Machining Titanium Research Articles

Prediction and optimization of performance measures in electrical discharge machining using rapid prototyping tool electrodes

In this work, the performance of rapid prototyping (RP) based rapid tool is investigated during electrical discharge machining (EDM) of titanium as work piece using EDM 30 oil as dielectric medium. Selective laser sintering, a RP technique, is used to produce the tool electrode made of AlSi10Mg. The performance of rapid tool is compared with conventional solid copper and graphite tool electrodes. The machining performance measures considered in this study are material removal rate, tool wear rate and surface integrity of the machined surface measured in terms of average surface roughness (Ra), white layer thickness, surface crack density and micro-hardness on white layer. Since the machining process is a complex one, potentiality of application of a predictive tool such as least square support vector machine has been explored to provide guidelines for the practitioners to predict various machining performance measures before actual machining. The predictive model is said to be robust one as root mean square error in the range of 0.11–0.34 is obtained for various performance measures. A hybrid optimization technique known as desirability based grey relational analysis in combination with firefly algorithm is adopted for simultaneously optimizing the performance measures. It is observed that peak current and tool type are the significant parameters influencing all the performance measures.

Comprehensive experimental analysis and sustainability assessment of machining Nimonic 90 using ultrasonic-assisted turning facility

Many techniques have been developed to improve the machinability of aeronautical materials titanium and nickel-based alloys such as ultrasonic-assisted turning, laser-assisted turning, and cryogenic-assisted turning. This collaborative scientific investigation presents the steps taken to gain insight into the phenomena of machining Nimonic 90 (a nickel-based alloy) alloy using ultrasonically assisted turning. The cutting speed, feed rate, depth of cut, and frequency are taken as input parameters and average surface roughness (Ra), power consumption (P), and chip formation are considered as output parameters. The experiments are carried out with the full factorial design. The UAT (ultrasonically assisted turning) process gives a significant improvement in average surface roughness and power consumption because of the intermittent cutting action of the cutting tool. UAT process shows a 70–80% reduction in average surface roughness (Ra) and a 6–15% reduction in power consumption as compared with CT (conventional turning) process. Ultrasonically assisted turning also resulted in the thin and smoother chips as compared with CT process which helps to achieve a more superior machining effect. Finite element modeling shows that the quasi-static nature of the stress induced in the UAT process leads to lower force and ultimately lower power generation. Moreover, a sustainability assessment model is implemented to investigate the effect of UAT in terms of machining performance as well as sustainability effectiveness in a single integrated approach. The novelty of this work lies in providing an integrated concept that combines experimental analysis and sustainability assessment when using ultrasonic vibrational energy during turning of Nimonic 90.

Research on oxidation phenomenon during titanium machining and its prevention

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Modelling of Machining Characteristics During Green Machining of Biomaterials

Titanium and its alloys are gaining much attention in the biomedical field. Their biocompatibility makes them first choice for implants. However, machining of titanium is still a challenge owing to its unique properties. Beside this, industries are also looking for a solution to the economical and ecological machining of titanium and its alloys. Current research discusses a probable solution to it. This paper presents the modelling of machining characteristics during the green machining of titanium alloy. In this work, experimentation is performed with varying cutting speed, feed, and depth of cut following response surface methodology (RSM) approach. After that, the experimental results are analyzed and employed to develop an interactive model using back-propagation neural network (BPNN) technique. It is witnessed that the developed BPNN model is of higher accuracy than RSM model. Cutting inserts are further examined to gain a deeper insight into the process. Confirmation runs are also performed for adequacy check of the developed models.

