Machining Of Ti6Al4V Research Articles

Physic-chemical analysis for high-temperature tribology of WC-6Co against Ti–6Al–4V by pin-on-disc method

To study high-temperature tribological behaviors between tools and workpieces plays an active role in the development of high-speed machining. This original work dedicated to investigate high-temperature tribological behaviors of Ti–6Al–4V/WC-6Co interaction couples at the temperature ranging 20 °C, 320 °C, 620 °C, and 920 °C, which analyzed the physic-chemical properties of coefficient of friction, tribological topography, element diffusion, phase compositions, and nano-indentation hardness. Smaller coefficient of friction was existed under the high-temperature due to softer Ti–6Al–4V serving as lubricating layers at the interface. The tribological behaviors were gradually changed by the temperature conditions, which converted mechanical into the coupled mechanical-chemical induced wear. The effects of high-temperature conditions on WC-6Co could result in a certain degree of nano-indentation hardness weakening. This work provides an in-depth understanding of tribological behaviors and failure mechanism of tool materials in machining Ti–6Al–4V.

Study of Working Medium Performance by Acoustic Emission in EDM Machining of Ti6Al4V

In electrical discharge machining (EDM), the working medium plays an important role in the material removal process. Lots of methods have been utilized to study this process, but a widely accepted explanation about this process has not been yet accomplished. In this study, the acoustic emission (AE) sensor was fixed on EDM machine to study the material removal process by observing the expansion and contraction process of gas bubble surrounding the discharge plasma. The machining performance in different working mediums was studied for Ti‐6Al‐4V machining in air, kerosene, and water‐based emulsion. Discharge in different working mediums would result in different material removal rates and surface quality. The difference of AE wave frequency domain distribution for discharge in different working mediums was studied. It was observed that the frequency of acoustic emission wave generated by discharge in different working mediums would be different. The characteristic difference of single AE wave generated by discharge in air, kerosene, and water‐based emulsion was compared. It was found that the duration time and peak amplitude of acoustic emission wave generated by discharge in different working mediums were different, and the acoustic emission wave generated by discharge in water‐based emulsion would last longer and get higher peak amplitude compared to discharge in air and kerosene. The significant difference of AE wave generated by discharge in water‐based emulsion from that in kerosene was found. Based on the acoustic emission wave observation, the special characteristic of the material removal process for discharge in water‐based emulsion was found.

Tool wear-induced microstructure evolution in localized deformation layer of machined Ti–6Al–4V

The microstructure of localized deformation layers is inevitably altered in the machining process. In this study, the microstructural evolution of localized deformation layers due to tool wear in the turning of titanium alloy (Ti–6Al–4V) was examined via analysis of the grain boundaries, crystallographic texture, and phase transformation. The machined surface exhibited strong plastic activities within the flowing region in the case of a worn tool, and additional mechanical loads caused deeper deformation because of more ranges of the softened materials. The plastic activities in the localized deformation layer were enhanced by the additional thermomechanical loads because of tool wear, causing grain distortions, elongation, and deformed grain boundaries. High-density grain boundaries were clustered in the localized deformation layer with the increase in the tool wear, and the tool wear promoted the generation of local misorientation and a corresponding gradient. With the increase in the tool wear, the percentages of small grains increased, and various degrees of refinement occurred. The texture enhancement regions indicated that the preferential deformation texture was modified by the retained shearing, where the basal texture {10–10}〈0001〉 changed to shear C fibre textures. The phase transformation was analysed from the viewpoints of the variation in the relative peak intensities and the phase volume fractions. The microstructural evolution underwent a gradual transition process, which was determined by the thermomechanical conditions associated with the tool wear. The results have great significance for optimizing the tool wear values to improve the surface integrity and provide a novel avenue for material design.

