The article presents a new method called slide roller burnishing (SRB) for the cold working of cylindrical surfaces on machine tools implemented with a novel multi-functional device. The machined material is chromium–nickel austenitic stainless steel. The deforming element is a toroidal roller whose axis crosses that of the workpiece. As a result, a relative sliding velocity occurs in the contact zone between the roller and the machined surface. The sliding velocity vector is set using the burnishing device. The theoretical background of SRB is presented. When the two axes are parallel, the well-known roller burnishing (RB) method is implemented. Thus, RB is a special case of SRB. Both processes are realized using the multi-functional burnishing device. The RB process was studied experimentally and optimized according to three criteria, based on the relationship between the surface integrity and operating behavior of the respective component, to achieve three processes: smoothing, hardening, and mixed burnishing. Using the optimal RB parameters obtained, the dependence of the results of SRB on the crossing angle was investigated and optimized. A comparative analysis was performed between the optimized RB and SRB processes (respectively for their three variants: smoothing, hardening, and mixed) based on geometrical and physical–mechanical characteristics of the surface integrity. The main advantage of the SRB is that it provides smaller height roughness parameters (improvement by 42%) and a higher surface microhardness (improvement by 7%) than RB.

This work presents the results of an investigation into the influence of beam offset on the structure and mechanical properties of electron-beam-welded joints between Ti6Al4V and Al6082-T6 alloys. The experimental procedure involved the use of specific technological conditions: an accelerating voltage of 60 kV, an electron beam current of 35 mA, a specimen motion speed of 10 mm/s, and a beam offset of 0.5 mm towards both alloys, as well as welding without an offset. The phase composition of the joints was analyzed using X-ray diffraction (XRD). The microstructure and chemical composition of the seams were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results obtained for the structure of the joints show that the beam offset has a significant influence on the structure. The microhardness was studied by means of the Vickers method. The results for the microstructure showed that the welding procedure without offset and with an offset towards the Ti alloy leads to inhomogeneous welded joints with a significant amount of intermetallics. The offset towards the Al alloy leads to the formation of a narrow area of TiAl₃ phase. The measured microhardness corresponds to the increased amount of intermetallics in the case of offset towards the Ti alloy, with which the highest values were presented (about 58% higher than with Ti6Al4V plate). The results obtained for tensile properties show that the offset to the Al6082-T6 alloy leads to the highest values of tensile strength (TS) and yield strength (YS), which are twice higher than in welding without offsetting of the electron beam.

Fastener holes are among the most common natural stress concentrators in metal structures. The life cycles of various structural elements, such as those in aircraft structures, automobiles, and rail-end bolt joints, are limited by fatigue damage around the holes. An effective approach to delay the formation and growth of fatigue macrocracks is to introduce residual hoop compressive stresses around the holes. Two methods have become established in the prestressing of fastener holes in aircraft components, split sleeve and split mandrel, which implement one-sided processes. The common disadvantage of both methods is the complex procedure due to the need for high accuracy of the initial holes. This article presents a new modified split mandrel method providing the same tightness (interference fit) with a wide tolerance of the pre-drilled hole diameters, reducing the number of technological cycle steps and production costs. To implement the new method, a functionally connected tool and a device with a hydraulic drive were developed. An extensive experimental study of 2024-T3 AA specimens was carried out to evaluate the effectiveness of the method under a high scattering of the pre-drilled holes. The new method provided a deep zone of residual hoop compressive stresses on both faces of the specimens after cold working and after hole final reaming. The removal of a plastically deformed layer around the hole of suitable thickness during the final reaming decreased the axial gradient of residual hoop stress distribution. Fatigue tests on a tensile pulsating cycle verified the effectiveness of the modified split mandrel method to significantly increase the fatigue life by 6.6 times based on ${10}^6$ cycle fatigue strength compared to the conventional case of machining the holes. The obtained S-N curves for three groups of samples with initial hole diameters of 8.0, 8.1, and 8.2 mm, which were cold worked with the same tightness of 0.32 mm and final reamed, aligned well, indicating that the new method can provide constant fatigue strength for a given stress amplitude.