Performance and wear mechanisms of PCD and pcBN cutting tools during machining titanium alloy Ti6Al4V

The need for increased productivity in difficult-to-machine titanium alloys has pushed manufacturers to examine the potential of ultrahard cutting tool materials such as polycrystalline diamond and polycrystalline cubic boron nitride as alternative solutions to conventional cemented carbide tools. This study examines the performance of such advanced tool materials in high speed finishing machining of Ti6Al4V, with attained PCD superiority compared to pcBN. Wear mechanisms are experimentally investigated based on in-depth microscopic analyses using techniques such as scanning electron microscopy, transmission electron microscopy, electron diffraction and X-ray energy-dispersive spectroscopy. Main wear morphologies were flank wear and cratering in both tool materials. Flank fracture caused by micro-cracking was an additional deterioration mechanism of pcBN tooling. Diamond burn-out, likely in combination with graphitization of diamond, was causing channel like wear morphology. The PCD wear mechanism was diffusion dissolution of carbon in Ti6Al4V. (Ti,V)C diffusional barrier or Tool Protection Layer (TPL) was formed due to reaction of workpiece and tool materials in presence of cobalt. Controlled grain size and increased cobalt content resulted in higher performance as protective caps of (Ti,V)C merged to form a continuous TPL. Similarly for pcBN, (Ti,V)B2 and (Ti,V,Cr)B2 reaction products acted as TPLs which reduced the tool deterioration rate.

Grinding titanium alloys applying small quantity lubrication

Rapid progress of manufacturing industry intends to evolve an appropriate method to shape advanced materials, such as titanium and its alloys, with improved properties. Enhanced strength at elevated temperatures in addition to superior corrosion resistance and biocompatibility have made titanium a popular metal employed in manufacturing, petroleum, automobile, aerospace and medical industries. Although having relatively greater abundance than many metals, processing, machining and grinding of titanium are difficult. The present experimental investigation explores the effectiveness of the indigenously developed small quantity lubrication (SQL) technique using soap water along with liquid CO2 jet cooling technique. Variations in grinding forces, surface roughness, grinding ratio, chip form and surface morphology observed indicate that applying SQL along with liquid CO2 jet is much effective in improving grindability of Grade 5 and Grade 1 titanium alloys than dry grinding and grinding using liquid CO2 jet alone.

Feasibility study of minimum quantity lubrication assisted belt grinding of titanium alloys

ABSTRACT In order to investigate the feasibility of minimum quantity lubrication technique in precision machining titanium alloys using abrasive belt grinding method, theoretical calculations and a series of detailed experimental studies were conducted in this paper. Material removal rate, grinding force, grinding temperature, abrasive belt wear, and machined surface quality were determined as the corresponding evaluation indicators. The signals of force and temperature in the grinding process were continuously collected by dynamometer and infrared thermal imager, respectively. The surface topography of the abrasive belt and workpiece were detected by a scanning electron microscope, and the machined surface roughness was measured by a surface profiler. The experimental results showed that the minimum quantity lubrication technology had obvious advantages in reducing abrasive wear and improving machined surface quality with suitable lubricating and grinding parameters. The observation result indicated that the compact microstructure and preferable fatigue strength can be obtained by using this assisted technique. Moreover, the addition of carbon nanotubes in grinding fluids was proven to be an effective way to further improve the effect of minimum quantity lubrication on assisted abrasive belt grinding of titanium alloys.

Effect of cutting parameters and tool rake angle on the chip formation and adiabatic shear characteristics in machining Ti-6Al-4V titanium alloy

Ti-6Al-4V titanium alloy is widely used in aeronautical parts and the high-efficiency machining and manufacturing process is surely a challenging work. The cutting parameters’ proper selection and tool geometric angles’ adoption will affect the material removal process in terms of chip formation and machined surface formation processes. In this paper, Abaqus finite element software was utilized to model and simulate the Ti-6Al-4V titanium alloy cutting process. The setting and selection of the constitutive model, material failure criterion, friction attribute, and heat transfer model make sure that the simulation is more in line with the actual cutting process. The correctness of the simulation model is verified by comparing the cutting forces and chip morphological characteristics obtained by the simulation with the experiments. Then, the effect of cutting parameters and tool rake angle on the chip formation and analyses of the adiabatic shear banding process was investigated, by using the machining simulation tests with different tool rake angles and cutting speeds. Results illustrate that the chip segmentation degree increases with the increase of cutting speed and feed rate, while it decreases with the increase in rake angle. The adiabatic shear-banding chip formation mechanisms were revealed by analyzing the relationship between shear strain, shear stress, chip segmentation degree, and high-temperature shear zone in undeformed plot contours. The serrated chip formation process when machining titanium alloy accompanies with the dramatic changes of shear strain and stress in adiabatic shear banding.

