Papers by Keyword: Lubrication

Abstract: Ball bearings are crucial components in various machinery and mechanical systems, finding applications across numerous industries such as automotive, aerospace, manufacturing, robotics, and household appliances. Minimizing friction and wear in the bearings is essential to enhance the efficiency, reliability, and lifespan of equipment. Friction moments in ball bearings occur due to rolling-sliding motion at the ball-race contact and sliding between the ball and cage. The magnitude of these friction moments depends on factors such as surface topography, load, and speed. Understanding how surface topography influences the friction moments in these bearings is crucial. This paper investigates the effect of surface roughness on the friction moment between the ball and race contact, as well as between the ball and cage contact. An analytical model is employed to estimate the friction torque within ball bearings, considering the total friction torque generated at the contact points between the balls and the race, as well as at the ball-cage interface. A mixed elastohydrodynamic lubrication model is used to estimate the friction coefficient at these contact points.

Abstract: Wrinkling during diaphragm forming of engineering fabrics compromises structural integrity and surface quality. This study investigates two strategies—diaphragm pre-tensioning and fabric inter-ply lubrication—to mitigate wrinkle formation. A pre-tensioning (PT) blank holder was designed and evaluated through deep-draw experiments supported by finite element analysis (FEA). Results show that pre-tensioning (50% strain) significantly reduces wrinkle severity compared to a conventional blank holder. The PT blank-holder creates initial equi-biaxial strain consistent with analytical and FEA predictions. Resin inter-ply lubrication also decreased wrinkling and reduced forming force by approximately 70%, primarily by lowering inter-ply friction. However, pre-tensioning proved more effective overall. These findings demonstrate the potential of diaphragm pre-tensioning for improving forming quality and provide a foundation for advanced multi-step thermoforming processes.

Abstract: The lubricant thickness in cold forging was estimated by machine learning of the in situ captured images of the die–workpiece contact interface. The images were in situ captured by a high-speed camera from the backside of the transparent glass die during forging of commercially pure aluminum workpiece. On the other hand, the images of the lubricated workpiece were individually captured as training images for random forest with classification. The classification accuracy of the lubricant thickness was confirmed to be approximately 75% (classification ability: 5–10 μm in lubricant thickness) in the training images with 22,500 px (50 px/mm). The in situ captured images of the die–workpiece contact interface during forging were classified by random forest using the training images. The estimated lubricant thickness of the in situ captured image almost agreed with the lubricant thickness estimated from the mean brightness value of the in situ captured image.

Abstract: Most forming oils have changed to chloride-free oil containing no chloride additives to protect environments regarding as the big issue of sustainable manufacturing. Several high-performance oil without chloride and die coating has been developed recently. In this study, the effect of micro-dimples on a die formed by a cutting machine or a laser device was tried to use chloride-free oil for ironing of stainless steel. The heavy galling occurred during ironing of stainless steel when the normal die without micro-dimples is used under a condition lubricated with chloride-free oil. The micro-dimples formed by the cutting machine only promoted galling because a large amount of burr remained around the dimples. The micro-dimples formed by the ultrashort pulse laser prevent from galling. The dimples have a smooth and mild profile on the die. The coverage area ratio of micro-dimples larger than 20% is needed for better ironing. A zigzag arrangement of the dimples uses the oil efficiently for well lubrication because galling occurs at the no dimples line between two rows of dimples if the dimples are neatly arranged parallel to the ironing direction.

Abstract: In the numerous applications of technical polymers, it is a wide practice to compound them with solid lubricants in early steps of fabrication to improve the tribological behavior, considerably reducing friction and wear. Nonetheless, especially in injection molding, the inclusion of these lubricants often poses difficulties as they can significantly alter the viscosity and thermal behavior of the resin inside the screw. This practice is also quite inefficient due to the treatment of the whole bulk of the parts, where only the contact surfaces are affected by these inclusions. So, the aim of this work is to use lubricants with these solid particles in suspension, in order to have them permanently embedded in the working surfaces as they are put into service and then studying the impact that these inclusions have in the tribological behavior of the base polymer.

