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料拉伸实验装置，该装置由石英透明模具系统、带CCD摄像机的显微镜和视频系统组成，可直接观察工件表面凹坑中的润滑剂行为。铝的试样片具有均匀的去毛刺的模压痕，并以恒定的速度用具有不同粘度的油拉伸。如果油完全被困在表面的口袋里，几何形状几乎没有变化，而没有油的口袋里，它的变化显着。这表明，在完全被困在袋中的油中产生了高的静水压力。通过对中心锥形腔充油圆柱的轴对称型面的有限元计算，还表明在圆柱高度减小约5%时，油中的静压力接近作用在真实的接触面积上的法向压力。此外，直接观察到袋中的高压油均匀渗透到真实的接触区域中。对于粘度较低的油，油袋中的油向前渗透到真实的接触区域中，并且形状变化变得更大。粘度较高的石油被向后挤压的程度要比向前挤压的程度大得多。从上述结果，微观塑性流体动力润滑机制的存在被证实。

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.