Large Cutting Depth and Layered Milling of Titanium Alloy Thin-Walled Parts

Deformation of thin-walled titanium alloys can occur during the milling process due to the cutting force and chatter vibration, which can influence the precision of the finished parts. In this research, a new milling method without auxiliary support for machining of thin-walled parts was proposed. A large cutting depth and layered milling technology were used during rough machining, with a different machining allowance for each subsequent remaining layer. In the finishing stage, the surface of the previous layer needed to be dressed before processing the next layer. A TiAlSiN-coated, cemented carbide milling cutter was used to machine titanium alloy thin-walled parts, which are characterized by continuous multilayers of unequal thickness. The processing path was simulated using HyperMILL software, and the machining accuracy was detected by the 3D optical scanner. The measurement results indicated that the surface contour accuracy of the parts was ±0.21 mm, within a range of ±0.30 mm. The machining efficiency was increased by 40%, while guaranteeing machining accuracy.

Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser

The machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy.

Temporal and spatial crater wear prediction of WC/Co tools during dry turning of Ti6Al4V alloy

A new approach is developed to predict the crater wear variation on straight grade tungsten carbide tools during titanium machining. The effect of crater wear geometry has been considered on the variation of local state variables such as normal stress (σn), chip sliding velocity (vs), and cutting temperature (T) over the contact length at varying cutting times. Experimentally determined crater profiles at progressive wear stages were geometrically replicated on the cutting tool models and used for FEM analysis. In order to account for the variation of the state variables and wear rates with respect to the tool-chip contact length, the dimensionless fractional contact length parameter is introduced in the Usui characteristic wear equation. The thermo-mechanical state variables evaluated at different fractional contact lengths and cutting time were used to obtain the wear coefficients. The crater wear profile and wear depth are predicted and the same is experimentally validated over the contact length.

Experimental and Numerical Investigations of Reducing Stray Corrosion and Improving Surface Smooth in Macro Electrolyte Jet Machining Titanium Alloys

Recently, macro electrolyte jet machining has attracted considerable research attention because it is flexible and suitable for processing aerospace parts with complex profiles. However, in this process stray corrosion occurs easily at the edges of the grooves, affecting the machining localization. In the machining of titanium alloys, serious stray corrosion on the surface outside of the machining area occurs because titanium alloys are particularly sensitive to changes in the flow field and the electric field. Here, a method is proposed to reduce stray corrosion on the workpiece surface outside of the machining area during machining of titanium alloy. This method is shown to reduce the negative influence of the reflected electrolyte on the non-machined area near the machined groove edge and to improve the machining localization by restricting the jet direction and flow range of the reflected electrolyte. Based on an investigation of the slope of the tool end face and the distribution of the electrolyte gas–liquid phase, the end face of the tool was designed to slope downward. This reduced the electrolyte flow resistance and improved the electric intensity, which helped produce a smoother surface. Experiments show that the macro sinking and milling method not only removed electrolyte from the lateral edge of the groove, reducing stray corrosion and improving machining localization, but also rapidly removed electrolytic products in the machining area, improving surface quality. Brilliant silvery grooves were obtained using a tool with an appropriate downward slope angle along with the sinking and milling method.

Machining of titanium and titanium alloys by electric discharge machining process: a review

Electric discharge machining (EDM) process is a non-traditional thermal based machining process which is widely used for the machining of hard materials such as ceramics and super alloys. Titanium (Ti), whose hardness ranges from HRB 70–74, is one such hard material which can be machined by EDM process to create intricate shapes and contours. This review paper presents the contribution of different researchers in machining of titanium and its alloys by EDM process. Problems encountered during machining of Ti and its alloys are also discussed. New research avenues like introduction of abrasives and powder in dielectric fluid, use of hybrid techniques, introduction of cryogenic treatment, etc. to improve the machinability of Ti and its alloys by EDM process are highlighted. Use of modelling and optimisation techniques like Taguchi method, response surface methodology, artificial neural network, grey relational analysis, etc. to predict the behaviour of complex process during electric discharge machining of Ti and its alloys is also shown.

