Carbide Inserts Research Articles

Effects of Coated Carbide Insert on Surface Finish of Multiple Hardened EN31 Alloy Steel Using Regression, ANN, and RSM

Objectives: Surface finish plays an essential role in every machining process. The current study mainly focuses on multiple hardened EN31 alloy steel, using various machining parameters and optimizing using regression, ANN, and RSM. Methods: The experimentation was performed using a commercial CNC machine and a surface roughness tester, using machining parameters such as tool nose radius (re), cutting speed (v), feed (f), depth of cut (d), and hardness (H) of the material ranging from 0.4 to 1.2 mm, 160 to 260 m/min, 0.1 to 0.20 mm/rev, 0.05 to 0.15 mm, and 45 to 49 HRC, respectively. Findings: The study revealed that cutting speed and feed rate significantly affect the surface finish, followed by tool nose radius. With the help of optimization techniques, the surface roughness predicted through RSM was 99.91%, followed by Regression and ANN. The contour plot predicts Ra using the best possible combinations of machining parameters. Novelty: The current research compares the surface finish results of multiple hardened EN31 alloy steels predicted through regression, RSM, and ANN with experimental values. The generated correlations will undoubtedly assist researchers in determining surface finish for the defined ranges of machining parameters. Keywords: Hard Turning, Coated Carbide, EN31 Steel, Surface Roughness, Optimization, RSM

Chip formation analysis during dry turning of C45 steel

Machining is a material removal process that creates surfaces through chip formation using a cutting tool. The morphology of the chips and the mechanisms governing their formation directly affect the quality of machined parts. This experimental study examines chip formation mechanisms in the dry turning of C45 steel under various cutting conditions, utilizing coated carbide inserts. Machining performance was evaluated based on key chip morphology parameters, including shape, length, thickness, and volume. The results show that increasing cutting speed (Vc) produces shorter, thicker chips without significantly altering their predominantly helical shape. A higher feed rate (f) maintains the tangled ribbon form of the chips but leads to longer chip production. Additionally, changes in the depth of cut (ap) create instabilities that result in varied chip morphologies, including long tubular, short helical, and elementary forms. As the depth of cut increases, chips become shorter and thinner. These findings provide valuable insights into the material's deformation and fracture mechanisms, enhancing our understanding of chip formation and its impact on the efficiency of dry turning operations on C45 steel.

Investigation of Nano Cutting Oil Effects on Hard Milling Under Minimum Quantity Lubrication

The presented work aims to investigate minimum quantity lubrication (MQL) using cutting oil with/without Al2O3 nanoparticles for hard milling of 60Si2Mn steel (50-52 HRC) using carbide inserts. The effects of three different types of based cutting oils including emulsion, soybean oil and rapeseed oil on surface roughness Ra, Rz and tool life were studied and investigated. The experimental results show that the use of Al2O3 nano cutting oil has improved lubrication capability compared to base cutting oil, contributing to improve machined surface quality and tool life. Al2O3 emulsion-based nanofluid exhibited the best performance among the three surveyed oils, followed by rapeseed oil and finally soybean oil. Furthermore, the cutting speed of the carbide inserts was improved and the tool life was significantly increased with the help of nano cutting oil due to the improvement in lubrication effects in the cutting zone, thereby helping to reduce cutting forces and cutting heat.

Формообразование задней поверхности многогранных твердосплавных пластин на шлифовально-заточных станках с ЧПУ

The purpose of the work is to obtain a mathematical expression for calculating the coordinates of the workpiece center in relative movements in accordance with the third shap ing scheme. A certain algorithm for modeling the third kinematic scheme of forming a part with a tool can be implemented by means of an automatic design system. It is noted that the main shaping movements – translational in the direction of the X axis, rotational around the B and C axes are controlled by a numerical control system. This method of grinding makes it possible to process the rear surfaces of plates of any shape, including plates with a clearance angle on the edges and tops. The models of the tool I and the workpiece are shown in the ini tial II and one of the intermediate positions III, the models of the workpiece and the tool for their various relative positions. A relationship has been established between the corresponding translational and rotational motion of the workpiece. The obtained dependences were used in the preparation of control programs on the VZ-700F4 machine tool for grinding multifaceted carbide inserts along the contour.

