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Application of composite materials in sports optics
(J. E. Purkyne University in Usti nad Labem, 2020-08-18) Kupčák, Radim; Zouhar, Jan
CFRP (Carbon Fiber Reinforced Polymers) are often used when designing parts that need to be stiff, light and thermally stable. These benefits are a big motivation to use CFRP in many applications, one of them could be sports optics. However, optical devices require precise dimensions with tight tolerances for the optical assembly to work correctly. In order to determine if CFRP could be a suitable material of choice for sports optics a simplified body of binoculars was designed. The tubular body was manufactured by prepreg lay-up into a 3D printed mold, followed by curing in an autoclave. After the prototype was manufactured 3D measurements of the tube using 3D scanner GOM ATOS were made. As expected, shrinkage of the mold and the epoxy resin in the matrix of CFRP caused minor deformations. However, if the shape of the cured part remains unchanged during conditions similar to the general use of binoculars, then the initial deformations happening during manufacturing could be accounted for when designing the part. © 2020 Manufacturing Technology. All rights reserved.
Effect of high-speed steel screw drill geometry on cutting performance when machining austenitic stainless steel
(Springer Nature, 2023-06-07) Sedlák, Josef; Zouhar, Jan; Kolomý, Štěpán; Slaný, Martin; Nečesánek, Emil
Drilling into the solid material is one of the basic technological operations, which creates a cylindrical hole in an appropriate time with required quality. Drilling operation demands a favourable removal of chips from the cutting area because a creation of an undesirable shape of chips can impart a lower quality of the drilled hole corresponding with the generation of excess heat due to the intense contact of the chip with drill. The solution for a proper machining is a suitable modification of the drill geometry i.e., point and clearance angles as presented in current study. The tested drills are made of M35 high-speed steel characterized by a very thin core at the point of the drill. An interesting feature of the drills is the use of cutting speed higher than 30 m min(-1), with the feed of 0.2 mm per revolution. The surface roughness (Ra and Rz lower than 1 mu m and 6 mu m respectively), cylindricity (0.045 mm), roundness (0.025 mm), perpendicularity of the hole axis (0.025 mm), diameters and position of the individual holes were achieved for a drill with point angle 138.32 degrees and clearance angle 6.92 respectively. The increase of the drill point angle by 6 degrees resulted in the decrease in the feed force of more than 150 N. In addition, an increase of the clearance angle by 1 degrees resulted with a decrease in the feed force of 70 N. The results of the experiment showed that with the correct geometry of the tool the effective machining without using internal cooling can be realised.
High Cycle Fatigue Behaviour of 316L Stainless Steel Produced via Selective Laser Melting Method and Post Processed by Hot Rotary Swaging
(MDPI, 2023-04-26) Opěla, Petr; Benč, Marek; Kolomý, Štěpán; Jakůbek, Zdeněk; Beranová, Denisa
This paper deals with a study of additively manufactured (by the Selective Laser Melting, SLM, method) and conventionally produced AISI 316L stainless steel and their comparison. With the intention to enhance the performance of the workpieces, each material was post-processed via hot rotary swaging under a temperature of 900 °C. The samples of each particular material were analysed regarding porosity, microhardness, high cycle fatigue, and microstructure. The obtained data has shown a significant reduction in the residual porosity and the microhardness increase to 310 HV in the sample after the hot rotary swaging. Based on the acquired data, the sample produced via SLM and post-processed by hot rotary swaging featured higher fatigue resistance compared to conventionally produced samples where the stress was set to 540 MPa. The structure of the printed samples changed from the characteristic melting pools to a structure with a lower average grain size accompanied by a decrease of a high fraction of high-angle grain boundaries and higher geometrically necessary dislocation density. Specifically, the grain size decreased from the average diameters of more than 20 µm to 3.9 µm and 4.1 µm for the SLM and conventionally prepared samples, respectively. In addition, the presented research has brought in the material constants of the Hensel-Spittel formula adapted to predict the hot flow stress evolution of the studied steel with respect to its 3D printed state.
Influence of Aging Temperature on Mechanical Properties and Structure of M300 Maraging Steel Produced by Selective Laser Melting
(MDPI, 2023-01-20) Kolomý, Štěpán; Sedlák, Josef; Zouhar, Jan; Slaný, Martin; Benč, Marek; Dobrocký, David; Barényi, Igor; Majerík, Jozef
This paper deals with the study of high-strength M300 maraging steel produced using the selective laser melting method. Heat treatment consists of solution annealing and subsequent aging; the influence of the selected aging temperatures on the final mechanical properties-microhardness and compressive yield strength-and the structure of the maraging steel are described in detail. The microstructure of the samples is examined using optical and electron microscopy. The compressive test results show that the compressive yield strength increased after heat treatment up to a treatment temperature of 480 degrees C and then gradually decreased. The sample aged at 480 degrees C also exhibited the highest observed microhardness of 562 HV. The structure of this sample changed from the original melt pools to a relatively fine-grained structure with a high fraction of high-angle grain boundaries (72%).
Material and Dimensional Analysis of Bimetallic Pipe Bend with Defined Bending Radii
(Strojarski fakultet u Slavonskom Brodu, 2021-06-05) Slaný, Martin; Sedlák, Josef; Zouhar, Jan; Zemčík, Oskar; Chladil, Josef; Jaroš, Aleš; Kouřil, Karel; Varhaník, Matúš; Majerík, Jozef; Barényi, Igor; Čep, Robert
This paper deals with material and dimensional bending analysis of bimetallic pipes with defined bending radii. Basic characteristics of selected nickel superalloys with analysis of Inconel 625 and 16Mo3 steel in terms of primary mechanical properties and chemical composition are presented. The practical part where the bimetallic tube is analyzed in terms of material properties is also performed geometric dimensional analysis, for which test specimens with different bending radii are made.

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