Quantity Lubrication Research Articles

Model for atomization droplet size and energy distribution ratio at the distal end of an electrostatic nozzle

Electrostatic atomization minimum quantity lubrication (EMQL) employs the synergistic effect of multiple physical fields to atomize minute quantities of lubricant. This innovative methodology is distinguished by its capacity to ameliorate the atomization attributes of the lubricant substantially, which subsequently augments the migratory and infiltration proficiency of the droplets within the complex and demanding milieu of the cutting zone. Compared with the traditional minimum quantity lubrication (MQL), the EMQL process is further complicated by the multiphysical field influences. The presence of multiple physical fields not only increases the complexity of the forces acting on the liquid film but also induces changes in the physical properties of the lubricant itself, thus making the analysis of atomization characteristics and energy distribution particularly challenging. To address this objective reality, the current study has conducted a meticulous measurement of the volume average diameter, size distribution span, and the percentage concentration of inhalable particles of the charged droplets at various intercept positions of the EMQL nozzle. A predictive model for the volume-averaged droplet size at the far end of the EMQL nozzle was established with the observed statistical value F of 825.2125, which indicates a high regression accuracy of the model. Furthermore, based on the changes in the potential energy of surface tension, the loss of kinetic energy of gas, and the electric field work at different nozzle orifice positions in the EMQL system, an energy distribution ratio model for EMQL was developed. The energy distribution ratio coefficients under operating conditions of 0.1 MPa air pressure and 0 to 40 kV voltage on the 20 mm cross-section ranged from 3.094‰ to 3.458‰, while all other operating conditions and cross-sections had energy distribution ratios below 2.06‰. This research is expected to act as a catalyst for the progression of EMQL by stimulating innovation in the sphere of precision manufacturing, providing theoretical foundations, and offering practical guidance for the further development of EMQL technology.

Study on Temperature Field Distribution of a High-Speed Double-Helical Gear Pair with Oil Injection Lubrication

The temperature field distribution of high-speed double-helical gears under oil injection lubrication is investigated by obtaining heat flux density and convective heat transfer coefficients through theoretical calculations and CFD (computational fluid dynamics) simulations. Based on the CFD method, fluid simulations are performed to obtain the distribution of lubricating oil on the surface of the double-helical gears, the velocity streamline diagram of the lubricating oil, and the convective heat transfer coefficients of different surfaces of the gears. The friction heat flux density is calculated using Hertzian contact theory and theoretical formula of heat generation. The double-helical gears’ steady-state temperature field simulation uses this heat flux density as a boundary condition. The correctness of the calculation method is verified through experiments. The study shows that increasing the jet velocity allows the jet to reach the tooth surface more effectively, improving the cooling effect and reducing the maximum gear temperature. However, the relationship between the jet velocity and the minimum gear temperature is non-linear. Within a certain range, increasing the jet diameter makes the jet wider, and the area covered by the lubricating oil becomes larger as the jet spreads around the gear teeth, enhancing the cooling effect. An increase in gear speed leads to an increase in frictional heat flux density; moreover, the high-velocity airflow generated by the increased speed reduces the amount of lubricant entering the mesh zone, which in turn causes the maximum temperature of the gears to continue to rise.

Exploratory data analysis & EDS analysis on tool chip adhesion under dry and nano minimum quantity lubrication machining environment

Adhesion, abrasion, plowing and transverse displacement are the major causes of origin of friction. During dry machining of ductile materials, chips are fused with the rake face of the cutting tool and contribute to the formation of the built up edge. Built up edge protects the rake face of the tool from wear, but makes the machined surface rough. To improve the tribological properties and to decrease the tool-chip adhesion, cutting fluids are used. Cutting fluids are added to the machining zone to minimise cutting temperature and friction, but they result in environmental and health degradation. Surface texturing of tools is a potential way to modify the tribological properties of mating surfaces in order to increase the tribological qualities and decrease the tool-chip adhesion. The performance of surface textured tools depends upon orientation, dimple depth, width and pattern. Under lubrication regime, microholes in surface textured tools acts both as lubrication reservoir and traps wear debris to reduce abrasive wear. Nano Minimum Quantity Lubrication (nano-MQL) is an advanced lubrication technique used in machining processes, specifically designed to minimize the use of lubricants while maintaining effective lubrication. This method involves delivering an extremely small amount of high-performance lubricant directly to the cutting zone. The MoS2 lubricant with sunflower oil is typically in the form of nanodroplets, which are much smaller than conventional minimum quantity lubrication (MQL) droplets. The Exploratory Data Analysis (EDA) methodology enables the identification of patterns, trends, and outliers within the collected data, offering insights into the complex interplay of factors affecting the machining of Aluminium Alloy AA2024. At a spindle speed of 3500 rpm the feed force decreases by 37% under dry environment when compared with nano-MQL environment. Under dry environment average surface roughness reduces by 27% when compared with nano-MQL environment.