Modeling & Analysis of B4C Powder Mixed Wire EDM Process for Improving Performance Criteria of Ti6Al4V

The present investigation represents the effect of B4C powder properties on performance characteristics of Ti6Al4V material. Boron carbide has good chemical resistance, low density and non-oxide properties. Due to that, it has a great impact on powder mixed wire EDM. The machining of Ti6Al4V is very difficult by other non-conventional processes when it is considered particularly through cutting operation with desired surface quality and strong economically. In this study pulse on time, pulse off time, peak current and gap voltage are considered as input parameter and analyzed the performance characteristics such MRR and SR. B4C Powder concentration and size in the dielectric are analyzed to get significant output. The optimum result is obtained from machining condition i.e. powder size 10μm and concentration 6gm/lit as for both performances like MRR and SR while machining controllable parameters are fixed i.e. Ip=2, Ton=30 and Toff=8. The machined surface is studied through microstructure image

Experimental investigation of top burr formation in high-speed micro-milling of Ti6Al4V alloy

Miniaturization with superior quality product of super alloy is the demand of the industry. Ti6Al4V is the demanding super alloy due to its excellent material properties, although this super alloy is known for poor machinability in terms of burr formation, low tool life, and poor surface finish. Therefore, being a popular super alloy, it comes under the difficult-to-cut material. In the current work, burr formation on the machining of Ti6Al4V has been studied. Experimental investigation and characterizations of top burr formation on Ti6Al4V alloy using end milling process were carried out. A scanning electron microscopy identifies the burr formed on the machined surface. A new technique has been introduced to measure the top burr width (i.e. equivalent width) accurately. Equivalent burr width calculated as the ratio of total area of burr generated to the total height. It was observed that equivalent burr width in up milling was increased by 120%, while in down milling, it was decreased by 50% as the speed varies from conventional to high speed. Furthermore, the effects of different cutting parameters and tool parameters on top burr formation have been analyzed to establish correlation among them.

Investigation of the controllable characteristics of electrical discharge ablation of Ti6Al4V

The local excessive ablation of Ti6Al4V by electrical discharge machining ablation (EDMA) is investigated in the present work. In order to achieve the high efficiency and stable ablation machining of Ti6Al4V, a method of diluting the concentration of oxygen medium by the nitrogen is proposed; that is, a mixed gas medium composed of nitrogen and oxygen is used as a gas medium for EDMA. Firstly, the effects of the oxygen concentration, discharge energy, and gas pressure on the excessive ablation of Ti6Al4V are theoretically analyzed. Then, the quantitative correlation between the above three factors and the excessive ablation phenomenon is established through the experimental exploration. Finally, the Taguchi orthogonal method is applied to systematically investigate the effects of the mentioned factors on the material removal rate (MRR) and electrode wear rate (EWR), and compared with the conventional electrical discharge machining (EDM). The experimental results show that the discharge energy and the gas pressure decrease parabolically as the oxygen concentration increases, while discharge current decreases linearly as the gas pressure increases. Moreover, the pulse width decreases exponentially as the gas pressure increases. It is observed that the discharge current and oxygen concentration have significant effects on MRR, while pulse width has significant effects on EWR. The present work shows that the processing efficiency of EDMA is more than 9 times of that for EDM with solid electrode in water.

The role of high-pressure coolant in the wear characteristics of WC-Co tools during the cutting of Ti–6Al–4V

Aeronautic applications have been making use of titanium alloys for decades. Ti–6Al–4V is one of the most commonly applied alloys, and although its mechanical properties warrant its acceptance for many applications, the machinability of this alloy remains a challenge. So far, the most successful technique in facilitating this alloy's machining has been the application of High-Pressure Coolant Supply (HPC) on account of its influence on the tribological aspects of the cutting operation. On that premise, this work employs experimental and computational resources to advance the current understanding of the wear mechanism in terms of the tool-chip contact conditions and establish a correlation between coolant pressure, cutting speed, tool life, cutting forces, and chip formation when machining Ti–6Al–4V with HPC supply. Results showed that HPC plays a role in the reduction of tool-chip temperature profiles and contact stresses, positively impacting tool flank wear, oxidation levels and chip formation, also improving chip breakability.

