Search Results (38)

In this study, solid particle erosion tests were conducted to evaluate the resistance of AISI 4340 (EN24) and 8620 alloy steels against silicon carbide (SiC). These steels were selected due to their high hardness, yield strength (σ_y), ultimate tensile strength (σ_uts) and elongation (%), which are significant parameters, influencing wear resistance. An erosion rig based on the ASTM G76-95 standard was used to perform the testing. Tests were carried out using different impact angles, 30°, 45°, 60° and 90°, with a particle velocity of 24 ± 2 m/s. The abrasive flow rate was 0.7 ± 0.5 g/min and the temperature was between 35 °C and 40 °C. Characterization techniques such as SEM were employed to identify the chemical composition of AISI 4340 and AISI 8620 steels and optical microscopy to determine the morphology of SiC abrasive particles. In addition, the SiC particle size was between 350 and 450 µm; it was determined by the particle size distribution technique. SEM micrographs were obtained to classify the wear mechanisms, characterized by micro-cutting, micro-ploughing, grooves, pitting actions and embedded particles on the surface at 30° and 90°. The results showed that AISI 8620 steel exhibited higher erosion resistance than AISI 4340 steel. Finally, AFM was used to evaluate the roughness variations before and after erosion tests, specifically in the central zone of the wear scars at 30° and 90° for both materials. Full article

AISI 4340 steel has applications in gun barrels, where the surface quality of the barrel is the prime factor. This study explores the application of a machine learning (ML) approach to optimize the precision turning of an AISI 4340 steel alloy using both conventional and wiper tool nose inserts under varying cutting parameters, such as cutting speed, depth of cut, and feed rate. The analytical framework integrates experimental machining data with computational algorithms to predict key output parameters: surface roughness (Ra) and material removal rate (MRR). A Multi-Objective Optimization based on Ratio Analysis (MOORA) method is used for data normalization. Particle swarm optimization (PSO) further refines the process by optimizing the input parameters to achieve superior machining performance. Results show that under optimized conditions, a 118 m/min cutting speed, 0.22 mm depth of cut, and 0.2 mm/rev feed, wiper inserts provide a 50% improvement in Ra compared to conventional inserts, highlighting their potential for enhancing both productivity and efficiency. At the suggested setting, the surface roughness values are 0.59 µm for wiper inserts and 1.30 µm for conventional inserts, with a material removal rate of 4996.96 mm³/min. The developed empirical model serves as a powerful tool for improving precision hard-turning processes across manufacturing sectors. The present work employs the XGBoost model of ML along with MOORA and PSO to predict and optimize machining outcomes, advancing hard-turning practices by delivering quantifiable improvements in surface quality, material removal rate, and operational efficiency. Full article

The effects of laser powder bed fusion (LPBF) parameters, such as power (200 to 350 W) and scan speeds (from 200 to 2000 mm/s), on the microstructure and mechanical properties of high-strength, low-alloy (HSLA) AISI 4340 steel were examined. A wide range of volumetric energy density (VED) between 93 and 162 J/mm³ produced samples with relative densities greater than 99.8%. The optimal parameter set was identified with laser power = 200 W, scan speed = 600 mm/s, hatch spacing = 0.12 mm, and slice thickness = 0.03, corresponding to VED = 92.6 J/mm³. Scanning electron microscopy revealed a predominantly martensitic microstructure for all processing parameters examined, although X-ray diffraction revealed the minor presence of retained austenite within the as-fabricated 4340 steel. Using the optimized LPBF parameters, the as-fabricated 4340 steel exhibited a yield strength of 1317 MPa ± 16 MPa, ultimate tensile strength of 1538 MPa ± 22 MPa, and 18.6 ± 1% strain at failure. These are similar to wrought 4340 steel quenched and tempered between 400 and 600 °C. Full article