Improved Operating Behavior of Self-Lubricating Rolling-Sliding Contacts under High Load with Oil-Impregnated Porous Sinter Material

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and elaborate sealing requirements. One potential method of minimizing the amount of lubricant and simplifying sealing in gearboxes is the self-lubrication of tribosystems using oil-impregnation of porous materials. Although well established in low-loaded journal bearings, self-lubrication of rolling-sliding contacts in gears is poorly understood. This study presents the self-lubrication method using oil-impregnated porous sinter material variants. For this, the tribosystem of gear contacts is transferred to model contacts, which are analyzed for friction and temperature behavior using a twin-disk tribometer. High-resolution surface images are used to record the surface changes. The test results show a significant increase in self-lubrication functionality of tribosystems by oil-impregnated porous sinter material and a tribo-performance comparable to injection-lubricated tribosystems of a sinter material with additionally solid lubricant added to the sinter material powder before sintering. Furthermore, the analyses highlight a significant influence of the surface finish, and in particular the surface porosity, on the overall tribosystem behavior through significantly improved friction and wear behavior transferable to gear applications.

Strong, Smart, and Slippery Organo‐gels by Network Glassification

AbstractLubricant‐infused organo‐gels with low surface energy solvents represent an environment‐friendly lubricating material, while the poor mechanical performance incapacitates them to harsh and intricate service conditions. To address this challenge, a simple yet highly effective strategy to prepare strong, smart, and slippery organo‐gels by glassifying the polymer network is reported. As a proof of concept, appropriate amounts of rigid solvophobic poly(phenyl methacrylate) (PPMA) units are integrated into a solvophilic poly(cyclohexyl acrylate) (PCHA) network infiltrated with lubricant. Upon forming bicontinuous phase‐separated structures, the rigid solvent‐free PPMA segments stay in glassy states, serving as a load‐bearing phase to toughen the materials effectively. Meanwhile, the soft PCHA phase maintains lubricity and extensibility by holding a substantial amount of lubricant. Owing to the synergistic effect, the gels manifest glass‐like mechanical performance with high rigidity (46.6 MPa), strength (7.7 MPa), and toughness (23.7 kJ m−2). Moreover, the materials exhibit high thermo‐sensitivity with the elastic modulus reversibly decreasing from 46.6 MPa at 20 °C to 0.23 MPa at 50 °C, endowing the gels with shape‐memory properties. Furthermore, the organo‐gels display satisfactory anti‐adhesiveness to various foreign matters. Taken together, the work represents a facile and universal strategy to reinforce organo‐gels, thereby adapting them to various applications.

An enhanced water-lubrication method: Friction-reducing and diffusion properties of secondary lubricants

To prevent severe friction between water-lubricated bearings (WLBs) and stern shafts under harsh conditions, a method is introduced that uses a lubrication pump to supply a small amount of secondary lubricant into the bearing for a short period of time. The effect of the secondary lubricant viscosity on friction-reducing performance is investigated by a modified block-on-ring friction and wear tester. The transfer process of the secondary lubricant within the bearing is observed with a self-designed visualization experimental platform. A flow model for capturing the diffusion of the secondary lubricant is developed, and the flow velocity equations are used as a “bridge” to link the mixed lubrication model and Volume-of-Fluid (VOF) model. The results indicate that injecting the secondary lubricant in the mixed lubrication state has the effect of rapidly reducing the friction coefficient, while supplying the lubricant in the elastohydrodynamic lubrication state tends to increase the friction coefficient. The backflow zones are primarily located at the bearing inner surface and the upper half of the fluid. The high-viscosity secondary lubricant separates into “free lubricant” and “adhesive lubricant” during the transfer process. The “oil-free zone” appears in the lubricating film due to the obstruction of lubricant diffusion by the “backflow effect”. The area of the “oil-free zone” decreases with increasing lubricant viscosity and decreasing load. This study provides a reference for friction-reducing technologies of friction pairs under water-lubrication conditions.

