Minimum Lubrication Research Articles

Truncation effects on circular EHL contact film thickness

Predictions of film thickness in elastohydrodynamic lubricated (EHL) contacts generally rely on the assumption of a semi-infinite equivalent solid to calculate elastic deformations. However, this assumption often fails when the contact is near an edge of one of the solids. This paper explores the impact of a solid edge being close to or within a theoretical EHL contact area on film thickness. We specifically highlight the advantages of a sharp edge over a chamfer, and the non-monotonous effect of the fillet radius on the minimum film thickness. Semi-analytical equations are developed to determine the maximum and minimum lubricant film thickness in a truncated contact and compare numerical results with experimental data in cases involving a chamfer.

Stochastic uncertain lubrication in gear transmission subjected to tribodynamic loading

A stochastic uncertain tribodynamic model is established for a spur gear pair for the first time. The stochastic uncertainty of pinion rotation speed propagated to lubrication performance is investigated. The probability density function of the minimum lubricant film thickness hmin evolves over time periodically at interval of an engagement process. Correspondence between abrupt increase in meshing force and amplification of hmin uncertainty is found. Robust and reliable lubrication performance can be achieved by suppressing the hmin uncertainty and decreasing the lubrication failure probability. This can be done by increasing lubricant viscosity, and decreasing input torque and uncertainty level of input rotation speed. This work lays a solid foundation for robust and reliability based optimization for tribodynamic gear system.

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Electric vehicle (EV) transmissions operate at high speeds. High-speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. The high mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATFs. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matching the lubricant and hardware characteristics for optimal performance. In the present communication, we demonstrate the effects of different lubricants and surface finishing technologies on the tribology of high-speed gears using tribological tests and advanced thermal elastohydrodynamic (TEHD) simulations. The important roles of lubricity additives and surface finish optimization are highlighted in conjunction with a move towards ultralow viscosity EV transmission fluids.

Machinability of Inconel 718 using unitary and hybrid nanofluids under minimum quantity lubrication

ABSTRACT In the current study, unitary and hybrid nanofluids are used with minimal lubrication to examine Inconel 718’s machinability. Nanofluids are obtained by dispersing unitary and mixed amounts of aluminium oxide, multi-walled carbon nanotubes, and graphene nanoparticles into palm oil. Initially, turning experiments were performed with pure palm oil and different unitary and hybrid nanofluids using differently coated carbide tools to obtain the best combination of the type of nanofluid(s) and coated tool for the lowest tool wear. Further, the cutting forces, surface roughness, chip thickness ratio, chip morphology, and shear angle were obtained, varying with the cutting parameters for the best combination of nanofluid(s) and the tool. The analysis of worn-out tools has been performed through images captured using optical and scanning electron microscopes. The study indicates that aluminium titanium nitride-coated tools outperform titanium aluminium nitride-coated tools with hybrid aluminium oxide and multi-walled carbon nanotube-based nanofluid, followed by a unitary aluminium oxide-based nanofluid. It could be attributed to the higher thermal conductivity and surface tension of aluminium oxide nanoparticles and the better lubricating and cooling capabilities of multi-walled carbon nanotubes. Comparatively lower performance was observed with graphene-based nanofluid due to severe agglomeration that adversely affected the homogeneity of the fluid.

Evaluation of new nano-cutting fluids for the processing of carbon fiber-reinforced composite materials

Carbon fiber-reinforced composites (CFRP), known for its impressive specific strength and modulus, finds extensive applications in defense, aerospace, automotive, and various other industries. Nevertheless, the widespread application of dry cutting in machining Carbon Fiber Reinforced Polymer (CFRP) presents significant challenges, including dust pollution, fiber layer delamination, and uneven surface quality. These issues make the machining of CFRP a formidable task. In the present investigation, a novel nanohybrid cutting fluid was successfully prepared by adding molybdenum disulfide (MoS2)/silicon carbide (SiC) nanoparticles to a base-cutting fluid synthesize from ethanol, polyethylene glycol, and sodium dodecyl sulfate. Moreover, employing minimal lubrication techniques, the nano-cutting fluid was applied to the milling process of CFRP. The feasibility of applying the cutting fluid to CFRP machining was demonstrated through short beam shear tests. Horizontal comparative milling tests were executed on CFRP, varying operational parameters and cooling-lubrication scenarios. The cooling-lubrication mechanisms of the nanofluid were analyzed, providing further validation of the effectiveness of the cutting fluid in CFRP machining. The results suggest that the nanofluid has a negligible impact on the interlaminar shear strength of CFRP, with only a 3.85% reduction. In comparison to other cooling-lubrication conditions, milling CFRP with the novel nanofluid resulted in a reduction of milling forces by 4.78%–24.84%, a decrease in milling temperatures by 15.38%–69.37%, a lowering of surface roughness by 10.78%–35.93%, and a reduction in tool tip wear by 6.25%–53.81%. Observable phenomena such as fiber pull-out and fracture were significantly reduced.

