Machining Of Ti6Al4V Research Articles

Physical characterization and wear behavior of laser processed and PVD coated WC/Co in dry sliding and dry turning processes

The present study is an attempt to integrate the laser surface modification techniques with PVD-coatings. AlTiN and AlCrN coatings were deposited on different laser shock peened (LSP) and laser surface textured (LST) WC/Co surfaces. The developed surfaces and PVD coatings were characterized for surface morphology, elemental composition, surface topography, substrate/coating phases, and adhesion behavior. Tribological tests were performed to understand the friction and wear performance of developed surfaces against Ti6Al4V counter pair at varying sliding speeds. Tribo test results revealed that the coatings deposited on laser processed surfaces are helpful in reducing the coefficient of friction (COF) and wear loss. The associated wear mechanisms are discussed with the help of proposed wear models. For laser textured surfaces, the experimental evidence of texture induced micro cutting mechanism has been reported. The generation of weaker carbides for LSP surfaces reduced the coating adhesion and resulted in poor tribological performance. For machining of Ti6Al4V, improved performance of coated LST surfaces was achieved. Apparent friction coefficient and flank wear were reduced by 64% and 65% respectively.

Finite element modelling to predict machining induced residual stresses in the end milling of hard to machine Ti6Al4V alloy

Machining is one of the methods to produce components and products from raw material. Many factors influence the outcome of the machining process and the life of the components there after. Researchers have tried to understand the underlying principles of machining using finite element analysis since many years. In the present work the authors have made an attempt to study few behaviour namely, stress distribution, force variation and machining induced residual stresses while machining hard to machine Ti6Al4V alloy using finite element analysis. The model that is presented in this work is an improvisation of some of the existing models overcoming some of the shortcomings of the existing model. The work presented here uses the time tested Johnson-Cook model, but unlike the many other works sacrificial layers is not being used rather, Johnson-Cook damage model is being used. In addition, the authors have considered opted for oblique cutting in spite of high computational time due to the want of more accurate results.

A New Cutting Tool Design for Cryogenic Machining of Ti⁻6Al⁻4V Titanium Alloy.

Titanium alloys are extensively used in aerospace and medical industries. About 15% of modern civil aircrafts are made from titanium alloys. Ti–6Al–4V, the most used titanium alloy, is widely considered a difficult-to-machine material due to short tool life, poor surface integrity, and low productivity during machining. Cryogenic machining using liquid nitrogen (LN2) has shown promising advantages in increasing tool life and material removal rate whilst improving surface integrity. However, to date, there is no study on cutting tool geometry and its performance relationship in cryogenic machining. This paper presents the first investigation on various cutting tool geometries for cryogenic end milling of Ti–6Al–4V alloy. The investigations revealed that a 14° rake angle and a 10° primary clearance angle are the most suitable geometries for cryogenic machining. The effect of cutting speed on tool life was also studied. The analysis indicated that 110 m/min cutting speed yields the longest tool life of 91 min whilst allowing for up to 83% increased productivity when machining Ti–6Al–4V. Overall the research shows significant impact in machining performance of Ti–6Al–4V with much higher material removal rate.

Experimental Study of Machining Characteristics of Ti6Al4V in EDM Using Tapered Tool

Abstract Ti6Al4V is a widely used grade-V, alpha-beta phase Titanium alloy. As it is a high strength material, machining of Ti6Al4V with the help of conventional processes is very difficult. That’s why, non-conventional machining processes, like electro-discharge machining process (EDM), have been chosen to machine this material. EDM is an electro-thermal, non-traditional machining process where spark is generated in between tool and workpiece to machine conductive materials by melting and vaporization. In case of EDM the strength of the workpiece material has no influence on machining, rather machining depends on thermal properties of the material. The main difficulty faced in EDM is the accumulation of debris in the machining zone which hampers the stability of the machining and finally hampers the machining characteristics. In the present research, a simple and cost-effective method using tapered tool, has been introduced to counter this problem. In this paper, the effect of tool taper angle, as well as peak current (Ip), pulse-on-time (Ton), duty factor (Tau) and flushing pressure, on material removal rate (MRR) and diametric overcut (DOC), have been investigated