Machining of titanium and titanium alloys by electric discharge machining process: a review

Electric discharge machining (EDM) process is a non-traditional thermal based machining process which is widely used for the machining of hard materials such as ceramics and super alloys. Titanium (Ti), whose hardness ranges from HRB 70–74, is one such hard material which can be machined by EDM process to create intricate shapes and contours. This review paper presents the contribution of different researchers in machining of titanium and its alloys by EDM process. Problems encountered during machining of Ti and its alloys are also discussed. New research avenues like introduction of abrasives and powder in dielectric fluid, use of hybrid techniques, introduction of cryogenic treatment, etc. to improve the machinability of Ti and its alloys by EDM process are highlighted. Use of modelling and optimisation techniques like Taguchi method, response surface methodology, artificial neural network, grey relational analysis, etc. to predict the behaviour of complex process during electric discharge machining of Ti and its alloys is also shown.

A Novel Test Bench to Investigate the Effects of the Tool Rotation on Cutting Fluid Jets to Improve the Tool Design via Additive Manufacturing

Abstract The focused cutting fluid supply into the contact zone between the rake face of a cutting tool and the emerging chip, increases tool life and enables the application of higher cutting parameters for increased productivity in various machining processes. However, different workpiece materials cause different wear mechanisms on the cutting tools. As a result, the effectiveness of the focused cutting fluid supply depends on the adaption of the supply strategy to the demands of the workpiece material. Previous investigations showed that for workpiece materials, which cause abrasive wear, such as the quenched and tempered steel 42CrMo4+QT, a wide-spread supply on the rake face of the cutting tool was beneficial. In contrast, when machining titanium Ti-6AL-4V, a focused cutting fluid jet aligned to the corner of the cutting edge was beneficial in order to cool and lubricate where the elastic behavior of the titanium, caused by the low Young’s modulus, leads to severe flank wear. Hence, different workpiece materials demand different coolant nozzle designs for improved machining results. In order to achieve the individual coolant nozzle design for milling tools, additive manufacturing technologies are predestined, because they feature an enhanced freedom of design compared to conventional manufacturing technologies. However, there is little knowledge about designing cutting tools adapted for additive manufacturing in regards of coolant nozzle design. Moreover, the influence of the tool rotation on the impact point at the cutting edge is unknown. Therefore, a test bench was developed, which allowed to investigate the influence of the tool rotation in milling on the cutting fluid free jet. With this knowledge, tools can be designed to compensate the deflection of the fluid jet caused by the tool rotation. A milling tool was then additively manufactured and investigated in machining experiments with titanium Ti-6AL-4V in comparison with a conventional milling tool.

Investigation of surface integrity and it’s optimization on pure titanium using molybdenum wire by reciprocated travelling WEDM – A review

The universal function of hybrid manufacturing processes is to have power over different machining philosophy or material removal mechanism. Wire electric discharge machining (WEDM) is one of the hybrid machining processes. WEDM is used in machining conductive materials where it is obligatory to get hold of problematical and intricate shapes with high accuracy. Machining of commercial pure titanium by conventional technique is intricate because of its very high specific potency, abrasion and corrosion resistances and finds enormous applications in bio-implants and aerospace components. The reciprocated travelling WEDM is a distinctive type of WEDM machine in which the Molybdenum wire electrode is not redundant after passing the discharge gap but being re – winded on the wire drum instead. In this research the input parameters are taken as wire feed, variable frequency and dielectric fluid flushing volume. Even though WEDM can pull off high dimensional accuracy, its thermal life causes great anxiety regarding surface integrity. Hence surface integrity aspects such as micro structure analysis have to be investigated. A desirability optimization algorithm has to be fashioned between the surface integrity aspects and process parameters.