An application of hybrid Taguchi-ANN to predict tool wear for turning EN24 material

This work is an attempt to predict tool wear for turning EN24 material by the hybrid Taguchi-ANN (Taguchi-Artificial Neural Network) method. The objective is to minimize the tool wear. The independent factors are cutting environment, feed rate, depth of cut, nose radius, and tool type. A Spinner numerical control lathe is used to assess performance. As per the Taguchi orthogonal array, 27 experiments are conducted for each value of the uncontrollable factor (spindle vibration). Optimal setting is structured by Taguchi analysis and the response table. The additive model is used to predict the response. Conformity test is carried out to check whether the predicted and experimental values of response are within the range given by the confidence interval. Furthermore, the ANN is used to predict and analyze the tool wear. The result showed that the supremely important parameter is depth of cut and the least important parameter is tool type. The ideal set found is A3, B3, C3, D1, and E3. Through ANN analysis, it is observed that the experimental values are very close to the predicted values of tool wear. The predicted value at optimal setting is 0.0401 mm. The experimental values at optimal setting is 0.0422 mm. In addition, the study showed that when the feed rate and nose radius are both set to high levels and the depth of cut is medium, using an uncoated tungsten carbide tool with minimal lubrication results in the least amount of tool wear.

Sustainable machining: A review

This paper's goal is to review pertinent material on machining with minimum lubrication for green manufacturing. Due to the fact that it has an impact on so many various industrial businesses, sustainability has grown to be a very important research topic. The implementation of sustainable manufacturing techniques and technologies has given the sector a workable way to enhance its performance in terms of the economy, environment, and society. The machining system is a crucial component of sustainable manufacturing on the factory floor since it is a significant production process. Therefore, leaders should prioritise technology for monitoring, evaluating, estimating, and optimizing machining systems' impact on the environment. The study also discusses the testing procedures, results, and use of a variety of workpiece materials, tool materials, and cutting solutions made of vegetables. The results show that the MQL system is effective in achieving a smoother surface, decreasing friction, removing chips, and cooling the workpiece. The literature review demonstrates that the MQL system outperforms both dry machining and wet machining in terms of performance. This paper provides a quick overview of the machining of various materials utilizing the MQL system as a sustainable machining.

Multi-Response Optimization of Milling Process of Hardened S50C Steel Using SVM-GA Based Method

This study aims to find the optimized parameters for surveying the milling process of S50C steel in a minimum quantity lubrication (MQL) environment using a support vector machine-genetic algorithm (SVM-GA). Based on the experimental matrix designed by the Taguchi method, surface roughness and cutting force data were collected corresponding to each experiment with changes in input parameters such as cutting speed, tooth feed rate, and axial depth of cut, along with changes in two parameters of the minimum lubrication system: flow rates and injection pressure. Through analysis by the SVR-NSGAII method, the study obtained the optimal parameters of cutting and lubricating conditions when prioritizing either surface roughness or focusing on the cutting force; however, the most comprehensive result is believed to be achieved by balancing these two factors. So, when striving for the neutral value of both output parameters, which are surface roughness (µm) and cutting force (N), the optimum parameters including injection pressure (MPa), flow rates (mL/h), cutting speed (m/min), feed rate (mm/tooth), and axial depth of cut (mm) are proposed.

Machinability of nickel-titanium shape memory alloys under dry and chilled air cutting conditions

Nickel-titanium (NiTi) shape memory alloys (SMAs) undergo phase transformation between austenitic and martensitic phases in response to applied thermal or mechanical stress, resulting in unique properties and applications. However, machinability often becomes challenging due to property and temperature sensitivity attributes. The use of chilled air to influence machinability in macro-milling was investigated in this study. Other than that, differential scanning calorimetry (DSC) was used to determine the temperature of phase transformation. The results showed that milling with chilled air and minimal lubrication significantly improved machining performance by reducing tool wear and burr formation. Moreover, surface quality has also improved significantly. A notable discovery is that the machining process can change the critical conditions for phase transition, enabling new performance capability of tuning material hysteresis.

