个物体之间形成物理屏障或薄润滑膜，可以减少摩擦。 3D切削力测量结果表明，低温下强化的工件材料增加了低温加工中的切削力分量，但由于进给力降低而导致摩擦力分量减小。此外，进行了刀具寿命测试，结果表明，与乳液冷却相比，使用LN2进行加工的刀具磨损更少。从切屑微观结构观察到，增加的剪切角和二次变形区的厚度以及切屑厚度的减小，提供了另一个证据，表明在LN2辅助加工中刀具-切屑的摩擦减小了。建立了三个数学模型，即投影，矢量和几何方法，以将在斜切中使用工具坐标系中测量的3D力转换为工具前刀面上的法向力和摩擦力分量，然后转换为评估表观摩擦系数。已经发现，与传统的乳化液加工相比，在低温加工中刀具-芯片界面上的表观摩擦系数大大降低。另外，在与实际加工相同的法向载荷和表面速度下，模拟了滑动接触的摩擦行为。 LN2的有效润滑行为已从滑动摩擦测试中揭示出来。发现在钛合金和低碳钢的纯滑动摩擦试验中，低温润滑也显示出更好的性能。为了验证提议的LN2机制并加以区分，进行了理想化的平盘接触测试。从测试结果来看，低温下的LN2润滑效果取决于材料对。 （摘要由UMI缩短。）

著录项

  • 作者

    Jeong, Woo-Cheol.;

  • 作者单位

    Columbia University.;

  • 授予单位 Columbia University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 230 p.
  • 总页数 230
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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