Most cited article - PubMed ID 33374722
Monotonic Tension-Torsion Experiments and FE Modeling on Notched Specimens Produced by SLM Technology from SS316L
The purity of a steel is an important factor influencing the quality of the final products. Therefore, it is important to optimize the existing and develop new steelmaking technologies that affect the resulting purity. Electro slag remelting is a technology of tertiary metallurgy, which can advantageously be used to fabricate high quality steels. The study presents selected theoretical aspects of oxide systems and their specific influences on effectiveness of the electro slag remelting technology. The aim of this work was to experimentally analyze the purity of a tool steel fabricated by electro slag remelting using two different oxide systems (fused slags). The core of the study is the determination of the overall presence of elements in the steels, a thorough investigation of the presence of (not only) oxide-based inclusions within the investigated tool steel, and a detailed analysis of their chemical composition, including the size of these non-metallic inclusions, using energy dispersive X-ray (EDX) on the scanning electron microscope (SEM). Last but not least, the determination of the modification of the occurring non-metallic inclusions and verification of the experimentally acquired results as well as the calculation of the liquid and solid temperature and the calculation of the viscosity of the slags using the FactSage calculation software was performed. The results showed that the used slag influenced especially the occurrence of Mg and Al-based oxide inclusions. The CaS-type inclusions were present within all of the examined samples. The slag type influenced not only the typical morphology and size of the inclusions (especially of the CaS type), but also the tendency of the steel to exhibit localized corrosion when exposed to the ambient environment. This research can contribute to a better understanding of the effect of oxidation systems on the resulting purity and properties of ESR steels, thereby advancing the production of tool steels with higher quality and performance requirements.
- Keywords
- chemical composition, electro slag remelting, non-metallic inclusion, slag, thermodynamics,
- Publication type
- Journal Article MeSH
The presented work is focused on the influence of imposed strain on the weldability of Dievar alloy. Two mechanisms affecting the microstructure and thus imparting changes in the mechanical properties were applied-heat treatment (hardening and tempering), and rotary swaging. The processed workpieces were further subjected to welding with various welding currents. In order to characterize the effects of welding on the microstructure, especially in the heat-affected zone, and determine material stability under elevated temperatures, samples for uniaxial hot compression testing at temperatures from 600 to 900 °C, optical and scanning electron microscopy, and microhardness testing were taken. The testing revealed that, although the rotary swaged and heat-treated samples featured comparable microhardness, the strength of the swaged material was approximately twice as high as that of the heat-treated one-specifically 1350 MPa. Furthermore, it was found that the rotary swaged sample exhibited favorable welding behavior when compared to the heat-treated one, when the higher welding current was applied.
- Keywords
- Dievar, heat treatment, microstructure, rotary swaging, tool steel, weldability,
- Publication type
- Journal Article MeSH
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.
- Keywords
- 316L steel, high cycle fatigue, hot compression testing, hot rotary swaging, microstructure, selective laser melting,
- Publication type
- Journal Article MeSH
The constant effort of all metal alloy manufacturing technologies and processes is to improve the resulting quality of the processed part. Not only the metallographic structure of the material is monitored, but also the final quality of the cast surface. In foundry technologies, in addition to the quality of the liquid metal, external influences, such as the behaviour of the mould or core material, significantly affect the cast surface quality. As the core is heated during casting, the resulting dilatations often lead to significant volume changes causing stress foundry defects such as veining, penetration and surface roughness. In the experiment, various amounts of silica sand were replaced with artificial sand and a significant reduction in dilation and pitting of up to 52.9% was observed. An important finding was the effect of the granulometric composition and grain size of the sand on the formation of surface defects from brake thermal stresses. The specific mixture composition can be considered as an effective prevention against the formation of defects instead of using a protective coating.
- Keywords
- CERABEADS, artificial ceramic sands, foundry moulding mixture, silica sands, surface defects, surface roughness, surface structure, thermal expansion, veining,
- Publication type
- Journal Article MeSH
The study aims to compare mechanical properties of polymer and metal honeycomb lattice structures between a computational model and an experiment. Specimens with regular honeycomb lattice structures made of Stratasys Vero PureWhite polymer were produced using PolyJet technology while identical specimens from stainless steel 316L and titanium alloy Ti6Al4V were produced by laser powder bed fusion. These structures were tested in tension at quasi-static rates of strain, and their effective Young's modulus was determined. Analytical models and finite element models were used to predict effective Young's modulus of the honeycomb structure from the properties of bulk materials. It was shown, that the stiffness of metal honeycomb lattice structure produced by laser powder bed fusion could be predicted with high accuracy by the finite element model. Analytical models slightly overestimate global stiffness but may be used as the first approximation. However, in the case of polymer material, both analytical and FEM modeling significantly overestimate material stiffness. The results indicate that computer modeling could be used with high accuracy to predict the mechanical properties of lattice structures produced from metal powder by laser melting.
- Keywords
- additive manufacturing, analytical modeling, laser powder bed fusion, lattice structures, numerical simulation, titanium alloys,
- Publication type
- Journal Article MeSH
Reverse engineering is the process of creating a digital version of an existing part without any knowledge in advance about the design intent. Due to 3D printing, the reconstructed part can be rapidly fabricated for prototyping or even for practical usage. To showcase this combination, this study presents a workflow on how to restore a motorcycle braking pedal from material SS316L with the Powder Bed Fusion (PBF) technology. Firstly, the CAD model of the original braking pedal was created. Before the actual PBF printing, the braking pedal printing process was simulated to identify the possible imperfections. The printed braking pedal was then subjected to quality control in terms of the shape distortion from its CAD counterpart and strength assessments, conducted both numerically and physically. As a result, the exterior shape of the braking pedal was restored. Additionally, by means of material assessments and physical tests, it was able to prove that the restored pedal was fully functional. Finally, an approach was proposed to optimize the braking pedal with a lattice structure to utilize the advantages the PBF technology offers.
- Keywords
- 3D scanning, SS316L, electronic speckle pattern interferometry, lattice structure, powder bed fusion, printing simulation, reverse engineer,
- Publication type
- Journal Article MeSH
The spring-loaded camming device (SLCD), also known as "friend", is a simple mechanism used to ensure the safety of the climber through fall prevention. SLCD consists of two pairs of opposing cams rotating separately, with one (single-axle SLCD) or two (dual-axle SLCD) pins connecting the opposing cams, a stem, connected to the pins, providing the attachment of the climbing rope, springs, which simultaneously push cams to a fully expanded position, and an operating element controlling the cam position. The expansion of cams is thus adaptable to allow insertion or removal of the device into/from a rock crack. While the pins, stem, operating element, and springs can be considered optimal, the (especially internal) shape of the cam allows space for improvement, especially where the weight is concerned. This paper focuses on optimizing the internal shape of the dual-axle SLCD cam from the perspective of the weight/stiffness trade-off. For this purpose, two computational models are designed and multi-step topology optimization (TOP) are performed. From the computational models' point of view, SLCD is considered symmetric and only one cam is optimized and smoothened using parametric curves. Finally, the load-bearing capacity of the new cam design is analyzed. This work is based on practical industry requirements, and the obtained results will be reflected in a new commercial design of SLCD.
