Investigation on diffusion wear during high-speed machining Ti-6Al-4V alloy with straight tungsten carbide tools

During high-speed machining Ti-6Al-4V alloy, high-temperature at the tool–chip interface and the concentration gradient of chemical species between tool material and workpiece material support the activation of diffusion process, and therefore the crater wear forms on the rake surface of the cutting tool at a short distance from the cutting edge. In this paper, the diffusion analysis was theoretically proposed. The constituent diffusion at the contact interface between tool material and Ti-6Al-4V alloy at high-temperature environment, the crater wear on the rake surface of the tool, and the chips collected from high-speed milling Ti-6Al-4V alloy with straight tungsten carbide tools were analyzed by the scanning electron microscope with energy dispersive X-ray spectroscopy. The constituents inside the tool could diffuse into the workpiece and the diffusion layer was very thin and close to the interface. Compared with the diffusion of tungsten and carbon atoms, the pulling out and removing of the tungsten carbide (WC) particles due to cobalt diffusion dominated the crater wear mechanism on the rake surface of the cutting tool.     

Tool wear in turning of titanium alloy after thermohydrogen treatment

The influence of hydrogen contents on the tool wear has been mainly focused on the flank wear of the common tool,and the influence of hydrogen contents on the rake crater wear(main wear type) of the tool,particularly for the fine granular material tool,has been less investigated comprehensively.In this paper,for the purpose of researching the influence of hydrogen contents on tool wear,the titanium alloy Ti-6Al-4V is hydrogenated at 800 ℃ by thermohydrogen treatment technology and the turning experiments are carried out by applying uncoated WC-Co cemented carbide tool.The three-dimensional video microscope is used to take photos and measure tool wear.The results show that both of crater wear depth(KT) and average flank wear width(VB) firstly decreases and then increases with the increasing of hydrogen content.The maximum reducing amplitude of KT and VB is about 50% and 55%,respectively.Under the given conditions,the optimum hydrogen content is 0.26%.It is considered that the reduction of cutting temperature is an important factor for improving tool wear after the Ti-6Al-4V alloy is properly hydrogenated.Furthermore,the reasons of hydrogen effect on the tool wear are chiefly attributed to comprehensive effect of hydrogen contents on microstructure,physical properties and dynamic mechanical properties of the Ti-6Al-4V alloy.The proposed research provides the basic data for evaluating the machinability of hydrogenation Ti-6Al-4V alloy,and promotes practical application of thermohydrogen treatment technology in titanium alloys.     

硬质合金刀具高速车削钛合金的切削性能研究

采用单因素试验法,用未涂层硬质合金刀具和TiAlN涂层硬质合金刀具对Ti-6Al-4V钛合金进行了高速干车削试验,通过对切削过程中切削力、刀具寿命、切削温度以及加工表面粗糙度的分析,得出了两种刀具高速干车削钛合金的切削性能,为钛合金高速切削刀具的设计提供了试验依据。     

Performance evaluation of PVD TIALN coated carbide tools vis-à-vis uncoated carbide tool in turning of titanium alloy (Ti-6Al-4V) by simultaneous minimization of cutting energy,dimensional deviation and tool wear

Titanium alloys are difficult-to-machine materials because of their poor machinability characteristics. Machining and machining performance evaluation for such materials is still a challenge. Individual machining performance indices like cutting forces, cutting energy and tool wear lead to ambiguous understanding. In this work, a Cumulative Performance Index (CPI) is defined which amalgamates non-dimensional forms of specific cutting energy, back force and average principal flank wear in turning. The CPI focuses upon simultaneous minimization of specific cutting energy, dimensional deviation and average principal flank wear. The defined index is then used to evaluate performance of five commercially available physical vapor deposited (PVD) TiAlN coated tungsten carbide/cobalt inserts vis-à-vis uncoated tungsten carbide/cobalt insert in turning of Ti-6Al-4V. Cutting forces were monitored during turning and tool wear was measured after turning experiments. The results showed that the performance of coated inserts was either comparable or poor than uncoated insert; and in no case, coated inserts performed better than uncoated insert. Although commercial recommendations are in place to use PVD coated inserts for enhanced machinability of titanium alloys, the use of coated inserts is not justified keeping in view the energy spent in coating and insignificant improvement in performance.     

