Machining of Titanium Alloy (Ti-6Al-4V)—Theory to Application

This article correlates laboratory-based understanding in machining of titanium alloys with the industry based outputs and finds possible solutions to improve machining efficiency of titanium alloy Ti-6Al-4V. The machining outputs are explained based on different aspects of chip formation mechanism and practical issues faced by industries during titanium machining. This study also analyzed and linked the methods that effectively improve the machinability of titanium alloys. It is found that the deformation mechanism during machining of titanium alloys is complex and causes basic challenges, such as sawtooth chips, high temperature, high stress on cutting tool, high tool wear and undercut parts. These challenges are correlated and affected by each other. Sawtooth chips cause variation in cutting forces which results in high cyclic stress on cutting tools. On the other hand, low thermal conductivity of titanium alloy causes high temperature. These cause a favorable environment for high tool wear. Thus, improvements in machining titanium alloy depend mainly on overcoming the complexities associated with the inherent properties of this alloy. Vibration analysis kit, high pressure coolant, cryogenic cooling, thermally enhanced machining, hybrid machining and, use of high conductive cutting tool and tool holders improve the machinability of titanium alloy.     

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.     

EFFECT OF COOLANT PRESSURE,NOZZLE DIAMETER,IMPINGEMENT ANGLE AND SPOT DISTANCE IN HIGH PRESSURE COOLING WITH NEAT OIL IN TURNING Ti-6AL-4V

Though titanium alloys are being increasingly sought in a wide variety of engineering and biomedical applications, their manufacturability, especially machining and grinding imposes lot of constraints. Titanium alloys are readily machinable provided the cutting velocity is in the range of 30–60 m/min. To achieve higher productivity, if the cutting velocity is enhanced to 60–120 m/min and beyond, rapid tool wear takes place diminishing the available tool life. Tool wear in machining of titanium alloys is mainly due to high cutting zone temperature localised in the vicinity of the cutting edge and enhanced chemical reactivity of titanium with the tool material. Rapid tool wear encountered in machining of titanium alloys is a challenge that needs to be overcome. High pressure cooling in machining is a very promising technology for enhancing tool life and productivity via appropriate cooling and lubrication. The present investigation is an attempt to study the effects of jet application parameters, i.e., coolant pressure, angle of impingement of the jet, spot distance and nozzle diameter on tool wear and chip morphology and to compare the effectiveness while turning Ti-6Al-4V bars under high pressure cooling with neat oil. Results indicated that at a cutting speed of 85 m/min and feed of 0.2 mm/rev, high pressure cooling provided a tool life of 24 min vis-à-vis 12 min under cryogenic cooling.     

高速干切削铁基粉末冶金零件时细晶粒硬质合金刀具的切削性能研究

用细晶粒硬质合金刀具进行了铁基粉末冶金零件的高速干切削试验。研究了切削参数与刀具耐用度以及加工表面粗糙度的关系,给出了刀具的主要磨损形态,通过能谱分析研究了刀具的磨损机理。结果表明:所选用细晶粒硬质合金刀具具有较高的刀具耐用度和较好的加工表面粗糙度,适合于铁基粉末冶金的加工;细晶粒硬质合金的主要磨损形态是前刀面的月牙洼磨损;主要磨损机理是扩散磨损、粘结磨损。     

高速切削钛合金PCBN刀具损坏机理的研究

通过扫描电子显微镜(SEM)观察和能量分散光谱(EDS)扫描分析,对PCBN刀具高速切削钛合金Ti6Al4V时的刀具损坏机理进行了研究,发现PCBN刀具损坏机理主要是机械磨损、氧化磨损和脆性破损。研究还证明了在不同的切削条件下,占主导地位的损坏机理有所不同,当切削用量处于低水平或切削初期和中期时,以机械磨损为主,而随着切削用量的增加或是切削后期,切削热增加,氧化磨损和脆性破损越来越突出。     

钛合金零件高速铣削刀具磨损的试验研究

高速铣削钛合金时,由于切削区内的切削温度高,加剧了刀具的磨损。通过对钛合金TC4的高速铣削实验,得出带TiA lN涂层的硬质合金刀具切削钛合金TC4时的刀具磨损的变化规律和刀具耐用度公式。通过对刀具磨损特性的分析,研究结果主要是刀具表面层的粘结相Co在高温下丧失对WC颗粒的结合强度,磨损机理以高温下的粘结层撕裂磨损为主。     

陶瓷刀具材料切削加工G4335V高强钢时的耐磨性能研究

本文对Ａｌ２Ｏ３／ＴｉＣ陶瓷刀具材料切削加工Ｇ４３３５Ｖ高强钢时的切削性能和耐磨性进行了试验研究。结果表明：在低速切削条件下，Ａｌ２Ｏ３／ＴｉＣ陶瓷刀具和硬质合金刀具（ＹＴ１５）的抗后面磨损能力相差不大，而在高速切削条件下，前者的抗后面磨损能力远高于后者。Ａｌ２Ｏ３／ＴｉＣ陶瓷刀具前面的磨损形式主要为粘结磨损，后面的磨损形式主要为磨粒磨损。     

