International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The metal materials are subject to severe temperature variation during the application of the welding process. The heat input and thermal shock during arc welding cause change of the base material properties in the heat affected zone. Temperature measurements and destructive tests of sample pieces, subjected to different process parameters and conditions, enable identification of minimum and maximum cooling rates, at which the material properties remain in pre-defined limits. Temperature measurements on the surface of the material in proximity to the weld seam enables cooling rate monitoring and material properties evaluation at manufacturing or site installation conditions, when the products could not be subjected to destructive tests. The requirements to the surface temperature measurement during welding and the characteristics of the different measuring devices were investigated for fitness to the purpose of cooling rate calculations, material properties evaluation, as well as for calibration of welding process simulations in volumes in close proximity to the arc welding seams.

In this article,tensile creep elongation of PE plastic films with two configurations of open holes stressed at the incremental temperatures of 23,30,37,43,51,58 degrees and a constant dead weight of 50 kg will be analyzed. The aim of the article is to analyze influence of the two configurations of open holes on the relative elongation. The test was conducted with the same blend, under the same test conditions. The test was conducted entirely according to the conditions established in the ASTM D6992 standard.

An coupled analytic-numerical model for calculation of distortions arising by welding fabrication is introduced. Target of the analytical model is the calculation of the inherent strains after the local thermal-mechanical influence of the welding or thermal straightening process. Following the fabrication processing chart the strains are loaded on an elastic FE-model of the structure and the residual stresses and distortions of the whole structure are calculated. The consideration of welding and thermal straightening scenarios, inclusively the assembling stages, is done by taking into consideration the intermediate variation of the strain state in the FE-model of the structure at every processing step. The important physical relations are demonstrated. The model is intended to be used for solving industrial tasks, i.e. intending acceptable precision and calculation time as well as low simulation costs.

In many cases, the importance of electromagnetic fields or the so-called “electromagnetic smog” on human health, living organisms, and the environment is ignored or at least minimized. The electromagnetic field (EMF) is a combination of invisible electric and magnetic fields with charge that occur in nature. Today, the impact of electromagnetic fields on the environment is increasing from human activities with the development and application of telecommunication technologies. Measurement, continuous monitoring, database creation, and evaluation of electromagnetic field parameters in urban environments are important aspects of optimizing EMF levels to achieve a healthy living environment. The paper presents an analysis and evaluation of electromagnetic radiation measurements from base stations of mobile operators, at one site, in a lightly urbanized urban environment over a certain time interval. Initial measurements showed exceeding the levels of electromagnetic emissions according to national legislation. During the repeated measurements, it was found that mobile operators, after correcting the radiation from base station antennas, have brought the radiation levels within the permissible limits. This underscores the necessity of ongoing monitoring.

The aim of this paper is the calculation of the PLEM (Pipeline End Manifold) System of the 18″ dia. subsea pipeline, according to the International Codes and Standards. A Geotechnical survey was carried out to define soil – structure interaction, effect of scour, soil stratigraphy and susceptibility to liquefaction. Then were defined the acting forces on PLEM, pipeline and submarine hoses taking in consideration the total buoyancy as well. The calculation was carried out for filled pipeline (in service), as well as for empty pipeline. The ground conditions along the sealines and at the location of the PLEM have been investigated by a dedicated additional site investigation, consisting of 12 no. vibrocore samplings and the related laboratory testing. The stability of PLEM was checked for several load combination. This calculation it was very important for environmental reason and shows that the structure meet the requirements of the project.

This paper discusses contact interaction under mechanical stress and how vibrations change the physical properties of conductor materials, which affects their ability to provide reliable contact. It also analyzes the causes of contact failures, which allows us to better understand the mechanisms that lead to problems in the operation of electrical connectors. These factors can lead to serious consequences, including breakage and reduced reliability of connectors, and also considers the possibilities of improving the characteristics of electrical contacts at the stage of their creation, using various technologies for applying and creating an approximately ideal molecular structure of the contact surface of detachable electrical connectors, with an increase in the surface layer of the contact and a decrease in the coefficient of friction.

In the article, experimental results according to ASTM D6992 standard test method for accelerated tensile creep of plastic films were investigated and analyzed. A regression model was created based on the obtained results. Real and theoretical data were compared. In order to determine deviations of the model and what is the reliability of the theoretical data.

