An approach to the study of plasto-elastohydrodynamic lubrication in the wire drawing process part 1: Experimental

This paper describes an experimental study of hydrodynamic lubrication in wire drawing in which different types of lubricants (straight oils, emulsions and grease) are used. The experiments were conducted on a specially designed laboratory wiredrawing test rig, to assess the frictional force and film thickness, while drawing an aluminium wire at different speeds. Hydro-dynamic performance, including frictional force and film thickness, were measured and plotted graphically, showing lubricant and drawing speed as the main influences. Results indicate that the frictional force decreased and the oil film thickness increased using straight oils with high viscosity at high drawing speed.     

Hydrodynamic lubrication of the ironing process

A theoretical model is presented to calculate the lubricant film thickness in an unsteady hydrodynamic lubrication of cup-shaped products to be formed by the ironing process. The model covers the development of hydrodynamic lubrication in various phases of the ironing process. The model provides equations for estimating the lubricant film thickness for each phase. Experiments were conducted to study the effect of lubricant viscosity on die expansion and punch force in making cup-shaped products by the ironing process. It was found that the die expansion varied between unlubricated and lubricated cups and depended on the lubricant viscosity. The film thickness was estimated from the difference between the increased die/punch clearance, which was calculated from the expansion, and the lubricated cup wall thickness. The theoretical film thickness was compared with the estimated film thickness based on the die expansion measurement.     

Viscous Lubrication in Wire Drawing

A scheme for the promotion of viscous lubrication in wire drawing is analyzed. Lubricant pressure is built up by means of close tolerance tube installed in front of the die. In the die, plasticity is maintained by the combination of fluid pressure and wire tension. In the analysis presented here the lubricant flow rate and film thickness variation in the die are solved for as well as the necessary length of pressure tube. Pressure and temperature effects on the lubricant viscosity and strain hardening effects on the wire metal are included in the analysis.     

Non-newtonian thermal analysis of an EHD contact lubricated with MIL-L-23699 oil

A thermal and non-Newtonian fluid model under elastohydrodynamic lubrication conditions is proposed, integrating some particularities, such as the separation between hydrodynamic and dissipative phenomena inside the contact. The concept of apparent viscosity is used to introduce the non-Newtonian behaviour of the lubricant and the thermal behaviour of the contact into the Reynolds equation, acting as a link element between the hydrodynamic and dissipative components of the EHD film, independently of the rheological and thermal models considered. The apparent viscosity enables the application of the rheological model better adapted to each lubricant, without appealing to special formulations of the EHD problem.The Newton–Raphson technique is used to obtain the lubricant film geometry and the pressure distribution inside the EHD contact. The shear stresses developed in the fluid film are evaluated assuming the non-linear Maxwell rheological model. The surfaces and lubricant temperature distributions are determined using the simplified Houpert's method, applied to the inlet contact zone, and the thermal method proposed by Tevaarwerk is applied in the high pressure contact zone.The non-Newtonian thermal EHD model is applied to the analysis of a contact lubricated with MIL-L-23699 oil. Significant results are obtained for the centre and minimum film thickness, for the inlet shear heating and film thickness reduction factor (φ_T), for the temperature rise of the lubricant and of the surfaces and for the friction coefficient inside the contact, considering wide ranges of the operating conditions (maximum Hertzian pressure, inlet oil temperature, rolling speed and slide-to-roll ratio).Finally, the numerical traction curves determined are compared with the corresponding experimental results, showing very good correlation.     

In lubro 3D measurement of oil film thickness at the interface between tool and workpiece in sheet drawing using a fluorescence microscope

In order to understand quantitatively the micro-contact and lubricant behavior at the interface between a tool and a workpiece in sheet drawing, a method for mapping the oil film thickness in lubro has been developed. This is based on the use of a fluorescence microscope. It is shown, firstly, that the in situ oil film thickness between the tool and the workpiece can be measured three dimensionally, and, secondly, that the in situ surface topography of the workpiece can be visualized clearly. From the 3D surface topography, the permeation of the trapped lubricant into the real contact area can be observed.     

Elastohydrodynamic Lubrication of Rough Surfaces under Oscillatory Line Contact with Non-Newtonian Lubricant

This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally.

For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.     