Tool Wear in Ultra-Precision Diamond Cutting of Non-Ferrous Metals with a Round-Nose Tool

Tool wear causes the loss of the original profile accuracy of the cutting edge and degrades the form accuracy of machined surfaces. The purpose of this research is to clarify the tool-wear mechanism and its effect on machining accuracy in ultra-precision diamond cutting with a round-nose tool. Controlled cutting tests of Al 6061 were performed on a two-axis, ultra-precision turning machine. Single-crystal diamond tools were used in the experiment. The tool-wear pattern was studied based on the observation of the wear zone using a scanning electron microscope. The topographic characteristics of the chips were examined and the effect of the micro-cutting geometry on the tool wear was investigated theoretically and experimentally. The mutual effects of crystallographic dependence of wear resistance of diamonds and the change in the cutting velocity during machining are believed to be the main reasons causing uneven wear along the cutting edge. Measures for reducing the effect of tool wear are also discussed.     

Analysis of tool wear patterns in finishing turning of Inconel 718

This paper focuses on the analysis of tool wear mechanisms in finishing turning of Inconel 718, one of the most used Ni alloys, both in wet and dry cutting. Cemented carbides, ceramics and CBN tools are suitable for machining Ni alloys; coated carbide tools are competitive for machining operations of Ni alloys and widely used in industry. Commercial coated carbide tools (multilayer coating TiAl/TiAlN recommended for machining Ni alloys) were studied in this work. The feasibility of two inserts tested for dry cutting of Inconel 718 has been shown in the work. Experimental test were performed in order to analyze wear patterns evolution. It was found great influence of side cutting edge angle in tool wear mode.     

铁基粉末冶金材料的高速干切削试验研究

用陶瓷刀具、涂层刀具和硬质合金刀具进行了铁基粉末冶金零件的干切削对比试验,研究了切削速度、切削深度以及进给速度与刀具耐用度和加工表面粗糙度的关系,分析了陶瓷刀具的磨损机理。结果表明所选用陶瓷刀具的切削性能明显优于涂层刀具和硬质合金刀具;陶瓷刀具前刀面主要磨损形式为月牙洼磨损与剥落,后刀面的主要磨损原因为磨粒磨损;认为陶瓷刀具更适合用于粉末冶金零件的切削加工。     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.     

激光超声复合切削硬质合金的刀具磨损及其对工件表面质量的影响

基于激光加热辅助切削和超声椭圆振动切削提出了激光超声复合切削加工工艺。采用聚晶立方氮化硼(PCBN)刀具对YG10硬质合金进行了常规切削,超声椭圆振动切削,激光加热辅助切削和激光超声复合切削对比试验。检测了刀具磨损量、刀具磨损形貌、工件表面粗糙度以及工件表面形貌,并通过扫描电镜(SEM)对刀具磨损区域进行了能谱分析,同时研究了激光超声复合切削硬质合金时PCBN刀具的磨损及其对工件表面质量的影响。最后,与常规切削、超声振动切削及激光加热辅助切削进行了对比试验。结果表明:激光超声复合切削时刀具使用寿命显著增加,加工后的工件表面粗糙度平均值分别降低了79%、60%和64%,且工件表面更加平整光滑。激光超声复合切削硬质合金时,PCBN刀具的前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为较窄的三角形磨损带和较浅的凹坑和划痕;刀具的失效机理主要为黏接磨损、氧化磨损和磨粒磨损的综合作用。     

基于后刀面磨损的铣削加工误差研究

对铣削加工过程中后刀面磨损对加工精度的影响进行了分析和研究,建立了基于刀具后刀面磨损的铣削加工误差的数学模型。     

Problems and solutions in machining of titanium alloys

Titanium alloys are known as difficult-to-machine materials. The problems of machining titanium are many folds which depend on types of titanium alloys. This paper investigates the underlying mechanisms of basic challenges, such as variation of chip thickness, high heat stress, high pressure loads, springback, and residual stress based on the available literature. These are responsible for higher tool wear and worse machined surface integrity. In addition, many cutting tool materials are inapt for machining titanium alloys as those materials are chemically reactive to titanium alloys under machining conditions. To address these problems, latest techniques such as application of high pressure coolant, cryogenic cooling, tap testing, thermally enhanced machining, hybrid machining, and use of high conductive cutting tool and tool holder have also been discussed and correlated. It seems that all the solutions are not yet well accepted in the industrial domain; further advancement in those fields are required to reduce the machining cost of titanium alloys.     

