Papers by Keyword: Boundary Lubrication

Abstract: The frictional properties of diamond-like carbon (DLC) films under boundary lubrication with a synthetic base oil were investigated. The specimens tested were a-C:H, Cr-a-C:H, Ti-a-C:H, W-a-C:H, WC-a-C:H, Mo-a-C:H, MoS2-a-C:H, and Sn-a-C:H films. The tribological properties of DLC/steel contacts were evaluated using a reciprocating-type cylinder-on-disk tribotester. The DLC films exhibited different frictional properties depending on the type of doping elements and compounds used. Notably, the Sn-a-C film gave the lowest friction. The friction tests and static contact angle analyses revealed that the average friction coefficient decreased with a decrease in the static contact angle of the worn DLC film surface, demonstrating that the DLC films with relatively high surface wettabilities exhibited relatively low friction properties. Therefore, surface wettability plays an important role in determining the frictional properties of DLC films under boundary lubrication with synthetic base oil..

Abstract: In this report, rolling contact fatigue (RCF) progression in two-cylinder type RCF testing is evaluated by using an X-ray diffraction ring analyzer, which can rapidly obtain tri-axial stress and the orientation of crystallite. The large compressive and three principal stresses on the RCF surface are observed under boundary lubrication. It is considered that the crack occurrence and its propagation by asperity contact of surface roughness are caused by residual principal shear stress and the repeated contact stress. In addition, the behavior of RCF progression from the point of view of the X-ray measurements is similar for the driving and driven specimen until the generation of peeling begins. This supports the conclusion of Kaneta et al. that the RCF progression for the driven cylinder is the same as that for driving cylinder until peeling occurs.

Abstract: The paper introduces an alternative approach to predict boundary friction for rough surfaces at micros-scale through the empirical integration of asperity-like nanoscale friction measurements. The nanoscale friction is measured using an atomic force microscope (AFM) tip sliding on a steel plate, confining the test lubricant, i.e. base oil for the fully formulated SAE grade 10w40. The approach, based on the Greenwood and Tripp’s friction model, is combined with the modified Elrod’s cavitation algorithm in order to predict the friction generated by a slider-bearing test rig. The numerical simulation results, using an improved boundary friction model, showed good agreement with the measured friction data.

Abstract: The use of different process media such as cutting fluids, coolants, honing oil and washing media in typical machining operations exceeds 5,000 m³ per year. These media support critical functions such as lubrication, corrosion protection, cleaning and cooling, and have an enormous effect on the manufacturing performance. The tribological properties of these media are improved by using additive molecules, which are physically or chemically adsorbed on the surface of tools and workpieces. The additive performance is especially important in water lubricated tribosystems, where the environment is highly corrosive. The role of corrosion inhibitors typically applied is to neutralize the pH of contaminants in the fluid. Ethanolamines and ethylamines are known as ligands which can form chelate bonds with metals via their amino, hydroxyl and deprotonated hydroxyl-groups. In tribology they are widely spread, as corrosion inhibitors and detergents especially for water based lubricants. This study inquires the tribological performance of amine-based solutions in two types of tribotesters which apply different contact conditions. The dissimilar behaviour under rolling and sliding contact is explained in terms of the structure of the adsorbed compounds. Understanding the performance of the first chemisorbed layers of additives on the workpiece provides essential information for optimizing lubrication in aqueous solutions.

Abstract: The wear experimental project on main influencing factor with load, sliding speed, surface hardness and lubrication was instituted by the uniform design, the wear properties were investigated on a MMW-1 friction and wear tester. The predication formula for wear rate was defined. The wear rate predication model was established by the partial least squares based on the test data, the influencing degree on the main influencing factors was analyzed, the results show the influence on wear rate from big to small is in turn load, lubrication, surface hardness and sliding speed. The lubrication property improved is a handy valid path to decrease the wear rate. The check results show that it is a valid method by partial least squares to establish wear predication model based on test data.

Abstract: Low frequency torsional vibration tapping is an effective method to solve the problem of tapping in difficult to cut materials. Tapping parameters affect tapping torque and service life of tap, and cutting angle is the key parameter. Experiments were conducted to study the lubrication mechanism and the influence of cutting angle on lubrication effect. Experimental results indicate that the separate type boundary lubrication mode greatly enhances the lubrication effect of cutting fluid and the lubrication effect decreases with the increase of cutting angle. To obtain good technological effect, the smaller cutting angle should be selected.

Abstract: Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. In this paper, the distinguish method of lubricating behavior in wafer CMP had been analyzed in theory firstly. Then, the tests of wafer CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal wafer CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on wafer surface constantly. The contact form between the Wafer and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP. Keywords: Chemical mechanical polishing, material removal mechanism, lubrication form, boundary lubrication.

Abstract: The effects of friction speed and ultrasonic vibration on friction reduction and anti-wear properties of GCr15/45# steel frictional pairs under oil lubrication were investigated by a modified MFT-R4000 reciprocating friction and wear tester. The mechanism of friction reduction and anti-wear under ultrasonic vibration was discussed. The results showed that, the ultrasonic vibration could influence the friction reduction and anti-wear properties of frictional pairs due to it could reduce the stress between the friction pairs and destroy the oil film on the surface of samples. When the friction frequency was 2Hz，ultrasonic vibration would reduce the friction coefficient and wear volume of the frictional pairs. When the load was 40N, the friction coefficient and wear volume of the frictional pairs attained under ultrasonic vibration decreased 8% and 44% respectively. However, ultrasonic vibration would increase the friction coefficient and wear volume when the friction frequency was 5Hz. When the load was 30N, friction coefficient and wear volume of frictional pairs increased 11% and 74% than that without ultrasonic vibration respectively.

Abstract: Green cutting is one of the developing tends in the industry field. Water vapor can be introduced in metal cutting as coolant and lubricant due to its pollution-free, generating easily and unneeded disposal. Therefore, a special generating system is developed to produce suitable water vapor, and a simulation to the velocity of water vapor jet flow is presented. Then tool wear was investigated and a new capillary model is proposed, based on the experimental results. According to the boundary-layer theory, the kinetics equations of flow were solute. The velocity and flux of molecule are presented. In the capillary, the adsorption of tool-chip interface results in boundary lubricating film; the conical shape of capillary limits the depth of coolant and lubricant penetrating; and the negative press is the motility for coolant and lubricant penetrating. The study results show water vapor can decrease tool wear about 10% times and 20% comparing to cutting fluids and dry cutting, and water vapor could be a potential solution of green cutting.

Abstract: Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the metal and hard-brittle crystal substrate manufacturing process. In this paper, the distinguish method of lubricating behavior in CMP had been analyzed in theory firstly. Then, the tests of CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on hard-brittle crystal substrate surface constantly. The contact form between the workpiece and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in hard-brittle crystal substrate CMP.