Jin Yao

Experimental Study on the Characteristics of a Miniature Laminar Plasma Torch with Different Gas Flow Patterns

AbstractnAs laminar plasma jet has long stable plasma jet, low temperature gradient, negligible noise emission, good processing reproducibility and controllability, it is suitable for industrial applications with high precision requirement. However, the conventional laminar plasma torches are large in size and thus can hardly be applied in processing occasions with space limitation. In this paper, a miniature DC non-transferred arc laminar plasma torch with an external size of about 57xa0×xa056xa0×xa042xa0mm is proposed to meet the processing requirements in these occasions. It can generate long laminar plasma jet with a maximum jet length of about 300xa0mm at atmospheric pressure with pure nitrogen. Experimental study on the proposed plasma torch has been carried out to obtain its arc voltage characteristics and the jet length characteristics. It has been founded that the plasma torch with spiral gas flow pattern generally has higher arc voltage and longer jet length than that with axial gas flow pattern. In addition, a special jumping arc voltage characteristic and the variation appearances of the plasma jet were founded, which may be used to design miniature laminar plasma torch with high arc voltage and thus low arc current for the same output power as the conventional ones.

Design of a curved surface constant force mechanism

ABSTRACT A new curved surface constant force mechanism which mainly consists of a roller and a curved surface has been proposed. The magnitude and the direction of normal force caused by squeezing between the roller and the curved surface satisfy a certain relationship, thus the decomposed force of the normal force keeps constant in a certain direction all the times. According to the envelope theorem, the trajectory of the roller center and the profile of the curved surface are obtained by ignoring friction. Then, the influence of the friction is discussed in detail. In addition, the simulation is performed to verify the theoretical calculation. The simulation results show that the output force is relatively constant and the friction has little effect on the output force.

Design and Characteristics of a Laminar Plasma Torch for Materials Processing

Thermal plasma jets have been widely used in various materials processing techniques. However, the conventional thermal plasma torches usually generate turbulent plasma jets with the disadvantages of high axial temperature gradient, a short jet length and difficulties in the process control relatively, limiting its applications to materials processing. Therefore, this paper proposes a new laminar plasma torch (LPT) working with pure nitrogen to generate laminar plasma jet (LPJ). Its design and structural characteristics, e.g. segmented anode, axial gas injection, parallel water cooling structure, etc., are detailed to ensure the stability, the favorable temperature and velocity distribution of the generated LPJ. Experiments on the characteristics of the LPT showed that the generated LPJ possessed high specific enthalpy (ranging between 10 and 90xa0kJ/g), long jet length (maximum length: 480xa0mm) and low axial temperature gradient, and its output power a current and the gas flow rate. In addition, the thermal efficiency of the LPT was experimentally determined to be ranging between 25 and 45xa0%. Furthermore, experiment and simulation on the application of the LPJ for surface quenching verified the even radial temperature distribution of the plasma jet and high heat flux density brought to the surface.

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.

Optimization Design of Rectangular Cross-Sectional Wire Race Ball Bearing

Wire race ball bearing with large radial size and small axial size, saves space extremely, and is widely used in rotary devices of large machineries. This paper establishes a mathematical model of optimization design of rectangular cross-sectional wire race ball bearing,and considers minimum friction torque as objective function, and analyses constraints of contact intensity and design specifications of wire race ball bearing, and forges an optical design method that determines the number of balls, the diameter of ball, the contact angle and the diameter of ball center circle as optimal design parameters, to attain the purpose of extending bearings life. Comparing results of Optimization with original sample, the friction torque of ball that bears maximum load reduces by 10.20%. This method provides a reference for conducting further scientific researches on wear of wire race ball bearing.

Design of the Half Toroidal CVT Controller Based on ADRC

The system considered in this paper is a half toroidal Continuously Variable Transmission (CVT) system for cars. The existing CVT controllers most adopt to PID to design the controller, but the precision and reliability do not meet the requirements of the CVT well. The ADRC (Auto Disturbances Rejection Controller) technology is able to solve the nonlinear systems whose model is difficult to get and has many uncertain external disturbances. The ADRC in this paper is used to combine with the half toroidal CVT to design a robust, reliable, anti-jamming and feasible controller.

A New Method to Extract Substructures for the Multi-Shaft Transmission

Dynamic substructure method has been widely used in analyzing the torsional vibration characteristics of multi-shaft transmission. However, the existing literatures extract substructures of the multi-shaft transmission by treating its gears and shaft as several rotors, resulting in complex displacement coordination relationships and making it difficult to build dynamic model for the whole system. In this paper, a new method to extract substructures of the multi-shaft transmission is proposed when analyzing its torsional vibration characteristics using the dynamic substructure method. The proposed method avoids analyzing the displacement coordination relationships for the gear meshing, making it easier and more effective to establish the dynamic model for multi-shaft transmission.