Study on tool wears in turning Al2219, unhybrid and hybrid metal matrix nano composites by CCD design of experiment

In this article, Aluminum (Al2219) as a matrix, and particles of n-B4C and MoS2 were chosen as reinforcements. By means of the stir casting technique, the unhybrid and hybrid nano metal matrix composites were prepared. The turning experiment was done through CCD design of experiment with TiN coated carbide insert using a Computer Numerically Controlled Lathe. Also, for turned inserts tool wear measurement was done using a Mitutoyo profile projector with digital readout. By ANOVA the significant contribution for tool wear of each parameter can be identified and the confirmation test is performed in sort to validate the tool wear results. Furthermore, the formation of chips during turning nano MMCs (unhybrid and hybrid) are studied for different feed rates ( f) and cutting speeds ( v) at 0.5 mm constant depth of cut. The outcome showed that both increases in cutting speed and feed rate increase the tool wear. For Al 2219, unhybrid and hybrid nano metal matrix composites feed rate is the important factor. The value of tool wear of the Al2219 matrix is minimal and for unhybrid nano composite is maximum. The leading wear mechanism in unhybrid nano composite is abrasion. Moreover, with the addition of 2%MoS2 in the hybrid nanocomposite the tool wears is decreased. The development of Build Up Edge (BUE) was seen on the flank face of the cutting tool for hybrid nanocomposite at 0.5 mm depth of cut, (v = 114.64 m/min) and (f = 0.441 mm/rev). The obtained % error among the modeled and experimental values is <5% and it is well within the limit. The analysis of chip formation was studied for nanocomposites at lower as well as higher feed rates, cutting speeds, and constant depth of cut during turning.

COMPARATIVE ANALYSIS OF MACHINING AISI 1020 MILD STEEL USING MINERAL OIL BASED AND NEEM SEED OIL BASED CUTTING FLUIDS

Retaining workpiece dimensional accuracy and quality, elongated tool life, minimal surface roughness, minimum tool wear and overall high productivity in metal cutting (machining) operations are areas the cutting fluids plays pivotal role. This study focuses on surface roughness, cutting temperature and tool wear by evaluating their optimal factor effectiveness during turning of AISI 1020 Mild Steel using an environmentally friendly cutting fluid. Serious concern has been raised about the non-biodegradable and non-recyclable of the conventional (mineral based) cutting fluid and this prompted the renewal of research interest in environmentally friendly cutting fluids such as the neem seed oil based cutting fluid. The locally sourced neem seed oil (NSO) was characterized by investigating the physiochemical properties and the fatty acid composition (FAC). Surface roughness, cutting temperature and tool wear were minimized during turning of AISI Mild Steel using coated carbide insert with the evaluation compared with the mineral oil based cutting fluid. Taguchi experimental design was employed during the optimization. The formulated fluid showed 8.35 pH value, 0.896 m 2/s viscosity, good resistance to corrosion, stable and milkfish colouration. The S/N ratio for NBCF and MBCF are 800 CS, 0.4 FR and 0.6 doc; and 800 CS, 0.4 FR and 0.6 DOC respectively with R-sq and R-sq(pred) values as 98.37% and 97.38 under the NBCF and lastly 94.53% and 91.25% under the MBCF for surface roughness respectively. For cutting temperature and tool wear, S/N ratios show A 1B 1C 1 under both NBCF and MBCF. The findings shows that the neem seed oil based cutting fluid outperform the mineral oil-based fluid under the same cutting parameters and this has contributed to the science of machining.

Investigations on the machinability performance of Al2O3/TiCN CVD coated carbide tools in sustainable high-speed hard-turning of AISI 4340 alloy steel