球形件反复拉深成形工艺有限元模拟及试验

提出了球形件反复拉深成形工艺,对该工艺进行了有限元模拟与试验验证。与一次拉深成形工艺进行了对比分析,结果表明：凹模圆角区与法兰区应力状态及大小基本相同,但在球底区,反复拉深时径向应力和周向应力都远小于一次拉深的应力,球底区径向应力和周向应力基本为压应力或很小的拉应力;反复拉深时球底区厚度方向应变明显减小,一次拉深、二次反复拉深、三次反复拉深成形的制品最薄点减薄率分别为0.189、0.122、0.049,三次反复拉深可实现近等壁厚制品的拉深成形。该工艺与筒底冷校形工艺相结合,可实现近等壁厚深筒形零件的拉深成形。     

LOADING CAPACITY ANALYSIS OF THE MISALIGNED CONICAL-CYLINDRICAL BEARING WITH NON NEWTONIAN LUBRICANTS

A novel numerical method to lubricate a conventional finite diameter conical-cylindrical bearing with a non-Newtonian lubricant, while adhering to the power-law model, is presented. The elastic deformation of bearing and varied viscosity of lubrication due to the pressure distribution of film thickness are also considered. Simulation results indicate that the normal load carrying capacity is more pronounced for higher values of flow behavior index n, higher eccentricity ratios and larger misalignment factors. It is found that the viscosity-pressure to the effect of lubricant viscosity is significant.     

润滑油粘度对缸套/活塞环摩擦学性能的影响

在内燃机实际运行中,润滑油的粘度直接影响到润滑油膜的状态,因而活塞环在缸套中不同位置时的摩擦、润滑状态各不相同。文中以缸套活塞环为研究对象,建立了润滑计算模型,并运用该模型对缸内压力、温度、油膜厚度和摩擦系数进行了分析。结果表明,润滑油膜厚度和摩擦系数随转速改变而发生变化,而剪切稀化导致润滑油粘度减小是引起该变化的主要原因。最后,通过对计算结果的分析,提出了适用于缸套活塞环的润滑油粘度指标。     

A model of thick film lubrication by soaps in wire drawing using a pseudo-plastic rheological law

A model for wire drawing lubrication by soap using realistic soap rheology, plastic at low temperature, non-Newtonian viscous at high temperature, is presented. A simplified analysis of the lubricant flow gives film thickness as a function of soap rheology and drawing pass parameters, which is shown to agree with experiment     

油膜润滑径向轴承的全域解模拟计算-宽轴承解

雷诺方程的适用范围一般是在微米级膜厚，对纳米级膜厚由于粘度随油膜厚度的改变而改变，粘度成为更重要的润滑剂性能指标，本文采用粘度修正广义雷诺方程求解轴承的性能，对无限宽轴承来说，可得出全域的解析解，其公式可用于任意工作条件，从而为其它轴承的计算提供依据。     

Lubricant Flow and Evaporation Model for Heat-Assisted Magnetic Recording Including Functional End-Group Effects and Thin Film Viscosity

The lubricant covering a hard disk in a heat-assisted magnetic recording drive must be able to withstand the writing process in which the disk is locally heated several hundred degrees Celsius within a few nanoseconds to reduce the coercivity of the media and allow writing of data. As a first step in modeling a robust lubricant, we have developed a simulation tool based on continuum theory that incorporates previously proposed variations of viscosity and an additional component of disjoining pressure due to functional end-groups with film thickness. Here we apply this simulation tool to a conventional perfluoropolyether lubricant, Zdol 2000, for which there exists experimental data. The simulation tool can be used equally well for other lubricants once their properties become known. Simulations at small length and time scales that are unobservable with current experimental capabilities are performed. We investigate the effect of the total disjoining pressure and thin film viscosity on evaporation and lubricant flow for different initial thickness. For films thicker than 1 nm, the inclusion of polar disjoining pressure suppresses the lubricant thickness change due to evaporation and thermocapillary shear stress compared with cases without this component. Thin film viscosity is an important property to consider for thinner lubricants. We also consider how lubricant depletion depends on laser spot size and thermal spot maximum temperature. The smaller spot profiles exhibit side ridges due to thermocapillary shear stress while the larger spot profiles show no side ridges, only a trough due to evaporation. The lubricant depletion zone width and depth increase with increasing thermal spot maximum temperature.     

Investigation of the strain distribution with lubrication during the deep drawing process

A lubrication/friction model can be implemented in FEM codes to predict the contact area ratio, friction coefficient and strain distribution in lubricated deep drawing process. In the lubrication analysis, the surface roughness effect on lubrication flow is included by using Wilson and Marsault's average Reynolds equation that is appropriated for mixed lubrication with severe asperity contact. With regard to the asperity contact theory, the well-known flattening effect is considered. Friction is expressed in terms of variables such as lubricant film thickness, sheet roughness, lubricant viscosity, interface pressure, sliding speed, and strain rate. The proposed lubrication/friction model combined with a finite element code of deep drawing process to predict the contact area ratio, friction coefficient and strain distribution. Numerical results showed that the present analysis provides a good agreement with the measured strain distributions.     

