Search Results (46)

The work aimed to investigate the possibility of improving the mechanical properties, and therefore the wear resistance, of coated tools in manufacturing processes with continuous or interrupted cutting loads through appropriate annealing. In this context, PVD CrAlN coatings were deposited on cemented carbide inserts. A part of these coated tools was annealed at a temperature of 400 °C, which was close to the deposition temperature, in an inert gas atmosphere. The annealing duration ranged up to 60 min. Nanoindentations and repeated perpendicular and inclined impact tests were carried out to characterize the strength, fatigue, and adhesion of the tool coatings before and after annealing. According to the results, the mechanical properties of the coating and the fatigue resistance were maximized after a short annealing period of about 15 min, while the adhesion of the coating remained unchanged. These facts led to a large increase in tool life in milling 42CrMo4 QT, when annealed coated tools were applied at 400 °C for 15 min. Furthermore, turning experiments using the mentioned hardened steel as well as GG30 cast iron to produce continuous or interrupted chips, respectively, confirmed the obtained results in milling. Therefore, annealing of coated cutting tools at an optimized duration is recommended as an effective method to extend tool life. Full article

The problem of increasing the tool durability (service life) when machining hard-to-machine materials is one of the major practical problems of modern mechanical engineering. This paper aims to improve the wear resistance of modular disk mills using the pre-processing method. Second-order rotatable planning was applied for the experimental study of the pre-processing of modular disk mills. Experimental research on the pre-processing of modular disk mills was carried out on a vertical milling machine XH950A when milling a workpiece made of steel 45. It was revealed that the increase in pre-processing modes up to specific values (f = 60 mm/min; $v_c$ = 17 m/min; t = 6 min) on the tool durability period has a positive effect. At the same time, the tool durability period was increased up to T = 155 min. Tests of the machined modular disk mills were carried out in the conditions of the laboratory base to determine the durability period. After pre-processing at different modes, each modular disk mill was used to machine the workpiece until wear signs appeared on the cutting edge. At the same time, the time was recorded to determine the durability period. It was found that the optimum mode of tool preliminary pre-processing provides the best deformation and thermal conditions for hardening the tool cutting part. As a result of modeling with the ANSYS 2024 R1 program, it was found that a hardened layer is indeed formed on the cutting part of the modular disk mill after pre-processing. The results obtained show the possibility of using the preliminary pre-processing method to improve the wear resistance of other metal-cutting tools. Full article

In the present work, the microstructure and texture evolution of ferritic stainless steel during unidirectional cold rolling were investigated, and the Visco-Plastic Self-Consistent (VPSC) polycrystal model was used for the simulation of texture during cold rolling. Comparison of different interaction models was made to obtain a model that better reproduces the texture evolution of ferritic stainless steels. The as-received hot-rolled samples were unidirectionally cold rolled in a laboratory rolling mill, and the thickness was reduced by 30%, 60% and 80%. Electron backscatter diffraction (EBSD) was used to observe the microstructure evolution and texture evolution, and micro-hardness was used to evaluate the work hardening of the sample. The important feature of the microstructure was the presence of shear bands (SBs), the frequency of which increased with the increase in cold-rolling reduction and was found to be orientation dependent. We found that the geometrically necessary dislocation (GND) density increased with cold-rolling reduction in accord with Ashby’s theory of work hardening, and higher GND density accumulates near the grain boundary. The grain fragmentation, Goss texture distribution and orientation gradient were found to be orientation dependent. The cold-rolled texture was composed of strong α-fiber and weak γ-fiber. The relative plastic compliance of grain and the homogeneous effective medium (HEM) were explored. The tangent interaction model was found to match reasonably well with the experimental texture. This work has great significance for achieving online monitoring of the texture of ferritic stainless steel under different industrial production processes and enhancing the intelligence level of ferritic stainless steel production process. Full article