高速车削钛合金时硬质合金刀具和涂层刀具的寿命分析

采用硬质合金刀具和硬质合金TiMN涂层刀具对Ti-6Al-4V钛合金进行高速干车削正交试验,并通过多元线性回归分析得出硬质合金刀具和涂层刀具的寿命经验公式.分析表明:随着所选用的切削参数值的升高,刀具的使用寿命急剧减少,其中速度v对刀具使用寿命的影响最大.涂层刀具在低速切削加工钛合金时其寿命优于未涂层刀具,随着速度的提高,涂层刀具的优势迅速减小.当切削速度低于85 m/min,刀具寿命经验公式可以作为数控机床自动换刀的刀具寿命标准.     

钛合金切削加工中刀具寿命和刀具磨损的研究

钛合金是典型的难加工材料,提高钛合金的加工效率和刀具寿命是急需解决的问题。本文选用Ti-6Al-4V作为工件材料,选取两种不同的硬质合金和一种聚晶金刚石(PCD)作为刀具材料,对切削加工中刀具寿命和刀具磨损进行了试验研究。研究结果表明:PCD刀具寿命明显高于硬质合金刀具,在高速下优势尤其明显;两种硬质合金刀具低速下主要是粘结磨损,高速下主要是粘结磨损、扩散磨损和氧化磨损;PCD刀具主要是微崩刃和石墨化引起的沟槽磨损。     

Influence of cutting speed on cutting force,flank temperature,and tool wear in end milling of Ti-6Al-4V alloy

Tool wear is one of the most important problems in cutting titanium alloys due to the high-cutting temperature and strong adhesion. Recently, the high-speed machining process has become a topic of great interest for titanium alloys, not only because it increases material removal rates, but also because it can positively influence the properties of finished workpiece. However, the process may result in the increase of cutting force and cutting temperature which will accelerate tool wear. In this paper, end milling experiments of Ti-6Al-4V alloy were conducted at high speeds using both uncoated and coated carbide tools. The obtained results show that the cutting force increases significantly at higher cutting speed whether the cutter is uncoated carbide or TiN/TiAlN physical vapor deposition (PVD)-coated carbide. For uncoated carbide tools, the mean flank temperature is almost constant at higher cutting speed, and no obvious abrasion wear or fatigue can be observed. However, for TiN/TiAlN PVD-coated carbide tools, the mean flank temperature always increases as the increase of cutting speed, and serious abrasion wear can be observed. In conclusion, the cutting performance of uncoated inserts is relatively better than TiN/TiAlN PVD-coated inserts at a higher cutting speed.     

Wear characteristics of cemented carbide tool in dry-machining Ti-6Al-4V

In machining titanium alloys, due to the low thermal conductivity and high chemical activity of titanium alloys, tool wear is serious and processing efficiency is very low. To avoid the effects of impurities, which were brought by the cutting fluid, the uncoated cemented carbide tool (WC-Co), which was suitable for cutting titanium alloys, was used for the experiments of dry-turning titanium alloy Ti-6Al-4V. A scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometer (EDS) was used to analyze tool wear mechanism. Based on analyzing the friction characteristic of tool–chip interface, tool wear mechanism was also studied and a physical evolution model of tool wear was established. The results showed that there existed serious adhesion, diffusion and oxidation at tool–chip interface and increasing cutting speed accelerated their occurrence. The physical evolution of tool wear behavior can reflect the loss process of tool material very well.     

