Effect of Zonal Laser Texturing on Friction Reduction of Steel Elements in Lubricated Reciprocating Motion.

During co-action between contact elements in reciprocating motion, different working conditions exist in outer and inner zones of stationary elements. Because the tribological effects of surface texturing depend on the operating conditions, various dimple patterns were created in the middle part of the steel disc and near the reversal points. The behaviors of variable dimple patterns were compared with those of uniform texturing and untexturing. It was found that the dimple patterns in the middle disc zone depended on the resistance to motion. The best tribological behavior was obtained for a pit area ratio of 13% and diameter of 0.4 mm in the inner zone, and pit area ratio of 3% and diameter of 0.2 mm in the outer zones. Low resistance to motion and the smallest friction variation of all tested sliding pairs were achieved. For the same pit area ratio of 13% in a disc of 0.4 mm, the dimple diameter behaved better than in the 0.2 mm diameter disc. The greatest decrease in the coefficient of friction of 85% compared to untextured sliding pair was achieved for uniform laser texturing with a pit area ratio of 13% and dimple diameter of 0.4 mm, when the normal load was 40 N and frequency of displacement was 20 Hz.

Analysis of Surface Texture and Roughness in Composites Stiffening Ribs Formed by SPIF Process.

Studying roughness parameters and the topography of stiffening ribs in composite sandwich structures is important for understanding these materials' surface quality and mechanical properties. The roughness parameters describe the micro-geometry of the surface, including the average height deviation, roughness depth, and waviness. The topography of the surface refers to the spatial arrangement and distribution of features such as bumps, ridges, and valleys. The study investigated the roughness parameters under three scenarios based on two SPIF process parameters: tool rotational speed(N) and feed rate (f). The vertical step was held constant at 0.4 mm across all scenarios. In scenario A, the process parameters were set at f = 300 mm/min and n = 300 rpm; in scenario B, f = 1500 mm/min and n = 3000 rpm; and in scenario C, f = 1500 mm/min and n = 300 rpm. The experimental research topography analyses revealed that the surface roughness of the stiffened ribs was highly dependent on the SPIF process parameters. The highest feed rate and tool rotational speed produced the smoothest surface texture with the lowest maximum height (Sz) value. In contrast, the lowest feed rate and tool rotational speed resulted in a rougher surface texture with a higher maximum height (Sz) value. Furthermore, the contour plots generated from the topography analyses provided a good visual representation of the surface texture and roughness, allowing for a more comprehensive analysis of the SPIF process parameters. This study emphasizes optimizing the SPIF process parameters to achieve the desired surface quality and texture of stiffened ribs formed in Litecor® panel sheets.

Effects of Operating Conditions and Pit Area Ratio on the Coefficient of Friction of Textured Assemblies in Lubricated Reciprocating Sliding.

The experiment was carried out in a reciprocating lubricated conformal sliding contact between steel discs of the same hardness. The effects of disc surface texturing on the friction coefficient at various operating conditions (temperature, normal load, and frequency of oscillations) were studied. Under various conditions, surface texturing caused friction reductions of sliding pairs. The largest reduction was 4.6 times at a lower temperature and 2.5 times at a higher temperature. The effect of the pit area ratio on the friction reduction was visible at a higher temperature. The highest dimple density of 25% corresponded to a lower coefficient of friction than the smallest density of 9%. The sliding pair with a dimple density of 17% led to large variation of the friction force. At lower temperatures, the coefficients of friction were lower compared to tests at higher temperatures.

Investigation of Surface Roughness in Incremental Sheet Forming of Conical Drawpieces from Pure Titanium Sheets.

The article presents the results of the analysis of the influence of incremental sheet forming process parameters on surface roughness measured on both sides of conical drawpieces made from pure titanium Grade 2 sheets. The experimental plan was created on the basis of a central composite design. The study assumed the variability of feed rate, spindle speed, and incremental step size in the following range: 500-2000 mm/min, 0-600 rpm, and 0.1-0.5 mm, respectively. Two strategies differing in the direction of the tool rotation in relation to the feed direction were also analysed. Analysis of variance is performed to understand the adequacy of the proposed model and the influence of the input parameters on the specific roughness parameter. The sensitivity of the process parameter on the selected surface roughness parameters was assessed using artificial neural networks. It was found that the change in the surface roughness of the inner surface of the drawpiece is not related to the change of surface roughness of the outer side. The morphology of the outer surface of the draw pieces was uniform with a much greater profile height than the inner surface that had interacted with the tool. Taking into account the outer surface of the drawpiece, the direction of tool rotation is also most closely correlated with the parameters Sa, Sz, and Sku. Step size and feed rate provide the highest information capacity in relation to skewness and kurtosis of the inner surface of the drawpiece.

Surface Finish Analysis in Single Point Incremental Sheet Forming of Rib-Stiffened 2024-T3 and 7075-T6 Alclad Aluminium Alloy Panels.