Couple stresses in the elastohydrodynamic film in rolling bearings

Couple stresses may appear, when additives are present in a lubricant or when the lubricant molecules are long chains. Couple stresses are particularly probable in the elastohydrodynamic lubrication of gears or of heavily loaded rollers, where the film thickness is exceptionally small. For simplicity, the Grubin-type approximation is used in the present analysis to study the effect of couple stresses on the minimum film thickness between elastic rollers. A new parameter is defined and used to study the effects of couple stresses. The appearance of couple stresses has the desirable effect of increasing the minimum film thickness, especially when the chain length of the additive molecule or of the lubricant molecule is large.     

Viscosity–pressure–temperature behaviour of mineral and synthetic oils

A new high‐pressure viscometer that can measure viscosity at pressures up to 0.8 GPa has been developed in the authors' laboratory. The ‘modulus equation’ has been used to compare the behaviour of mineral and synthetic lubricants. Among the oils investigated there was one ester that biodegraded rapidly both before and after ageing in a long‐term test‐rig operation. To facilitate a comparison or application of the results to other oils, an analysis of the correlation between the viscosity—pressure coefficient and the kinematic viscosity measured at atmospheric pressure has been provided. A prediction of lubricant film thickness based on high‐pressure viscosity data is compared with film thickness measurements in a roller bearing.     

The Influence of Lubricant Upon EHD Film Behavior During Sudden Halting of Motion

Although steady state elastohydrodynamic (EHD) lubrication is quite well understood both from the theoretical and from the experimental point of view, studies of transient effects in EHD are currently far less developed. This paper describes an experimental investigation into EHD film behavior during sudden halting of motion. A technique has been devised which enables both central lubricant film thickness and film thickness profiles to be measured every millisecond during halting of a ball on flat, sliding contact. This has enabled detailed information of influence of lubricant on film collapse during halting to be obtained. It is shown that film collapse occurs in two stages. The first is a very rapid reduction in film thickness with only very small changes in film geometry and thus pressure distribution. This is followed, as soon as entrainment ceases, by the formation of a lubricant entrapment, and subsequent slow leakage of fluid from the central film region. This paper focussed on the formation of this entrapment and the influence of the rheological properties of the lubricant, i.e. viscosity and pressure-viscosity coefficient, on its development and behavior.     

A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction

We present a realistic elastohydrodynamic lubrication (EHL) simulation in point contact using a Carreau-like model for the shear-thinning response and the Doolittle-Tait free-volume viscosity model for the piezoviscous response. The liquid lubricant modeled is a high-viscosity polyalphaolefin which has been shown by high-pressure viscometry to possess a relatively low threshold for shear-thinning as a single-component liquid lubricant. As a result, the measured EHL film thickness is about one-half of the Newtonian prediction. We derived and numerically solved the two-dimensional generalized Reynolds equation for the modified Carreau model based on Greenwood. In this simulation, viscosity was not treated as an adjustable parameter; the models used for the pressure and shear dependence of viscosity were obtained entirely from viscometer measurements. Truly remarkable agreement is found in the comparisons of simulation and experiment for traction coefficient and for film thickness in both pure rolling and sliding cases.     

Effect of lubricant viscosity grade on mechanical vibration of roller bearings

This work aims to characterize vibration behavior of roller bearings as a function of lubricant viscosity. Experimental tests were performed in NU205 roller bearings, lubricated with mineral oil of three different viscosity grades (ISO 10, 32 and 68). The mechanical vibration was determined through the processing and analysis of bearing radial vibration data, obtained from each of the lubrication conditions, during 2 h of test run for temperature stabilization and under several bearing shaft speeds. The applied radial load was 10% of the bearing nominal load. Through root mean square (RMS) analysis of the vibration signals, it was possible to identify specific frequency bands modulated by the change in lubricant viscosity, which was related to change in oil film thickness.     

Hydrodynamic deep drawing process assisted by radial pressure with inward flowing liquid

A radial pressure can reduce drawing force and increase drawing ratio in hydrodynamic deep drawing. However, conventional hydrodynamic deep drawing cannot attain a radial pressure higher than the pressure in the die cavity. In this research, a modified method, named hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid, was proposed and investigated using both primarily experimental and numerical simulation analysis. A radial pressure higher than the pressure in the die cavity was realized by means of the inward flowing of the liquid during this process. After preliminary experimental validation, FEM was used to explore the forming process. The results from the simulation were compared with those from the experiment. The effects of the radial pressure on the wall thickness distribution, punch force, and compressive stress in the blank flange were studied with assistance of numerical simulation. The process window for radial pressures versus drawing ratios was established in 2Al2O alloy experimentally and cups with drawing ratio of 2.85 were successfully formed.