Direct Observation of the Micro-Plasto-Hydrodynamic Lubrication Mechanism at the Interface between Workpiece and Die by Microscope

本文介绍了一种新研制的板材拉深实验装置，该装置由一套四方透明模压系统、带一台ccd摄像机的显微镜和一台摄像系统组成，用来直接观察被困在工件表面凹槽中的润滑剂行为。所述铝试片具有均匀分布的金字塔形凹痕，并用具有不同粘度的油以恒定速度拉伸。如果油完全被困在表面的口袋里，几何形状几乎没有变化，而口袋里没有油的话，它会发生显著的变化。这表明，在完全被困在口袋中的石油中产生了高静水压力。对具有中心锥形凹模充油的圆柱体的轴对称压型的有限元计算还表明，在圆柱体高度降低约5%时，油中的静液压力接近作用在实际接触区域上的法向压力。此外，甚至可以直接观察到袋子中的高压油渗入实际接触区域。对于粘度较低的油膜，油腔内的油膜向前渗入实际接触区域，形状变化较大。粘度较高的油会被向后挤压，而不是向前挤压。上述结果证实了微塑性流体力学润滑机制的存在。

A newly developed sheet drawing experimental apparatus which consists of a transparent die made system of quatrz, amicroscope with a CCD video camera and a video system is used to observe directly the lubricant behavior trapped in the pockets on the workpiece surface. The specimen sheets of aluminum are provided with uniformly destributed pyramidel indentations and drawn at a constant speed with oils having various viscosities. If the oil is completely trapped in the surface pockets, the geometry shows little change, while without oil in the pocket it changes markedly. This indicates that a high hydrostatic pressure is generated in the oil trapped completely in the pocket. From a FEM calculation of an axi-symmetric ypsetting of a cylinder having a central conical impression filling with oil, it is also shown that the hydrostatic pressure in the oil approaches the normal pressure acting on the real contact area at about 5% reduction in height of the cylinder. Moreover, even permeation of the highly pressurized oil in the pocket into the real contact area is directly observed. For the oil having lower viscosities the oil in the pocket permeates forward into the real contact area, and the shape change becomes larger. The oil with higher viscosities is squeezed much more backward than forward. From the above results, the existence of the micro-plastohydrodynamic lubrication mechanism is confirmed.