Lidia Galda

This study presents the results of applying a CrNmod coating to 42CrMo4 steel surfaces with and without spherical surface texturing. The CrNmod thin-film ceramic coating, deposited by a physical vapour deposition (PVD) process, is characterised by excellent wear resistance. As an additional surface engineering modification, spherical dimples were introduced prior to the PVD coating process. Appropriately designed surface textures, in terms of geometry and distribution, can enhance the tribological performance of sliding pairs. The primary objective of this study was to investigate the influence of the CrNmod coating and surface texturing on friction force. Surface topography and selected surface layer properties were characterised before tribological testing. The tribological performance of the specimens was evaluated using a T-11 tribometer operating in a ball-on-disc configuration. To achieve conformal contact, the ball counter-specimen was modified by precision grinding. All tribological tests were performed under lubrication with L-AN 46 mineral oil. The experimental results demonstrated that the application of the CrNmod coating significantly reduced friction compared with the uncoated steel surface. A further reduction in friction force was achieved when the coated surface was additionally modified with spherical surface texturing, indicating a synergistic effect of the combined surface engineering treatments on tribological performance.

Additive-manufactured (AM) 316L stainless steel, produced via direct metal laser sintering (DMLS) and characterised by a surface topography of high irregularities and tensile residual stresses with specific anisotropy, was subjected to milling and shot peening. The milling process caused a reduction in surface topography parameters, but tensile residual stresses increased significantly. The shot peening process was carried out according to the full factorial design 3² and technological parameters such as a shot diameter in the range of 1-3 mm and an air supply pressure between 0.2 and 0.6 MPa. As a result of the experiments and the analysis, reduced surface topography was achieved, and a favourable residual stress state was formed with compressive stresses. The mechanism of the changes was demonstrated via microstructure observation and statistical models obtained by mathematical analysis.

Various types of bushings or pins are widely used in the machinery industry, i.e. in the automotive industry, agricultural machinery and production lines. Such machine components operate in a diverse environment, not infrequently in polluted or dusty environments and these components may be subjected to intensive wear. Particles circulating in various types of machine kinematic pairs contribute to accelerated or even emergency wear of the equipment. One way to prevent such dangerous failures is to use an additional machining to create dimples in the surface, which are a place to collect lubricant but also abrasive particles. The article presents a method of burnishing a cylindrical surface after carburizing treatment and after hardening, after which the hardness of the surface layer was about 60 HRC. As a result of using appropriate tools, it was possible to create regular and reproducible dimples in the surface. A surface topography parameter was also proposed, which makes it possible to evaluate the increase in oil capacity of the created cavities quickly and with high quality standards.

With the wire electrical discharge machining (WEDM), good quality machined surfaces can be achieved. The WEDM is worth considering for machining fasteners used in assembly processes. This paper presents a study of the WEDM cutting process of aluminum 2017A using an WEDM machine of the FR 400 type. After applying different cutting speeds, the characteristics of the cut surface were evaluated. Despite some differences in the shape of surface profiles and surface morphology noted after WEDM cutting at different speeds, the analysis of variance concluded that the WEDM cutting speed in the studied variation range of 23-125 μm/s has no significant effect on surface roughness. At the highest speed studied, machining efficiency can be increased, affecting cost and energy reduction, while maintaining an acceptable and comparable level of surface quality after WEDM cutting.

Under hard operating conditions such as high load, low speed and a lack of a sufficient quantity of lubricant, the sliding pairs could suffer serious damage. One of the methods that improves the tribological performance of sliding elements in hard operating conditions is the appropriate surface creation that keeps lubricating substance in cavities. This article presents the results obtained in experimental investigations of the oil film thickness in lubricated non-conformal contact with a different surface topography of the sliding element. The tests were conducted on a ball-on-disc instrument equipped with colorimetric interferometry. Balls of diameter equaled to 19.05 mm were produced from 100 Cr6 steel. To provide hard operating conditions, the glass disc rotated at small speeds in the range of 0.1–0.2 m/s. The tests were carried out at loads of 20 N and 30 N. As a result, in most cases, the highest minimum and average oil film thickness values were obtained when the surface of steel balls was characterized by high negative asymmetry with mainly shallow cavities and some valleys of great depth compared to the height of the peaks. The modified sliding surface that had better performance comprised a comparatively small number of peaks and the curvature of the peaks were large.

The article presents selected characteristics of journal bearings calculated with the use of various methods and compared to the results obtained with application of the basic bearing characteristics calculation procedure, as described in the ISO 7902:2020 standard. Additionally, the presented calculation results were compared with the parameters measured during experimental tests of the sliding bearings, working under loads and at sliding velocity, and maintaining other operating conditions, as assumed in theoretical research. The regula falsi iteration method was successfully implemented. The research results have confirmed the usefulness of various calculation methods since the values of selected characteristics of the journal bearing obtained were comparable.

The paper presents results obtained by SiC ceramic implementation for slide burnishing. Analyzes of the effect of the burnishing force and feed on selected surface texture parameters were conducted. The influence of technological parameters was assessed according to the analysis of variance. The burnishing force and feed affected most of the examined surface texture parameters in the analyzed ranges. Optimal values were found for the technological parameters. In most cases, the minimum of height parameters were achieved for 80 N of burnishing force and 0,063 mm/rev of feed. Limitations in the increase in the burnishing force were also found.