Tool crater wear depth modeling in CBN hard turning

Hard turning has been receiving increased attention because it offers many possible benefits over grinding in machining hardened steel. The wear of cubic boron nitride (CBN) tools, which are commonly used in hard turning, is an important issue that needs to be better understood. For hard turning to be a viable replacement technology, the high cost of CBN cutting tools and the cost of down-time for tool changing must be minimized. In addition to progressive flank wear, microchipping and tool breakage (which lead to early tool failure) are prone to occur under aggressive machining conditions due to significant crater wear and weakening of the cutting edge. The objective of this study is to model the CBN tool crater wear depth (K_T) to guide the design of CBN tool geometry and to optimize cutting parameters in finish hard turning. First, the main wear mechanisms (abrasion, adhesion, and diffusion) in hard turning are discussed and the associated wear volume loss models are developed as functions of cutting temperature, stress, and other process information. Then, the crater wear depth is predicted in terms of tool/work material properties and process information. Finally, the proposed model is experimentally validated in finish turning of hardened 52100 bearing steel using a low CBN content tool. The comparison between model predictions and experimental results shows reasonable agreement, and the results suggest that adhesion is the dominant wear mechanism within the range of conditions that were investigated.     

Improvements in the thread cutting torque for a 6082-T6 aluminum-based alloy with tapping tools utilizing diamond coating

The use of thin film diamond as a hard tool coating offers a significant wear protection in numerous machining operations and increases considerably tool's lifetime. The extreme hardness of the diamond is especially needed in machining highly abrasive materials such as aluminum-silicon alloys. Tapping is widely used for thread fabrication and it is often a time consuming process causing a delay on an automated production line. This study investigated diamond coatings in thread cutting and the aim was to gain knowledge about the performance of diamond-coated taps. PVD diamond coatings were deposited using ultra short pulsed laser deposition (USPLD) techniques. Another type of nanodiamond coating was a chrome-nanodiamond (CND) coating deposited by a two-phase electrochemical process to produce a metal matrix with embedded detonation nanodiamond (DND) particles. The main points were the analysis of tool torques of the thread machining data, sticking of aluminum alloy and wear behavior and mechanism of tested tapping tools. The tested tools were analyzed by Scanning Electron Microscopy (SEM) regarding tool wear and sticking of aluminum on tool surface caused by mechanical interaction. Coating approaches turned out to provide 13–30% improvements in cutting and 37–51% improvements in reversing for overall mean torques compared to uncoated reference tools.     

Tool wear monitoring in ramp cuts in end milling using the wavelet transform

Tool wear identification and estimation present a fundamental problem in machining. With tool wear there is an increase in cutting forces, which leads to a deterioration in process stability, part accuracy and surface finish. In this paper, cutting force trends and tool wear effects in ramp cut machining are observed experimentally as machining progresses. In ramp cuts, the depth of cut is continuously changing. Cutting forces are compared with cutting forces obtained from a progressively worn tool as a result of machining. A wavelet transform is used for signal processing and is found to be useful for observing the resultant cutting force trends. The root mean square (RMS) value of the wavelet transformed signal and linear regression are used for tool wear estimation. Tool wear is also estimated by measuring the resulting slot thickness on a coordinate measuring machine.     

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.     

Enhancing the machining performance by cutting tool surface modifications: a focused review

In machining, cutting tools suffer from severe surface wear, especially in the cutting of difficult-to-cut materials. A major cause of tool wear is the friction generated at the tool-work and tool-chip interfaces, which produces a great deal of frictional heat and abrasion. In order to extend tool life and improve the quality of machined components, a host of techniques have been applied to modify the rake and flank faces of cutting tools. These techniques aim at providing cutting tools with improved resistance to external loading, better tribological performance and/or better chemical stability. This article presents a review of the fundamentals behind which the friction and wear in machining are reduced by modifying the cutting tool surface with the commonly used techniques, such as surface coating, high energy beam treatment, and surface texturing. The effects of these surface modifications on improving the cutting performance are also analyzed. Future research directions are finally discussed.     

The effect of cutting parameters and cutting tools on machining performance of carbon graphite material

Abstract

The present study focuses on the effects of cutting speed, feed rate and cutting tool material on the machining performance of carbon graphite material. Polycrystalline Diamond (PCD) cutting tools are used in machining experiments and its performance is compared with the tungsten carbide (WC) and Cubic Boron Nitride (CBN) tools. Machining performance criteria such as flank and nose wear and resulting surface topography and roughness of machined parts were studied. This study illustrates that feed rate and cutting tool material play a dominant role in the progressive wear of the cutting tool. The highest feed rate and cutting speed profoundly reduce the tool wear progression. The surface roughness and topography of specimens are remarkably influenced from the tool wear. Major differences are found in the wear mechanisms of PCD and WC and CBN cutting tools.