Paper deals with determining the possible savings of electrical energy in a passenger elevator. After carrying out calculations with a set number of floors of an administrative building and number of passengers according to a proven and widely used methodology in Bulgaria, an appropriate three-phase squirrel-cage induction motor has been selected to drive the considered elevator system. Calculations have been also carried out on the possible recovery, i.e. returning electrical energy back to the supply power grid when the driving rotating electrical machine is switched to generator mode. Variants with different number of passengers and movement of the cabin in upward and downward directions were theoretically studied. The active power, time to work in recovery mode and the active energy returned to the power grid are defined for each specific case. Calculations of possible electrical energy return in generator mode would be of interest to specialists dealing with these technical facilities.

Additive manufacturing (AM) of metal structures is transforming industries by enabling the creation of complex, efficient, and customizable components. This article explores key AM technologies for metals, including Powder Bed Fusion (PBF), Directed Energy Deposition (DED), Binder Jetting, Metal Extrusion, and Sheet Lamination. Each is analyzed in terms of principles, strengths, limitations, and applications. A comparative evaluation highlights factors like precision, scalability, cost, and environmental impact to identify optimal technologies for various industries. Despite its advantages, challenges remain in material quality, process reliability, cost, and certification. Emerging trends such as hybrid manufacturing, AI-driven process optimization, advanced materials, and sustainable practices hold promise for overcoming these barriers. By examining current technologies and future opportunities, this article provides valuable insights for advancing metal AM in diverse applications.

In the knowledge society (KS) and ”Industry 4.0” (I4.0) in the 21st century and today’s rapidly developing world with a large number of important applications, one of the most advanced and growing areas of manufacturing technologies is micro- and nano-machining (traditional and non-traditional) and micro- and nano-aditive manufacturing. Certainly one of the most important technologies of micro and nano machining is micro drilling. Micro-drilling (MD or D) is type of machining (processing) technology used for the drilling of miniaturized parts of small diameter in micro-scale, i.e. diameter in a range of a few microns to several hundred microns. In this paper is given a brief description of the development of micro-drilling process, as well as the basic division of micro-drilling process.

Industrial robots are one of the main driving forces of the fourth industrial revolution and one of the most promising technologies for increasing the degree of automation in modern production. Since their entry into mass industrial production in the 1960s, they have evolved significantly, and today they are being implemented in the construction of high-tech smart manufacturing enterprises. With the development of technique and technology, industrial robots are becoming more productive, flexible, versatile, safe and easy to use, revealing new possibilities for modern industrial ecosystems. As a key tool for improving efficiency and productivity, they enter a number of sectors such as automotive, mechanical engineering, energy, electronic production, food industry, space sector, defense, etc.
The purpose of this report is to present the status and trends in the development of robotics and its spread among the industrial sectors of the economy. The results of the research show the state of the global robotics market and Bulgaria’s place in it.

The growing environmental concern about plastic waste has prompted research into sustainable recycling of polymer, particularly for widely used polymers such as polyethylene from the spools used in the textile industry in the second half of the 20th century. This study investigates the feasibility and optimization of recycling Polypropylene to make filaments suited for 3D printing applications, notably Fused Deposition Modelling (FDM). The study is divided into three phases: collecting and preparing post-consumer Polypropylene spools, extruding recycled Polypropylene into filaments, and optimizing the filament for 3d printing using FDM Technology.
Polyethylene spools are cleaned, shredded, and treated to ensure consistent feedstock quality. The extrusion process entailed controlling factors like temperature, screw speed, and cooling rate to produce filaments with constant diameter with less distortion. Following material characterisation, the printability of recycled Polypropylene filaments was evaluated using an FDM 3D printer. The Taguchi method is used to carefully study the influence of printing parameters such as nozzle temperature, bed temperature, print speed, and layer height to determine optimal parameters. The printed examples showed reasonable dimensional accuracy and layer adhesion, with surface roughness values within acceptable limits for practical applications.
This thorough study plan focuses on recycled Polypropylene as a feasible and sustainable material for FDM 3D printing. The findings indicate that with proper optimization, recycled Polypropylene can match the performance requirements of a variety of applications, helping to reduce waste and promote the circular economy in additive manufacturing. Long-term performance testing and the development of recycling processes will be the primary focus of future research to improve the material’s characteristics and broaden its application range.