Abstract: When the partially porous aerostatic thrust bearing and the journal bearings of an aerostatic spindle in a vertical milling machine are subjected to cutting load and gravitational force, the thicknesses of gaps between the thrust plate and the spindle flange will change. This study applied CFD software to analyze the effect of variations of gap thickness and rotating speed on the pressure in the gaps of the bearings and the stiffness of the spindle. The results revealed that, when the thrust plate and the spindle flange were pushed back and forth by external loading, the pressure in the gap between the spindle flange and the thrust plate was affected significantly. The pressure in the gap between the spindle and the journal bearing was slightly affected. When the spindle rotated faster, the pressure on the surface of spindle became higher and the stiffness of spindle was increased.
Abstract: The influence of the spacing of the partially porous aerostatic journal bearings and the rotating speed of the spindle on the pressure distribution in the bearing gap and the housing gap were studied. 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 figure out the pressure in the bearing gap and the housing gap. The computed results indicated that when the spacing of the bearings between air outlets was increased, the pressure got higher not only in the bearing gap, but also in the housing gap. The load carrying capacity of the bearings and the stiffness of the spindle could be improved. If the spacing of bearings was reduced by adding one more bearing to the location between the original bearings, the pressure in the narrower housing gap would decrease, while that in the wider housing gap would increase. Though the extra bearing could not help increase the net pressure exerted on the spindle effectively, it did help redistribute the housing gap pressure so that the pressure difference in the air gap could be reduced and the spindle was able to rotate stably.
Abstract: In this paper, the influence of friction on static, dynamic characteristics, the strength and lifetime of a 3-axes flexible CNC machine tool are taken into account. The machine tool is first modelled by using finite element method (FEM) to perform static structural analysis. After that, the dynamic effects caused by the inertia forces and the displacement of moving part of the machine on contact stress are considered in this study. Then, the stress and contact force distributions on solid-flexible contact are also obtained. Finally, the influence of dynamic structure, cutting conditions and material properties on strength and lifetime of CNC machine tool are discussed by using fatigue analysis. Consequently, the proposed method can be used for efficient simulation of structural dynamics, lifetime assessment as well as interactions of the real CNC machine with the machine tool structure in a virtual environment.
Abstract: An experimental investigation was performed to study the wear of a promising dental ceramic, i.e., machinable lithium disilicate glass ceramic, under lubrication conditions, in particular, to examine effects of the surface finish and applied load on wear. Our previous work has shown that a fine finish in a dry condition did not necessarily translate to the lowest wear volume due to changes in the dominant wear mechanisms. This study tested the ceramic specimens with four average surface roughness values of Sa = 143 nm, 217 nm, 353 nm, and 692 nm on a reciprocating sliding friction rig against alumina balls with two applied forces of 5 N and 25 N in a bath of distilled water. Comparing with the results obtained in the dry conditions, this study shows that surface roughness of approximately 200 nm may be suitable for surface preparation of crowns made from the material in the wet and dry wear conditions in the oral environment.
Abstract: The main purpose of this study is to research the tribological properties and mechanical properties of diamond-like carbon coating (DLC) used unbalanced magnetron sputtering system (UBMS). The objective is influence of various Zr target current on the properties of coatings, current from 0.0 A to 0.5 A. The cross-section morphology was observed by field emission scanning electron microscopy (FE-SEM). With the increase of the Zirconium targets current, the quantity contained of the Zirconium increases. Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the microstructure properties of the coatings. The nanoindentation tester was used to measure the mechanical properties. Furthermore, the wear tests were achieved through the Schwingung Reibung and Verschliess (SRV) reciprocating wear tester under dry condition. The DLC coating was deposited used 0.4 A Zr target current possessed the lowest I(D)/I(G) ratio, the highest sp3 content and highest hardness. The DLC coating (0.4A) also displayed excellent tibological properties including the lowest friction coefficient, and wear depth.
Abstract: In this paper an adaptive Ni-Mo-Al-Ag-BN composite coating was deposited by plasmaspraying. Its tribological property from 20°C-600°C were evaluated by using high temperature tribometer. Scanning electron microscopy and Raman spectroscopy were used to characterize the coating and corresponding wear tracks to determine the lubrication mechanisms. The result shows that the friction coefficient of the Ni-Mo-Al–Ag-BN composite coating from 200°C to 400°C is about 0.4 and declines very slightly at 600°C . The wear rates of the coating is 2.0×10-4mm3/N*m at 600°C and the downward trend is obvious compared with 400°C. Silver provide lubrication below 400 °C. Ag2MoO4 were formed with the temperature raised, and acted as high-temperature lubricants above 400 °C. Ni-Mo-Al–Ag-BN composite coating established a new lubrication mechanism model at 600°C . It can be concluded that the plasma sprayed Ni-Mo-Al - Ag - BN composite coating can keep good tribological property at wide range of temperature.
Abstract: In this research, we focus on the improvement of frictional performance of piston ring achieved by Laser Surface Texturing. Five kinds of samples (non-texture, dimple 100μm, dimple120μm, groove 45 degrees to sliding direction and groove 90 degrees to sliding direction) were tested under reciprocating sliding condition. The results showed that the sample of groove 90 degrees to sliding condition has the maximum decrease on either average friction coefficient (26%) or friction coefficient at end points of stock (33%). And we think that under boundary lubrication regime, the uniformity of distribution of the texture and flow of oil in contact surface are the key factors which affect the friction coefficient.
Abstract: This study examined the optimal abrasive wear performance of kenaf-reinforced polymer composite under different sliding conditions. Three different fiber loadings i.e. 43.05, 49.30 and 55.33 vol.% of kenaf fiber was reinforced into a polyester resin using the pultrusion technique. Optimal responses of wear rate and average coefficient of friction (COF) for kenaf fiber-reinforced polyester composites, based on different levels of control factors (fiber loading, applied load, counterface roughness and sliding speed) were determined by the Taguchi Design of experiment (DOE) with L9 (34) orthogonal array and Analysis of variance (ANOVA) methods. The wear behaviour of kenaf fiber-reinforced composites were investigated using DUCOM pin-on-disc tester with three levels of applied loads (10-30 N), sliding speeds (0.42-1.3 m/s) against different grit sizes of silicon carbide abrasive papers (average grain size~2.2-25.2 μm) under dry sliding condition. The optimization of S/N ratio and degree of significance of the control variables to minimize the wear rate and average COF of kenaf fiber-reinforced polyester composites was carry out. The results showed that the counterface roughness is the most significant factor in affecting the wear rate, followed by applied load, sliding speed, and fiber loading. For average COF, the fiber loading is the most significant factor followed by applied load, sliding speed and counterface roughness.
Abstract: The processing parameters of friction stir welding for 6061 aluminum alloy were optimized by using the orthogonal experimental design in the range analysis and variance analysis with the tensile strength and elongation as the parameters. The results show that the stirring speed is the key factor, even welding speed, pressure and stirring head working angle also influence welding quality. The highest tensile strength can reach to 251MPa as the elongation reached to 7.5% with the optimum parameters of rotating speed of 800r/min, welding speed of 200~220mm/min, pressure volume of 0.4mm and stirring head working angle of 3°. The weld nugget zone (NZ) is composed of uniform fine equiaxed grains, while thermo mechanically affected zone (TMAZ) is composed of slender coarse grains. The structure of heat affected zone (HAZ) is developed along the deformation direction with the effect of thermal cycle.The fracture morphology of the FSW joints shows ductile dimple features which validates the high ductility of the joint during the tensile testing.