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

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.

Nowadays, development trends in induction motor electrical drives indicate that the next generation of electrical drives will include sensorless speed control. Speed control systems of induction motor drives without using mechanical sensors for speed measuring have the advantage of being low cost, and they are very robust due to the absence of mechanical component. In most cases, induction motor electrical drives used in industry do not require high speed dynamics. This paper gives sensorless scalar speed control of squirrel cage three phase induction motors based on slip frequency compensation by using a sinusoidal pulse width modulation strategy. Simulation results were obtained by using the Matlab/Simulink software. The proposed sensorless scalar speed control method is simple and is adequate for low-dynamics applications in industry.

Gamma radiation treatment for the destruction of biological pests is a widely applied method, due to its high efficiency, penetrating power of gamma rays, the ability to control the absorbed dose, speed and absence of toxic residual products. The application of gamma irradiation processing for preservation and conservation of artefacts made of wood requires knowledge of the possible radiation effects on the structure of its components and the selection of an appropriate absorbed dose and dose rate. Тhe present study is devoted to the side effects of gamma irradiation decontamination on the structure of two ebony woods dated to different radiocarbon ages. The changes induced by gamma irradiation at two dose rates: 0.037 Gy/s and 1 Gy/s with absorbed doses from 5 to 25 kGy using differential scanning calorimetry are presented. The effects of the absorbed dose, the dose rate and the age of the samples on the observed radiation effects are considered. Higher effects on the enthalpy of water loss were registered in the younger ebony wood after irradiation at low dose rate. Slight changes of the temperatures of water loss were found in the younger ebony wood sample. No significant changes in the temperatures of thermal decomposition in both ebony wood samples were measured.

Lasers have found extensive applications in metal processing, including cutting, welding, drilling, surface treatment, cladding, marking, additive manufacturing, and peening. Each application involves different physical phenomena and mathematical principles, and requires different laser parameters and processing conditions. The mathematical models and equations presented here provide a fundamental understanding of these applications.

This paper explores the application of text-to-image generative models in the production of composite guitars. By converting textual descriptions into detailed visual designs, we create the design process, enhance customization options, and improve overall production efficiency, offering a novel approach to guitar manufacturing

Since 1960, an economic policy of specialization in machine-building production began in Bulgaria, thanks to which a number of new types of production were developed in our country, which subsequently acquired a key importance for the further development of the industry. As a result of the implementation of this policy for twenty years, qualitative changes have occurred in the Bulgarian economy: intensification of production, orientation towards productions providing higher added value, inclusion in the international division of labor, constant growth of social productivity, raising the general technological level of industry, multiple increase in the class of technical intelligence, etc. Thanks to the implemented policy of specialization in machine-building production, Bulgaria overcomes the general economic backwardness of other countries.

The authors propose the development of a framework using simulation modelling technology. The aim is to simulate the behavior and the interaction and interoperability of the components of the modern communication infrastructure of the national security systems in various crises. The focus is on cyber security and cyber defence, from the point of view of risks and threats to the security of communication infrastructure such as disasters and other crisis situations.

An original installation and method for the preparation of ash with a predominant content of amorphous SiO2 (96-97 %), which is a technological residue after thermal treatment of agro-biological waste (rice husks), are presented. The resulting product is a complete raw material for the production of materials with a variety of functional characteristics, using different technological designs (in combination with other components). The design parameters of the installation and the different stages of the developed technological approach are discussed. The basic operating mode of the installation within one operating cycle is presented. The design features and technical equipment of the installation allow controlled creation, maintenance and modification of the necessary technological conditions for the effective thermal processing of the waste biomass.

The article examines the morphology of high-entropy coatings formed using vacuum technologies on low-carbon steel substrates. Studying the morphology of the surface layers of TiAlSi (N ,C ) coatings formed on low-carbon steel substrates using atomic force and optical microscopy methods made it possible to establish the dependence of the morphological parameters of the coatings on the energy parameters and chemical composition of the substrate. The dependence of the morphological parameters of coatings on the conditions for the formation of vacuum layers on low-carbon steel substrates is also shown.

In recent years, constantly changing global conditions and the increasing use of digital media have significantly impacted the printing industry, causing almost a complete transformation in this field. Newspaper circulations are declining, a trend substantially accelerated by the pandemic. On the other hand, the demand for paper or cardboard packaging increased during the pandemic, showing a promising future. The largest and fastest-growing market for corrugated cardboard is China, with its rapidly growing middle class and ecommerce giants. Prices of wood fibers, the primary raw material for paper production, have risen in recent years. This is due to various factors such as environmental regulations and so on. Rising energy prices have significantly contributed to the increase in production costs. Due to the rising prices of wood fibers, the APPLAUSE project was initiated, where papers and cardboards were made from invasive alien plants: Japanese knotweed (Fallopia japonica), Canadian goldenrod (Solidago canadensis), and Black locust (Robinia pseudoacacia), as well as waste tomato stems (Solanum lycopersicum). All produced materials were also practically tested with various prototype products.”