Surface texture parameters are a quantitative way of characterising surface topographical features and are closely related to tribological properties. In this paper, the correlation between surface topographic features and friction coefficient is investigated on the basis of the proposed improved correlation analysis model for high-speed milling surface topography of hardened steel. It was found that the friction coefficient could not be accurately reflected by a single parameter, so a prediction model for the friction coefficient based on Sxp, Sq, Sp, Sz, Sku and Sdq was developed. In this paper, the parameter screening was completed based on the changing characteristics of the data, and a multi-parameter prediction model of the friction coefficient in the stable wear stage was established, which provides a new idea to investigate the influence of the characteristics of surface topography on tribological performance. Full article

In tool and mold making, components are typically first pre-machined in a soft state with residual stock allowance, as economical production is not possible in a hardened state due to the enormous tool wear. This extends the process chain and therefore also the throughput times. This paper presents an innovative tool concept for a solid carbide end mill in order to be able to carry out roughing and finishing in a hardened state. First, the structure of the innovative solid carbide end mill is described. Afterwards, the results of experimental tests are presented and discussed. These describe the suitability of the tool concept and include further investigations that examine the influence of the helix angle on the process behavior during the machining of the tool steel Toolox 44. To evaluate the process behavior, the development of process forces, chip formation, tool wear and component quality over the tool life are analyzed. Full article

In the die and mold industry, tempered JIS SKD11 steel is selected to manufacture cold-forming dies that require an optimum balance of toughness, strength, and wear resistance. Therefore, the machinability of tempered JIS SKD11 in the milling machining process is challenging. The use of eco-friendly machining settings is intended to diminish tool wear and enhance the quality of the machined surface as well as the accuracy of the machined components. Adapting to the aforementioned factors for cold-forming dies is a pivotal issue. In this study, the machinability of tempered JIS SKD11 steel was analyzed under dry, MQL, cryogenic cooling with liquid nitrogen (LN₂), and liquid carbon dioxide (LCO₂) machining settings during open slot milling operations with varying input parameters, including cutting speeds and cutting feeds. An in-depth evaluation of output responses, including tool wear, surface roughness, cutting temperature in the cutting zone, and microhardness of the machined surface, was also conducted. The findings unveiled that the flank wear of the cutters and surface roughness of the machined surfaces obtained minimum values of 0.22 mm and 0.197 µm, respectively, during open slot milling operations at a cutting speed of 100 m/min and a cutting feed of 204 mm/min under cryogenic cooling with liquid carbon dioxide (LCO₂). The findings from this study suggest that employing cryogenic cooling with LCO₂ could serve as a viable substitute for dry, MQL, and cryogenic cooling with LN₂ methods to enhance the machinability of hardened JIS SKD11 steel. Full article

304 stainless steel demonstrates a low thermal conductivity and work hardening characteristics, resulting in its processing, and will adhere to the tip of the tool; as well as the phenomenon of chipping, shortening the life of the tool. AlTiN coatings are representative of coatings applied to carbide tools. In this paper, AlTiN coatings with different arc current processes were deposited on carbide milling inserts using arc ion plating. The microstructure, mechanical properties, and milling properties of the coatings were investigated by using the SEM, EDS, XRD, scratch meter, friction and wear meter, and vertical machining center. The findings revealed that all coatings displayed columnar crystal growth, free from cracks and voids. With an increasing arc current, there was a notable increase in surface droplets, pits, and coating thickness. The coating deposited at a 140 A arc current showed a pronounced (200) orientation preference. The adhesion force peaked at 56.0 N with a subsequent decline, and the friction coefficient hit its lowest point of 0.429 at 140 A, contrasting with its highest value of 0.55 at 160 A. After 39 min of dry milling, the tool with a 140 A AlTiN coating exhibited minimal wear of 0.196 mm, just below the 0.2 mm failure threshold, indicating superior performance at this arc current setting. Full article

The management of waste, especially ferrous waste, poses great problems in the steel industry due to strict regulations on preventing, reducing, or even eliminating the factors that generate a high degree of environmental pollution (landfills resulting from the steel industry and adjacent industries—mining, energy, etc.). The present paper presents a synthesis of the specialized literature regarding the processes used, both worldwide and nationally, regarding the transformation of raw materials (ores or concentrates) and iron-containing waste (steel mill dust, mill scale and scale, sludge from agglomeration factories, sideritic waste, etc.) into by-products that can be used in the steel industry. For technological reasons, the option of pelletizing powdered waste was applied—in laboratory conditions, according to its own recipes, with results that justify the application of the technology on an industrial scale (appearance after hardening; drop resistance). The aim of the paper was to identify a practical solution; based on this solution, original conceptual models of organizational strategies (management and processing, respectively, recovery of ferrous waste within steel companies) were developed, such as a concentration strategy, diversification, vertical integration, etc. Within graphical representations of the proposed strategies, other processing variants were mentioned: agglomeration; briquetting. Full article

