Lubricant Penetration Research Articles

A facile method for fabricating super-slippery surface with long term and high-efficiency sustained release performance

Slippery liquid infused porous surfaces (SLIPS) process potential applications in surface liquid repellency, self-cleaning and anti-adhesion, while exhibiting long-term and stable release of lubricants is remaining a great challenge. Herein, an efficient liquid injection method was proposed to construct SLIPS by altering the surface energy and adjusting the inner porous structure using the facile method of direct UV irradiation. The infusion efficiency and release behavior were significantly improved and verified with various techniques such as wetting measurement, confocal fluorescence microscopy and optical microscopy. It was found that the infusion and release behavior of lubricants were varied for different specimens with different UV irradiation time. Compared to the prime substrate, PDMS treated with 90 min UV irradiation showed the highest volume of lubricant penetration which was increased almost by 833 %. Additionally, the amount of infusion consisted with the surface energy and specimens with moderate wetting exhibited the most effective lubricating performance. For the sample with 90 min UV irradiation, an ultra-low friction coefficient of 0.018 was observed under water lubrication and its releasing could be detected even after a long period of 768 h. Our results provided a facile method for the future development of long-term lubricating surfaces which may broaden their applications in fields of anti-corrosion, anti-icing and anti-fog, anti-fouling, micro-flow control and oil-water ultra-slippery occasions.

Effect of electroosmosis on lubricant penetration at the tool–chip interface

Conventional microcapillary lubrication theories explain lubricant penetration into capillaries at the tool–chip interface under the action of atmospheric pressure and capillary force without considering the electrokinetic effect caused by triboelectrification. In this study, the effect of electroosmosis on the penetration of water-based cutting fluid at the tool–chip interface of a turning process was investigated for the first time. An ionic adsorption model was proposed to adjust the zeta potential of different tool and workpiece materials in fluids, and a self-excited electric field at the tool–chip interface was obtained using an exoelectron emission test. The electroosmotic force related to the zeta potential and electric field intensity can regulate electrically driven fluid penetration. Cutting tests with a fixed self-excited electric field indicated that the cutting force obtained using a higher zeta potential fluid was lower than that obtained using deionized water and reversed zeta potential fluids (e.g. significant declines of 31.1 % and 44.3 % in AISI 304 turning). Moreover, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses on the worn tool edges produced using the above fluids indicated a transfer from adhesive wear to micro breakage, which explains the positive correlation between penetration and zeta potential, owing to an elevated electroosmosis effect. The results presented in this paper are significant for understanding the influence of the electroosmosis effect on lubricant penetration to perfect the microcapillary lubrication theory and provide a reference for formulating metal working fluids.

Capillary electroosmosis properties of water lubricants with different electroosmotic additives under a steel-on-steel sliding interface

The process of lubricant penetration into frictional interfaces has not been fully established, hence compromising their tribological performance. In this study, the penetration characteristics of deionized water (DI water) containing an electroosmotic suppressant (cetyltrimethylammonium bromide (CTAB)) and an electroosmotic promoter (sodium lauriminodipropionate (SLI)), were investigated using steel-on-steel friction pairs. The results indicated that the lubricant with electroosmotic promoter reduced the coefficient of friction and wear scar diameter, whereas that with an electroosmotic suppressant exhibited an opposite behavior compared with DI water. The addition of SLI promoted the penetration of the DI water solution, thus resulting in the formation of a thick lubricating film of iron oxide at the sliding surface. This effectively reduced the abrasion damage, leading to a lower coefficient of friction and wear loss.

Optimization of the micro-textures on the cutting tool based on the penetration of the lubricant in the micro-textures

In recent years, surface textures in micron scale is introduced into the rake face of cutting tools to facilitate the lubricant penetration into the cutting area and improving the friction conditions between tool-chip contact area. The penetration process of lubricant into micro-textures introduced into the rake face of the cutting tool during machining process is analyzed through theory calculation, FEA analysis and penetration experiments. It is found that the initial penetration velocity increases as the size of the micro-texture decreases; However, due to the combined effect of capillary pressure and friction force, the penetration distance for micro-texture with larger size is longer than that for micro-texture with smaller size when the penetration distance is larger than 0.15 mm; micro-texture with smaller size is suitable for smaller chip width, 0.15 mm under the conditions in this study, and micro-texture with a larger size is more effective for large back engagement in consideration of lubricant penetration. Also, an optimum size of micro-texture on the rake face of cutting tools should take both lubricant penetration and strength of the cutting tool into consideration. The results of this study would benefit for the designation of micro-textures in the future.

