Manufacturing Method and Antifriction Performance of Oriented Micro-Groove Produced by High SpeedBall-End Milling Process

Due to the structure characteristics and the moving way of ball-end milling cutter during ball-end milling process, regularly distributed residual material would be introduced on the high speed ball-end milled surface. This study aimed at directly utilizing the regularly distributed residual material to generate oriented micro-groove features on the high speed ball-end milled surface and investigate the anti-friction performance of this kind of surface texture. On the one hand, in view of the flexible cutting tool path during high-speed ball milling process and the controllable geometric size and distribution of the surface residual material, the way of how to generate oriented micro-groove through high-speed ball-end milling technology was illustrated at length by combining topography simulation and high speed ball-end milling tests. The workpiece material chosen in this study was cold working die steel Cr12MoV with hardness about HRC 59. Milling tests were carried on a five-axis high speed machining center DMU 60P duoblock. On the other hand, the anti-friction property of ball-end milled surface with micro-groove features was evaluated by using fluid simulation analysis and high-speed ring-on-block friction and wear tests based on hydrodynamic lubrication theory. The main research results could be summarized into the following three aspects. Firstly, micro-groove features could be generated on the high speed ball-end milled surface in the case of radial depth of cut obviously larger than feed per tooth and the orientation of surface micro-grooves could be controlled conveniently by adjusting the cutting tool path. Secondly, the surface bearing capacity was closely related to the orientation of micro-grooves. As the orientation angle of micro-grooves decreased from 90° to 20°, the bearing capacity of micro-grooves increased by 20.64% and the surface friction coefficient decreased from 0.028 45 to 0.021 65. It was attributed to combined action of the wedging effect and the reverse flow phenomenon occurred during the sliding friction process. With the decrease of orientation angle, the range of negative pressure zone and positive pressure zone were strengthened. Consequently, the reverse flow phenomenon in the oil film was gradually weakened and the dynamic pressure effect was gradually enhanced. This was responsible for the improvement of anti-friction property of high speed ball-end milled surface with micro-groove features. Lastly, the surface bearing capacity decreased when an excessively small orientation angle was selected during ball-end milling process. This was because the range of negative and positive pressure zones was too small to form an effective converging wedge on this condition. Taken together, it was feasible to use high speed ball-end milling technology to fabricate oriented surface micro-grooves. Furthermore, the anti-friction performance of this kind of surfaces closely related to the orientation angle. In terms of the ability to reduce friction coefficient, the optimal anti-friction performance was obtained when the orientation angle was set as 20° during high speed ball-end milling process within the angle range of this study. The findings of this paper could not only provide a new fabrication method for surface texture, but also have certain guiding significance for the manufacture of component surfaces with anti-friction performance requirements in actual production.