Despite the prevalent application of 18% Ni maraging steel in critical sectors such as aerospace and automotive due to its unique characteristics, including high ductility, yield strength, and hardenability, its machining presents enormous challenges, categorizing it as a difficult-to-machine material. The cutting tool’s geometry is crucial in machining, significantly affecting chip formation, cutting forces, power consumption, and obtainable surface quality. In particular, wiper insert technology, characterized by its multi-radius design, offers an increased contact area compared to conventional inserts, potentially enhancing the quality of the machined surface. This study explores the effectiveness of wiper inserts in the face-milling of maraging steel 350, conducting a comparative analysis across three distinct machining setups. These setups vary by alternating the number of wiper and conventional inserts within the same cutter, thereby examining the influence of insert configuration on machining outcomes. The research employs a reliable and well-established statistical approach to evaluate how different variables, such as cutting speed and feed rate, affect surface quality, power consumption, and material removal rate (MRR). It also sheds light on the material removal mechanisms facilitated by each type of insert. The findings reveal that incorporating a higher number of wiper inserts significantly enhances the surface finish but concurrently increases power consumption. Thus, the study successfully identifies an optimal set of process parameters that attain a balance between achieving superior surface quality and maintaining energy efficiency in the machining of maraging steel 350. This balance is crucial for optimizing manufacturing processes while adhering to the stringent quality and sustainability standards required in aerospace and automotive manufacturing. Full article

Although chip morphology changes according to the machining method and related cutting parameters, chip formation affects the quality of the machined surface. In this context, it is very important to understand the relationship between chip morphology and surface quality, especially in materials that are difficult to machine. In the presented study, the changes in chip morphology, surface morphology, and surface quality criteria (Ra and Rz) that occurred during the milling of precipitation-hardened steel in different cutting environments were analyzed. Milling experiments were carried out in dry, MQL (minimum quantity lubrication), nano-MQL (graphene), nano-MQL (hBN), Cryo, and Cryo-MQL environments using TiAlN-coated inserts and three different cutting speeds and feed rates. While the highest values in terms of Ra and Rz were measured in dry machining, the minimum values were obtained in a nano-MQL (hBN) cutting environment. Due to the lubrication and low friction provided by the MQL cutting environment, chips were formed in thinner segmented forms. This formation reduced the chip curve radius and thus provided a more stable surface morphology. On the other hand, Cryo-ambient gas could not effectively leak into the cutting zone due to the intermittent cutting process, but it increased the brittleness of the chips with the cooling effect and provided a similar surface morphology. The values of minimum Ra and Rz were obtained as 0.304 mm and 1.825 mm, respectively, at a 60 m/min cutting speed and 0.04 mm/rev feed. Consequently, the use of nano-MQL cutting medium is seriously recommended in terms of surface quality in milling operations of difficult-to-machine materials. Full article

This study investigates the synergistic effect and mechanism of gelling materials with blast furnace slag (BFS), steel slag (SS) and desulphurization gypsum (DG) as the main components on the hardening of heavy metal ions by lead and zinc tailings. It is found that lead and zinc tailing (LZT) is mainly composed of dolomite and quartz and contain small amounts of calcium, aluminum, iron, magnesium and other elements as well as heavy metals such as lead and zinc. By the mechanical activation method, it is found that the lead and zinc tailings powder has the largest specific surface area and the highest activity index when the ball milling time is 2 h. At a hardening timepoint of 28 d, the calcite crystals in the samples are intertwined with the amorphous C-S-H gel (C-S-H gels are mainly composed of 3CaO∙SiO₂ and 2CaO∙SiO₂), which enhances the structural strength of the samples. The chemical reaction analysis confirmed that the formation of calcite is a major driver for the hydration reaction of the steel slag–desulphurization gypsum (SSSDG) system. Overall, the slag, steel slag and desulphurization gypsum solid waste-based gelling materials have synergistic effects in hardening heavy metals by limiting the leaching of metal ions, adsorbing metal ions and hardening heavy metals, and facilitating the hydration process through the formation of compound salt precipitates. Full article