Development of novel cutting tool with a micro-hole pattern on PCD insert in machining of titanium alloy

The development of a novel cutting tool that had a micro-hole pattern on their rake and flank face of cutting tool surface has found wider potential in the field of manufacturing. Micro-hole pattern features on a tool rake face help in controlling the tribological characteristics of the cutting tool. Micro-holes with the different number of holes orientation, diameter and depth were fabricated using the advanced application of the electrical discharge super drilling machine with the view to assist lubricant penetration and retention. A comparative study has been conducted between micro-hole patterned Polycrystalline Diamond (PCD) cutting insert and the commercially available PCD cutting insert. The effect of micro-hole pattern on the machining of Titanium alloy (Ti-6Al-4 V) is investigated with the application of the Minimum Quantity Lubrication (MQL) method in turning operation. Vibration signals were captured in feed force direction and measured using the tri-axial accelerometer. The cutting temperature, tool-wear, and chip-morphology were measured with an infrared thermometer and Scanning Electron Microscope (SEM). It was found that micro-hole textured inserts reduced the friction on the rake face resulting in the decrease of vibration up to 30–50%. The cutting temperature, tool wear and surface roughness were reduced to 30%, 50% and 40%, respectively. The conical and helical chips were produced in micro pool lubrication system. The friction coefficient can be minimized at the tool-chip interface by using liquid lubrication method. There is no unfavourable effect on the performance of cutting tools having holes on the cutting tool surface. All these parameters led to the improvement in the tool life.

A comparative study on torsional fretting and torsional sliding wear of CuNiAl under different lubricated conditions

Torsional fretting and torsional sliding wear behaviors of CuNiAl against 42CrMo4 were comparatively investigated in oil, filtered water and artificial seawater. Most experiment parameters except the angular displacement amplitude were set the same for all the tests. Compared with sliding tests, the averaged fretting friction torque of fretting tests tended to be higher but the wear rate was much lower, resulting from the influence of wear trace roughness, lubricant penetration behavior, surface strain hardening and third body effect. The fretting and sliding wear traces were mainly characterized by abrasion. The fretting wear traces under the filtered water and artificial seawater lubrications were also scattered with cracks and delamination, resulting from the frequent shear stress and poorer lubrication condition.

Measurement of lubricant layer thickness in anodised alumina using confocal fluorescence microscopy

Aluminium alloys are anodised to improve hardness, corrosion protection and paintability, but their wear resistance is poor, so lubricant impregnation might often be necessary. It is problematic to measure lubricant penetration into the nanopores, which are formed during anodisation, because oil molecules contain C, H and O atoms only. Type III anodised coatings of 60 µm on 6082 alloy were impregnated in fluorophore-spiked methyl oleate with or without sonication. Ball-on-plate tribotests demonstrated that sonicated specimens were more wear resistant. Confocal fluorescence microscopy showed that lubricant penetrated deep into the anodised coating after sonicated impregnation, while conventional submersive impregnation led to lubricant layer of less than 15 µm thickness. Such non-destructive methodology can scan at least 60 µm depth of anodised coatings and rapidly quantify lubricant penetration, becoming instrumental in technological applications.

The roles of contact conformity, temperature and displacement amplitude on the lubricated fretting wear of a steel-on-steel contact.

This paper investigates the effect of contact geometry, temperature and displacement amplitude on the fretting behaviour of an aero-turbo oil lubricated cylinder-on-flat contact. To be effective, the lubricant needed both to penetrate the contact and then offer protection. Lubricant penetration into the fretting contact is found to be controlled by two physical parameters, namely (i) the width of the contact that remains covered throughout the fretting test and (ii) the lubricant viscosity. The protection offered by the lubricant (assuming that it has successfully penetrated the contact) is influenced by four physical parameters, namely (i) lubricant viscosity, (ii) traverse velocity, (iii) nominal contact pressure, and (iv) chemical effects. The relationship between the three experimental parameters which were varied in the programme of work (temperature, fretting displacement and cylinder radius) and physical parameters which influence the protection offered by the lubricant film can be competing, and therefore complex wear behaviour is observed. The roles of the various parameters in controlling the wear behaviour are presented in a coherent physical framework.