基于XPS硬质合金刀具氧化磨损的试验分析

采用多功能表面分析系统对车铣加工Ti6Al4V钛合金的硬质合金刀具进行X射线电子能谱分析(XPS)。通过对磨损区域进行全谱扫描和精细谱扫描,应用XPSPEAK4.1和Origin7.5对所得数据进行分峰拟合处理,最后分析了所生成的氧化物对刀具磨损和刀具寿命的影响。试验结果表明涂层材质为S30T的刀具磨损表面有Ti O_2、Al_2O_3、Co O和Ti N等物质生成;H13A非涂层材质刀具磨损表面有Ti O_2、WO3和Co_3O_4等氧化物生成。     

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

ABSTRACT

Superalloys with burr-free parts are most preferably used in biomedical, aerospace, marine and automotive applications. In order to reduce the global pollution content, industries strive to execute stringent green manufacturing technologies. There is a need to investigate the different available tools in high-speed micro-milling process to achieve desired burr free with good surface finish on super alloys without using traditional coolants. In machining of titanium and its alloys, because of low thermal conductivity and reactivity with tool materials instigate the burr formation on work material and lowers the tool performance. The main objective of this article is to investigate the top burr formation in high-speed micro-end milling of alpha + beta-titanium alloy-grade 23 ELI (Ti-6Al-4V) under dry cutting conditions using Uncoated and physical vapor deposition coated AlTiN, TiAlN tungsten carbide end mills. Machining performance of the three cutting tools was compared. From the comparison of cutting tools for machining titanium alloy-grade 23, it is found that coated TiAlN tools produce less burr formation than coated AlTiN and uncoated tungsten carbide tools.     

A Preliminary Study of Chemical Solubility of Ultra-Hard Ceramic AlMgB14 in Titanium: Reconciliation of Model with Experiment

This article investigates the chemical wear behavior of the ultra-hard ceramic AlMgB₁₄ and cemented tungsten carbide for machining aerospace alloys. The chemical interdiffusivity of AlMgB₁₄ against pure Ti and Ti-6Al-4V, in comparison with cemented carbide (WC-6%Co) cutting tool was investigated by means of diffusion couple experiments. The chemical composition profiles of various tool-workpiece combinations were determined by electron probe microanalysis after exposing the couples to 1000°C for 120 h in vacuum. Thermodynamic calculations of the chemical solubility of AlMgB₁₄ show that the experimental diffusion results are in reasonable agreement with the predicted behavior. It is shown that AlMgB₁₄ is significantly less soluble in titanium under static diffusion conditions, and therefore, shows considerable promise as a potential cutting tool for machining Ti alloys.     

Progressive tool failure in high-speed dry milling of Ti-6Al-4V alloy with coated carbide tools

This paper presents a detailed analysis of tool failure progression through an experimental study of high speed milling of Ti-6Al-4V alloy with CVD (Ti(C, N)-Al₂O₃)-coated carbide tools. The progressive tool failure characteristics under a variety of different cutting conditions were investigated. Cutting forces components and transient infrared temperature during the machining processes have been measured along with corresponding progressive tool wear when milling using coated carbide inserts under dry machining conditions. Optical microscope and scanning electron microscopic analysis results clearly show the different dominant wear regions at different stages of machining with coated carbide tools. The experimental results demonstrate that the cutting forces and the cutting temperature produced during the machining process showed an increasing trend with the tool failure progression, which in turns accelerated the tool wear progression and caused the change of the tool failure mechanisms. Furthermore, the progressive tool failure mechanisms were analyzed qualitatively. The cutting speed was correlated with progressive tool failure mechanisms, and the different conditions of friction and normal stresses caused by different cutting force and cutting temperature under different cutting speeds resulted in the varieties of progressive tool failure mechanisms.     