Analiza stabilności skrawania z dużą prędkością stopów aluminium

Progress in the production of cutting tools, CNC machine tools, and CAM software has contributed to improvement in subtractive machining processes, including milling, the so-called high speed cutting (HSC) and high performance cutting (HPC) machining. The cutting parameters that define the boundaries between the aforementioned technologies and conventional machining are not clearly defined. This is due to the close correlation between the process conditions and the types of processed material. High speed cutting and high performance cutting can be used for processing such as: machining of materials in the hardened state, machining without cutting fluid and with minimal lubrication, and thin-wall integral aerospace structures. The study examined complex analyses of HSC machining due to the process stability. The test results prove the dominant influence of cutting speed changes on a method’s effectiveness for spindle speeds up to 80,000 rpm.

On the influence of axial cylinder distortions on lubricant film and friction force of top piston ring conjunction near to TDC

ABSTRACT The purpose of this paper was to understand how axial cylinder distortions influence the tribological performance of piston ring. The current model contains the effects of axial distortions and ring conformability under mixed to hydrodynamic regimes of lubrication through computational fluid dynamics predictions. The axial cylinder profiles were modelled using series of sinusoidal waves. The effect of axial distortions on ring wear rate was determined using the Archard’s model. The ring friction and minimum lubricant film were predicted for low and high combustion pressures near to top dead centre. The study shows that, when the maximum combustion pressure rises, the different wear identities affect the operation of the ring friction much more limited, while the number of sine waves are more pronounced. Finally, it is proved that, even the increase of oil film thickness, it does not presuppose the reduction of friction when it comes to shaping the surface of the cylinder liner.

Machine Learning-Based Modelling and Predictive Maintenance of Turning Operation under Cooling/Lubrication for Manufacturing Systems

Cutting force is one of the significant parameters in the metal cutting process. The metal cutting process is the primary in the production and manufacturing industry to produce high-quality products. Every production and manufacturing needs to develop a technology, i.e., a cooling or lubrication system at the cutting zone while doing the metal cutting process. This current work focuses on developing the machine learning algorithm by using three different types of regression processes, namely, polynomial regression process (PR), support vector regression (SVR), and gaussian process regression (GPR). These three processes are developed to predict the machine learning force, cutting power, and cutting pressure by controlling primary factors (cutting speed, depth of cut, and feed rate). The cooling or lubrication process also affects the machining process. We need to maintain the minimum qualifications to perform under minimum quality lubrication (MQL) and high-pressure coolant (HPC). The ANN algorithm was used to run different parameters, and these parameters are optimized for cutting force.

Wear assessment of a Ti–6Al–4V motion-preserving porous artificial-cervical-joint fabricated by SLM after surface carburization

Adjacent segment degenerative diseases are a major clinical concern for anterior cervical corpectomy with fusion surgery. In this study, a hybrid motion-preserving cervical prosthesis consists of two articulating joints and one porous fusion body is designed to provide motion ability and reduce the occurrence of degenerative diseases. The hybrid design is fabricated from Ti–6Al–4V (TC4) alloy using selective laser melting (SLM) technology. After carburization pretreatment, two types of bearing couple SLM-TC4 self-mating and SLM-TC4/UHMWPE were studied in terms of lubrication regime, contact mechanics and wear performance. According to the ISO 18192-1 standard, five million cycles (Mc) of in vitro spine simulator wear tests were conducted in bovine serum lubricated condition.Hamrock-Dawson minimum lubrication film thickness analysis stated that both bearing was likely under boundary lubrication only, with extensive surface asperities contact. And, the contact stress encountered during in vitro condition was not enough to cause surface fatigue failure of any bearing couple. In term of wear performance, the obtained steady state wear rates were 0.160 ± 0.004 mm3/Mc for SLM-TC4 self-mating and 8.57 ± 0.06 mm3/Mc for SLM-TC4/UHMWPE bearing couples, respectively. According to these outcomes, SLM-TC4 self-mating couple was more promising for the articulating joint bearing design.For SLM-TC4 self-mating couple, the initial wear mechanism was abrasion with potential third-body abrasion wear. As the wear cycle proceeding, the TiC cermet layer was gradually damaged and exposed the local bare metal. Under this circumstance, material loss was consisted of abrasion wear, adhesion wear, and tribo-corrosion. In comparison, the wear mechanism of SLM-TC4/UHMWPE bearing was always abrasion-adhesion of UHMWPE. The surface of UHMWPE socket was severely plowed by the hard micro bulge of the TiC layer, and material loss and plastic deformation occurred only on the UHMWPE socket. In conclusion, carburization pre-treatment causes a hard TiC cermet layer formation on the SLM-TC4, which enhance its hardness and protect underling material from corrosion damage. The thickness and quality of the TiC layer directly affect the longevity of the joint prosthesis in vivo.