There is a lack of information in the literature on the influence of technological heredity on surface integrity characteristics after diamond burnishing (DB). The present study fills this gap. Here, we present the effects of DB on the roughness parameters and surface microhardness of heat-treated C45 steel under conditions of changing initial roughness (Ra^init) due to wear on the cutting insert in the previous turning. The aim was to quantitatively assess the ability of DB to maintain sustainable surface integrity characteristics. We found that the service life of the cutting insert up to complete wear or fracture when operating at an optimal feed rate and cutting velocity was 163 min, at which point the roughness changed unevenly from an average roughness (Ra) value of 0.38 to 1.31 μm and an average height of the profile microroughness (Rz) value of 2.21 to 6.13 μm. Under conditions of an artificially created Ra^init (through different combinations of feed rate and cutting velocity) of 0.308 to 10.688 μm, DB provided Ra values in the range of 0.042 to 0.316 μm, with the surface microhardness varying from 461 to 568 HV. Stable Ra values were maintained from 0.042 μm to 0.089 μm, after which the Ra^init increased to 3.379 μm. Under production conditions, where the previous turning was performed at an optimal feed rate of 0.05 mm/rev and a cutting velocity of 180 m/min, DB provided a stable Ra of ≤0.059 μm of a resulting mirror-like surface during the first 90 min of operation of a new (unused) cutting insert, after which the Ra values increased linearly from 0.059 to 0.133 μm in the 150th minute. After 30 min of operation, until the cutting insert was completely worn, the microhardness after DB varied from 676 to 795 HV, the high surface microhardness resulting from a complex process of surface thermo-mechanical strengthening (including strain and transformation hardening) in the previous turning due to wear on the cutting insert.

CuZn39Pb3 leaded brass is one of the most widely used alloys in machining, with a 100% machinability index. However, there has been a lack of research on the effects of coldworking on surface integrity (SI) and operating behaviour of CuZn39Pb3 components. This study addresses this knowledge gap by examining the effects of three optimised combined processes on surface roughness, a key SI characteristic. Specifically, samples were subjected to a turning process followed by diamond burnishing (DB); this combined process was performed under three conditions: conventional flood lubrication (F), dry (D), and dry and cool-assisted (D+C) conditions. Cool-assisted conditions were achieved using a special device with a cold air nozzle operating on the vortex tube principle. The D and D+C conditions represent environmentally sustainable alternatives because they eliminate the use of cutting fluids, thereby reducing their adverse effects on both the environment and human health. The resulting surfaces obtained after each of the three optimised combined processes (F, D, and D+C) exhibited mirror-like finishes with minimum average roughness Ra values of 0.054, 0.079, and 0.082 μm, respectively. In addition, the F- and D+C-processes resulted in surface profiles with negative skewness and kurtosis values greater than three. Since roughness shape parameters are known to influence the operating behaviour of machined components, these processes are suitable for improving wear resistance in boundary lubrication regimes.

Diamond burnishing (DB), based on cold severe surface plastic deformation, is a method for modifying the surface layers of metal components in order to improve surface integrity (SI). This study aims to establish explicit correlations between the five main governing factors (burnishing force, feed rate, burnishing velocity, diamond radius, and number of passes) of DB 304 stainless steel and the main SI characteristics, including average roughness parameter Ra, shape roughness parameters skewness and kurtosis, and microhardness. DB was undertaken on a CNC lathe using flood lubrication and a one-way working scheme. A burnisher with elastic contact and a spherical-ended polycrystalline diamond insert was used. The steel, with a hardness of 250 HB, was tested in its as-received state. An experiment with a second-order composition plan, analysis of variance (ANOVA), and regression analyses was employed. The significance of the variables in the regression models was assessed using various methods to determine the influences of the governing factors and the interactions between them on the characteristics of SI. Finally, various optimizations were conducted depending on the functional purpose of the diamond-burnished surface using a non-dominated sorting genetic algorithm and QStatLab software.