Abstract This study investigates the effectiveness of CVD coated carbide inserts in turning hardened AISI 4340 steel at high-machining speed V=300,350m/min under sustainable dry cutting environment. Experiments were executed in accordance to Taguchi L4 orthogonal array and crucial machinability aspects tool life, tool wear progression and mechanism, cutting force, and surface roughness were evaluated in detail. The results of this study revealed that Al2O3/TiCN coating successfully inhibited the faster progression of tool wear at low cutting speed (300m/min), feed rate (0.05mm/rev) and depth of cut (0.1mm), thus delivering the highest tool life of 19.25 min and lowest cutting force of 76.8 N. However, better surface finish of 0.305µm was obtained at high cutting speed (350m/min), low feed rate (0.05mm/rev), and high depth of cut (0.1mm). Nevertheless, at high cutting speed (350 m/min) and feed rate (0.1 mm/rev), involvement of intense thermal-mechanical effects suppressed the effectiveness of coating and tool completed its useful life at 9.24 min. Severe flaking on the cutting edge was observed at high machining parameters. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed that adhesion, oxidation, and small scale chipping and abrasion were the primary wear mechanisms attributing in competing the tool life criteria (Vb=300µm) in all cutting conditions. Furthermore, it was established that the cutting force and surface roughness increased with increasing tool flank wear due to coating delamination, material adhesion and tool chipping. This research emphasizes the significant potential of adopting Al2O3/TiCN coated carbide inserts for high-speed industrial hard-turning of AISI 4340 steel.

Performance assessment of the multi-nozzle injection MQL system for cleaner machining of hardened AISI D2 steel concerning power consumption

ABSTRACT Sustainable hard machining is a pressing need in manufacturing industries for techno-social, economic and environmental benefits to machine difficult-to-cut materials. Thus the present study investigates finish turning of hardened AISI D2 steel using a MTCVD coated carbide insert (TiN-TiCN-Al2O3) with geometry CNMG120408FW and grade WK05CT under a multi-nozzle MQL system using LRT 30 mineral oil (50 ml/hr flow rate, 6 bar compressed air pressure, 30 mm nozzle distance from tool tip) for minimal quantity lubrication at both the rake and flank zones for assessment of machinability. Flank wear lies between 0.79 and 0.155 mm and within the failure criterion limit of 0.2 mm. Arithmetic surface roughness trials have been within 0.361–0.877 microns and within the 1.6 microns acceptable range. The cutting temperature has been between 80.7°C and 226.9°C and even below 200°C in the majority of runs. The cutting power lies within 0.432kW–0.804kW. The optimal parametric combination has been found to be d=0.1 mm, f=0.05 mm/rev and v=80 m/min respectively and improvement has been observed over dry cutting. RSM models are found to be statistically significant. Application of multi-nozzle MQL in machining of hardened steel outperformed through machinability assessment and may be adopted in shopfloor for sustainability..

Novel Approach to Monitoring the Surface Integrity of Aluminum 5052 Using Sound and Vibration Signals during Turning with Titanium-Coated Carbide Inserts

Novel Approach to Monitoring the Surface Integrity of Aluminum 5052 Using Sound and Vibration Signals during Turning with Titanium-Coated Carbide Inserts

Machinability evaluation of inconel 600 by cryo-processed carbide inserts

ABSTRACT This work investigates the characterization of a cryo-processed AlTiN-coated tool and its turning characteristics for Inconel 600. The microhardness was enhanced by 3.68% under cryo-treatment when compared with the as-received condition of the inserts because of the wear-protective coating formed on the surfaces of the cutting tool. This was confirmed through EDS elemental analysis of carbon element growth and change in chemical composition, as well as XRD phase analysis. Next, this work studied the influence of cryo-treated inserts on roughness and mechanism of wear during turning Inconel 600 using varying cutting velocities (37, 60, and 100 m/min) under dry conditions. The output responses revealed that the use of cryo-treated tools reduced the roughness of the product by 11–27% and the rate of tool wear when compared with the untreated conditions. Due to these enhanced properties with cryo-treated conditions, it remains a suitable cutting tool for a significant contribution to sustainable machining toward dry cutting of aerospace alloys.

Prediction of specific cutting energy consumption in eco-benign lubricating environment for biomedical industry applications: Exploring efficacy of GEP, ANN, and RSM models

This study emphasizes the criticality of measuring specific cutting energy in machining Hastelloy C276 for biomedical industry applications, offering valuable insights into machinability and facilitating the optimization of tool selection, cutting parameters, and process efficiency. The research employs artificial intelligence-assisted meta-models for cost-effective and accurate predictions of specific cutting energy consumption. Comparative analyses conducted on Hastelloy C276, utilizing a TiAlN-coated solid carbide insert across various media (dry, MQL, LN2, and MQL+LN2), reveal the superiority of hybrid LN2+MQL in reducing specific cutting energy consumption. Subsequently, the analysis of variance underscores the cutting speed as the most influential parameter as compared to other inputs. Finally, a statistical evaluation compares the Gene Expression Programming (GEP) model against the Artificial Neural Network (ANN), and Response Surface Methodology model, demonstrating the superior predictive performance of the GEP meta-model. The GEP model demonstrates validation results with an error range of 0.25%–1.52%, outperforming the ANN and RSM models, which exhibit an error range of 0.49%–8.33% and 2.68%–10.18%, respectively. This study suggests the potential integration of contemporary intelligent methodologies for sustainable superalloy machining in biomedical industry applications, providing a foundation for enhanced productivity and reduced environmental impact of surgical instrument and biomedical device machining.

