Deping Yu

Analytical design method of a device for ultrasonic elliptical vibration cutting

Ultrasonic elliptical vibration cutting (UEVC) is effective in ultraprecision diamond cutting of hard-brittle materials and ferrous metals. However, its design is quite empirical and tedious. This paper proposes an analytical design method for developing the UEVC device which works at the Flexural-Flexural complex-mode to generate the elliptical vibration. For such UEVC device, the resonant frequencies of the two flexural vibrations are required to be the same. In addition, the nodal points of the two flexural vibrations should be coincident so that the device can be clamped without affecting the vibrations. Based on the proposed analytical design method, an UEVC device was first designed. Modal analysis of the designed UEVC device was performed by using the finite element method, which shows that the resonant frequencies coincide well with the targeted ones. Then a prototype UEVC device was fabricated, and its vibration characteristics were measured by an impedance analyzer and a laser displacement sensor. Experimental results indicate that the designed UEVC device can generate elliptical vibration with the resonant frequencies closed to the target ones. In addition, the vibration trajectory can be precisely tuned by adjusting the phase difference and the amplitude of the applied voltage. Simulation and experimental results validated the effectiveness of the analytical design method.

Influence of the Gas Injection Angle on the Jet Characteristics of a Non-transferred DC Plasma Torch

The non-transferred direct current (DC) plasma torch has been widely used in various industrial applications due to its special jet characteristics. The jet characteristics are determined by different factors, including the working parameters, the torch construction, the gas injection angle (GIA) etc. As there is little study on the influence of the GIA on the jet characteristics, experimental study on the GIA’s effects on the jet characteristics has been carried out on a specially designed non-transferred DC plasma torch, whose GIA can be changed by replacing a gas injection component. The arc voltages and thermal efficiencies of the plasma torch, the specific enthalpies and jet lengths of the plasma jets at different working conditions were obtained and analyzed. It has been found that the GIA greatly affects the arc voltage, the thermal efficiency, the specific enthalpy and the jet length. Based on these findings, plasma torch with appropriate GIA could be used to help generating the plasma jet with desired characteristics.

Effects of thermal plasma surface hardening on wear and damage properties of rail steel

The aim of this study is to investigate the effects of thermal plasma surface hardening on wear and damage properties of rail steel. Wear tests of the rail steel treated by thermal plasma jet and untreated one were carried out on a block-on-ring wear test machine. Their corresponding wear and damage properties were contrasted. Results indicate that the microstructure of the heat-affected zone of the rail steel treated by thermal plasma surface hardening was transformed. It mainly consists of lath and acicular martensite and also small amount of sorbite, bainite, and retained austenite. As a result, the thermal plasma surface hardening effectively improves the wear resistance of the rail steel. The main wear mechanism of the treated rail steel is mild plowing wear, while that of the untreated rail steel is a combination of severe plowing wear and adhesion wear. Therefore, it is verified that thermal plasma surface hardening is effective in improving the wear resistance, alleviating the surface damage and thus prolonging the service life of the rail steel.

Investigation of variable spindle speed in slow tool servo-based turning of noncircular optical components

Ultra-precision noncircular optical components, e.g. hyperbolic quadrupole in mass spectrometer, can be machined by diamond turning assisted by slow tool servo (STS). However, the bandwidth of STS is usually small, which limits the STSs capability in following the required tool path, leading to a large form error. To reduce the form error, this paper proposes an approach to apply variable spindle speed (VSS) to STS-based turning. Design of the VSS trajectory based on the noncircular profile of the optical component was investigated in detail. To validate the proposed approach, simulation on the application of VSS in the STS-based turning process was established and applied to the machining of typical noncircular optical components. Simulation results show that the proposed approach is effective in reducing the requirement on the bandwidth of the STS, resulting in higher form accuracy of the machined noncircular optical components.