Abstract: This study investigates the impact of lubrication on friction factors during the hot ring compression test of BS 080M46 medium carbon steel. Hot forging processes are crucial in industries due to the strength and durability of forged products, but friction-related issues can arise. Four lubrication conditions are focused: dry, oil to black graphite, water to black graphite, and water to colorless graphite. The ring compression test procedure, including sample dimensions and lubrication application, is explained. By employing predictive calibration curves generated through FEM which monitored height and internal diameter changes during compression. The study successfully aligns FEM simulation results with experimental data, thereby enhancing the accuracy of friction factor estimations and visualizing material behavior under various lubrication conditions. Results indicate that lubrication significantly affects friction factors, with oil to black graphite performing the best, yielding a friction factor of 0.15. A comparison between theoretical and experimental friction factors shows varying agreement levels, with water-to-black graphite, and water-to-colorless graphite respectively demonstrating excellent alignment with 0.990% and 0.971%. This study has practical implications for selecting lubricants in industrial applications, potentially enhancing manufacturing processes and product quality.

Abstract: This research aims to investigate the properties of elastohydrodynamic rotational lubrication analysis on journal-bearing systems. To simulate elastohydrodynamic lubrication on journal-bearing systems, the Elasto-Hydro-Dynamic (EHD) solver is combined with the Multi-Body Dynamic (MBD) solver to create MBD virtual environment with lubricant. The hydrodynamic lubricant is governed by using the Reynolds equation, whereas the elastic contact is governed using Greenwood and Tripp theories. The simulation is performed by changing the operating conditions such as the speed, load, and clearance between two surfaces. One can find these parameters’ effects such as film thickness, hydrodynamic pressure, and friction. The result shows that the friction induced by shaft speed is similar to the Stribeck curve on mixed lubrication regime. Consequently, the clearance, speed, and load will not only affect the friction but also affect the hydrodynamic pressure and film thickness.

Abstract: The conventional milling process is difficult due to the high strength and hardness of Cr12MoV, which can cause the rapid tool wear, premature failure,and poor milling quality of work platform. The ultrasonic vibration machining technology has been founded to be effective in the milling process of hard-to-cut materials like die tool steel and nickel alloys. The ultrasonic vibration assisted milling (UVM) technology is carried out the axial milling of Cr12MoV in this paper, and the average impact force F_i is influenced by the vibration amplitude A, the vibration frequency f, and equivalent mass of the vibrating part M. The mean value of cutting force F_x, F_y, and F_z decreases by 25%, 15.04%, and 17.46%, respectively. With the increase of vibration amplitudes, the value of surface roughness firstly decrease and then increase, and it is obviously lower than conventional milling. The experimental results demonstrated that the UVM technology is a feasible method for the low cutting force and high quality process of cutting Cr12MoV.

Abstract: Lubrication is one of the important factors for a journal bearing to function well. Therefore, the use of bio-lubricants such as coconut oil and vegetable oil are highly recommended for their high level of biodegradability to reduce the risk of environmental pollution. Vegetable oil like coconut oil has a great lubricating quality including low friction coefficient and improved oxidation stability which is very suitable to be used as a lubricant. The performance assessment of journal bearings utilizing coconut oil as a bio-lubricant and varying angular velocity and eccentricity ratio will be the main emphasis of this study. The behavior of the journal bearing with coconut oil as the lubricant will be examined using the Computational Fluid Dynamics (CFD) program, ANSYS Fluent. Using ANSYS Fluent, the pressure distribution of pure coconut oil is analytically studied. To evaluate the efficacy of each lubricant with a varied value of angular velocity utilized by the journal in journal bearings, average viscosity, viscosity index, and produced maximum pressure can be discovered under the lubrication of the journal bearing. Using the values of angular velocity with the same value of dynamic viscosity and density as properties for the coconut oil were used to run the simulation for the journal bearing. The result obtained from the simulation for eccentricity ratio of 0.2 with an angular velocity of 5000rpm is 205926.1 meanwhile the result for eccentricity ratio of 0.8 with same angular velocity value is 9661441. Each result signifies those different value of angular velocity with different value of eccentricity ratio that effects the bearing design itself occurs different result.

Abstract: Dual-pressure tube hydroforming (THF) is a tube hydroforming process variant whereby deformation of the tubular specimen is achieved by exerting fluid pressure on both the inside and outside surfaces of the tube. Dual-pressure THF experiments are conducted to study tribological conditions when producing pear-shaped and triangular parts. The pressure-loading paths are designed to exert pressure in oscillatory pattern: I.e., the pressure on the inside was alternated with pressure on the outside causing the tube to expand and contract/buckle as deformation progressed. During tube contraction, the metal-to-metal contact area is substantially reduced. This leads to reduction in friction stress at the tube-die interface, thus increasing formability. Comparing the geometries of the formed parts produced by dual-pressure THF and conventional THF reveals that the former results in a substantial increase in the protrusion height of a pear-shaped specimen.