The cutting force exerted on steel bars plays a crucial role in determining tunneling parameters for shield tunneling, especially when cutters are used to cut through existing pile foundations. This research focuses on the cutting force during the initial phase of the cutting process. Using 2D finite element analysis, this study examines the early stage of orthogonal cutting with negative rake angle cutters, exploring the formation of a slip plane mode. By combining slip line theory with the shear band model, a computational model is developed to calculate the cutting force for negative rake angle cutters when cutting a circular steel bar cross-section at various depths. In addition, with the incorporation of the Johnson–Cook model, this study models cutting forces under various conditions, taking into account factors such as material strength, strain rate sensitivity, and temperature effects. The steels studied include AISI 1040, AISI 4340, and AISI 304, which are commonly used in construction, with attention given to how their mechanical properties, such as strength and hardness, affect the cutting forces. While this study acknowledges the steels’ manufacturing conditions, the primary focus remains on the cutting process and its impact on force predictions. The model’s calculated horizontal cutting force is compared to numerical simulations, showing a maximum absolute error of 33.85% and an average error of 14.23%. The vertical cutting force calculations are less accurate, with a maximum error of 64.2% and an average error of 14.06%. The analysis further reveals that chip accumulation significantly impacts the horizontal cutting force, while the variation in average stress along the slip line has a smaller effect. This study also examines how factors like material properties, initial temperature, low friction coefficients, and steel bar radius contribute to the model’s accuracy and reliability. Full article

Hard turning is a precision machining process used to cut materials with hardnesses exceeding 45 HRC using single-point tools. It offers an efficient alternative to traditional grinding for finishing operations in manufacturing. This paper explores the machinability of hardened AISI 4340 steel for a hard turning process utilizing dry and cryogenic (Cryo) plus minimum quantity lubrication (MQL) (Cryo+MQL) techniques, focusing on critical machinability aspects such as cutting force, surface roughness, and tool life. The orthogonal dry turning was performed with a cutting speed (V) ranging from 300–400 m/min, a feed rate (f) between 0.05 and 1 mm/rev, and a depth of cut (doc) from 0.1 to 0.3 mm. A statistical analysis of the obtained results revealed that the feed rate was the most influential parameter, contributing 50.69% to the main cutting force and 80.03% to surface roughness. For tool life, cutting speed was identified as the dominant factor, with a contribution rate of 39.73%. Multi-objective optimization using Grey relational analysis (GRA) identified the optimal machining parameters for the hard turning of AISI 4340 alloy steel as V = 300 m/min, f = 0.05 mm/rev, and doc = 0.1 mm. The Cryo+MQL technique was subsequently applied to these parameters, yielding significant improvements, with a 48% reduction in surface roughness and a 184.5% increase in tool life, attributed to enhanced lubrication and cooling efficiency. However, a slight 4.6% increase in cutting force was observed, likely due to surface hardening induced by the low-temperature LN₂ cooling. Furthermore, reduced adhesion and tool fracture on the principal cutting edge under Cryo+MQL conditions justify the superior surface quality and extended tool life achieved. This research highlights the industrial relevance of hybrid lubrication in addressing challenges associated with hard turning processes. Full article

This study investigated the thermophysical properties of TWIP steel with respect to grain size. The coefficient of thermal expansion (β) of TWIP steel was approximately 22.4 × 10⁻⁶ °C⁻¹, and this value was hardly affected by the grain size. Therefore the density of TWIP steel was also unaffected by grain size within the tested range. The β in TWIP steel was higher than that of plain carbon steels (13–15 × 10⁻⁶ °C⁻¹) such as interstitial free (IF) steel and low-carbon steel, and stainless steels (18–21 × 10⁻⁶ °C⁻¹) such as X10NiCrMoTiB1515 steel and 18Cr-9Ni-2.95Cu-0.58Nb-0.1C steel. The specific heat capacity (c_p) increased with temperature because the major factor affecting c_p is the lattice vibrations. As the temperature increases, atomic vibrations become more active, allowing the material to store more thermal energy. Meanwhile, c_p slightly increased with increasing grain size since grain boundaries can suppress lattice vibrations and reduce the material’s ability to store thermal energy. The thermal conductivity (k) in TWIP steel gradually increased with temperature, consistent with the behavior observed in other high-alloy metals. k slightly increased with grain size, especially at lower temperatures, due to the increased grain boundary scattering of free electrons and phonons. This trend aligns with the Kapitza resistance model. While TWIP steel with refined grains exhibited higher yield and tensile strengths, this came with a decrease in total elongation and k. Thus, optimizing grain size to enhance both mechanical and thermal properties presents a challenge. The k in TWIP steel was substantially lower compared with that of plain carbon steels such as AISI 4340 steel, especially at low temperatures, due to its higher alloy content. At room temperature, the k of TWIP steels and plain carbon steels were approximately 13 W/m°C and 45 W/m°C, respectively. However, in higher temperature ranges where face centered cubic structures are predominant, the difference in k of the two steels became less pronounced. At 800 °C, for example, TWIP and plain carbon steels exhibited k values of approximately 24 W/m°C and 29 W/m°C, respectively. Full article