Tribological behavior of Inconel 718 alloy when cutting with a carbide insert prepared using the SPS technique under dry and lubricated sliding conditions

The paper presents the results of the wear mechanisms research of uncoated cutting inserts of tungsten carbides (WC) without Co matrix made by the SPS technique in finish turning Inconel 718. The tests were performed with the application of coolant/lubrication and in dry condition. Moreover, morphology of the obtained chips was evaluated, as well as the topography of the machined surface. The coefficient of the chip shortening and the frequency of the chip vibration during machining were also determined. For the inserts used in the test, the friction coefficient, µ, has also been determined. Significant differences in the wear of the tool flank face for various feed speeds where the dominating sign was abrasive wear and oxidation. It has been found that the dominating mechanism of the wear of the rake face was adhesion of the material under machining whose surface exceeded beyond the field of the chip cross section regardless of value of feed and machining conditions (machining with cooling or without cooling). SEM analysis has shown that, in addition to adhesion, the major symptom of wear at lower feed values was delamination of the inserts; at higher feeds the major symptom of wear was chipping growing with the increase of feed. Machining with SPS inserts without the cooling and lubricating liquid has generated surfaces with lower average values of the roughness heights, Sa. It has been found that the chip shortening coefficient depends on the conditions of cooling/lubrication and that it decreases with the increase of the feed. The chip vibration frequency shows higher values in dry machining.

The performance of grooved turning tools under distinct cooling environments

This work investigates the performance of modified tungsten carbide inserts when turning supermartensitic stainless steel with cutting fluid and/or air jet applied in two directions: either cutting fluid under high pressure or compressed air under low pressure supplied on the back of the chip (through a hole produced near the principal cutting edge), together with either cutting fluid or compressed air, both under low pressure, directed at the clearance face. Tool performance is evaluated by means of the principal cutting force, temperature distribution (using FEM), visual evaluation of the rake face, morphology of the chips and the quality of the machined surface. The findings indicate that the groove reduces the cutting force when dry cutting. Cutting fluid applied under low pressure at the clearance face is more efficient in decreasing both the cutting force and chip temperature than cutting fluid at high pressure supplied at the back of the chip. A chrome oxide layer is formed on the chip when air jet is applied, thus leading to an unfavorable cutting condition. The simultaneous application of cutting fluid under high pressure to reach the back of the chip and compressed air supplied through the clearance face provides the best surface quality.

Evaluation of the turning parameters of AISI 5115 steel in dry and MQL cutting environments with the use of a coated carbide cutting insert: An Experimental Study

This study investigates the effects of cutting parameters on turning AISI 5115 steel in both dry and MQL environments using a coated carbide insert. The cutting parameters are determined using a full factorial design. A comprehensive full factorial experimental design was executed in order to investigate the effect of cutting parameters, including cutting speed, feed rate, and depth of cut, on surface roughness, cutting force and cutting temperature. Following the completion of the turning trials, surface roughness measurements were meticulously recorded. Also cutting force and cutting temperature were measured. The results of the study indicated that the most significant influence on surface roughness is exerted by the feed rate. Moreover, the impact of the depth of cut became more significant as the cutting speed decreased. While the surface roughness increased by 23% in the dry environment due to the increased feed rate at low cutting speed, the increase in the MQL environment was 32%. The cutting temperature is influenced by a number of factors, including the cutting parameters and the material properties. The maximum temperature for turning in the MQL environment was 381°C compared with an average cutting temperature of 430°C in dry machining conditions. The application of high-speed cutting in a dry cutting environment was found to result in a 10% increase in cutting temperature. The influence of cutting speed on the outcome was less pronounced in the MQL environment. At high cutting speeds and low parameter values in the MQL environment, the cutting force decreased by 75% in contrast to the low cutting speeds and high cutting parameters in the dry environment. The optimal cutting conditions for minimising cutting force were identified in the MQL environment, characterised by high cutting speeds and low feed rates.

