Seznam abstraktů 2024: SEKCE B - TVÁŘENÍ KOVŮ

In numerical process design, the heat transfer coefficient (HTC) is used to model the heat transfer. In most finite element calculations for bulk metal forging, a constant HTC is currently assumed, as there is no complete understanding of the relationships between the heat transfer coefficient and its influencing variables (e.g. contact pressure or temperature), which leads to inaccuracies in the simulation results. However, specifically set temperature profiles are necessary, particularly in the composite forging of aluminum and steel, in order to match the forming properties of the dissimilar semi-finished products. Setting incorrect boundary conditions in the compound forging process can lead to temperature profiles that cause the aluminum semi-finished products to melt when the solidus temperature is reached. However, the investigation of the HTC in forging processes represents a major challenge from an experimental point of view due to the very short pressure contact times and the high heating rates that occur. According to the current state of the art, there is currently no method for determining the prevailing HTC within a compound forging process as a function of relevant effective variables with reasonable effort.
This paper presents a new test setup for recording HTC for the composite forging of aluminum and steel. In addition to the first prototype of the test setup, the test materials EN AW-6082 and 1.0038 were investigated with regard to their plastic behavior and their thermally induced elongation. These material properties are used to define process windows for joint forming as well as for joint heating.

The combination of steel and aluminium enables the production of components with adapted functional areas and reduced weight. Using the Tailored Forming process chain, the dissimilar materials are first joined using rotary friction welding. Subsequently, a cup backward extrusion at elevated temperatures takes place to create a preform for a hollow demonstrator shaft. The hybrid semi-finished product is heated inductively on the steel part to equalise the differing yield stresses of the materials during forming in order to achieve a favourable material flow resulting in a sound bond. In the case of steel (20MnCr5) and aluminium (EN AW-6082), a brittle intermetallic compound emerges in the interface during rotary friction welding, which grows under high temperatures during the following heating step for impact extrusion. Above certain thicknesses, the intermetallic compound has a detrimental effect on the component properties and is considered a weak point in the interface due to its high hardness and brittleness. The use of a copper interlayer during rotary friction welding can increase the ductility of the interface in the forming operation. Therefore, higher true plastic strains can possibly be induced in the subsequent forming process without damaging the joining zone. To investigate the influence of the copper interlayer on the interface properties, different layer thicknesses are applied. The bond is evaluated by uniaxial tensile tests after rotary friction welding and metallographically after joining and forming using hardness measurements, SEM as well as EDX analyses.

Despite the continuous development of new materials and technologies for obtaining casting alloys, iron alloys, including gray cast iron, are still common. Due to the cost of production and expected range of strength and e.g. tribological properties, it is still a material eagerly used in various industries, mainly in the automotive industry. Only the type of alloy additives changes, which further improves the individual performance of properties. The best way to assess their impact is to evaluate crystallization using thermal analysis, e.g. ATD. GJL-150 cast iron, applied for brake disc castings, was selected to analyze the crystallization process. The research was carried out at Brembo Poland Sp. z o. o. Thermal analysis was carried out in industrial conditions at the ITACAX Proservice station. On registered crystallization curves, specific temperatures of phase changes were indicated using various additives.

The paper is focused on experimental research with the goal of enhancing cold mill capability by improving the currently used coolant setting (various types of emulsions) and cooling configuration (type of nozzle, nozzle position, distance and inclination angle of headers with respect to the roll).
The experimental research was divided into two phases. The initial phase examined the impact of various emulsion types on cooling intensity. Pure water, coconut, lard and palm oil-based emulsions with various oil concentrations were tested. The highest cooling intensity was found for the pure water. The heat transfer coefficient decreased with the increase of the oil concentration. The cooling intensity was comparable for different emulsions.
The second phase was focused on cooling optimization. The goal was to enhance cooling intensity while reducing the consumption of the cooling medium. The research methodology was based on the specialized experimental stand that simulated cooling processes on a rotating surface. The heat transfer coefficient was investigated for a typical cooling system. Then, the cooling configuration (nozzle size, type, position and header inclination angle) was optimized and the comparison of a new and old cooling system shoved higher cooling efficiency with lower water consumption (25% less).
Finally, roll cooling simulations were conducted for both cooling variants to compare the impact on roll temperature during rolling. The advantage of the optimized cooling system was minimal (roll temperature decreased by 5°C) due to the small difference between the coolant temperature (55°C) and the strip temperature (200°C). However, lowering the coolant temperature to 20°C caused the roll temperature decrease by 30°C.

Extrusion of long products using the KoBo method is an advancement of conventional direct extrusion, which, by introducing cyclic rotational movement of the die, enables the application of lower punch pressure to achieve plastic deformation. The process offers several advantages, including obtaining ultrafine-grained microstructure in the shaped product, cold joining of feedstock components for recycling fine waste, and even producing metal composites. Research findings on the physical modeling of the KoBo extrusion process, elucidating material flow within the die, have been documented and disseminated within academic circles. However, studies on the physical modeling during the extrusion of two different materials to demonstrate the diversity of local deformation across the cross-section of the extruded element are rare. This paper presents the results of experiments aimed at modeling plastic flow in the direct extrusion process using the KoBo method, using samples of 7075 aluminum alloy interleaved concentrically with layers of DHP copper (Deoxidized High Phosphorus Copper) acting as markers. As a result of cold extrusion, for the obtained rods of various diameters, local deformations across the rod's cross-section were calculated, and a comparative analysis of the results with other physical material flow models for direct extrusion, both conventional and KoBo methods, was conducted. The analysis of the results enabled the determination of deformation distribution across the cross-section of extruded rods, facilitating the prediction of KoBo process parameters necessary to attain products characterized by uniform deformation distribution.