Tool wear in machining is inevitable, and determining the precise moment to change the tool is challenging, as the tool transitions from the steady wear phase to the rapid wear phase, where wear accelerates significantly. If the tool is not replaced correctly, it can result in poor machining performance. On the other hand, changing the tool too early can lead to unnecessary downtime and increased tooling costs. This makes it critical to closely monitor tool wear and utilize predictive maintenance strategies, such as tool condition monitoring systems, to optimize tool life and maintain machining efficiency. Acoustic emission (AE) is a widely used technique for indirect monitoring. This study investigated the use of Short-Time Fourier Transform (STFT) for real-time monitoring of tool wear in machining AISI 4340 steel using carbide tools. The research aimed to identify specific wear mechanisms, such as abrasive and adhesive ones, through AE signals, providing deeper insights into the temporal evolution of these phenomena. Machining tests were conducted at various cutting speeds, feed rates, and depths of cut, utilizing uncoated and AlCrN-coated carbide tools. AE signals were acquired and analyzed using STFT to isolate wear-related signals from those associated with material deformation. The results showed that STFT effectively identified key frequencies related to wear, such as abrasive between 200 and 1000 kHz and crack propagation between 350 and 550 kHz, enabling a precise characterization of wear mechanisms. Comparative analysis of uncoated and coated tools revealed that AlCrN coatings reduced tool wear extending tool life, demonstrating superior performance in severe cutting conditions. The findings highlight the potential of STFT as a robust tool for monitoring tool wear in machining operations, offering valuable information to optimize tool maintenance and enhance machining efficiency. Full article

AISI 4340 is a medium-carbon low-alloy steel that has gained distinctive attention due to its advanced properties including high strength, high toughness, and heat resistance. This has led to its commercial usage in a wide variety of industries such as construction, automotive, and aerospace. AISI 4340 is usually machined in a hardened state through a hard-turning process, which results in high heat generation, accelerated tool wear, low productivity, and poor surface quality. The application of high-speed machining helps improve the material removal rate and surface finish quality, yet the elevated temperature at the cutting zone still poses problems to the tool’s lifespan. Apart from using advanced cutting tool materials, which is costly, researchers have also explored various cooling methods to tackle the heat problem. This paper presents a review of a sustainable cooling method known as minimum quantity lubrication (MQL) for its application in the high-speed turning of AISI 4340 steel. This study is centered on high-speed turning and the application of MQL systems in machining AISI 4340 steel. It has been observed that the hard part turning of materials with a hardness exceeding 45 HRC offers advantages such as improved accuracy and tighter tolerances compared to traditional grinding methods. However, this process leads to increased temperatures, and MQL proves to be a viable alternative to dry conditions. Challenges in optimizing MQL performance include fluid penetration and lubrication effectiveness. Full article

To curtail the negative effects of traditional flood machining, dry cutting using carbide tools has emerged as a prominent alternative for manufacturers, owing to its low cost and phenomenal surface qualities. In line with this view, high-speed machining of high-strength AISI 4340 alloy steel was carried out using multilayer Al₂O₃/TiCN-CVD and TiAlN/AlCrN-PVD carbide tools in a dry environment. The experimental scheme was adopted, as per Taguchi’s L₁₈ orthogonal array, to investigate the two most crucial machinability aspects, namely tool life and surface roughness. An analysis of variance (ANOVA) was performed on the obtained data, and it was inferred that the feed rate exhibited the strongest effects on both the tool life and surface roughness, with corresponding percentage contributions of 46.22% and 68.96%, respectively. The longest tool lives of 14.75 min and 10.08 min were obtained at a low cutting speed and feed rate for CVD and PVD tools, respectively. However, the lowest surface roughness of 0.276 µm and 0.307 µm was achieved at a high cutting speed and low feed rate for PVD and CVD tools, respectively. The evolution of tool wear, studied through the microscopic images of the worn tools, revealed that a high cutting speed and feed rate accelerated the flank wear for both types of tools. Nevertheless, the CVD tool exhibited better results due to the thick and effective Al₂O₃/TiCN coating layer, which protected the carbide substrate against thermal–mechanical loads. Moreover, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) performed on the worn tools revealed that adhesion, oxidation, diffusion, and abrasion were the main wear mechanisms for both types of tools. Full article