Assessment of the machinability of Ti-6Al-4V alloy using the wear map approach

The high strength to density ratio of titanium alloys coupled with excellent corrosion resistance even at elevated temperatures make them ideal for aerospace applications. Moreover, the biocompatibility of titanium also enables its widespread use in the biomedical and food processing industries. However, the difficulty in machining titanium and its alloys along with the high cost of its extraction from ore form presents a major economic constraint. In the context of machining economics, the wear map approach is very useful in identifying the most suitable machining parameters over a feedrate–cutting velocity plane. To date, wear maps have only been prepared for the machining of ferrous alloys. In this article, a review of the machinability of Ti-6Al-4V alloy is presented with emphasis on comparing the wear performance of various tool materials. In addition, a new wear map for Ti-6Al-4V alloy is presented based on unified turning tests using H13A grade carbide inserts. This wear map can be used as a guide in the selection of cutting variables that ensure the least tool wear rates. This article contrasts the occurrence of a safety zone in the case of machining steels to that of an avoidance zone for Ti-6Al-4V alloy.     

Comparative investigation on using cryogenic machining in CNC milling of Ti-6Al-4V titanium alloy

Ti-6Al-4V titanium alloy is one of the most important materials in industry, 80% of which is used in aerospace industry. Titanium alloys are also notoriously difficult-to-machine materials owing to their unique material properties imposing a major bottleneck in manufacturing systems. Cryogenic cooling has been acknowledged as an alternative technique in machining to improve the machinability of different materials. Although milling is considered to be the major machining operation for the manufacture of titanium components in aerospace industries, studies in cryogenic machining of titanium alloys are predominantly concentrated on turning operations. To address this gap, this article provides an investigation on the viability of cryogenic cooling in CNC end-milling of aerospace-grade Ti-6Al-4V alloy using liquid nitrogen in comparison with traditional machining environments. A series of machining experiments were conducted and surface roughness, tool life, power consumption, and specific machining energy were investigated for cryogenic milling as opposed to conventional dry and flood cooling. Analysis revealed that cryogenic machining using liquid nitrogen has the potential to significantly improve the machinability of Ti-6Al-4V alloy in CNC end-milling using solid carbide cutting tools and result in a paradigm shift in machining of titanium products. The analysis demonstrated that cryogenic cooling has resulted in almost three times increased tool life and the surface roughness was reduced by 40% in comparison with flood cooling.     

Experimental investigations on effects of tool flank wear on surface integrity during orthogonal dry cutting of Ti-6Al-4V

Machining titanium alloy Ti-6Al-4V is a challenging task since tool flank wear adversely affects surface integrity. Quantitative effects of predetermined tool flank wear values (VB) on the surface integrity were investigated through the orthogonal dry cutting of Ti-6Al-4V. Experimental results indicated that three-dimensional (3D) average surface roughness increased with the VB ranging from 0 to 0.2 mm but decreased at VB = 0.3 mm. Given the effects of rubbing and ironing enhanced, surface material burning and plastic flows emerged on the machined surface at VB = 0.3 mm. Not only the plastic deformation layer became deeper but also the grains were greatly distorted with the increase of tool flank wear. When machined by using the tool at VB = 0.3 mm, the β phase of Ti-6Al-4V decreased near the machined surface layer than that of using the fresh tool. Besides, the depth of work-harden layer increased from 20 to 60 μm with the VB increasing from 0 to 0.3 mm. The softened layer was generated near the machined surface by using the tool at VB = 0.3 mm. In addition, the residual compressive stresses of the machined surface had the trend of decreasing. Experimental results indicated that the VB less than 0.2 mm was the most suitable condition for better surface integrity during orthogonal dry cutting of Ti-6Al-4V. This study aims at providing experimental data for optimizing the processing parameters and improving the surface integrity of Ti-6Al-4V.     

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti₆Al₄V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5 mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti₆Al₄V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.     