Work co-financed under the Research University - Excellence Initiative - Project Based Learning 4th Edition, Silesian University of Technology, title: Comparative analysis of the microstructure and properties of light metal alloys processed with selected SPD methods.

The work includes an innovative way of forming thin-walled parts, which is a research topic in only four countries worldwide, including Poland. The technology discussed is an alternative to the 3D printing process. The paper presents the results of research into spinning axisymmetric forming of thin-walled parts made of aluminium alloy 1050A and steel DC04. As part of the study, technological parameters were determined and the influence of the trajectory on the forming of the material was investigated. Among other things, the springback of the material formed during the spinning process and the distribution of material thickness on the side of the shaped part were determined. Two methods representing how the trajectory of a spinning tool can be generated by applying the principle of constant contact between tools and the principle of constant tool tangency were presented. Advantages and disadvantages are discussed and the author's solution, which aims to significantly reduce process development time, is presented.

Designing processes for producing responsible structural elements from steel in the hot forging process requires knowledge of the relationship between the process parameters, the microstructure that is formed under the assumed deformation conditions as well as the quality and properties of the forgings. The analysis of flow curves and the assessment of the microstructure after deformation allows the identification of phenomena occurring during hot processing, such as work hardening, recovery and recrystallization. On this basis, it is possible to determine both favorable sets of deformation parameters and to identify their combinations that lead to the risk of microstructural defects. However, during multi-stage free forging on hydraulic presses, the deformation rate does not change significantly, but the temperature gradually decreases during subsequent operations. Then, if necessary, the temperature is raised to the upper limit during intermediate reheating. As a result, the process is often carried out over a wide temperature range and cannot be maintained within a favorable temperature range.
Selected results of comprehensive tests were presented, which were aimed at controlling the state of the microstructure and, therefore, the properties of forgings made of 80MnSi8-6 steel shaped in multi-stages. This goal was achieved by analyzing and controlling subsequent stages of the forging process, taking into account both the quality of the shape and the state of the microstructure. To perform this research task, numerical modeling using the finite element method and forging tests in laboratory conditions, conducted using anvils of various shapes, were used.

This study focuses on the experimental evaluation of the effect of angular positioning errors on the quality of micro laser spot welding in stainless (inox) kitchen and hotel equipment applications. Obtaining the correct welding parameters to join thin stainless materials without causing visible defects is an extremely delicate process. The welding process must be precise enough to avoid any visual defects on the visible part of the stainless surface while also ensuring that the connection is strong enough to withstand the life of the device. Experiments conducted in this study reveal that the most common operator error in manual spot welding is angular misalignment between the laser beam and the plate surface. Certain welding parameters, such as laser signal intensity and duration, were kept constant to demonstrate the effect of welding angles. Then, welded samples were prepared with various laser beam angles, and tensile tests were used to measure the maximum loads each weld point could carry. Experiments show that when spot welding is done on thin stainless steel at angles larger than the critical welding angle, heat-induced scars or micro deformations occur on the visible surface of the thin stainless material. In addition, the flow of the lens protective gas is blocked as the outlet opening narrows and the life of the lens is shortened. On the contrary, it is understood that a sufficiently wide weld area cannot be created at angles larger than the critical weld angle. The study uses experimental findings to determine the optimal torch angle range for available laser welding parameters. The results highlight that the laser beam angle must be precisely adjusted within a narrow range in visual micro-laser welding applications, making it difficult for the operator to distinguish by sight.

Over the past twenty years, there has been a rising interest in heat-treatable 6xxx series aluminum alloys, primarily due to their impressive strength-to-weight ratio, excellent formability, and outstanding corrosion resistance characteristics [1]. In conventional manufacturing processes, those alloys are solution heat treated and artificially aged following a hot forging process [2]. Besides heat treatment, forging conditions have a major effect on the final properties and grain structure of the forged products. In the current study, effect of the forging temperature on the mechanical properties as well as microstructure of EN AW 6056 aluminum alloy has been investigated. Cylindrical samples with a diameter of 65 mm and length of 160 mm are upset forged with flat dies in their radial direction using a mechanical press. Forging temperature is varied between 150°C and 450°C with 100°C steps. Afterwards, all forged samples are solution heat treated at 550°C for 90 minutes and quenched in water at room temperature. Subsequently, samples are artificially aged at 190°C for 4 hours. Contrary to the common believe, although solution heat treatment is applied at a relatively high temperature, forging temperature had a major influence on the hardness of samples. Moreover, as forging temperature decreased, grain size of the forged samples also decreased.

This research focuses on sustainable production method for high-quality grinding media, crucial for efficient comminution processes. By integrating, innovative skew rolling technology with in line quenching and self-tempering techniques, grinding media with diameters ranging from 25mm to 150mm and a target surface and volumetric hardness range of 60 to 65 HRc are achieved. Through optimized alloy composition with less than 3% of total alloying content and process parameters, a microstructure of fine-grained tempered martensite is attained, with less than 5% retained austenite for enhanced wear resistance. Additionally, this study demonstrates a significant decrease in specific consumption of grinding media, reduced by 11% in iron ore grinding, when employing these sustainable grinding media instead of conventional 12-18% high-chromium cast grinding media. These findings highlight the potential of sustainable grinding media production methodologies for various industrial applications, where superior mechanical properties contribute to prolonged operational efficacy in challenging environments.