Cutting performance of coated carbide inserts in hard turning of hardened AISI D2 cold work tool steels

Hard turning is a dry machining process that is often preferred over conventional grinding to achieve final dimensions on a workpiece that is already in a hardened state. In this study, hard turning process was preferred due to its numerous advantages such as low machining time, low total production cost, better surface integrity and better environmental effect because of elimination of coolant. The hardness of the material being machined can cause significant wear on the cutting insert. This study investigated the effects of TiCN + Al2O3 + TiN coated carbide inserts on the machining process of hardened AISI D2 cold work tool steel. The temperature of cutting zone, tool wear, flank wear, surface roughness, hardness, chip formation, and microstructure were all measured as a function of cutting speed. A real-time monitoring system was used to measure wear at the tool edge and temperature on the flank face of the cutting insert. The results showed that increasing cutting speed from 100 to 157 m/min led to higher cutting edge temperatures (from 585 to 713°C, respectively) and lower tool flank wear (from 14.6 to 10.8µm, respectively). The multilayer coated carbide inserts produced a ground-quality surface finish with a roughness value of 0.10–0.15 μm. Achieving high cutting edge temperature, low tool flank wear and fine-grinding quality surface finish underscore the effectiveness of using multilayer-coated carbide inserts in the hard turning of hardened steels.

Prediction of power consumption and its signals in sustainable turning of PH13-8Mo steel with different machine learning models

Due to extensive distribution and huge demand of energy efficient processes, the energy-saving of machining processes draws more and more attention, and a significant variety of methods have evolved to prognosis or optimise the energy consumption in machining operations. Similarly, the estimation of power consumption-cutting conditions relationships is of great importance for optimizing processing costs and for cleaner machining. Compared to traditional methods, machine learning (ML) approach is one of the effective analysis options to model machinability indicators such as cutting force, tool wear, power consumption and surface quality. In this study, PH13-8Mo stainless steel was machined with coated carbide inserts using primarily Dry, MQL, nano-Graphene + MQL, nano-hBN + MQL, Cryo, Cryo + MQL cutting environments. Power consumption and its signals during milling were measured and different machine learning models were applied to estimate the Pc. To develop the Pc model based on the ML algorithm, 70% of the power consumption data is reserved for training and 30% for testing. In all cutting environments, power consumption increased by an average of 3.14% as feed speed increased. The reduction in Pc compared to the dry cutting was calculated as an average of 2.2%, 3.17%, 2.57%, 4.88% and 5.45% for MQL, nano-Graphen + MQL, nano-hBN + MQL, Cryo, Cryo + MQL, respectively. It is seen that the developed prediction model can reflect the power consumption-parameter relationships at high accuracy.

Cryogenic and conventional milling of AZ91 magnesium alloy

Use of magnesium is the need of the hour due to its low density as well as its high strength-to-weight and stiffness-to-weight ratio etc. This study focuses on the effectiveness of liquid nitrogen (LN2) assisted cryogenic machining on the surface integrity (SI) characteristics of AZ91 magnesium alloy. Face milling using uncoated carbide inserts have been performed under liquid nitrogen (LN2) assisted cryogenic condition and compared with conventional (dry) milling. Experiments are performed using machining parameters in terms of cutting speeds of 325, 475, 625 m/min, feed rates of 0.05, 0.1, 0.15 mm/teeth and depth of cuts of 0.5, 1, 1.5 mm respectively. Most significant surface integrity characteristics such as surface roughness, microhardness, microstructure, and residual stresses have been investigated. Behaviour of SI characteristics with respect to milling parameters have been identified using statistical technique such as ANOVA and signal-to-noise (S/N) ratio plots. Additionally, the multi criteria decision making (MCDM) techniques such as additive ratio assessment method (ARAS) and complex proportional assessment (COPRAS) have been utilized to identify the optimal conditions for milling AZ91 magnesium alloy under both dry and cryogenic conditions. Use of LN2 during machining, resulted in reduction in machining temperature by upto 29% with a temperature drop from 251.2 °C under dry condition to 178.5 °C in cryogenic condition. Results showed the advantage of performing cryogenic milling in improving the surface integrity to a significant extent. Cryogenic machining considerably minimized the roughness by upto 28% and maximised the microhardness by upto 23%, when compared to dry machining. Cutting speed has caused significant impact on surface roughness (95.33% – dry, 92.92% – cryogenic) and surface microhardness (80.33% – dry, 82.15% – cryogenic). Due to the reduction in machining temperature, cryogenic condition resulted in compressive residual stresses (maximum σ║ = -113 MPa) on the alloy surface. Results indicate no harm to alloy microstructure in both conditions, with no alterations to grain integrity and minimal reduction in the average grain sizes in the near machined area, when compared to before machined (base material) surface. The MCDM approach namely ARAS and COPRAS resulted in identical results, with the optimal condition being cutting speed of 625 m/min, a feed rate of 0.05 mm/teeth, and a depth of cut of 0.5 mm for both dry and cryogenic environments.