WED-machining characteristics of Ti6Al4V alloy based on central composite design

The paper presents the optimisation of process parameters during wire electrode discharge machining (WEDM) of Ti6Al4V (grade 5) alloy using the response surface methodology (RSM) and desirability approach, as unique set of properties of Ti6Al4V is being increasingly utilised in various industries including biomedical and aerospace. However, due to low thermal conductivity and being highly reactive at elevated temperatures tool wear is a significant problem during conventional machining operations. Hence, WEDM may be a viable alternative in certain applications when machining titanium alloys. In this investigation the effect of WEDM process parameters such pulse on time, pulse off time, servo voltage and wire feed are evaluated for material removal rate (MRR) and surface roughness. The optimum process parameters were obtained for the selected range of experiments using a desirability approach. Confirmation experiments were conducted to validate the empirical models of MRR and surface roughness that indicated developed models are suitable for predicting the response parameters.

WED-machining characteristics of Ti6Al4V alloy based on central composite design

The paper presents the optimisation of process parameters during wire electrode discharge machining (WEDM) of Ti6Al4V (grade 5) alloy using the response surface methodology (RSM) and desirability approach, as unique set of properties of Ti6Al4V is being increasingly utilised in various industries including biomedical and aerospace. However, due to low thermal conductivity and being highly reactive at elevated temperatures tool wear is a significant problem during conventional machining operations. Hence, WEDM may be a viable alternative in certain applications when machining titanium alloys. In this investigation the effect of WEDM process parameters such pulse on time, pulse off time, servo voltage and wire feed are evaluated for material removal rate (MRR) and surface roughness. The optimum process parameters were obtained for the selected range of experiments using a desirability approach. Confirmation experiments were conducted to validate the empirical models of MRR and surface roughness that indicated developed models are suitable for predicting the response parameters.

Experimental Investigation of Oil Mist Assisted Cooling on Orthogonal Cutting of Ti6Al4V

Abstract In this study, a thermo-mechanical model of machining of Ti6Al4V using different oil-mist combination is developed to predict the tool and workpiece temperature at different cutting speed. Machining of chemically reactive materials like Ti6Al4V causes high localization of heat, which contribute to the high tool wear or even premature failure of the tool. The thermal gradient effect is dominating in machining under dry conditions because of its low thermal conductivity. This induces thermal stresses and microstructural changes in the workpiece, thus damaging the workpiece surface integrity. The objective of present work is to understand the effect of different oil mist cooling mixtures at the tool-chip interface and to evaluate the tool and workpiece temperature. Experiments were performed using various mist conditions for different cutting parameters and its effect on the temperature has been studied. Temperature measurement was carried out using a thermal imaging camera. A 2-D finite element thermo-mechanical model is developed using ABAQUS TM to predict the tool and workpiece temperature. Provision of mist cooling has shown a large reduction in the tool and workpiece temperature. It was observed that at low cutting speeds, lubrication characteristics of mist is predominant while at higher cutting speed lubrication suffers.

Formation of TiC by the application of Ti6Al4V machining chips as flux compounds of tubular wires

Titanium carbonates (TiC) have high hardness and wear resistance, being thus widely present as a phase present in various mechanical components subject to wear mechanisms. Its application on a large industrial scale becomes relatively low, due to the high cost of titanium commercial alloys. On the other hand, large amounts of chips are generated in the manufacture of prostheses and orthodontic implants, where titanium alloys (ASTM F67 and ASTM F136) are widely applied. The attractiveness of these residues lies in the fact that titanium is the major element present in alloys (at least 90% by weight) and are discarded at low cost when compared to commercial alloys. In order to re insert these residues in the production chain, ASTM F136 (Ti6Al4V) alloy chips were subjected to grinding processes to obtain powders with a grain size of less than 40 mesh and used as flux components in tubular type wires MCAW for manufacturing consumables, promoting the formation of TiC in the welding metal. The deposited cords presented low weld discontinuity index with a uniform distribution of TiC particles along the microstructure, resulting in considerable fractions of carbonate areas in the welds and presenting a considerable increase in micro hardness.

