Study on Tribological Properties of Ultrasonic Vibration Assisted Milling Surfaces
|Course||Mechanical Manufacturing and Automation|
|Keywords||ultrasonic vibration milling surface texture tribology properties CFDanalysis|
Ultrasonic vibration cutting, which can reduce the cutting force, improve the tool life and surface quality, is increasingly being paid more attention to by some scholars. In addition, surface texture can efficiently improve the tribology properties of friction pairs, which has become an indisputable fact. But little research has been done on ultrasonic vibration assisted milling (UVAM) surface texturing. A systemic study has been conducted on tribology properties of UVAM surface texturing by theoretical and experimental methods.Kinematics analysis of tool tip for the milling with ultrasonic vibration assisted in feed direction was conducted. A model about tool tip trajectories was established and simulative analysis of tool tip trajectories was made. Simulation results of the tool tip trajectories showed that the separation between cutting tool and workpiece can be achieved under the conditions that the ratio of ultrasonic frequency to spindle rotating frequency is not even and the ratio of ultrasonic vibration amplitude to feed per tooth is less than2.UVAM aluminum alloy experiments were carried on and the sample surface topographies were investigated. Research results showed that there were lots of adhesions between the tool and the workpiece on conventional milling surfaces, while regular textures were evenly distributed on the UVAM surface. And the size and density of the surface textures were effected by spindle speed, feed per tooth and ultrasonic vibration amplify. The change of any of the above machining parameters would cause a great change of the surface topographies.The surface roughness of the workpiece machined with UVAM is larger than that machined with traditional milling under certain spindle speed, and the surface roughness increases with the increase of the ultrasonic vibration amplitude. At the condition’of the same feed per tooth and ultrasonic vibration amplitude, the surface roughness of the workpiece machined under the spindle speed of3000r/min is larger than that of5000r/min.The tribology properties of milling surfaces were investigated and research results showed that in the breaking-in stage compared with traditional milling surface, UVAM surfaces reduced friction coefficient curve fluctuations and had better friction stability even with no obvious transition. In normal wearing stage, in the condition of A=5μm, the surface roughness, load carrying capacity of oil film and wear rate all had a significiant improvement when fz=8μm/z, while little improvement had occurred in the when fz=4μm/z. In the condition of A=10μm, the surface roughness, load carrying capacity of oil film and wear rate all had a significant improvement when fz=8μm/z and fz=4m/z.Simulation study of the hydrodynamic lubrication characteristics of the UVAM surfaces was conducted. The results showed that the surface texture of the UVAM surface affected the pressure distribution, the fluid state, load carrying capacity of the oil film and friction of the fluid zone. Compared with traditional milling surface, the pressure curves show a upward/downward trend. A bigger relative depth(h’), smaller relative width(d’) and bigger Reynolds number is more likely to cause erratic flow. The friction increases while the bearing ability is improved with the increase of relative width(d’). The friction decreases while the bearing ability falls with the increase of relative depth(h’) and decrease of the Reynolds number.The research results of this paper create a new research field and methods for surface texturing and offer data support for UVAM surface texturing.