Monitoring chip color change in Ti6Al4V alloy milling and investigating the effects of cooling/lubrication on chip morphology

This study investigated how image processing technology and cooling/lubrication methods affect the change in chip color and chip shape when milling Ti6Al4V alloy. The focus was on solving the high temperature problem in the machining of titanium alloys, which are hard and have limited thermal conductivity. The experiment was carried out under the same standards as dry, coolant, MQL (minimum amount of lubrication), and cryogen. Experiment results showed that cooling and lubricating methods had an influence on chip morphology, with the chips morphing into tubular long spiral chips, conical short spirals, and short tubular chips. Dry machining produced distinctively adiabatic bands and saw-type chip formations. These structures were found to be at a lower level in the cryogenic cooling process than in other methods. Methods of cooling and lubrication were found to be effective on chip thickness, width, and radius. In addition, the color difference caused by burning in the chip depending on the machining temperature was investigated. The S (saturation ratio) of colors in the chip image processing rose in the order of cryogen, coolant, MQL, and dry machining (0.131623, 0.150836, 0.208414, 0.230374) technique. When the temperature change was evaluated according to the cooling and lubrication techniques, the lowest temperature was found in cryogenic processing; the temperature value rose by 25 % in fluid, 35 % in MQL, and 55 % in dry machining. As a result, the intention of this study is to improve machining performance by monitoring chip structures.

Coercivity enhancement of sintered NdFeB magnets by powder Refinement, lubricant increment and Hydrogen-Containing sintering manufacturing

This study investigates powder refinement, lubricant increment, and hydrogen-containing sintering procedures to develop high coercivity in NdFeB magnets. To improve the intrinsic coercivity iHc of sintered NdFeB magnets, it is proposed to control the average particle size and distribution of the magnetic powder by increasing the classification wheel speed of the jet mill during the jet milling process. Additionally, the incremental addition of lubricant is carried out in the additive mixing stage after the magnetic powder is refined. Through the increase of lubricant, the amount of lubricant is enough to completely cover the surface of the powder; hence, the alignment of the powder in the magnetic field forming process is improved, thereby increasing the maximum magnetic energy product (BH)max of the magnet. However, the magnetic properties of the magnet are improved through the refinement of the powder and the increase of the lubricant, but it also leads to the residue of impurities inside the magnet, which actually deteriorates the iHc. Different from the traditional process, this study moved the dehydrogenation procedure to the sintering process, thus reducing the residue of impurities inside the magnet, which is beneficial to the improvement of the magnetic properties of the magnet. Herein, we report a new commercial-scale process (100 kg batches) integrating all the above-modified procedures that reached the best experimental results of iHc = 20.79 kOe, (BH)max = 44.46 MGOe and BHH = 65.25 (i.e., BHH= iHc + (BH)max). The iHc, (BH)max, and BHH of the NdFeB magnet obtained by the new process proposed in this study are 16.47 %, 0.33 %, and 5 % higher than the traditional process, respectively. As a result, iHc has been greatly improved, making NdFeB magnets more conducive to meeting a wide variety of end-user applications, including high-coercivity (>20 kOe) sintered magnets suitable for equipment operating in high-temperature environments.

Research on the lubricating oil leakage characteristics in the vapor compression heat pump system under refrigerant leaking

Refrigerant leakage is a situation that often occurs in refrigeration equipment such as heat pumps. However, certain alternative refrigerants, while exhibiting superior environmental performance, possess varying levels of flammability. The leakage of flammable refrigerants into confined spaces can pose a significant risk of explosion. The amount of lubricant in the leaking refrigerant will undoubtedly affect the flammability characteristics of the refrigerant. In this paper, the content of PVE32 oil in the leaking refrigerant during the operation of a heat pump was investigated. The results showed that, under the five leakage rate scenarios set up in the experiment, the oil concentration was highest when the leakage occurred at the condenser inlet and lowest when the leakage was at the evaporator outlet. During the leakage process of the experiment, as the mass flow rate of the leakage increased, the oil content in the early stage of the leakage increased, but the oil content in the late stage of the leakage decreased. The reasons for the change in oil content were analyzed by the oil circulation rate and the degree of phase separation. The decrease of the oil circulation rate and the change of the degree of phase separation were the key factors affecting the magnitude of the oil content as the leakage proceeded. The results of the study reveal the leakage characteristics of lubricating oil with refrigerant leakage.