Investigation on EDM machining of Ti6Al4V with negative polarity brass electrode

ABSTRACTThis research paper focus on the machinability studies of Ti6Al4V material during electrical discharge machining (EDM) process. Discharge time, current, and discharge voltage are taken as input process variables. Experiments are conducted on Ti6Al4V material to explore the effect of these input variables on material removal rate (MRR), surface roughness, thickness of white layer and microcracks taken as output variables. The machined components are analyzed using three-dimensional surface topography and scanning electron microscope micrographs. It is found, by increasing discharge time and current, MRR and thickness of white layer is increased whereas surface finish gets worsened. Microcracks, blow holes, and redeposition of workpiece as debris are perceived on machined workpiece. A modified equation is proposed to estimate diameter of crater taking into account the discharge energy and latent heat of vaporization of workpiece material. Compared with experimental data, the proposed equation predicts diameter of crater an error of 16.89%.

Multi-objective optimization for sustainable turning Ti6Al4V alloy using grey relational analysis (GRA) based on analytic hierarchy process (AHP)

Sustainable machining necessitates energy-efficient processes, longer tool lifespan, and greater surface integrity of the products in modern manufacturing. However, when considering Ti6Al4V alloy, these objectives turn out to be difficult to achieve as titanium alloys pose serious machinability challenges, especially at elevated temperatures. In this research, we investigate the optimal machining parameters required for turning of Ti6Al4V alloy. Turning experiments were performed to optimize four response parameters, i.e., specific cutting energy (SCE), wear rate (R), surface roughness (Ra), and material removal rate (MRR) with uncoated H13 carbide inserts in the dry cutting environment. Grey relational analysis (GRA) combined with the analytic hierarchy process (AHP) was performed to develop a multi-objective function. Response surface optimization was used to optimize the developed multi-objective function and determine the optimal cutting condition. As per the ANOVA, the interaction of feed rate and cutting speed (f × V) was found to be the most significant factor influencing the grey relational grade (GRG) of the multi-objective function. The optimized machining conditions increased the MRR and tool life by 34% and 7%, whereas, reducing the specific cutting energy and surface roughness by 6% and 2% respectively. Using Taguchi-based GRA by analytic hierarchy process (AHP) weights method, the benefits of high-speed machining Ti6Al4V through multi-response optimization were achieved.

Finite element modeling of friction at the tool-chip-workpiece interface in high speed machining of Ti6Al4V

For achieving the accurate FE modeling of friction, a new analytical formula of the friction coefficient at tool-chip-workpiece interface is first derived, which takes into account the actual cutting tool's blunt radius rather than conventionally simplified sharp edge. And the mean friction coefficient μm applied to the FE model in HSM of Ti6Al4V is obtained by using three-method combination of the new analytical formula and the FE simulation as well as the experimental verification of outside-diameter grooving with uncoated carbide tool. The results show that μm is between 0.4 and 0.5 in the grooving speed range from 49.4 m/min to 122.5 m/min. The validity of μm value is further verified by the agreement of the simulated chip shapes with the experimentally measured SEM morphologies.

Surface quality monitoring in abrasive water jet machining of Ti6Al4V–CFRP stacks through wavelet packet analysis of acoustic emission signals

