Key Engineering Materials Vol. 642

Abstract: In this paper, the EHL oil film thickness and shape between a needle roller and a flat rectangular glass in pure rolling oscillated working conditions had been measured based on optical interferometry. The EHL behavior affected by the applied load, oscillating frequency was investigated. The typical film shape varies of interference pictures on the maximum needle roller rotation velocity was obtained and compared each other. It is found the side constrictions are always the most severe and they are strongly speeds and loads dependence.

Abstract: In general, the thin fluid film problems are explained by the classical Reynolds equation, but this approach has some limitations. To overcome them, the method of Computational Fluid Dynamics (CFD) is used in this study, as an alternative to solving the Reynolds equation. The characteristics of the two cylinders contact with real surface roughness are investigated. The CFD model has been used to simulate the behavior of the fluid flows at the conjunction between two different radius cylinders. The non-Newtonian fluid is employed to calculate the lubricant viscosity, and the thermal effect is also considered in the evaluation of the lubricant properties. The pressure distributions, the fluid film thickness and the temperature distributions are investigated. The obtained results show clearly the significance of the surface roughness on the lubricant flow at the contact center area. The fluctuated flow also affects the pressure distribution, the temperature and the lubricant viscosity in a similar pattern to the rough surface profile. The surface roughness effect will decrease when the film thickness is increased.

Abstract: The Finite Element Method (FEM) is used to analysis multiply asperity sliding contact surface. The various distributions of stress and strain along the asperity contact profile are shown for various pressure, roughness, sliding velocity, friction coefficient, and thermal conductivity. The results show that equivalent strain increases as the friction coefficient decreases. Similar results are found for the shear stress. However, the maxima equivalent stress at the center peak increases as the roughness, thermal conductivity, or loading force increases. Instead of the peak point, maxima equivalent stress and strain can be found at the contact/non-contact interchange point of the contact profile. The equivalent stress and strain increase as the loading force increases. In addition, the normal stress increases as the friction coefficient and loading force increase. The maxima normal stress can be found at the center peak point.

Abstract: In the present study, SiC reinforced particles were introduced to the Ni-P plating bath, and developed high SiC content composite coatings. Thin films nature properties and mechanical performances were evaluated well. The results showed that the Ni-P alloy embedded SiC particles formed a few cavities, and reduced coatings hardness and wear resistance in as-plated condition. After 400°C heat-treatment, Ni₃P crystalline phase formed and reached the max hardness, and conducted excellent trybological performances. SiC particles were decoposited in 600°C and reacted with Ni to form Ni₃Si and Ni₅Si₂, caused the decreasing in hardness.

Abstract: In present study, a gear transmission system was used to evaluate the effects of oil viscosity, speed, oil temperature as well as the applied load on torque efficiency. The experimental results reveal that the efficiency is increased with the increasing oil temperature and/or applied load whether the multigrade or singlegrade oil was employed. Under a constant torgue, the power loss is increased with the increasing pitch line velocity. The above characteristic resulting from the use of high-viscosity oil yields the substantial variations. However, as the oil film thickness is quite small, the viscosity speed, oil temperature and applied load produces the limited effect on torque efficiency, It indicate that EP additives create an opposite effect on torque efficiency at poor lubrication.

Abstract: Ball screw is a very important element in precision machine industry. It has a lot of superior characteristics such as low friction coefficient, long life, high positioning accuracy and as well as converting rotational motion to linear motion. Therefore, the lubricant used in the ball screw should be low friction and wear in order to meet the aims of the above mentioned properties. The ultra-dispersed nanodiamond (UDD) is dispersed in the dispersant. The UDD is served as an extreme pressure additive in the test grease that is applied to the ball screw. Four-ball extreme pressure tests and bearing life tests were conducted in this study to evaluate the extreme pressure performance and durability enhancement of the test grease. The four-ball test results showed that the optimum selection of the dispersant category, UDD mean particle diameter and concentration added to the test grease provided by the cooperated ball screw manufacturer in this study are OLA, 200 nm and 100 ppm, respectively.

Abstract: This study analyzes the tribological performance of the test results of the journal bearing wear tester designed for the simulation of the toggle pin motion in the plastics injection molding machine. Grease with or without the addition of ultra-dispersed nanodiamond (UDD) particles were all tested in the durability tests. It showed that the grease with UDD additive could effectively extend the life of grease more than twice as long as the grease life without UDD additive in the reciprocating heavy-load and low-speed journal bearing tests.

Abstract: A ball-screw system is widely used in high speed transmission platforms. High transmission speed brings high frictional force, heat and thermal expansion occurring on contact areas of ball, screw and nut. Positioning error of platform is affected by the thermal expansion during linear transmission. A vertical motion of ball-screw driving system was used for high speed transmission test. Thermal expansion of screw and positioning error were measured for discussion their effects. Cyclic vertical motion during a long transmission distance, 2 km, will integrate thermal heat to ball, screw and nut, thermal expansion of screw is also occurred. From experiments, temperature rising and thermal expansion of screw and nut were recorded and calculated for estimate elongation and positioning error of a vertical motion high speed ball-screw. Positioning error is not totally respected thermal elongation effects of screw and nut owing to contact forces caused by wear and thermal expansion at contact areas comparing to the heavy axial load is relative small in a vertical motion ball-screw system. Therefore, the structure stiffness is not affected significantly by thermal effect and wear.

Abstract: This study investigated the effect of the spindle speed on pressure distribution in the air gap and the load carrying capacity of a porous aerostatic annular thrust bearing. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, a CFD software was used to solve the Navier-Stokes equations to calculate pressure and velocity of the air flow. The results revealed there were positive pressure zones and vacuum pressure zones in the air gap between the thrust disk and the bearing. Under the same spindle speed, the pressure difference between the positive peak and the negative peak in the case of incompressible air was greater than that in the case of compressible air. The averaged pressure on the surface of the thrust disk with compressible air flow was higher than that with incompressible air flow. So was the load carrying capacity of the bearing, which increased when the spindle rotated faster.

Abstract: In this paper, a synchronous approach for dynamic simulation of machine tools is described. Computer Aided Engineering (CAE) method models and analyzes a dynamical parameter prototype of machine tools. In which, the flexible structure, interactive movement, non-linear factor effects as well as characteristics of resonance frequencies and mechanical transfer function are considered. The integrating Finite Element Method (FEM), Multi-Body Dynamics (MBD) and control carries out a solution of machine tools simulation for predicting dynamic machine behaviors. The static analysis and modal analysis of components are presented with sample examples. Cybernetic characteristics like Bode diagram and such a controller are implemented for movement tailors. The synchronous approach deduces a practically technical method for machines tools.