The article presents the results of the analysis of the interactions between the single point incremental forming (SPIF) process parameters and the main roughness parameters of stiffened ribs fabricated in Alclad aluminium alloy panels. EN AW-7075-T6 and EN AW-2024-T3 Alclad aluminium alloy sheets were used as the research material. Panels with longitudinal ribs were produced with different values of incremental vertical step size and tool rotational speed. Alclad is formed of high-purity aluminium surface layers metallurgically bonded to aluminium alloy core material. The quality of the surface roughness and unbroken Alclad are key problems in SPIF of Alclad sheets destined for aerospace applications. The interactions between the SPIF process parameters and the main roughness parameters of the stiffened ribs were determined. The influence of forming parameters on average roughness Sa and the 10-point peak-valley surface roughness Sz was determined using artificial neural networks. The greater the value of the incremental vertical step size, the more prominent the ridges found in the inner surface of stiffened ribs, especially in the case of both Alclad aluminium alloy sheets. The predictive models of ANNs for the Sa and the Sz were characterised by performance measures with R2 values lying between 0.657 and 0.979. A different character of change in surface roughness was found for sheets covered with and not covered with a soft layer of technically pure aluminium. In the case of Alclad sheets, increasing the value of the incremental vertical step size increases the value of the surface roughness parameters Sa and Sz. In the case of the sheets not covered by Alclad, reduction of the tool rotational speed increases the Sz parameter and decreases the Sa parameter. An obvious increase in the Sz parameter was observed with an increase in the incremental vertical step size.

The Effect of Surface Texture on Lubricated Fretting.

Experiments were conducted using an Optimol SRV5 tester in lubricated friction conditions. Steel balls from 100Cr6 material of 60 HRC hardness were placed in contact with 42CrMo4 steel discs of 47 HRC hardness and diversified surface textures. Tests were carried out at a 25-40% relative humidity. The ball diameter was 10 mm, the amplitude of oscillations was set to 0.1 mm, and the frequency was set to 80 Hz. Tests were performed at smaller (45 N) and higher (100 N) normal loads and at smaller (30 °C) and higher (90 °C) temperatures. During each test, the normal load and temperature were kept constant. We found that the disc surface texture had significant effects on the friction and wear under lubricated conditions. When a lower normal load was applied, the coefficient of friction and wear volumes were smaller for bigger disc surface heights. However, for a larger normal load a higher roughness corresponded to a larger coefficient of friction.

The Effect of Isotropic One-Process and Two-Process Surface Textures on the Contact of Flat Surfaces.

The contact of random modeled one- and two-process textures with smooth, flat surfaces is discussed in this paper. An elastic-plastic contact model was applied, assuming a distributed radius of summits. A one-process surface was characterized by the standard deviations of height and the correlation length; however, it also had a two-process texture by the standard deviations of the plateau and valley structures, the material ratio at the transition point, and the correlation lengths of the plateau and valley parts. It was found that the contact characteristics depended on the height and spatial properties of the surface texture. The plateau part governs the contact characteristics of two-process surfaces, while the effect of the valley surface portion is smaller. The plastic deformation leads to a smaller effect of the surface texture on the contact characteristics.

The Effect of Disc Surface Topography on the Dry Gross Fretting Wear of an Equal-Hardness Steel Pair.

Experimental investigations were carried out with an Optimol SRV5 tribological tester in a flat-on-sphere scheme. The balls co-acted with the discs in a gross sliding fretting regime. The balls and discs were made from the same steel with a very similar hardness. Tests were conducted at 25-35% relative humidity, 30 °C, and a constant normal load and number of cycles (18,000). The discs had different textures after various machining treatments. It was found that the total wear level of the tribological assembly was proportional to the disc surface amplitude. The influence of the disc roughness on the coefficient of friction was evident only for the smallest stroke of 0.1 mm, and the frequency of oscillation affected this dependency.

Variability of areal surface topography parameters due to the change in surface orientation to measurement direction.

Several random surface topographies were analyzed. They were measured by optical (Talysurf CCI Lite) method. They represent one- and two-process anisotropic and isotropic surfaces. These surfaces were rotated of ± 1° and ± 2° by two methods: on the plane table (before measurement) and virtually (after measurement) using the software TalyMap Gold. After each measurement or surface rotation, each surface was levelled. Then, the forms were removed using polynomial of the 3rd degree. Areal surface topography parameters from standard ISO 25178 were calculated. The relative deviations of parameters were determined. The tendency of surface topography changes characteristic to various surface types were analyzed. It was found that change in orientation to the measurement direction of both isotropic and anisotropic surfaces could be substantial source of the measurement uncertainty. Functional parameter Smr and also feature parameters Sda, Sha, Sdv, Shv, and Spd are the mostly sensitive on measurement orientation. Statistical amplitude parameters Sa and Sq are more stable than parameters describing maximum surface height, like Sz, Sp, and Sv. The effect of surface orientation to measurement direction on values of functional parameters from V group was small. It was shown that changes of Sdq, Sdr, and Spc parameters describing hybrid properties due to surface rotation before measurement were smaller than those caused by change in surface orientation after measurement.