Machining such as trimming and drilling of aerospace composite structures is often required to meet the intended geometric tolerances and functional requirements. Abrasive water jet (AWJ) is a primary candidate for high speed machining of difficult-to-cut materials. The AWJ process performance is sensitive to the online faults and non-optimal process parameters, necessitating efficient techniques for online process control. In this study, acoustic emission (AE) signals are used to monitor AWJ machining of stacked titanium-CFRP. Owing to the non-stationary nature of the AE signals, this work is focused on the precision-driven predictive approach in simultaneous time-frequency domain. The AE signals were analyzed using wavelet packet transform (WPT), and an algorithm was proposed to identify and characterize these signals. Thirty-five different mother wavelets and decomposition levels up to 10 were used. The wavelet parameters (mother wavelet and decomposition) were deemed optimal when the identified signal characteristics could strongly correlate with the process parameters and kerf wall quality (surface roughness). Coiflets and Symlets were identified as the optimal wavelets with energy-entropy coefficient as the qualifying characteristic of the wavelet packet resulting in R2 > 90%. A comparative study was conducted to qualify the proposed algorithm against standard time domain analysis measures. The maximum R2 and CV (RMSD)—coefficient of variation of root mean square deviation for time domain was observed as 88.6% and 12.5% respectively as opposed to R2 = 97.12% and CV (RMSD)= 6% for the proposed WPT algorithm. Overall, an efficient algorithm was proposed in monitoring the process quality and controlling the process parameters based on the identified signal signatures.

Investigation, modelling and validation of material separation mechanism during fiber laser machining of medical grade titanium alloy Ti6Al4V and stainless steel SS316L

In the laser machining of titanium alloy (Ti6Al4V) and stainless steel (SS316L), it was observed that Ti6Al4V was machinable at higher cutting speeds and lower laser power than SS316L, despite higher melting temperature of Ti6Al4V. Three millimeters thick Ti6Al4V and SS316L substrates were machined using 400 W fiber laser machining system with cutting velocities ranging from 75 to 800 mm/min in the presence of Argon (at 10 bar pressure) as the shield and assist gas. At 300 W laser power and velocities of 150 mm/min or less, material separation was observed in Ti6Al4V but not in SS316L. An investigation into the laser machined surfaces confirmed that the primary mode of material separation in both the materials was melt & blow cutting. However, the secondary modes of machining investigated via XPS, XRD and EDX confirmed substantial transformation of Ti6Al4V constituents into oxides regardless of the fact that argon gas was used for shielding. Analytical modelling of the laser machining process also suggested substantial dilatational and transformational strains in Ti6Al4V while thermo-elastic, plastic and transformational strains were relatively equivalent in both materials. It was hypothesized that laser machining of Ti6Al4V was assisted by larger amount of chemical transformation but not in SS316L. The hypothesis was validated by laser machining experiments in the presence of varying pressures of oxygen and argon.

Wear Characteristic Evaluation of Electrical Discharge Machined Ti6Al4V Surfaces at Dry Sliding Conditions

The low tribo-characteristics of Ti6Al4V (Ti64) have delimited its range of applicability. To elucidate the underlying mechanism, the friction and wear behavior of Ti64 at elevated pin speeds (200 rpm, 300 rpm and 400 rpm), constant load (50 N) and temperature (ambient) conditions were initially evaluated. The wear, coefficient of friction and frictional force characteristics of the material were identified to follow incessant unsteady transitions, during test run. The pin speed of 300 rpm marked the highest wear, governed by the frictional heating, asperity flattening, centrifugal forced clearance (of the wear track) and third-body abrasion-assisted delamination. The reduced wear trend at 200 rpm and 400 rpm could be attributed to the protective coatings formed by tribo-oxidation and mechanically mixed layer, respectively. Further, the electrical discharge machined Ti64 samples were developed and subjected to friction and wear analyses at varying loads of 50 N and 100 N. In contrast, at similar testing conditions (load 50 N, speed 200 rpm, temperature ambient, sliding distance 1000 m), the electrical discharge machined Ti64 (with a peak wear value of 220 μm) showed enhanced tribo-characteristics compared to that of bare Ti64 (with a peak wear value of 370 μm). The improved tribo-behavior of the former was due to the presence of hard, fine-grained and non-etchable recast layer, which got spalled off at an increased load of 100 N.