This study investigates the impact of material parameters such as yield strength (S_y), Young’s modulus (E), and tangent modulus (T) on the safety factor (SF) of autofrettaged cylinders under 400 MPa working pressure, considering the three scenarios: no machining, internal machining, and external machining. Finite element (FE) simulations were conducted based on the Taguchi experimental design and converted into signal-to-noise (S/N) ratios to determine the optimal settings. ANOVA was utilized to evaluate the significance and percentage contributions of each factor. The analysis indicated that S_y is the most influential parameter on SF, contributing approximately 98.20% across all scenarios, including no machining, internal machining, and external machining. The contributions of E and T were minimal, but T had a slightly greater effect than E. The analytical validation of the FE model showed good agreement, with a maximum deviation of 4.37% for no machining, 4.75% for internal machining, and 5.20% for external machining. Regression analysis further confirmed the high prediction capability of the model, validated using AISI 4340 steel. The study concludes that internal machining results in higher residual stress loss compared to external machining. Overall, the analytical method tends to provide lower SF values than the numerical method, highlighting its conservative nature. Full article

In this study, novel surface engineering strategies to improve the wear performance of AISI 4340 were investigated. The strategies were as follows: (i) NiP deposition on a previously nitrided steel substrate, followed by NiP interdiffusion heat treatment at either 400 °C or 610 °C (referred to as duplex treatment); (ii) the deposition of AlCrN PVD coating on NiP layers on a previously nitrided steel substrate (referred to as triplex treatment). Prior to the deposition of AlCrN, the NiP was subjected to the interdiffusion heat treatment at either 400 °C or 610 °C. These strategies were compared with the performance of the AlCrN coating directly applied on nitrided steel. To characterize the microstructural features of each layer, X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) analysis were conducted. We also carried out mechanical and tribological behavior assessments. The tribological tests were carried out using a ball-on-disc tribometer under a constant load of 20 N and a tangential speed of 25 cm/s; cemented carbide spheres with a diameter of 6 mm were the counterpart body. The friction coefficient was continuously monitored throughout the tests. The results reveal that the wear mechanism for the AlCrN coating is predominantly oxidative. The most wear-resistant surface architecture was the one comprising AlCrN over the NiP layer subjected to interdiffusion heat treatment at either 400 °C or 610 °C. Full article

Materials with enhanced wear resistance are constantly in high demand. Nickel-based self-fluxing materials deposited by atmospheric plasma spraying (APS) have feasible wear resistance performance. This study aimed to evaluate the results of a nickel-based self-fluxing alloy coating deposited on AISI 4340 steel substrate using APS. Additionally, the temperature at which the remelting process achieved optimal results was investigated. The AISI 4340 steel substrate samples were coated with a self-fluxing NiCrBSiCFe powder by APS. The post-coating remelting process was performed in a controlled atmosphere tube furnace at 900, 1000, and 1100 °C. Microstructural analysis was carried out by Scanning Electron Microscopy (SEM) before and after remelting. The estimated porosity of the as-sprayed sample was 3.28%, while the remelted coating sample at 1100 °C had only 0.22% porosity. Furthermore, a microhardness measurement was conducted, and the best condition yielded an average value of 750 HV_0.5. Tribological tests were performed to evaluate the coefficient of friction and wear rates, revealing that at 1100 °C, the as-sprayed coating had a wear rate of 9.16 × 10⁻⁵ [mm³/(N*m] and the remelted coating had 4.106 × 10⁻⁵ [mm³/(N*m]. The wear-loss volume was determined to be 14.1 mm³ for the as-sprayed coating sample and 3.6 mm³ for the remelted coating at 1100 °C. Full article