Analysis and optimization of process energy consumption and environmental impact in electrical discharge machining of titanium superalloys

Abstract Process energy consumption and environmental impact have been considered as important performance indicators for the sustainable electrical discharge machining (EDM) process. This paper presents a sustainable manufacturing technique known as magnetic field-assisted EDM (MF-EDM) to enhance the machine characteristics for the purpose of reducing the energy consumption and environmental hazards of the conventional EDM machining Ti6Al4V. Firstly, the principles of energy consumption, machining noise impact, and MF-EDM are respectively described. Thereafter, a set of experiments is carried out to investigate the effects of the main process parameters on the electrode wear rate ( E W R ), energy consumption ( S E C ), and environmental impacts (including carbon emission and machining noise) extensively, using the Taguchi method. The results indicate that the pulse on time (ranging from 100 to 200 μs) and magnetic field intensity (ranging from 0.05 to 0.10 T) are the two most significant factors affecting the MF-EDM sustainable manufacturing performance. Furthermore, the optimal process parameters were obtained by optimizing the MF-EDM process economically and environmentally using the modified non-dominated neighbor immune algorithm (M-NNIA) method. Compared to the minimum outputs of the experimental results, the optimal solutions of the E W R , S E C , and machining noise were significantly decreased, by 18.30%, 61.43%, and 20.95%, respectively. Therefore, it can be concluded from the above research that the proposed hybrid MF-EDM technique offers significant advantages and potential for applications in the sustainable manufacturing field.

A nonuniform moving heat source model for temperature simulation in ultrasonic-assisted cutting of titanium alloys

The ultrasonic-assisted machining (UAM) technique has been widely used in machining of difficult-to-cut materials for its well comprehensive performance, especially in the mechanical and thermal aspects. In this paper, a nonuniform moving heat source model is proposed to analyze the heat transfer problem during ultrasonic vibration-assisted machining of Ti6Al4V. The influences of ultrasonic vibration amplitude and frequency on temperature distribution are discussed in detail. Two main characteristics are observed according to the temperature contours caused by the ultrasonic-assisted machining: one is that the equivalent heat source center tends to move backward the tool rake face, and the other is that the temperature gradients in cutting direction and depth direction are inconsistent. For further study, the temperature variation with respect to vibration parameters near the shear plane and machined surface is calculated. Results show that the increase of vibration amplitude and frequency can reduce the temperature near the shear plane due to a large temperature gradient. Besides, a large vibration amplitude can obtain a low temperature on the machined surface while the increased vibration frequency results in a higher surface temperature after machining. The research can be used to provide guidance for improving the quality and efficiency of difficult-to-cut material machining.

Exploring the influence of constitutive models and associated parameters for the orthogonal machining of Ti6Al4V

Ti6Al4V is known as difficult-to-cut material due to its inherent properties such as high hot hardness, low thermal conductivity and high chemical reactivity. Though, Ti6Al4V is utilized by industrial sectors such as aeronautics, energy generation, petrochemical and bio-medical etc. For the metal cutting community, competent and cost-effective machining of Ti6Al4V is a challenging task. To optimize cost and machining performance for the machining of Ti6Al4V, finite element based cutting simulation can be a very useful tool. The aim of this paper is to develop a finite element machining model for the simulation of Ti6Al4V machining process. The study incorporates material constitutive models namely Power Law (PL) and Johnson – Cook (JC) material models to mimic the mechanical behaviour of Ti6Al4V. The study investigates cutting temperatures, cutting forces, stresses, and plastic strains with respect to different PL and JC material models with associated parameters. In addition, the numerical study also integrates different cutting tool rake angles in the machining simulations. The simulated results will be beneficial to draw conclusions for improving the overall machining performance of Ti6Al4V.

Experimental Investigation of Process Parameters in Orthogonal Machining of Ti6Al4V with TiC Coated PCBN Inserts – A Finite Element Analysis

Aeronautical industry requires material having high resistance as well as high hardness. As it is common fact that, the machining of these metals has continuously been a boundless task. Metal cutting of these titanium alloys required for cutting great-strength materials, which occasionally is not cost-effective and from time to time even unreasonable. These metals incline to stick to the machining tool surface and chips are stuck to the flank. This sticking of cut materials will induce tool damage entailing a reduction of tool life. It also affects the surface roughness and perfection in dimension of finished product. To evade the prerequisite of wide-ranging experiments and to appreciate the orthogonal material removal of Ti6Al4V, FEA is employed. This work mainly focuses on learning the impact of metal cutting parameters on machinability of Ti6Al4V using PCBN tool inserts in dry machining and by analyzing the stress, temperature and effective strain scattering through finite element analysis. Various experiments were conducted by varying the machining speeds and feed rates. The machining process was also simulated in DEFORM – 2D software to study the corresponding effective strain, effective stress, and the temperature scattering.