Performances of micro-textured WC-10Ni3Al cemented carbides cutting tool in turning of Ti6Al4V

Cutting performances of micro-textured WC-10Ni3Al cutting tools compared with micro-textured WC-8Co cutting tools in turning of Ti6Al4V was investigated in this study. Cutting forces, cutting temperature, and tool life based on the criterion of a 300 μm flank wear were measured. The wear tracks of the rake face and flank face for micro-textured WC-10Ni3Al cutting tools were analyzed. It is found that WC-10Ni3Al cutting tools had smaller heat damages during LST compared with WC-8Co cutting tools, which was benefit for avoiding premature tool failure during Ti6Al4V machining process. Micro-textures on the rake face could effectively reduce cutting forces, cutting temperature, adhesion on the rake face, and hence increase tool life, especially at higher cutting speed.

Integrirana statistična metodologija za optimiziranje parametrov brušenja površine Ti6Al4V zlitine z EDDSG procesom v mešanici s SiC prahom

Integrirana statistična metodologija za optimiziranje parametrov brušenja površine Ti6Al4V zlitine z EDDSG procesom v mešanici s SiC prahom

Generation of Stepped Profiles on Ti6Al4V by Electrochemical Milling

Generation of accurate complex-shaped products on various high-strength temperature-resistant (HSTR) alloys such as titanium and nickel alloys is a key feature for many kinds of machine parts widely used in diverse industries starting from biomedical to defence industries. Being free of tool wear, thermal stresses and residual stresses, electrochemical machining has great potential of machining those HSTR metal structures. The process of EC milling is similar to conventional ECM, where the material is removed by a simple geometric tool following a predefined path in a layer-by-layer fashion. EC milling avoids complex electrode design which is often a burden in sinking ECM. In this paper, attempts have been made to investigate the influence of different process parameters on various performance characteristics of EC milling of Ti6Al4V by generating stepped profiles, and then, optimization of process parameters have been done using Taguchi and grey relation analysis (GRA). Experiments were conducted based on Taguchi’s L27 orthogonal array with five important process parameters, i.e. electrolyte concentration, milling layer depth, feed rate, frequency and duty ratio. From analysis of variance, it was observed that electrolyte concentration and milling layer depth are the significant process parameters that mostly affect the responses. The experimental results show that for successful machining of Ti6Al4V by EC milling process, the optimal parametric combinations are 0.5 M electrolyte concentration, 0.15 mm milling layer depth, 0.04 mm/s feed rate, 5 kHz frequency and 50% duty ratio; and milling layer depth has a major influence on all the responses of EC milling of Ti6Al4V.

Comparison of Laser Milling Performance against Difficult-To-Cut Alloys: Parametric Significance, Modeling and Optimization for Targeted Material Removal.

During laser milling, the objective is not always to maximize the material removal rate (MRR). Milling of new material with targeted MRR is challenging without prior knowledge and established sets of laser parameters. The laser milling performance has been evaluated for three important aerospace alloys, i.e., titanium alloy, nickel alloy and aluminum alloy using the response surface method experimental plan (54 experiments for each alloy). Parametric effects of five important laser parameters, statistical analysis (main effects, interaction effects, strength and direction of effects), mathematical modeling and optimality search is conducted for the said alloys. Under the non-optimized laser parameters, the actual MRR significantly varies from the targeted MRR. Variation in the aluminum alloy is at the top as compared to the other two alloys. Among other significant terms, three terms have the largest effect on MRR in the case of TiA, two terms in the case of NiA, and five terms in the case of AlA. Under the optimized sets of laser parameters, the actual material removal highly close to the desired level (100%) can be achieved with minimum variation in all the three alloys. Mathematical models proposed here have the capability to well predict material removal prior to the actual machining of Ti6Al4V, Inconel 718 and AA 2024.