CFD Analysis of the Effect of Dimples and Cylinder Liner Honing Groove on the Tribological Characteristics of a Low Displacement Engine

The contact between the piston rings and the cylinder liner is an interface with a strong influence on the tribological behavior and, therefore, directly affects the useful life of the engine components and fuel consumption. Due to this importance, the present investigation carried out an analysis of the effects of dimples and the honing groove in the cylinder liner on the tribological characteristics. A tribological model was developed to study the friction forces, minimum film thickness, and friction coefficient for the present investigation. Similarly, a computational fluid dynamics model was built to determine the dynamic movement of the piston. The validation of the numerical model showed a close similarity with the real behavior of the engine, obtaining an average relative error of 14%. The analysis of the results showed that a 3% increase in dimples’ density leads to a 3.79% increase in the minimum lubricant film and a 2.76% decrease in friction force. Additionally, it was shown that doubling the radius and depth of the dimple produces an increase of 3.86% and 1.91% in the thickness of the lubrication film. The most suitable distribution of the dimples on the surface of the cylinder liner corresponds to a square array. In general, the application of dimples and honing grooves in the cylinder liner are promising alternatives to reduce energy losses and minimize wear of engine components.

Study of roller-shoe contact during high-pressure injection pump normal operation

Roller-shoe mechanism is very often used in diesel high pressure pumps. The most encountered issues are caused by this mechanism components which are in direct contact. Lubrication, roughness, elements dimensions and profiles, coatings, working conditions can be adjusted so that the issues are reduced. Our paper aims to identify the most critical factors which influence the roller-shoe mechanism and to calculate the contact parameters during normal engine operation. The loads applied on the components are the key factors which contribute to all parameters calculation that ensure the contact optimization. The components clearance, friction coefficients, medium contact pressure, minimum lubricant film, equilibrium temperature are some of important parameters which are the basis of a correct functioning. Analysing the obtained results, it can be observed that the lubricant film thickness can be adjusted to establish a minimum safely drive shaft rotation. Considering these results new improvements methods will be analysed for roller-shoe contact development.

Influence of Lubricant Film Cavitation on the Vibration Behavior of a Semifloating Ring Supported Turbocharger Rotor With Thrust Bearing

Abstract This contribution investigates the influence of outgassing processes on the vibration behavior of a hydrodynamic bearing supported turbocharger rotor. The examined rotor is supported radially by floating rings with outer squeeze-film damping and axially by thrust bearings. Due to the highly nonlinear bearing properties, the rotor can be excited via the lubricating film, which results in subsynchronous vibrations known as oil-whirl and oil-whip phenomena. A significant influence on the occurrence of oil-whip phenomena is attributed to the bearing stiffness and damping, which depend on the kinematic state of the supporting elements, the thermal condition, and the occurrence of outgassing processes. For modeling the bearing behavior, the Reynolds equation with mass-conserving cavitation regarding the two-phase model and the three-dimensional (3D) energy as well as heat conduction equation is solved. To evaluate the impact of cavitation, run-up simulations are carried out assuming a fully (half-Sommerfeld) or partially filled lubrication gap. The resulting rotor responses are compared with the shaft motion measurement. Also, the normalized eccentricity, the minimum lubricant fraction, and the thermal bearing condition are discussed.

Effect of reversing duration time and commutation meshing state on the elastohydrodynamic lubrication of reciprocating spur gear rack

AbstractReciprocating spur gear rack is prone to lubrication failure near the reversing dead center position. Ree‐Eyring lubrication fluid, multigrid method and multigrid integral method were used to calculate the pressure profile, film thickness and oil temperature rise. Compared with linear motion, the process of reciprocating commutative movement is more complicated and the lubrication state are more unstable. The effects of different reversing duration time and commutation meshing state on lubricant film were analysed. The results show that, the oil thickness during the gear reversing process is significantly reduced. While shortening the reversing time can improve the lubricating film thickness, it causes the instantaneous oil temperature to rise. Therefore, the gear tooth damage caused by high temperature can be avoided by prolonging the reversing duration time properly. The longer the reversing duration time, the minimum value of central film thickness and central pressure is closer to the meshing outlet area. No matter what the reversing time change, the minimum lubrication film thickness is in the reversing dead center position. So the reversing dead center is still the dangerous point for the lubrication failure of the spur gear rack mechanism. When the reversing dead center is in the leading tooth of double‐tooth meshing, the gear has the largest film thickness and the largest contact area. In addition, the synthetic radius of curvature and entrainment velocity become larger so the lubrication conditions have been improved. The results provide the theoretical basis and guidance for the reasonable design of the spur gear rack and the improvement of its lubricating performance.