Effects of Cooling Conditions on Surface Integrity in Turning of TC4 Alloy

Machined induced surface integrity of titanium alloy is of great importance due to its strong correlation with the functional performance and service life. In this paper, the effects of different cooling conditions on the surface integrity of TC4 alloy were studied experimentally. The results showed that the values of surface roughness and surface residual stress under cryogenic condition were lower than those under dry condition and emulsion cooling condition with the same cutting parameters, while the influence of cooling condition on the microhardness of the machined surface is not obvious. Cryogenic cutting is an effective way to machine titanium alloy.

Optimization of relative wear ratio during EDM of titanium alloy using advanced techniques

This study presents the relative wear ratio (RWR) optimization of Titanium alloy 685 for electric discharge machining (EDM). Titanium alloys are widely used in modern industry due to its excellent engineering property like high strength to weight ratio, corrosion resistance. There is difficulty in the machining of titanium alloy with conventional machining processes, hence EDM used to machine titanium alloy. The objective is to maximize the material removal rate (MRR) while the tool wear rate (TWR) should be minimized. The machined surface is an exact replica of the tool face. If TWR increases then the quality of the machined surface deteriorate. A new term introduces a RWR which represents the ratio of MRR to the TWR. The high value of RWR is desired to improve the quality of the machined surface. In this paper RWR is optimized. Response surface model used to develop a regression model of RWR. Optimization of RWR is done by advanced optimization techniques, Jaya Algorithm, teaching-learning-based optimization and response optimizer. Parameters optimization of peak current (Ip), pulse on time (Ton), duty factor (t) and voltage (V) done in this study to maximize RWR.

Machinability of green titanium powder compacts during drilling using HSS twist drills

The poor machinability of titanium-based alloys has until now been addressed by either choosing a suitable tool material, management of the heat generated during machining or by thermally assisted machining. This article reports on a new technique, called green machining, defined as the machining of compacted powders. Commercially pure titanium powder compacts possessing different strengths, called green strengths, were generated by uniaxial compaction and their drilling machinability characterized using the size of breakouts, surface finish of the drilled holes, and cutting forces. The cutting force for drilling sintered compacts was also determined for comparison purposes. The study found that all the green powder compacts could be drilled at high speeds regardless of their green strength. While high green strength, high speeds, and feed rates all affected machinability, feed rate was the main controlling factor. Also, depending on the binder used, cutting speed and feed rate could interact and worsen the machinability. However, compared to sintered compacts, the twist drills used on the green powder compacts did not catastrophically fail, and cutting forces were an order of magnitude less. It was concluded that green machining of titanium is a viable strategy to improve the poor machinability of the alloys.

Performance analysis of tool electrode prepared through laser sintering process during electrical discharge machining of titanium

Nowadays, additive manufacturing (AM)-based rapid prototyping (RP) is used as a convenient route for making tool electrodes required in electrical discharge machining (EDM). AM enables direct fabrication of complex shaped EDM electrode in comparatively less time in contrast to subtractive machining processes. In this study, an EDM electrode is prepared directly by selective laser sintering (SLS) process using metal matrix composite of aluminium (Al), silicon (Si) and magnesium (Mg). To study the performance of the prepared RP tool electrode in electrical discharge machining, titanium is used as workpiece material and EDM-30 oil as dielectric medium during machining. The performance of the prepared tool electrode is compared with conventional copper and graphite tool electrodes. Experiments have been conducted changing EDM process parameters viz. open circuit voltage (V), peak current (Ip), duty cycle (τ) and pulse duration (Ton) along with three tool electrodes such as RP, graphite and copper tool electrodes. The performance measures considered during the experimental study are material removal rate (MRR), tool wear rate (TWR), average surface roughness (Ra), white layer thickness (WLT), surface crack density (SCD) and micro-hardness (MH) on white layer. SEM and EDX of the machined surface reveal that tool material is generally eroded and deposited on the machined surface with formation of metal carbides. However, tool erosion is more pronounced in case of RP tool electrode. XRD analysis reveals the formation of titanium carbides on the machined surface resulting in increase in the micro-hardness of white layer. Discharge current and tool type are found to be significant parameters influencing the performance measures considered in the study. The surface produced when machined with RP tool electrode exhibits superior surface characteristics while graphite tool electrode produces better MRR and TWR.