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- ItemEffect of microstructure on machinability of extruded and conventional H13 tool steel(ELSEVIER SCI LTD, 2025-06-09) Kolomý, Štěpán; Malý, Martin; Doubrava, Marek; Sedlák, Josef; Zouhar, Jan; Čupera, JanH13 tool steel samples were fabricated using material extrusion to explore their machinability, offering a promising alternative to laser powder bed fusion for producing complex parts like moulds and cores. Three material states were studied: as-built (AB), heat-treated additively manufactured (HTAM), and heat-treated wrought (HTW). Machining tests focused on cutting speed, feed per tooth, and cooling conditions (dry/flood), while tracking their effect on cutting forces, surface roughness, hardness, microstructure, and residual stresses. Heat treatment significantly reduced porosity (similar to 45 % decrease between AB and HTAM) and transformed the microstructure to full martensite, increasing hardness and cutting forces. Interestingly, the HTAM sample showed lower cutting forces than HTW-by 23.7 % in dry and 24.5 % under flood cooling. HTW generally produced smoother surfaces at lower cutting parameters, but its roughness increased at higher conditions compared to HTAM. The softest AB sample experienced the highest surface hardening (similar to 12 %) when machined at low cutting speeds, while the HTW sample showed most uniform plastic deformation, extending up to similar to 50 mu m below the surface. Dominantly tensile residual stresses were measured in HTW, while AB and HTAM showed mainly compressive residual stresses under dry conditions. This study highlights viability of extruded H13 for industrial use, particularly in mould applications.
- ItemThe Effect of Strain Rate on the Friction Coefficient(Jan Evangelista Purkyne University in Usti nad Labem, 2024-04-30) Svoboda, Petr; Jopek, MiroslavThe Male and Cockroft ring compression test is one of the methods used to determine the coefficient of friction in forming. This method can be used to determine the coefficient of friction without the need to measure the force. This paper describes the results of the Male and Cockroft ring compres-sion test for the Hardox 450 material at different strain rates. The experiment was performed on ZD40 hydraulic press and CFA-80 pneumatic die hammer at the Faculty of Mechanical Engineering of Brno University of Technology. The test results were recorded in a calibration diagram. The results show that the strain rate has a significant effect on the coefficient of friction, specifically such that as the strain rate increases, the coefficient of friction decreases.
- ItemTribological Properties of 3D Printed Materials in Total Knee Endoprosthesis(UJEP, 2024-04-30) Varhaník, Matúš; Sedlák, Josef; Studený, Zbyněk; Janigová, Patrícia; Chromjaková, FelicitaThe submitted paper deals with biotribological contact in total knee arthroplasty. The goal was to evaluate the influence of the metal component production technology on tribological parameters in defined environments. The reference sample was a standard available test ball made of the subject material, used in testing tribological properties by the "Ball on Pin" method. The preparation of the experiment consisted in the production of test disks from UHMWPE (Ultra High Molecural Weight Polyethylene) material and the production of a metal test component with a spherical surface. The condition of the experiment and the basis of this contribution is to compare the properties of conventionally produced metal material against 3D printing. Using the SLM method, a sample with a semi-spherical surface on a cylindrical shank was produced, which was subsequently ground and polished to reflect the characteristics of the standard supplied test ball. The last step was the production of a suitable fixture in order to fit the sample into the tribometer. The so- called dry friction of the heterogeneous Ti6Al4V-UHMWPE pair and the friction in a biological lubricating environment represented by bovine serum were evaluated. The evaluation of the contact surfaces took place using a profilometer and an electron microscope. The coefficient of friction was determined directly from the test device - tribometer.
- ItemPerspectives on Using Alder, Larch, and Birch Wood Species to Maintain the Increasing Particleboard Production Flow(MDPI, 2024-06-19) Réh, Roman; Krišťák, Ľuboš; Král, Pavel; Pipíška, Tomáš; Jopek, MiroslavParticleboard, engineered wood products as part of a large family of wood composite materials, developed in use mainly in the 1950s and 1960s to utilize inferior wood and wood waste when good-quality wood was in short supply; the annual production capacity worldwide is over 100 million m3. It is also necessary to have a lot of wood raw material for its production, although raw material resources are limited on our planet. In addition to the main wood species, it is therefore possible to think about the wider use of alternative, lesser-known European species of alder, larch, and birch in particleboard production. These three wood species represent an eco-friendly and sustainable wood alternative to the conventional wood raw materials used. This review confirms the diversity of the use of these three species in different fields and proves their suitability in relation to particleboard production. Fundamental research is ongoing in certain universities to determine the proportional shares of use of these tree species in particleboard (in a certain weight proportion in their core layers) for the purpose of formulating the correct technology shares and rules for their application in the wood-based panel industry.
- ItemMechanical Properties, Structure and Machinability of the H13 Tool Steel Produced by Material Extrusion(Jan Evangelista Purkyne Univ, 2024-07-08) Malý, Martin; Kolomý, Štěpán; Kasan, Radek; Bartl, Lukáš; Sedlák, Josef; Zouhar, JanThe study focuses on an evaluation of mechanical properties of the H13 tool steel manufactured by the material extrusion and further comparison with conventionally produced material. Notably, for achieving sufficient surface quality of functional parts further post-processing is required. Thus, a comprehensive investigation, encompassing hardness, ultimate tensile strength (UTS) and yield strength (YS) measurement, microstructure, and machinability was performed. The material extrusion, an increasingly utilized additive manufacturing (AM) technique, offers a viable alternative to the prevalent laser powder bed fusion (LPBF) methods. The investigation revealed that the horizontal orientation of parts yielded the highest mechanical properties, reaching the ultimate tensile strength of approximately 1200 MPa. Additionally, the material exhibited the hardness of 47 HRC in the as-built state. The conventionally produced steel resulted in the higher UTS and YS in comparison to the AM material. The machinability of the as- built material in regard to cutting forces and surface roughness was also evaluated Lower surface roughness was achieved by decreasing feed per tooth. Optically measure material porosity was 6.13 % with maximum pore size 7.43 mu m. The primary objective of this research is to optimize the mechanical properties of H13 tool steel post-printing, with a broader aim to apply the gained insights to improve other materials produced by the material extrusion.