Influence of Nanoparticles in Lubricant on Sliding Contact of Atomic Rough Surfaces—A Molecular Dynamics Study

In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface roughness. Three lubricating conditions were compared based on considerations of different amounts of fluid molecules. The lubricant was not able to separate the frictional contact surfaces if the quantity of lubricant molecules was insufficient. Particularly, there were no lubricating contributions when the amount of lubricant was too low, and the lubricant therefore only filled the pits in the surface roughness. Thus, the normal load was primarily supported by the contact between the two surfaces and nanoparticles, leading to significant surface morphology changes. In contrast, the frictional contact surfaces were able to be completely separated by the lubricant when there was a sufficient amount of fluid, and a very good lubricating effect could thus be achieved, resulting in a smaller friction force. In addition, the changes in surface morphology, contact area, and RMS are discussed in this paper, in order to reveal the dynamic frictional process.

The role of coatings on the sealing of cork stoppers

Natural cork stoppers, renowned for their sealing efficacy in wine bottles, face challenges in gas-tightness due to cork surface irregularities. This study investigates the impact of lubricant coatings (silicone or paraffin emulsions), on cork stopper gas-tightness. These coatings facilitate cork conformity to glass, minimizing gaps at the interface and significantly improving sealing capacity. A small amount of lubricant leads to a two-order-of-magnitude reduction in gas flow. However, careful control of coating is crucial to ensure reliable sealing. Additionally, water absorption by cork is proposed to contribute to sealing by generating expansion forces and softening the cork, enhancing conformity to glass.This study emphasizes that natural cork stoppers should be viewed as both sealants and membranes. These findings shed light on the importance of surface treatments and water interaction in achieving reliable sealing in cork stoppers, ultimately ensuring the preservation and quality of bottled wine.

Lubricant savings in sheet metal forming through thermally oxidized wear protection layers

Increasing demands on quality, variety of shapes and complexity of deep-drawn components with simultaneous price stability make the development of innovative solutions in the field of deep-drawing indispensable. For ecological and economic reasons, there is a great interest in reducing the amount of lubricant required in forming processes to a minimum. In this work, tool coatings for forming tools are to be investigated and further developed in order to use their friction-reducing properties on the tribo-system and thus enable a reduction in the use of lubricants. For this purpose, in this research strip drawing tests are carried out to investigate the friction-influencing properties of different coatings and their potential for lubricant saving. Therefore, cylindrical forming heads are provided with different coating systems. Strips of aluminum sheet are drawn around the forming heads at an angle of 90°. The amount of lubricant applied is varied. Friction values are recorded and analyzed for each system. Wear mechanisms are identified, examined and evaluated macroscopically and microscopically. For this purpose, energy dispersive X-ray spectroscope (EDX) and scanning electron microscope (SEM) examinations are carried out. A statement on the potential of the investigated coatings for lubricant saving is derived from the results.

A Review: Nanofluids in Machining for Performance and Sustainability

This study examines the use of hybrid and normal nano cutting fluids in drilling, a process commonly used by sectors of the economy that normally depend on gulf cut or dry cut oil. These lubricants work well for drilling, but they don’t improve surface smoothness enough and might shorten the tools lifespan. In order to mitigate these problems, scientists are investigating nanofluids as an alternative to conventional lubricants. They are experimenting with different mixtures of nanofluids as a foundation in drilling operations. Multiple investigations demonstrate that the utilization of nanofluid as cutting fluid can improve lubrication as well as cooling in comparison to conventional cutting fluids. Various drilling techniques, such as dry machining, minimum quantity of lubrication, and solid lubricant, are employed however literature suggests that MQL is the most environmentally friendly option. Given that drilling involves working on tough surfaces, it is imperative to have a high-quality coolant lubricant. While there are several choices available for base lubricants, none of them can achieve the required level of surface finish during drilling. As a possible lubricant option in the future, the research suggests using a hybrid nanofluid in combination with multiple base lubricants.