Blend of sharpness and strength on a ball nose endmill geometry for high speed machining of Ti6Al4V

The applications of titanium alloys are increasingly common at marine, aerospace, bio-medical and precision engineering due to its high strength to weight ratio and high temperature-withstanding properties. However, whilst machining the titanium alloys using the solid carbide tools, even with application of high pressure coolant, reduced tool life was widely reported. The generation of high temperatures at the tool–work interface causes adhesion of work material on the cutting edges, and hence, shorter tool life was reported. In order to reduce the high tool–work interface temperature-positive rake angle, higher primary relief and higher secondary relief were configured on the ball nose endmill cutting edges. Despite of careful consideration of tool geometry, after an initial working period, the growth of flank wear accelerates the high cutting forces followed by work material adhesion on the cutting edges. Hence, it is important to blend the strength, sharpness, geometry and surface integrity on the cutting edges so that the ball nose endmill would exhibit an extended tool life. This paper illustrates the effect of ball nose endmill geometry on high speed machining of Ti6Al4V. Three different ball nose endmill geometries were configured, and high speed machining experiments were conducted to study the influence of cutting tool geometry on the metal cutting mechanism of Ti-6Al-4V alloy. The high speed machining results predominantly emphasize the significance of cutting edge features such as K-land, rake angle and cutting edge radius. The ball nose endmills featured with a short negative rake angle of value ?5° for 0.05～0.06 mm, i.e. K-land followed by positive rake angle of value 8°, has produced lower cutting forces signatures for Ti-6Al-4V alloy.     

Experimental studies and optimization of process parameters for burrs in dry drilling of stacked metal materials

In the drilling of stacked materials, burrs produced on both the surface layer and the interlayer have some undesirable characters with regard to assembly quality, and deburring is a time consuming and costly operation. This paper presented an experimental study on the dry drilling of Ti-6Al-4V titanium alloy and 7075-T6 aluminum alloy stacked materials, which was performed by using uncoated cemented carbide drills. The burr size was evaluated at various spindle speeds, feed rates, stacking sequences, and clamp forces. After which, the burr morphology was observed and analyzed. Finally, a new multi-objective optimization algorithm, which was derived from the game theory, was used to select optimum process parameters to minimize burr size. The best process parameters recorded in this paper were at the spindle speed of 2,000?r/min, the feed rate of 0.075?mm/r, the pressure of 0.3?MPa, and the stacking sequence of the Ti-6Al-4V titanium alloy on top of the 7075-T6 aluminum alloy.     

The effect of cryogenic treatment on tapping

This study was realized with two different types (flat and thread rolled) of coated (TiAlN), uncoated, and cryogenically treated taps (uncoated). The tapping processes were carried at four different cutting speeds (2, 3, 4, and 5 m/min) and 1.25 mm/rev feed rate under dry and wet cutting conditions on the Ti-6Al-4 V alloy. The measured cutting forces (cutting torque) were evaluated according to the cutting tool and cutting parameters. The best results in terms of cutting torque were obtained with straight flutes with spiral point taps. For the coated cutting tools, it was seen that the cutting torque was higher with respect to the other tools. The cutting fluid caused decreases in cutting forces for both of the cutters. Under dry cutting conditions, in the cryogenically treated tool, cutting torques came out to be lower with respect to the coated and uncoated tool.     

Study on cutting forces and experiment of MoS2/Zr-coated cemented carbide tool

MoS₂/Zr composite films were deposited on the cemented carbide YT14 (WC+14%TiC+6%Co) by medium-frequency magnetron sputtered coupled with multi-arc ion plating techniques. The thickness, micro-hardness, and coating/substrate adhesion strength of the coatings were tested. Surface morphologies of the composite coatings, as well as wear features, were investigated by scanning electron microscopy. Dry machining tests on hardened steel were carried out with the coated tool and uncoated YT15 tool. The variation of cutting forces for 45# hardened steel was tested by the Kistler force tester. The result shows that the cutting forces of coated tool were decreased by 25–30%, and flank wear resistance was improved by 30–35% in comparison with the uncoated YT15 tool. Through the analysis of cutting force distribution theory, the lower mean shear stress on the MoS₂/Zr-coated tool face leads to the decrease of cutting force and increase of tool wear resistance.