Technological lubricating means: Evolution of materials and ideas

The main stages of technological lubricating material development from ancient times to date are described. How the chemical composition of these products changed with time, how new ideas revealing the physical and chemical basics of external media that influence the mechanical processing of materials appeared, how these ideas explained the differences between traditional tribology and specific technology of metal processing are discussed. The question of the possible realization of Rehbinder’s adsorption effect in contact zone is also stated. The description of a very captivating problem is related to the explanation of the mechanism of lubricant penetration into the contact zone between the material being processed and the tool. The birth and development of the hypothesis of microcapillary penetration of the lubricant into the dynamically changed intersurface clearance that has finally led to formulating the “necessary kinetic condition of the lubricating activity” is relayed.

Structure and Friction of Stearic Acid and Oleic Acid Films Adsorbed on Iron Oxide Surfaces in Squalane

The structure and friction of fatty acid surfactant films adsorbed on iron oxide surfaces lubricated by squalane are examined using large-scale molecular dynamics simulations. The structures of stearic acid and oleic acid films under static and shear conditions, and at various surface coverages, are described in detail, and the effects of unsaturation in the tail group are highlighted. At high surface coverage, the measured properties of stearic acid and oleic acid films are seen to be very similar. At low and intermediate surface coverages, the presence of a double bond, as in oleic acid, is seen to give rise to less penetration of lubricant in to the surfactant film and less layering of the lubricant near to the film. The kinetic friction coefficient is measured as a function of shear rate within the hydrodynamic (high shear rate) lubrication regime. Lubricant penetration and layering are observed to be correlated with friction coefficient. The friction coefficient with oleic acid depends only weakly on surface coverage, while stearic acid admits more lubricant penetration, and its friction coefficient increases significantly with decreasing surface coverage. Connections between film structure and friction are discussed.

Analytical model of metalworking fluid penetration into the flank contact zone in orthogonal cutting

Metalworking fluids (MWFs) are used widely in machining process to dissipate heat, lubricate moving surfaces, and clear chips. They have also been linked to a number of environmental and worker health problems. To reduce these impacts, minimum quantity lubrication (MQL) sprays of MWF delivered in air or CO2 have been proposed. MQL sprays can achieve performance comparable with conventional water-based or straight oil MWFs while only delivering a small fraction of the fluid. This performance advantage could be explained by the enhanced penetration into the cutting zone that results from delivering MWF in high pressure and precise sprays. To explore this hypothesis, an analytical model of MWF penetration into the flank face of the cutting zone is developed and validated using experimental data. The model is based on a derivation of the Navier–Stokes equation and the Reynolds equation for lubrication and applied to an orthogonal cutting geometry under steady-state conditions. A solution to the model is obtained using a numerical strategy of discretizing the analytical scheme with two-dimensional centered finite difference method. Penetration into the cutting zone is estimated for MQL sprays delivered in air, CO2 and N2 as well as two conventional MWFs, straight oil and semi-synthetic emulsion. The model suggests that conventional MWFs, do not penetrate the cutting zone fully and fail to provide direct cooling to the flank zone where wear is most likely to occur. MQL sprays do penetrate the cutting zone completely. Using convective heat transfer coefficients from a previous study, a finite element heat balance is carried out on the tool to understand how each fluid impacts temperature near the flank tip of the tool. The results of the modeling effort are consistent with experimental measurements of tool temperature during turning of titanium (6AL4V) using a K313 carbide tool. The prediction of temperature near the flank indicates that MQL sprays do suppress temperatures near the flank effectively. These results help explain the low levels of tool wear observed for some MQL sprays, particularly those based on high pressure CO2. This modeling framework provides valuable insight into how lubricant delivery characteristics such as speed, viscosity, and cutting zone geometry can impact lubricant penetration.

A Theoretical Investigation on the Capillary Model of Lubricant Penetration

In metal processing, lubricant penetration process can be explained by the capillary model theory. Observed through microscope, cylindrical capillary model was chosen and was analyzed on the basis of hydrokinetics. Moreover, it was indicated of the basis for dividing the entire penetration process. Based on kinetic theory of gases, the penetration of gas-liquid two-phase flow in minimum quantity lubrication (MQL) machining was simply analyzed and it was pointed out that there was only gaseous phase filling process.