Electrical properties evaluation of corn oil biodiesel mixed with lubricant as a potential source of energy

The main aim of this study is to assess the electrical characteristics pertaining to a biodiesel derived from corn oil and lubricant. The first step in the synthesis of biodiesel from corn oil involves the transesterification process. Subsequently, the biodiesel is combined with a base lubricant (20W-40T) in varying proportions, spanning from 5% to 40% of the overall volume. The measurement and analysis of biodiesel blends necessitate consideration of crucial electrical parameters, including breakdown voltage, resistivity, permittivity and electrical conductivity. The decrease in breakdown voltage, permittivity, and electrical conductivity that ensues from an increase in diameter may be attributed to the corresponding increase in diameter. Nevertheless, a positive association exists between the greater quantity of base lubricant and an elevation in resistivity. Despite the positive correlation between resistivity and diameter, this phenomenon persists. The potential cause for the enhancement of the electrical properties might be attributed to the dispersion of the fundamental lubricant.

Effect of Minimum Quantity of Lubricant on Carbide Tools and Surface Integrity in the Machining of Titanium Aluminides

Titanium aluminides are being explored as potential materials for the aeronautical sector. However, their application is limited by the high costs of processing and their difficulties in machining. This research evaluates the effectiveness of the minimum quantity lubrication technique (MQL) on the turning process of Ti48Al2Cr2Nb aluminide in terms of tool wear, tool life, cutting forces, surface integrity, and temperature. It was found that MQL conditions can improve the process efficiency, reducing the thermally induced wear mechanisms and enlarging the tool life compared to dry machining. Furthermore, it allows the cutting speed to be incremented, leading to lower processing times. However, MQL seems to not be effective in the reduction of the strain-hardening effect near the machined surface and, although the number of microcracks is reduced, defect-free surfaces cannot be obtained. Moreover, similar microstructural alterations as for dry cutting were detected. The best cutting conditions in terms of surface quality were assessed using the central composite face (CCF) design and surface response methodology. Optimization of the surface roughness under industrially viable cutting conditions was achieved with an average surface roughness value, Ra, of 0.29 µm (feed rate of 0.05 mm/rev, a cutting speed of 54.6 m/min and a depth of cut of 0.125 mm).

Grindability Evaluation of Ultrasonic Assisted Grinding of Silicon Nitride Ceramic Using Minimum Quantity Lubrication Based SiO2 Nanofluid

Minimum quantity Lubrication (MQL) is a sustainable lubrication system that is famous in many machining systems. It involve the spray of an infinitesimal amount of mist-like lubricants during machining processes. The MQL system is affirmed to exhibit an excellent machining performance, and it is highly economical. The nanofluids are understood to exhibit excellent lubricity and heat evacuation capability, compared to pure oil-based MQL system. Studies have shown that the surface quality and amount of energy expended in the grinding operations can be reduced considerably due to the positive effect of these nanofluids. This work presents an experimental study on the tribological performance of SiO2 nanofluid during grinding of Si3N4 ceramic. The effect different grinding modes and lubrication systems during the grinding operation was also analyzed. Different concentrations of the SiO2 nanofluid was manufactured using canola, corn and sunflower oils. The quantitative evaluation of the grinding process was done based on the amount of grinding forces, specific grinding energy, frictional coefficient, and surface integrity. It was found that the canola oil exhibits optimal lubrication performance compared to corn oil, sunflower oil, and traditional lubrication systems. Additionally, the introduction of ultrasonic vibrations with the SiO2 nanofluid in MQL system was found to reduce the specific grinding energy, normal grinding forces, tangential grinding forces, and surface roughness by 65%, 57%, 65%, and 18% respectively. Finally, regression analysis was used to obtain an optimum parameter combinations. The observations from this work will aid the smooth transition towards ecofriendly and sustainable machining of engineering ceramics.

The Simulation of Ester Lubricants and Their Application in Weak Gel Drilling Fluids.

