Study On The Technology And Mechanism Of Ultrasonic Vibration Assisted Milling

Vibration cutting can improve cutting effects. There have been many researches and practical applications about vibration turning, vibration drilling and vibration grinding. However, little research has been conducted in vibration milling. This paper presents an exploratory study on the technology and mechanism of one-direction ultrasonic vibration assisted milling.The main content of this research covers the following aspects:?Kinematic analysis of one-direction ultrasonic vibration assisted milling;?Experimental study on milling force in ultrasonic vibration assisted milling;?Study on the temperature field of ultrasonic vibration assisted milling by Finite element method;?Study on the dynamic characteristics of workpiece in ultrasonic vibration assisted milling and the effects of ultrasonic vibration on machining accuracy;?Study on machined surface roughness of ultrasonic vibration assisted milling;?Study on tribological properties of surfaces produced in ultrasonic vibration assisted milling.Regarding end milling as the research subject, two-dimensional calculation of the trajectory of tool tip was made by studying normal direction(i.e. direction perpendicular to feed direction) vibration mode and feed direction vibration mode respectively. A proposed chip thickness mathematic model was built. The characteristics of milling force under the two different vibration modes were also discussed. As a result, the optimal vibration mode was confirmed. A slot milling experiment was then carried out to prove theoretical analysis conclusions. Research results indicate that matching reasonable cutting parameters and vibration parameters, feed direction ultrasonic vibration assisted milling (hereinafter referred to as ultrasonic vibration assisted milling, UVAM) can embody the characteristics of ultrasonic vibration cutting, and change traditional continuous milling into micro-segmentation intermittent cutting in a milling cycle. Accordingly, UVAM can greatly improve the cutting mechanism of conventional milling (CM).The effects of ultrasonic vibration on the peak values of component forces in feed and normal direction were experimentally studied. Then a statistical model of the maximum resultant force was build, and detailed analysis was made by RSM and ANOVA method. Research results indicate that ultrasonic has a significant effect on milling force in feed direction, and the peak value of feed direction component force can be obviously decreased when choosing proper ultrasonic amplitude. The maximum resultant force is determined by the combined function of several parameters including spindle speed, feed and ultrasonic amplitude, and ideal milling force can be obtained when matching reasonable process parameters.A two-dimensional finite element model of UVAM was built, and FEM was used to analyze the temperature field of UVAM. As simulation results, the dynamic distribution of temperature at deformation zone in CM and UVAM was obtained. Simulation results were verified by experimental data. Research results show that UVAM can greatly improve the temperature distribution of cutting area, drop the max temperature of tool, decrease the influences of various heating effect on cutting process.A tool-workpiece vibration system model was built, and the dynamic displacements of the workpiece along normal direction in CM and UVAM were calculated respectively. Research results show that UVAM can make a great contribution to reducing the dynamic displacement of the workpiece and have a positive influence on machining accuracy.The effects of ultrasonic vibration on finish size and the influence of process parameters matching on machining accuracy were experimentally studied. Research results show that by matching rational process parameters, intermittent milling will help to reduce the deformation of process system caused by cutting heat and cutting force, decrease size deviation. Among all experiment factors, ultrasonic amplitude has a dominant influence on machining accuracy.The effects of assisted ultrasonic vibration on the roughnesses of surfaces produced by bottom edge and side edge of an end mill in UVAM were systematically investigated. Research results show that roughness of surface produced by bottom edge could increase to varying degrees because of ultrasonic vibration in most of the studied cases because of the complexity of tool tip. As for the surface produced by side edge,there is an obvious improvement of surface roughness when ultrasonic vibration is applied owning to the effect of reciprocating ironing.RSM and ANOVA were used to make statistic analysis for roughness of surface produced by side edge. Research results indicate that the surface roughness is determined by several key machining parameters in UVAM, and spindle speed is the most significant factor. It is also found that in most cases, at certain amplitude, higher ratio of vibration frequency to the gyro-frequency of spindle tends to produce better surface finish in UVAM. When spindle speed is selected, only matching proper feed can obtain small surface roughness.The tribological performance of surface produced in UVAM was studied. The friction coefficient, wear rate and carrying capacity of different surfaces obtained under different processing parameters were compared and studied. Research results show that the fluctuation of friction coefficient curve of surfaced produced in UVAM becomes less, the wear rate drops obviously, and the carrying capacity is greatly improved. In UVAM, the topographies of surfaces obtained at different parameters condition is dissimilar, and therefore their tribological performances and friction mechanisms are different.