A Comparative Study of Polarity-related Effects in Single Discharge EDM of Titanium and Iron Alloys

In comparison to steel, titanium alloys react differently to the choice of process parameters in sinking electrical discharge machining (EDM), especially concerning the applied electrical polarity of the tool. With an anodic tool polarity, sinking EDM removal on titanium Ti6Al4V is scarce due to titanium carbide formation, while on steel removal occurs as expected. To understand the behavior of titanium alloys, a comparative study between titanium and iron alloys in single and successive discharge experiments is performed. Ironically, single discharge removal is scarce with an anodic tool on both iron and titanium alloys. However, in ten successive discharges experiments, removal with an anodic tool increases disproportionately. Finally, the continuous EDM process with an anodic tool stops to be effective for the Ti6Al4V machining while for steel is effective as well as efficient in terms of low tool wear. The explanation proposed is the recast layer that has a lower thermal conductivity on which successive discharges would remove material more easily. As a result, the formation of titanium carbide in Ti6Al4V machining is likely not occurring in single discharges due to lack of continuous heat needed for carbon transfer.

Fatigue life of machined Ti6Al4V alloy under different cooling conditions

This paper presents an extensive experimental study on the influence of machining parameters and cooling conditions on the overall fatigue life of a titanium component. In particular, dry, minimum quantity lubrication, cryogenic and high-pressure air jet were compared as cooling/lubrication strategies for the finishing operation. The obtained dog-bone cylindrical fatigue specimens were tested under uniaxial pull–pull cyclic loading in the high cycle fatigue range. An analytical model is proposed to predict the high cycle fatigue strength for the material under investigation demonstrating its effectiveness to reduce the number of tests needed.

Study of tool wear and chemical interaction during machining of Ti6Al4V

The present study concerns an investigation of the wear on three uncoated cemented carbide grades, with differing binder content and grain size, during longitudinal turning of Ti6Al4V as a function of cutting speed. The creater wear at end of tool life is studied in detail using electron microscopy and X-ray diffraction. It is observed that decreasing binder content results in slower wear progression and longer tool life. The microstructure of the adhered layer is also dependent on the binder content, where a lower amount of binder results in an increase of dark precipitates in the adhered layer. X-ray diffraction confirms the presence of bcc-W as a chemical wear product at the interface. Diffraction peaks corresponding to cubic (Ti,V)C are also occasionally observed.

Generation of segmental chips in metal cutting modeled with the PFEM

The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining of Ti6Al4V. In this work the method is revised and applied to study the influence of the cutting speed on the cutting force and the chip formation process. A parametric methodology for the detection and treatment of the rigid tool contact is presented. The adaptive insertion and removal of particles are developed and employed in order to sidestep the difficulties associated with mesh distortion, shear localization as well as for resolving the fine-scale features of the solution. The performance of PFEM is studied with a set of different two-dimensional orthogonal cutting tests. It is shown that, despite its Lagrangian nature, the proposed combined finite element-particle method is well suited for large deformation metal cutting problems with continuous chip and serrated chip formation.

High speed cryogenic finish machining of Ti-6Al4V with polycrystalline diamond tools