Today’s sustainable development policy in Europe, which is driven by concerns about the greenhouse effect and environmental protection, mandates a reduction in CO₂ emissions into the atmosphere. The cement industry and steel mills that produce reinforcing bars are among the largest and most emissions-intensive sectors emitting CO₂ into the atmosphere. This article analyzes the possibility of achieving significant reductions in CO₂ emissions by using basalt bars (BFRP) and glass bars (GFRP) in concrete structures, and—in the case of concrete—by using cement with the addition of metakaolinite and zeolite. There is a lack of literature reports on whether modifying concrete with the additions of metakaolinite and zeolite as substitutes for part of the cement affects the adhesion of FRP bars to concrete. It can be assumed, however, that improving the microstructure of concrete also improves the contact zone between the bar and the concrete. The aim of this research is to fill the aforementioned gap in the literature data by determining how the presence of metakaolinite and zeolite affects the adhesion of reinforcing bars to concrete and testing selected properties of hardened concrete. The test samples were prepared following the appropriate beam test procedure. The obtained results made it possible to perform a comparative analysis of reference samples and those with metakaolinite and zeolite additions. The research showed that introducing active pozzolanic additives in the form of metakaolinite and zeolite into concrete improved adhesion stress values by approximately 20% for glass GFRP bars and 15% for basalt BFRP bars, especially in the destruction phase. Full article

This study aims to find the optimized parameters for surveying the milling process of S50C steel in a minimum quantity lubrication (MQL) environment using a support vector machine-genetic algorithm (SVM-GA). Based on the experimental matrix designed by the Taguchi method, surface roughness and cutting force data were collected corresponding to each experiment with changes in input parameters such as cutting speed, tooth feed rate, and axial depth of cut, along with changes in two parameters of the minimum lubrication system: flow rates and injection pressure. Through analysis by the SVR-NSGAII method, the study obtained the optimal parameters of cutting and lubricating conditions when prioritizing either surface roughness or focusing on the cutting force; however, the most comprehensive result is believed to be achieved by balancing these two factors. So, when striving for the neutral value of both output parameters, which are surface roughness (µm) and cutting force (N), the optimum parameters including injection pressure (MPa), flow rates (mL/h), cutting speed (m/min), feed rate (mm/tooth), and axial depth of cut (mm) are proposed. Full article

Titanium and its alloys have excellent corrosion resistance, heat, and fatigue tolerance, and their strength-to-weight ratio is one of the highest among metals. This combination of properties makes them ideal for aerospace applications; however, high manufacturing costs hinder their widespread use compared to other metals such as aluminum alloys and steels. Powder metallurgy (PM) is a greener and more cost and energy-efficient method for the production of near-net-shape parts compared to traditional ingot metallurgy, especially for titanium parts. In addition, it allows us to synthesize special microstructures, which result in outstanding mechanical properties without the need for alloying elements. The most commonly used Ti alloy is the Ti6Al4V grade 5. This workhorse alloy ensures outstanding mechanical properties, demonstrating a strength which is at least twice that of commercially pure titanium (CP-Ti) grade 2 and comparable to the strength of hardened stainless steels. In the present research, different mixtures of both milled and unmilled Cp-Ti grade 2 powder were utilized using the PM method, aiming to synthesize samples with high mechanical properties comparable to those of high-strength alloys such as Ti6Al4V. The results showed that the fine nanoparticles significantly enhanced the strength of the material, while in several cases the material exceeded the values of the Ti6Al4V alloy. The produced sample exhibited a maximum compressive yield strength (1492 MPa), contained 10 wt.% of fine (milled) particles (average particle size: 3 μm) and was sintered at 900 °C for one hour. Full article

Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM^® software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525–550 °C/550–600 °C/600–650 ° C/650–700 °C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600–650 °C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values. Full article