Correlation of the fatigue impact resistance of bilayer and nanolayered PVD coatings with their cutting performance in machining Ti 6Al 4V

Abstract Titanium alloys are widely employed in aerospace and biomedical applications. During the cutting process of Ti 6Al 4V alloy, the material characteristics of high specific strength and poor thermal conductivity lead to a stress concentration occurred at the tool/chip interface, which may cause severe failure of the coated tools. Besides, the titanium alloy gives rise to serrated chips, whose thickness varies regularly in the cycle mode, which lead to the variation of cutting force and tool stress. So a cyclic impact with high frequency is applied on the coated tool surface, and this induces the fatigue fracture of coating. In this study, repetitive contact between the coating and Vickers diamond indenter through the high frequency cyclic impact tester was developed by employing the ultrasonic actuator device. High frequency cyclic impact testing has been used to study the impact resistance of the TiSiN/TiAlN bilayer coating and TiSiN/TiAlN nanolayered coating. Besides, stress concentration resulting in the failure of coatings can be generated by using the sharp Vickers indenter. The crack propagation in coatings was investigated by the scanning electron microscope (SEM), and the fracture processes of coatings were studied from the force measurement data acquisition system. In addition, the cutting performance of cemented carbide tools coated with these two coatings was evaluated in turning Ti 6Al 4V titanium alloy. The correlation between the fatigue impact resistance of coatings at high frequency and the wear behavior of coated tools under different cutting conditions was studied. It can be concluded that the TiSiN/TiAlN nanolayered coating showed better properties to resist fatigue impact at the lower impact load, but worse properties to resist fatigue impact at the higher impact load.

Research on machining Ti6Al4V by high-speed electric arc milling with breaking arcs via mechanical-hydrodynamic coupling forces

A sustainable and advanced manufacturing method named high-speed electric arc milling (H-SEAM) was presented in this research to solve the problems where of environmental pollution and low machining efficiency for difficult-to-cut materials in the traditional electrical discharge machining (EDM)EDM process. This method can achieve high material removal efficiency with arc breaking via a coupling of mechanical and hydrodynamic forces in H-SEAM. Firstly, the material removal mechanisms of H-SEAM and theoretical arc breaking conditions are analysed. Then, comparative experiments on machining titanium alloy Ti6Al4V by different arc breaking methods are conducted to study the material removal rate (MRR), tool electrode wear rate, and machined surface quality of the workpiece. Our experiment results showed that the MRR can reach 780 mm3/min when using a mechanical-hydrodynamic coupling method to break arcs, which is almost five times and nearly twice that when using independent mechanical or hydrodynamic methods to break arcs. Moreover, experimental results showed the machined grooves via mechanical-hydrodynamic coupling forces to break arcs in H-SEAM exhibited higher dimensional accuracy, lower tool electrode wear, lower surface roughness, thinner recast layers, and smaller heat-affected areas than those in arc breaking by independent mechanical or hydrodynamic methods. This can be attributed to the higher removal efficiency of molten metal material and the uniform distribution of energy when using mechanical-hydrodynamic coupling forces to break arcs.

Replacement of Hazard Lubricants by Green Coolant in Machining of Ti6Al4V: A 3D FEM Approach

Metalworking fluids (MWF’s) are frequently used for cooling and lubrication during machining processes in manufacturing industries. MWF’s such as soluble straight oils, synthetic oils, solid lubricants, bio lubricants contain a mix of water and mineral oil with some percentage of vegetable oils and petroleum. These MWF’s are hazardous for the environment and for human health. After using, the lubricants are disposed into the environment by burning or by dumping on the ground or in the sea water. Burning the lubricant creates pollution and airborne disease. To avoid these harmful effects of the lubricants sustainable machining technique is implemented in machining processes. In the present study, liquid nitrogen (green coolant) is used as a sustainable machining technique for cooling and lubrication. Finite element modeling is used to simulate the micro-end milling at different conditions of the workpiece (cryogenic plus preheated and cryogenic). The analysis of chip morphology and cutting forces measurement were done by applying these conditions. The predicted model is validated with the experimental results. It was observed that cryogenic with preheated workpiece (473 K) is the optimum condition with the application of green coolant. This study will clarify the behavior of cryogenic on the machining conditions and will solve the environmental problems.