SURFACE ROUGHNESS OF Ti6Al4V ALLOY PRODUCED BY LASER POWDER BED FUSION

Controlling the surface roughness of materials manufactured by laser powder bed fusion (L-PBF) is critical for achieving functional performance of components and improving their mechanical properties. This is important for components whose surfaces cannot be post-treated using subtractive methods. In this study, the surface roughness has been investigated by applying different laser power and scanning speed combinations. Furthermore, potential effects of different locations on the build platform have been considered as well. The regression models have been developed using significant predictor variables, with their levels defined using face-centered central composite design. The analysis of variance (ANOVA) procedure has been used to evaluate the statistical significance of factors and model performances for each prediction variable. It has been found that the average surface roughness of L-PBF Ti6Al4V alloy can be described with high fitting accuracy using laser power and scanning speed as predictor variables. The position of specimens on the build platform showed no statistically significant effect on the average surface roughness. The experimental research and statistical analysis reported in this paper will contribute to a better understanding of how position, laser power, and scanning speed influence the average surface roughness of L-PBF Ti6Al4V alloy

ANALYSIS OF VALIDITY OF USING THE MECHANISM FOR ADDITIONAL DOOR HOLDING ON WAGON TYPE FALNS

Današnji globalni trendovi željezničkog transportnog prometa nalažu skidanje svih nepotrebnih komponenata s vagona u cilju smanjenja mase vagona. Upravo zbog toga rodila se ideja analize opravdanosti upotrebe mehanizma za dodatno pridržavanje vrata vagona Falns 48. Vagon Falns 48 namijenjen je u prvom planu za prijevoz željezne rude. Naime, izbacivanjem ovog mehanizma masa vagona mogla bi se smanjiti za 276 kg, ali bi se maksimalni pomaci donjeg brida vrata vagona povećali s 0,04 mm na 3,76 mm. To povećanje maksimalnih pomaka donjeg brida vrata vagona, prilikom transporta tereta može uzrokovati njegovo istjecanje iz vagona te rasipanje po tračnicama, što je strogo zabranjeno. Prema tome, nužno je provesti optimiranje kako bi se pronašao određeni kompromis, odnosno pronašlo optimalno rješenje. Dakle, metodom konačnih elemenata analizirani su pomaci i naprezanja početne konstrukcije vagona s i bez upotrebe mehanizma za dodatno pridržavanje vrata te je proveden postupak optimiranja. Optimiranje je provedeno s ciljem smanjenja maksimalnih pomaka donjeg brida vrata vagona nauštrb povećanja mase. Isto tako, predloženo je novo konstrukcijsko rješenje vrata vagona te je provedeno optimiranje predloženog konstrukcijskog rješenja. Analizom dobivenih rezultata donesen je zaključak da upotreba mehanizma za dodatno pridržavanje vrata vagona Falns 48, za slučaj transporta željezne rude, nije opravdana.Today's global trends in freight transport demand removal of all unnecessary freight wagon components in order to reduce mass. Because of that, the idea of a validity analysis of the additional door holding mechanism on freight wagon type Falns 48 was born. By removing this mechanism, the mass of the wagon could be reduced by 276 kg, but the maximum deformation of the doors lower edges would increase from 0,04 mm to 3,76 mm. This increase in the maximum deformation of the wagon doors lower edges can cause the cargo to leak out the wagon and fall down on the rails, and that is strictly forbidden. Therefore, it is necessary to implement optimization to find a certain compromise, or find the optimal solution. By applying the finite element method the deformations and stresses of the initial constructional solution of the wagon doors, with and without using the additional door holding mechanism, were analyzed. After that, the optimization process was carried out. The aim of the optimization is to reduce the maximum deformation of the doors lower edges, at the expense of mass increase. Also, a new constructional solution of the wagon doors was proposed and optimization of the proposed constructional solution was carried out. By analyzing the results, it was concluded that the use of the additional door holding mechanism on freight wagon Falns 48, in the case of transporting iron ore, is not justified