In this work, Ti-6Al4V alloy was machined using polycrystalline diamond (PCD) tools under three different cooling/lubricating environments: cryogenic cooling (liquid nitrogen (LN2) at −195.8°C), hybrid cooling/lubrication (LN2 and oil based MQL − minimum quantity lubrication) as well as conventional flood cooling (emulsion). The machining parameters were selected to achieve very low kinematic surface roughness (f=0.01mm/rev, ap=0.1mm) and three cutting speeds of vc=120, 240 and 360m/min were evaluated. The as-machined surface integrity was compared for all conditions, showing significant improvements in surface and sub-surface properties with both cryogenic and hybrid cooling as compared to flood cooling. Although the PCD tools are not commonly used in high speed machining of Ti alloys because of the problem of thermally induced chemical wear, it was found that with the use of cryogenic cooling, the tribological system changed sufficiently to allow for sustained machining performance, with very low tool-wear (VBC(cryogenic)<10μm after 65min of cutting at vc=240m/min). Surface roughness values were as low as Ra=40nm for cryogenic machining. Interestingly, flood machining did not lead to reduce surface roughness values. However, hybrid cooling/lubrication did yield the lowest cutting forces compared to both flood and cryogenic conditions. All conditions evaluated during this study resulted in cutting forces of less than 15N, suggesting that cryogenic precision machining with PCD tools may be a suitable alternative to grinding, even for slender and thin-walled components.

Contribution to the FEM simulation of Ti6Al4V Machining

The paper briefly reviews current scientific publications related to machining of difficult to cut materials and finite element modelling methods (FEM) applied in various chip making processes. Simulations of the orthogonal machining process with regard to define optimal cutting parameters as well as cutting wedge geometry in hole making TiAlN alloy was performed according to test plan based on design of experiment (DoE) methodology. The numerical simulations were performed using commercial finite element software (AdvantEgde), which is suitable to solve complex thermo-mechanical problems occurring in cutting zone during chip making process. A Lagrangian finite element-based model is applied within simulation procedure. Results from experimental simulation were evaluated by main effect and surface response plots.

Microstructural evolution of Ti6Al4V in ultrasonically assisted cutting: Numerical modelling and experimental analysis

This paper aims to elucidate the effect of ultrasonically assisted cutting (UAC) on microstructure in a machined surface and a chip of Ti6Al4V alloy. To investigate microstructural evolution, a FE-based cutting model with an enhanced material formulation and temperature dependent material properties was developed. A Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the Ti6Al4V alloy was employed to simulate dynamic recrystallization and predict a resultant grain size. Due to a specific thermomechanical load in UAC, the distributions of strains, strain rates and temperatures in a workpiece in the machining process were investigated. In this study, five points under the machined surface and ten points under the unmachined one were tracked to compare the evolution of a grain size and its average magnitude in the alloy subjected to conventional cutting (CC) and UAC. Besides of numerical modelling and experimental studies for the resultant grain size were compared and additional validation using microhardness measurements were conducted. The results showed that the average grain size of the machined surface and the chip in case of UAC was larger and more uniform than that in case of CC. The study also presents discussions about the effect of a vibration amplitude, a feed rate and a cutting speed on the average grain size in machining of Ti6Al4V. The comparison between CC and UAC indicates that the change in average grain size in UAC was smaller than that in CC, thus demonstrating a lower level of damage in UAC.

Investigation of Temperature and Stress Distribution on High Speed Machining of Ti6Al4V and 316L Steel Biomaterials Using Explicit Dynamic Analysis

In high speed machining, to dynamically control the mechanical behaviour of the materials, it is essential to control temperature, stress and strain by appropriate speed, feed and depth of cut. In the present work, to predict the mechanical behaviour of Ti6Al4V and 316L steel bio-materials an explicit dynamic analysis with different cutting speeds was carried out. Orthogonal cutting of 316L steel and Ti6Al4V materials with 720 m/min, 900 m/min and 1200 m/min cutting speeds was performed, and the distribution of stress and temperature was investigated using Jonson-Cook material model. Additionally, the work aimed at determining the effect of cutting speed on work piece temperature, when cutting is carried out continuously. From the investigation, it was found that, while machining Ti6Al4V material, for the increase in cutting speed there was increase in tool-chip interface temperature. Specifically, this could found till the cutting speed 900 m/min. But, there was a decrease in tool-chip interface temperature for the increase in speed from 900 m/min to 1200 m/min. Similarly for 316L steel, the tool-chip interface temperature increased when increasing the cutting speed till 900 m/min. But reduction in temperature from 650 °C to 500 °C for steel and 1028 °C to 990 °C for Ti6Al4V were found, when the cutting speed increased from 900 m/min to 1200 m/min. The study can be used to conclude, at what temperature range the adoption of material with controlled shape and geometry is possible for potential applications like, prosthetic design and surgical instruments prior to fabrications.