The aim of this study was to determine the connection between oscillations in operating pressure values and the appearance of various irregularities on machined surfaces. Such oscillations are a consequence of the high water pressure generated during abrasive water jet machining. Oscillations in the operating pressure values are periodic, namely due to the cyclic operation of the intensifier and the physical characteristics of water. One of the most common means of reducing this phenomenon is installing an attenuator in the hydraulic system or a phased intensifier system. The main hypothesis of this study was that the topography of a machined surface is directly influenced by the inability of the pressure accumulator to fully absorb water pressure oscillations. In this study, we monitored changes in hydraulic oil pressure values at the intensifier entrance and their connection with irregularities on the machined surface—such as waviness—when cutting aluminum AlMg3 of different thicknesses. Experimental research was conducted in order to establish this connection. Aluminum AlMg3 of different thicknesses—from 6 mm to 12 mm—was cut with different traverse speeds while hydraulic oil pressure values were monitored. The pressure signals thus obtained were analyzed by applying the fast Fourier transform (FFT) algorithm. We identified a single-sided pressure signal amplitude spectrum. The frequency axis can be transformed by multiplying inverse frequency data with traverse speed; in this way, a single-sided amplitude spectrum can be obtained, examined against the period in which striations are expected to appear (in millimeters). In the lower zone of the analyzed samples, striations are observed at intervals determined by the dominant hydraulic oil pressure harmonics, which are transferred to the operating pressure. In other words, we demonstrate how the machined surface topography is directly induced by water jet pressure frequency characteristics.

Milling is one of the most important and most complex cutting machining processes. During the milling process, the cross-section of the chip is variable. Also, all milling operations are interrupted processes. The cutting edge of the mill tooth periodically enters and exits from the contact with the workpiece, which leads to periodic heating and cooling during the machining. This periodic change of temperature significantly affects the process of tool wear and therefore the quality of the machined surface. This paper aims at modeling and optimizing the parameters of the machining process to achieve the minimum temperature. In order to perform optimization, it was necessary to perform temperature measurements for the various parameters of the machining process. An infrared camera was used for the temperature measurement. Then, based on the measured values, the mathematical modeling of the temperature was performed depending on the cutting speed, the feed rate and the depth of cut. This model is then optimized using two different optimization techniques.

Technical drawing is a core of many engineering and design courses. The goals of this research are to assess whether engineering students who studied technical drawing at the university, using traditional tools for drawing and computer tools, improve their intellectual abilities, especially the effectiveness of perceptive and cognitive processors. The pilot research consists of two studies: (1) a correlation study of students’ abilities and pre-university experience with technical drawing courses; and (2) a quasi-experimental study of the effects of technical drawing courses on students’ abilities. The sample consists of 46 first-year undergraduate students in engineering departments (study 1) and 12 students selected from the first group after completing the course and passing an exam. The correlations between students’ ability to visualize spatial relationships and achievement in presenting a three-dimensional model in three projections are confirmed. The second study confirmed that the students’ perceptual processing abilities improved during the technical drawing course. In conclusion, the importance of learning technical drawing for some abilities development is emphasized, some research topics are opened, and some educational implications are suggested.

The subject of this research is the development of a classifier based on machine learning (ML) that is able to recognize defective and healthy ball bearings. For this purpose, vibration measurements were performed on the bearings, on a total of 196 samples. For each recorded vibration signal, a feature extraction was performed by digital processing in the time domain. The following ML algorithms were used to develop the classifier: K-nearest neighbor (KNN) and support vector machine (SVM) as well as improved versions of the aforementioned algorithms. Improved versions of the mentioned algorithms were obtained by optimizing their hyperparameters. The corresponding models of the KNN and SVM algorithms showed a high percentage of success in classification, 98.5 % and 99.5 %, respectively. By optimizing the hyperparameters, models with a maximum classification success of 100 % were achieved.

Temperature of cutting is a very important indicator of the cutting process. High specific pressures and high temperatures in the narrow cutting zone result in a drop of hardness of the tool material, the intensification of the abrasion and deformation of the cutting elements, losing the cutting abilities, and finally the failure of the cutting tool. The aim of this paper is to calculate the temperature fields using the existing numerical models for the simulation of thermodynamic processes on the wedge of the cutting tool (based on the finite element method). A special accent is given to the numerical calculation of temperatures in the conditions of continuous and discontinuous turning for specific cutting conditions (processing regime, tool geometry and thermo-mechanical characteristics of the tool materials and workpiece materials) using different simulation models. The Third Wave AdvantEdge software package was used for the simulation of orthogonal turning, and some of the results of the calculations of the temperature fields were compared with the results of experimental measurements.