Performance of electrical discharge textured cutting tools

Tool face friction adversely affects chip formation and consumes about 25% of the total cutting energy. Friction in cutting can be controlled by introducing a lubricant into the tool-chip interface, the effectiveness of which may be enhanced by surface texturing the tool. This paper details the innovative application of electrical discharge machining for generating an isotropic texture on the tool rake face, with a view to facilitating lubricant penetration and retention. A significant reduction in feed and cutting forces that ensues from said texturing is demonstrated, followed by a presentation of the features and application areas of the technology.

Effects of cooling air temperature on cryogenic machining of Ti–6Al–4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti–6Al–4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti–6Al–4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip–tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.

Penetration of lubricant and coolant fluid to the contact areas in metal cutting

Penetration of lubricant and coolant fluid to the contact areas in metal cutting

Wear and frictional behaviour of high strength steel in stamping monitored by acoustic emission technique

Friction surfaces can be monitored by acoustic emission (AE) technique and the AE-signal depends on the conditions prevailing between the friction surfaces. AE from a forming operation contains measurable data from events such as galling, tool wear, lubricant penetration, stick–slip, wrinkling, necking in the sheet material and cracking in the tool or the sheet material. The detected AE is directly proportional to the energy (mechanical) consumed between the contacting surfaces and can therefore be used to estimate the forces acting on these surfaces. A change in the tribological parameters, such as materials in contact, the efficiency of lubricants, the roughness of the contacting surfaces, relative velocity between the contacting materials and contact pressure can be monitored by AE technique. Wear tests have been made using flat dies and a U-bending tool. The results indicate that the U-bending tool can be used to study wear behaviour and it simulates forming over the linear portion of a stamping tool. AE, punch force and tool temperature are shown to be essential in the evaluation and understanding of the wear process. The result shows that the surface treatment and surface quality of the tool are important for the wear behaviour. These results indicate that it is possible to use uncoated hardened tools provided that a minimum tool surface quality is maintained. These results also show that hot-dip galvanised high strength steel (HSS) wears the tool out less than uncoated HSS.

Analysis of Viscous Lubricant Penetrating into Rolling Contact Fatigue Crack.

The penetration of a viscous lubricant into a three dimensional surface crack under a rolling contact stress was calculated. The finite element method was applied to solve the Reynolds equation coupled with the elastic deformation of the crack. The process of penetration is roughly the same as the two dimensional model. The lubricant begin to flow into the crack when the contact pressure is passing the crack mouth. The lubricant enters to the crack tip and increases the stress intensity factor, when a nondimensional parameter β=ηυE2/(ap30)is small. The crack does not open when β is large, because the contact pressure has passed before the lubricant flows into the crack. The critical value of β was calculated. The penetration of the lubricant is not easy as compared with the two dimensional model.

Analysis of Rolling Contact Fatigue Crack Filled with Viscous Lublicating Oil.

The penetration of a viscous lubricant into a two dimensional surface crack under a rolling contact stress was calculated. The finite element method was applied to solve the Reynolds equation coupled with the elastic deformation of the crack. The lubricant begins to flow into the crack when the contact pressure is passing the crack mouth. The lubricant enters to the crack tip and increases the stress intensity factor, when a nondimensional parameter β=ηνE2/(ap30) is small. The crack does not open when β is large, because the contact pressure has passed before the lubricant flows into crack. The critical values of β were calculated. The penetration of the lubricant becomes easy when a frictional stress acts as the crack opening.

The kinetics of lubricant penetration action during machining

AbstractA new model of cutting fluid penetration in the interface zone during metal cutting is proposed. This model includes three stages relating to processes in a single capillary: 1. liquid phase entry, 2. ‘micro‐droplet explosion’, and 3. filling the capillary by gas phase lubrication. Calculations of model parameters have been done for two different liquids: water and castor oil. The correlation between model data and known experimental results is also given.

An Analysis of Viscous Lubricant penetrating into Cracks.

A model for lubricant penetration into cracks under rolling contact was presented. The finite element method was applied to solve the Reynolds equation incorporated with the elastic deformation of the crack. When the lubricant pressure increases at the crack mouth, the pressure propagates toward the crack tip and its distribution becomes constant. The stress intensity factor increases as time passes, and approaches the constant value. The rise time of the stress intensity factor, that is, the time required to penetrate the lubricant, is calculated.