Optimizing input parameters not only improves production efficiency and processing quality but also plays a crucial role in the development of green manufacturing engineering practices. The aim of the present study is to conduct a comparative evaluation of the cutting performance and machinability process during the turning of AISI 4340 steel under different cooling conditions. The study analyzes cutting operations during turning using dry, minimum quantity lubrication, and nano- minimum quantity lubrication. As control parameters in the experiments, three different cooling types, cutting speeds (100, 150, 200 m/min), and feed rate (0.1, 0.15, 0.20 mm/rev) levels were applied. The experimental results show that the optimal output values are found to be Vb = 0.15 mm, Ra = 0.81µm, 88.1 dB for sound intensity and I = 4.18 A for current. Moreover, variance analysis was performed to determine the effects of input parameters on response values. Under dry, minimum quantity lubrication, and nano-minimum quantity lubrication processing conditions, parameters affecting tool wear, surface roughness, current by the motor shaft, and sound level were examined in detail, along with the chip morphology. The responses obtained were optimized according to the Taguchi S/N method. As a result of optimization, it was concluded that the optimum values for cutting conditions were nano-minimum quantity lubrication cooling and V = 100 m/min, f = 0.1 mm/rev cutting. Finally, it was observed that there was a 13% improvement in tool wear, 7% in current, 9% in surface roughness, and 8% in sound intensity compared to the standard conditions. In conclusion, it was determined that nano-minimum quantity lubrication with the lowest level of cutting and feed rate values provided the optimum results. Full article

In this study, FeCrMoNbB (140MXC) and FeCMnSi (530AS) coatings were simultaneously projected on the substrate AISI-SAE 4340 using the electric wire arc spraying technique. The projection parameters, such as current (I), voltage (V), primary air pressure (1st), and secondary air pressure (2nd), were determined using the experimental model Taguchi L9 (3⁴⁻²). Its main purpose is to produce dissimilar coatings and to evaluate the effect of the surface chemical composition on the corrosion resistance in the mixture of 140MXC-530AS as commercial coatings. Three phases were considered to obtain and characterize the coatings: Phase 1: Preparation of materials and projection equipment; Phase 2: Coatings production; and Phase 3: Coatings characterization. The characterization of the dissimilar coatings was carried out using the techniques of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX), Auger Electronic Spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The results of this characterization corroborated the electrochemical behavior of the coatings. The presence of B was determined with the XPS characterization technique in the mixtures of the coatings in the form of Iron Boride. Moreover, the XRD technique showed Nb in the form of FeNb as a precursor compound for the 140MXC wire powder. The most relevant contributions are the pressures, provided that the quantity of oxides in the coatings decreases with respect to the reaction time between the molten particles and the atmosphere of the projection hood; moreover, for the corrosion potential, the operating voltage of the equipment does not exert any effect since these tend to remain constant. Full article

This experimental study presents the machinability comparison of TiCN-Al₂O₃-TiN, TiAlN-TiN, and TiAlSiN coated carbide inserts in hard turning AISI 4340 steel. The primary purpose of this research is to determine the most appropriate cutting inserts in turning hardened AISI 4340 (30–40 HRC) steel considering surface roughness (Ra), cutting sound (Cs), power consumption (P), radial force (Fx), tangential force (Fy), and feed force (Fz). To fulfill this objective, the turning experiments for each tool were executed based on the Taguchi L₉ design. The comparative assessment of cutting tools revealed that the TiAlSiN coated tool exhibited superior performance compared to other tools. Machining with the TiCN-Al₂O₃-TiN coated tool showed 32.05% greater roughness than with the TiAlN-TiN coated tool, and 68.80% higher surface roughness than the TiAlSiN coated tool. The main novelty of this research is considering the cutting sound and power consumption as responses to select the most suitable cutting tools. Moreover, a novel grey-crow search hybrid was executed to perceive the optimal value of the input parameters. The optimal local value of cutting speed for the TiAlSiN coated tool was found to be 220 m/min, while for the TiCN-Al₂O₃-TiN and TiAlN-TiN tools, it was the same as 182 m/min. Considering the optimum cutting parameters, the material removal rate for TiCN-Al₂O₃-TiN, TiAlN-TiN, and TiAlSiN was found to be 639.9 mm³/min, 606.4 mm³/min, and 761.2 mm³/min, respectively. Thus, the TiAlSiN coated tool has greater MRR capability in comparison to other tools. Therefore, this leads to the conclusion that the TiAlSiN tool may be the better choice in comparison to other selected tools for turning hardened steels. Full article