Technical University of Gabrovo

Abstract This work investigates the impact of electron beam treatment (EBT) on Ti–Cu oxide coatings deposited on Ti6Al4V via reactive DC magnetron sputtering (MS). The as-deposited films, mainly anatase TiO 2 with minor Cu phases, were post-treated using beam currents of 1 mA and 2 mA. Surface and structural analyses (SEM/EDS, XRD) revealed densification and partial anatase-to-rutile transformation at higher energy input, accompanied by grain coarsening. Mechanical tests revealed a slight decrease in hardness but a significant improvement in adhesion, with critical loads exceeding 30 N following post-EBT treatment. Electrochemical studies in simulated body fluid indicated a strong reduction in corrosion current density for all coatings, with protection efficiencies above 98% at low beam energy. Additionally, EBT reduced copper ion release during immersion, linked to surface densification and phase evolution. The combined MS deposition + EBT treatment enhances adhesion, corrosion resistance, and ion release control, making these coatings promising for biomedical implant applications.

Laser surface hardening (LSH) is an efficient and flexible technique for improving the surface integrity of steel components used in high-load automotive applications. In this study, the surface changes occurring during laser hardening of 42CrMo4 steel were systematically investigated using a 4 kW high-power diode laser. The influence of laser power and scanning speed on surface roughness, hardness distribution, hardened layer depth, tribological behavior, and phase composition was analyzed. Surface topography was evaluated using three-dimensional laser scanning microscopy, while mechanical performance was assessed through microhardness and scratch testing. Phase transformations and residual structural changes were examined by X-ray diffraction (XRD) at different depths beneath the treated surface. The results demonstrate that laser processing parameters strongly affect surface integrity through competing mechanisms of surface melting, oxidation, and self-quenching. High laser power combined with low scanning speed produced deep hardened layers but promoted surface melting and retained austenite formation, whereas lower power and higher scanning speed yielded a stable martensitic surface with reduced roughness and a steep hardness gradient. XRD analysis confirmed that oxide formation was limited to the near-surface region, while the subsurface hardened zone consisted predominantly of martensitic/bainitic phases. An optimal processing window was identified that balances surface hardness, roughness, and microstructural stability without compromising surface integrity. These findings provide practical guidelines for optimizing diode laser hardening of 42CrMo4 steel gears in industrial automotive applications.

This paper presents an exploration of the electromagnetic field characteristics and parameters in the area of coverage of a particular base station, as well as the radio signal strength and the data speed values for optimal service.

Introduction. Modern mechanical engineering is characterised by a constant increase in the proportion of parts with complex configurations (bodies of revolution with rectilinear and curvilinear elements) manufactured using materials with special physical and mechanical properties. The production of such complex components requires high precision, flexibility, and efficiency. The complex shape and variety of technological manufacturing processes are most effectively determined by their efficient processing on automated multifunctional equipment with a central processing unit (CPU). Aim and tasks. This study aims to investigate the processing of complex-shaped details made of difficult-to-process materials on Computer Numerical Control (CNC) or CNC machining is the automated control of machine tools by a computer lathes to increase the efficiency of the technological process. Results. The efficiency of the technological process has been increased when processing complex-shaped parts made of difficult-to-process materials on CNC lathes, as a methodology has been developed for determining cutting modes using the criterion of “processing productivity”. The main task at the technological preparation stage of production is optimisation in determining the parameters of the cutting mode, based on the criterion of “durability at maximum productivity”. In the developed methodology for determining the cutting mode, the volume of material removed per unit time is used as a criterion for “processing productivity”, while simultaneously taking into account the relationship between ар, f, and vc through the cutting power and tool durability, which allows an increase in productivity of up to 74%. Multi-pass roughing is more effective for CNC lathes than single-pass, and maximum cutting productivity is achieved at maximum tool feed. Conclusions. The analysis showed that productivity gains from increasing the cutting depth are limited by machine power. Optimisation based on the "tool life at maximum productivity" criterion is effective only when the machine power is not a limiting factor. It was found that reducing the target tool life (T) does not always increase productivity. Reducing T is effective only in conditions where higher cutting speeds do not exceed the available machine power; otherwise, the actual tool life may even increase. The optimisation of T must consider machine power limitations: reducing T is effective only when higher cutting speeds do not exceed the permissible power.

The successful conversion of cars from internal combustion engines to electric motors involves the preliminary selection of a battery and battery management system (BMS). The publication offers a Spice model of the CA100 LiFePO4 battery for modeling the battery's performance during the conversion of an Opel Corsa vehicle in order to determine the SOC at different discharge currents and operating temperatures.

The paper presents a methodology for multi-purpose optimization of the turning process on CNC machines with robotic loading and its specific implementation for turning hardened steel 42CrMo4, using carbide inserts from various manufacturers. To optimize the process, models of the arithmetic mean utility function with weighting coefficients have been developed. The models are obtained as a result of a research and modelling of the main response variables (production rate, cutting tool life and surface roughness) of the CNC turning process depending on the cutting conditions. The optimal conditions for implementing the process of CNC turning have been determined, under which the generalized utility function has a maximum for each of the cutting tools used. The determined optimal solutions guarantee the best combination of process production rate, cutting tool life and roughness of the machined surfaces.

Software defined networks are an approach to the networking, which allows centralized monitoring and control of all the network devices through a software application. There are many possible approaches for the creation of such applications. Although some protocols and recommendations exist for communication between network devices and low-level software controllers, the upper layer applications are not standardized. This paper proposes a possible architecture for an application for software defined networks.

Abstract The article presents an accurate mathematical model of an electro-pneumatic drive system for positioning a pneumatic cylinder with a double-acting rod, controlled by PWM and four high speed On/Off pneumatic valves. The main elements of the system are included in the model: screw compressor, high-speed pneumatic valves, pneumatic cylinder with double-out rod, PID controller. A simulation of the pneumatic positioning system was carried out using the Simscape language in MATLAB. The system is built using the Simscape Foundation gas domain, implementing simulations of piston rod displacement. An analysis of the results obtained and the simulation model is performed.

The current article examines the connection between the obtained energy from a planar piezoelectric harvester and the characteristics and peculiarities of the passing pedestrians.