To enhance the performance and reduce the amount of ester-based lubricants used in weak gel drilling fluids, a shear dynamics simulation under extreme pressure conditions was employed to refine the formulation of the base oil and pressure additives. The simulation results were validated using fatty acid methyl, ethyl, and butyl esters. Fatty acid methyl ester demonstrated the lowest temperature increase and the highest load-bearing capacity post-shear. The four-ball friction test revealed that methyl oleate had a coefficient of friction of 0.0018, approximately a third of that for butyl oleate, confirming the simulation's accuracy. By using methyl oleate as the base oil and oleamide as the pressure-resistant component, the optimal shear stress was achieved with a 10% addition of oleamide. A lubricant composed of 90% methyl oleate and 10% oleamide was tested and showed a coefficient of friction of 0.03 when 0.5% was added to bentonite slurry, indicating a strong lubricating film. Adding 1% of this lubricant to a low gel drilling fluid system did not affect its rheological properties, and the gel structure remained stable after seven days of aging. Field tests at the Fu86-3 well in the Jiangsu Oilfield of Sinopec confirmed that adding 1% of the ester-based lubricant to the drilling fluid significantly improved drilling efficiency, reduced drag by an average of 33%, and increased the drilling rate to 22.12 m/h. This innovation effectively prevents drilling complications and successfully achieves the objectives of enhancing efficiency.

Multifunctional Aluminum Pre-treatments from End-Functionalized Phosphonic Acid Self-Assembled Monolayers.

Aluminum alloys are used in advanced engineering applications as they possess a combination of favorable properties, including high strength, lightweightness, good corrosion resistance, machineability, and recyclability. Such applications often require forming the sheets into the final components, which is typically aided by an oil-based lubricant, followed by joining them using adhesives, which is hampered by residual lubricant. In this work, aluminum surfaces were modified with different self-assembled monolayers (SAMs), with the goal of significantly reducing the amount of lubricant while simultaneously improving friction properties, forming, and bonding performance. Our results show that SAMs terminated with hydrophilic and nucleophilic end groups give rise to high-energy surfaces with wetting properties that are stable over time. These surfaces showed significantly improved surface wetting by the lubricant, which in turn resulted in an improved forming performance at reduced lubricant coat weights. Moreover, the nucleophilic SAM termination provided outstanding performance in adhesive bonding tests under corrosive conditions.

Influence of colloidal silicon dioxide‑magnesium stearate interaction on flow and compaction behavior of an MCC-Lactose binary mixture

The amount of glidant and lubricant in a tablet formulation is driven by their primary functionalities of enhancing flowability and reducing particle-wall friction. However, their interaction can lead to undesirable outcomes. This study has examined the influence of this interaction on powder flow and compaction, using colloidal silicon dioxide as a glidant and magnesium stearate as a lubricant in a 50:50 w/w MCC:Lactose binary blend. The findings suggest that nano-sized CSD particles coat other particles in a blend. However, increasing CSD decreases exposed MgSt and reduces its lubricity, resulting in intriguing powder flow and compaction phenomena. CSD impacts powder flow more than MgSt. Increasing the CSD reduces exposed MgSt and increases particle-wall adhesion. Higher CSD concentrations decreased powder bed bulk density and permeability due to the formation of porous structures on primary host particles. A complex interplay between CSD and MgSt during tablet compaction affected tensile strength. CSD promoted tablet picking due to reduced exposed MgSt and increased tablet-punch adhesion. This is the first study correlating tablet picking with take-off force, and it was found that >5 N take-off force risked picking. Ejection force increased with CSD and decreased with MgSt, reaffirming CSD's impact on particle-wall adhesion.

Experimental studies on the effect of application methods on the lubricant performance during serial production in automotive industry

Lubricant breakdown and galling phenomena are widely observed at the tooling surface during the stamping of aluminium components for the automotive industry, which compromise the formed surface quality and reduce tool-life. The lubricant performance has been found to be significantly influenced by its method of application. In the present research, a dedicated lubricant was evaluated by utilizing an advanced lab-scale friction testing system, TriboMate, and the effects of lubricant application method and lubricant quantity on the coefficient of friction evolution were investigated. It has been found that lubricant performance was significantly improved when the lubricant was applied on the hot workpiece blank, compared to the cold tooling surface, and when the lubricant quantity was increased. The gradual increase of friction evolution despite lubricant application on the workpiece blank was found to be due to the formation of an aluminium transfer layer at the tooling surface.