An Experimental Investigation of Cutting Condition Influences on Hard Milling of AISI D2 Tool Steel

The presented work aims to study the effects of cutting speed, feed rate and depth of cut on surface roughness Ra in hard milling of AISI D2 steel (58 ÷ 60 HRC) using carbide inserts. A factorial experimental design was used to evaluate the influence of input variables. The obtained results indicated that feed rate causes the most significant effect on surface roughness, whereas cutting speed and depth of cut have little influence. The interaction effects between cutting speed and depth of cut as well as between feed rate and depth of cut have the significant influences on surface roughness Ra. Moreover, the cutting speed of 92 ÷ 100 m/min, feed rate of 0.1 ÷ 0.11 mm/tooth, and cutting depth of 0.1 ÷ 0.12 mm should be recommended for reaching the smaller surface roughness Ra values, which play an important role for further studies on hard milling process.

Multiobjective Optimization of Hard Turning on OHNS Steel Using Desirability and TOPSIS Approaches

Machining hard materials with 45–48 HRC is difficult in turning operation because of the improvident cutting parameter selections for the operation. The OHNS (AISI/SAE-01–48HRC) steel is mainly preferred for the production of shafts, gears, cams, and press tools. The OHNS material was turned at a dry state using VP-coated carbide inserts. The seventeen experimental trials were designed by central composite design (CCD) with different levels of cutting parameters, like feed rate, cutting speed, and depth of cut. Design Expert-11 software desirability approach and TOPSIS (Technique for Order Preference by Simulating the Ideal Solution) were used to analyse the experimental results to obtain a single optimal solution that defines better results on metal removal rate (MRR) and surface finish (Ra). RSM solution with 81.3% desirability, the cutting speed of 60 m/min, feed rate of 0.08 mm/rev, and depth of cut 1 mm as the optimal cutting parameters; similarly, TOPSIS algorithm calculation identifies the cutting parameter combinations, such as 40 m/min cutting speed, 0.09 mm/rev feed rate, and 1 mm depth cut to enrich the quality of the machined steel; however, the desirability approach cutting parameter setting is better for the surface finish achievement, while TOPSIS solution is better to obtain significant MRR. The confirmation test results validated for the predicted values of both approaches; as such, the experimental results were maintained better convenience than the predicted one. For the optimum cutting parameter combinations, an MRR of 22.032 gm/min and surface roughness of 0.781 μm were obtained at 60 m/min cutting speed, 0.08 mm/rev feed rate, and 1 mm depth of cut.

Numerical Modeling on Ballistic Impact Analysis of the Segmented Sandwich Composite Armor System

This research delves into the design, modeling, and finite element impact analysis of the segmented sandwich composite armor system subjected to impact loading, considering different parameters such as materials to be used, armor height, and armor design configuration. Initial studies were performed to select the ideal model that will provide the best impact resistance at the least weight and with minimal fabrication requirements. Material type, thickness, and overall model configuration were defined during the initial model development period. Once the final design was defined, finite element analysis was performed using 2017 ABAQUS software to observe the performance of the model and to validate the efficiency of the chosen armor. Based on the results from the material selection and thickness validation, the optimal design with the best impact resistance was noted as 1.2 mm thick rectangular segmented silicon carbide tiles, serving as the top layer that covers the three-level gradient core composed of a titanium metal honeycomb frame filled with silicon carbide inserts, and finally a 2 mm thick glass epoxy composite layer made from four laminas in a 0/45/90/-45-degree configuration serving as the last layer of the armor.