Preparation of chemically etched surface texture and its friction characteristics in sheet forming

Abstract

The surface texture of die can reduce friction, and the reasonable texture type can also form oil film on the die surface to save the use of lubricant. In this paper, a method of preparing surface texture on the die by chemical etching is proposed. This paper mainly studies the law of preparation of surface texture by chemical etching and the effect of chemically etched surface texture on die friction. In the experiments, the surface of samples of Cr12 were treated by chemical etching to obtain several groups of surface texture, and the morphology of the chemically etched surface was observed by laser confocal microscope to obtain the characteristics of the surface. Then, four gradients of surface texture with different etching time are selected according to the three-dimensional parameters to obtain the frictional property of samples with chemically etched surface texture using the home-made friction testing machine. Finally, the mechanical rheological model is used to analyze the lubrication state and load-bearing mechanism to prove the results. The results show that the chemically etched surface texture was composed of asperities and pits. The characteristics of surface texture with different etching time show a certain pattern, and the surface of the die had certain hydrophilicity. In addition, the chemically etched surface texture can effectively reduce the friction coefficient between the die and the plate under high load condition (nominal pressure ≥ 32MPa), with an average reduction of 35.6%, a maximum reduction of 49.5% (nominal pressure = 72 MPa, arithmetical mean height of the scale limited surface Sn=1.3.And the analysis results show that the friction coefficient is mainly determined by the area ratio of closed oil pit which was obtained using the image processing technology of MATLAB to verification experiment results. The calculation data and the experiment results are consistent which proves the conclusion.