ANALYSIS OF VALIDITY OF USING THE MECHANISM FOR ADDITIONAL DOOR HOLDING ON WAGON TYPE FALNS

Današnji globalni trendovi željezničkog transportnog prometa nalažu skidanje svih nepotrebnih komponenata s vagona u cilju smanjenja mase vagona. Upravo zbog toga rodila se ideja analize opravdanosti upotrebe mehanizma za dodatno pridržavanje vrata vagona Falns 48. Vagon Falns 48 namijenjen je u prvom planu za prijevoz željezne rude. Naime, izbacivanjem ovog mehanizma masa vagona mogla bi se smanjiti za 276 kg, ali bi se maksimalni pomaci donjeg brida vrata vagona povećali s 0,04 mm na 3,76 mm. To povećanje maksimalnih pomaka donjeg brida vrata vagona, prilikom transporta tereta može uzrokovati njegovo istjecanje iz vagona te rasipanje po tračnicama, što je strogo zabranjeno. Prema tome, nužno je provesti optimiranje kako bi se pronašao određeni kompromis, odnosno pronašlo optimalno rješenje. Dakle, metodom konačnih elemenata analizirani su pomaci i naprezanja početne konstrukcije vagona s i bez upotrebe mehanizma za dodatno pridržavanje vrata te je proveden postupak optimiranja. Optimiranje je provedeno s ciljem smanjenja maksimalnih pomaka donjeg brida vrata vagona nauštrb povećanja mase. Isto tako, predloženo je novo konstrukcijsko rješenje vrata vagona te je provedeno optimiranje predloženog konstrukcijskog rješenja. Analizom dobivenih rezultata donesen je zaključak da upotreba mehanizma za dodatno pridržavanje vrata vagona Falns 48, za slučaj transporta željezne rude, nije opravdana.Today's global trends in freight transport demand removal of all unnecessary freight wagon components in order to reduce mass. Because of that, the idea of a validity analysis of the additional door holding mechanism on freight wagon type Falns 48 was born. By removing this mechanism, the mass of the wagon could be reduced by 276 kg, but the maximum deformation of the doors lower edges would increase from 0,04 mm to 3,76 mm. This increase in the maximum deformation of the wagon doors lower edges can cause the cargo to leak out the wagon and fall down on the rails, and that is strictly forbidden. Therefore, it is necessary to implement optimization to find a certain compromise, or find the optimal solution. By applying the finite element method the deformations and stresses of the initial constructional solution of the wagon doors, with and without using the additional door holding mechanism, were analyzed. After that, the optimization process was carried out. The aim of the optimization is to reduce the maximum deformation of the doors lower edges, at the expense of mass increase. Also, a new constructional solution of the wagon doors was proposed and optimization of the proposed constructional solution was carried out. By analyzing the results, it was concluded that the use of the additional door holding mechanism on freight wagon Falns 48, in the case of transporting iron ore, is not justified

CALCULATIONT AND DESIGN OF WORM GEAR UNITS WITH A SINGLE GEAR

Tema ovog završnog rada je Proračun i konstrukcija pužnog reduktora s jednim stupnjem prijenosa. U radu su opisane moguće izvedbe pužnih prijenosnika, njihove karakteristike i područja primjene. Također je izrađena i popratna konstrukcijska dokumentacija jednog pužnog reduktora koja se sastoji od idejnih i konstrukcijskih rješenja, specifikacije, proračuna, uputstva za puštanje u pogon i uputstva za eksploataciju, odnosno opisa održavanja pužnog reduktora. Određivanje osnovnih veličina pužnog reduktora provedeno je prema standardu DIN 3976 i kriterijima za dimenzioniranje strojnih elemenata. Izbor ležaja rađen je prema SKF katalogu te su na taj način odabrani odgovarajući ležaji za konstrukciju reduktora vodeći računa o ključnim radijalnim i aksijalnim silama u osloncima i dimenzijama pojedinih vratila.The subject of this final paper is Calculation and construction of single stage worm gear reducer. The paper describes the possible construction of worm gears, their characteristics and applications. This paper also contains construction documentation of one worm gear, consisting of conceptual and construction solutions, specifications, calculations, start up instructions and instructions for exploitation, or the description of maintenance worm gear. Determination of the basic size worm gear was carried out according to DIN 3976 and the criteria for sizing machine elements. The choice of bearings was done by the SKF catalogue and in this way appropriate bearings for the construction of the worm gearbox are selected considering the important radial and axial loads in the supports and the dimensions of individual shafts

Nano-Mechanical Behavior of Ti6Al4V Alloy Manufactured Using Laser Powder Bed Fusion

The microstructure of Ti6Al4V alloy, manufactured using laser powder bed fusion (L-PBF), is affected by process parameters and heat treatment. However, their influence on the nano-mechanical behavior of this widely applicable alloy is still unknown and scarcely reported. This study aims to investigate the influence of the frequently used annealing heat treatment on mechanical properties, strain-rate sensitivity, and creep behavior of L-PBF Ti6Al4V alloy. Furthermore, the influence of different utilized L-PBF laser power–scanning speed combinations on mechanical properties of annealed specimens has been studied as well. It has been found that the effect of high laser power remains present in the microstructure even after annealing, resulting in increase in nano-hardness. Moreover, the linear relation between the Young’s modulus and the nano-hardness after annealing has been established. Thorough creep analysis revealed dislocation motion as a dominant deformation mechanism, both for as-built and annealed conditions of the specimens. Although annealing heat treatment is beneficial and widely recommended, it reduces the creep resistance of Ti6Al4V alloy manufactured using L-PBF. The results presented within this research article contribute to the L-PBF process parameter selection, as well as to understanding the creep behavior of these novel and widely applicable materials