Повышение эффективности концевого фрезерования нержавеющих сталей применением модифицированной смазочно-охлаждающей технологической среды

This article considers the possibility of increasing the efficiency of end milling by using a modified lubricating-cooling technological medium, based on a water-miscible cutting fluid. The conditions for the effective use of modified coolant in processing stainless steels ensuring a decrease in cutting forces and therefore a decrease in vibrations, which contributes to an increase in the quality of manufactured products have been determined. A decrease in cutting forces is due to the presence of oleic acid in the modified cutting fluid, containing surfactants, forming a dense lubricating film on the surface of the cutting tool. When mixing oleic acid in a water-miscible cutting fluid, a special soap solution significantly improving the solubility is used. However, over time, stratification of liquids occurs. To ensure the homogeneity of the medium, a special device has been developed that allows continuous mixing of the compositions, due to the presence of impellers with differently oriented blades. To save a lubricant, the technology of minimum lubrication was used, which allows the lubricant to be supplied to the cutting zone in portions (dosed) using the Noga Minicool device.

Machinability investigations on CFRP composites: a comparison between sustainable cooling conditions

Carbon fiber–reinforced polymers (CFRPs) are vulnerable to damage locally through machining operations due to an applied cutting force and high-temperature generation. Though traditional lubri-cooling medium will reduce the heat-generated damage of CFRPs, the use of synthetic fluids, however, significantly affects the environment and public health equally. Therefore, this paper aims to explore the milling performance of CFRPs in sustainable lubri-cooling mediums, i.e., dry, minimal lubrication (MQL), cryogenic-liquid nitrogen (N2liquid), and carbon dioxide (CO2ice). Furthermore, the correct choice of process parameters and lubri-cooling environments influences the cutting mechanism in any metal cutting operations. Accordingly, response surface methodology (RSM) is used to create a relationship between responses to machining inputs. In addition, two evolutionary techniques named Non-dominated Sorting Genetic Algorithm II (NSGA-II) and Particle Swarm Optimization (PSO) were used to execute parametric optimization. Eventually, the performances of the adopted approaches are compared in this manuscript, which reveals the prediction made by NSGA-II and PSO is quite consistent with the experimental results. However, in view of convergence characteristics and computational time, the PSO is shown to surpass the NSGA-II approach. Moreover, empirical cumulative distribution–based data analysis indicates that all responses are good compatible with the function of the normal distribution. At the 95% confidence level, the established ANOVA models were found to be substantial. Furthermore, lubri-cooling medium was the most critical factor affecting the response parameters with a 49% contribution in minimizing Fr, 46% contribution in decreasing VB, 38.89% contribution in Ra, and 50.21% contribution in reducing the T value.

Heat transfer characteristics of successive oil droplet impingement under minimum quantity lubrication

During oil–gas minimum lubrication, lubricating oil droplets are easily formed into hollow oil droplets containing bubbles when disturbed by a high-speed airflow. Microbubbles have an important influence on the heat transfer characteristics and movement of multiple oil droplets successively impinging on an oil film. In this work, the behavior of multiple oil droplets successively impacting an oil film is numerically simulated on the basis of the coupled level set-volume fraction method, and the influences of different bubble distributions on the heat transfer characteristics of double oil droplets successively impinging on the oil film are investigated. The formation mechanism of some unique heat transfer phenomena in the impingement process is discussed, and the influences of different bubble distribution forms on the geometric size of the thermal wake and cooling effect of the impingement area are analyzed. Results showed that a “cicada wing-like” thermal wake appears during the falling process of high-temperature oil droplets. The combined effects of heat transfer, flow field, and air flow separation behavior are the main reasons behind this wake. During the falling and spreading process of solid and hollow oil droplets, the velocity gradient difference at the tail of the oil droplet affects the geometric size of the wake. In the later stages of the impingement process, a vortex is formed in the impingement pit under the combined action of the space flow field and the pressure field. This vortex strongly improves the heat flux density in the impingement area. Different bubble distribution forms have different effects on the cooling and heat dissipation effect during impingement, and hollow oil droplets are unfavorable for cooling and heat dissipation.