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Presented paper is focused on comparison of three types of steel for production of tubes with shaped internal surface for applications in energy producing industry. Simulations were performed in Deform-3D software with usage of finite elements method. Steels 20MnCr5, C10 and 34CrNiMo6 were selected for simulations. Obtained results are showing deformation, stress, strain and temperature during cold drawing of tubes with shaped internal surface and also resulting comparison of three tested materials depending on the course of load during the forming process. As a conclusion of the presented research is comparison of presented three steels according to the simulation results. Presented paper has potential to increase knowledge base in the area of forming tubes with shaped internal surface. Obtained results can contribute to a proper selection of tool material, coatings and process set up for forming process of tubes with shaped internal surface. [ABSTRACT FROM AUTHOR]

This article is focused on the prediction model of surface roughness parameters of structural steel created by plasma arc cutting. Optimization of the cutting process is very important from both quality and economy point of view. The presented paper shows the carrying out of the experiment with the specification of the design of experiments method. In these experiments, the influence of three factors ‐ the plasma current, the traverse speed, and plasma gas pressure was observed. Experimental material was selected structural steel S355. Along with the influence of controllable process factors was observed the influence of different plasma gasses. Application of different plasma gas significantly changes surface quality. The result of each experiment series is a regression function that can predict the Rz values according to the process parameters at given intervals. Presented equations can be applied in the production process for adjusting the plasma cutting process in order to achieve required surface quality. [ABSTRACT FROM AUTHOR]

This article is focused on studying and analysing the efficiency of the machinability of a high strength aluminium alloy (EN AW-AlZn5.5MgCu) in the high feed milling. The introduction of the article provides a brief description of high feed milling technology and presents best known research regards to the subject. The research of the time efficiency and economic efficiency of high feed milling of aluminium alloys consists of realization of two groups of experiments. The first group consists of four experiments carried out by progressive technology of high feed milling, and the second group contains one experiment conducted using conventional milling technology. The assessment of efficiency consists in determining the overall time and economic efficiency and also in comparison to the machining of aluminium alloys by high feed milling technology with conventional machining technology. The best results were obtained when the machining parameters were: cutting speed of 550 m/min, travel speed of 10600 mm/min, and feed per tooth of 0.85 mm. The material was removed in the contour roughing phase with a 42 mm plungecutting router. Using this cutter, it is possible to produce 19 pieces of components in a hour, which is more than half of the specified requirement. The production of components under the conditions and with this type of high feed milling cutter is more than 75 % shorter than production by a conventional method. [ABSTRACT FROM AUTHOR]

Presented article is focused on the effect of friction coefficient of drawing mandrel surface on parameters of the drawing process. Drawing of tubes with the internally shaped surface is complex problematics. Creation of internal ribbing is determined by many deformation zones which affect stress and strain acting in forming process. Finite elements method application on solving presented problematics gives the opportunity to simulate and optimize process without expensive prototype mandrels. Research if mainly focused on the shape and properties of drawing mandrel. For simulations purposes were selected three friction coefficients which are common in drawing process in dependence of tool surface and coating in combination with lubrication. Acquired results show behavior of strains and stresses in drawing process. Maximal values of observed parameters accompanied with jump changes are mostly pronounced in inner layer. Obtained values are applicable for setting of lubrication in drawing process from the perspective of elimination jump changes in stresses which can shorten life time of mandrel and lower quality of final product. [ABSTRACT FROM AUTHOR]

With the steady development of online education and online learning environments, possibilities to support social interactions between students have advanced significantly. This study examined the relationship between indicators of social presence and academic performance. Social presence is defined as students' ability to engage socially with an online learning community. The results of a multiple regression analysis showed that certain indicators of social presence were significant predictors of final grades in a master's level computer science online course. Moreover, the study also revealed that teaching presence moderated the association between social presence and academic performance, indicating that a course design that increased the level of meaningful interactions between students had a significant impact on the development of social presence, and thus could positively affect students' academic performance. This is especially important in situations when discussions are introduced to promote the development of learning outcomes assessed in courses. Another implication of our results is that indicators of social presence can be used for early detection of students at risk of failing a course. Findings inform research and practice in the emerging field of learning analytics by prompting the opportunities to offer actionable insights into the reasons why certain students are lagging behind. [ABSTRACT FROM AUTHOR]