Machinability of cobalt-based and cobalt chromium molybdenum alloys - a review

Cobalt chrome molybdenum alloy is considered as one of the advanced materials which is widely gaining popularity in various engineering and medical applications. However, it is categorized as difficult to machine material due to its unique combination of properties which include high strength, toughness, wear resistance and low thermal conductivity. These properties tend to hinder the machinability of this alloy which results in rapid tool wear and shorter tool life. This paper presents a general review of the materials’ characteristics and properties together with their machinability assessment under various machining conditions. The trend of machining and future researches on cobalt-based and cobalt chromium molybdenum alloys are also discussed adequately

A novel indirect cryogenic cooling system for improving surface finish and reducing cutting forces when turning ASTM F-1537 cobalt-chromium alloys

This paper presents a novel indirect cryogenic cooling system, employing liquid nitrogen (LN2) as a coolant for machining the difficult-to-cut ASTM F-1537 cobalt-chromium (CoCr) alloy. The prototype differs from the already existing indirect cooling systems by using a modified cutting insert that allows a larger volume of cryogenic fluid to flow under the cutting zone. For designing the prototype analytical and finite element, thermal calculations were performed; this enabled to optimize the heat evacuation of the tool from the rake face without altering the stress distribution on the insert when cutting material. Turning experiments on ASTM F-1537 CoCr alloys were performed under different cutting conditions and employing indirect cryogenic cooling and dry machining, to test the performance of the developed system. The results showed that the new system improved surface roughness by 12%, and cutting forces were also reduced by 12% when compared with the existing indirect cryogenic cooling technique

Prediction of Surface Quality Using Artificial Neural Network for the Green Machining of Inconel 718

Inconel 718 is a nickel-based heat resistant super-alloy (HRSA) that is widely used in many aerospace and automotive applications. It possesses good properties like corrosion resistance, high strength, and exceptional weld-ability but it is considered as one of the most difficult alloys to cut. Recently researchers have focused on employing many machining strategies to improve machinability of Inconel 718. This research work presents the experimentation of wet milling of Inconel 718 using a carbide tool with biodegradable oil. Surface quality is the major aspect of machinability. Hence input parameters such as depth of cut, cutting speed, and feed rate are considered to study their effect on surface quality. Nine experimental runs based on an L9 orthogonal array are performed. Additionally, analysis of variance (ANOVA) is applied to identify the most significant factors among cutting speed, feed rate, and depth of cut. Moreover, this research work presents the Artificial Neural Network (ANN) model for predicting the surface roughness based on experimental results. The ANN based-decision-making model is trained by using acquired experimental values. Visual Gene Developer 2.0 software package is used to study the efficiency of ANN. The presented ANN model demonstrates a very good statistical performance with a high correlation and extremely low error ratio between the actual and predicted values of surface roughness and tool wear

Advanced Powder Metallurgy Technologies

Powder metallurgy is a group of advanced processes used for the synthesis, processing, and shaping of various kinds of materials. Initially inspired by ceramics processing, the methodology comprising the production of a powder and its transformation to a compact solid product has attracted attention since the end of World War II. At present, many technologies are availabe for powder production (e.g., gas atomization of the melt, chemical reduction, milling, and mechanical alloying) and its consolidation (e.g., pressing and sintering, hot isostatic pressing, and spark plasma sintering). The most promising methods can achieve an ultra-fine or nano-grained powder structure, and preserve it during consolidation. Among these methods, mechanical alloying and spark plasma sintering play a key role. This book places special focus on advances in mechanical alloying, spark plasma sintering, and self-propagating high-temperature synthesis methods, as well as on the role of these processes in the development of new materials

Investigating the effects of cryogenic processing on the wear performance and microstructure of engineering materials

Cryogenic processing (or cryogenic treatment or ‘cryotreatment’) includes a range of batch heat treatment processes conducted at temperatures below 193K (-80°C). These processes have been industrially applied since the first half of the Twentieth Century and commercially available for around forty years in the United States and Europe. During this time remarkable improvements (of up to 1257%) in the wear resistance of tool steels have been reported, along with smaller but significant improvements in hardness and other mechanical properties. While martensitic tool steels have been the focus of the bulk of published research in this field, substantial effects have also been reported in other important engineering materials. However, coherent findings backed up by sound experimental results, analyses and appropriate metallurgical investigations have so far proved elusive. Currently, a significant portion of cryogenic treatment services are applied to automotive brake rotors and industrial cutting tools. Therefore a range of materials used in these applications were subjected to a combination of tribological testing and microstructural analyses to evaluate the effects of deep cryogenic treatment (93K). Deep cryogenic treatment (DCT) was determined to improve the sliding wear resistance of EN10083 C50R pearlitic carbon steel, and AISI A2, D6 and M2 austenitic (as-cast) tool steels. Qualitative observations suggested that improvements in these tool steels were due to an increase in <100nm carbides following DCT. In the case of pearlitic carbon steel, however, no such observations were made, even following further characterisation of the material. It was theorised that the precipitation of nano carbides, along grain boundaries that were unable to be thoroughly investigated, were instead responsible. Mixed changes in the wear resistance of SAE J431 G10 grey cast iron are reported, thought to be as a result of the degradation of graphite flakes, but with similar beneficial changes as theorised to occur in C50R steel thought likely. Furthermore, DCT was determined to have improved the abrasive wear resistance of SHM H13A cobalt-bonded tungsten carbide (WC-Co) turning inserts, when used to machine AISI 1045 steel, although indications of reduced toughness were also observed. DCT was determined to primarily effect the Co-binder phase, resulting in greater resistance to WC grain removal, but greater vulnerability to crack propagation. In discussing these results, methodologies necessary for understanding the effects of cryogenic treatments are reviewed from an industrial or ‘applications-based’ and a scientific or ‘materials-based’ perspective. Finally, the significance of these findings was critically assessed, with a range of improvements to methodologies suggested

On the mechanism of tool crater wear in titanium alloy machining

Today the aerospace industry spends hundreds of millions of dollars on the machining of titanium alloy components. And with increasing aircraft orders, there is pressure to machine at higher production rates and develop more machinable alloys (e.g. TIMETAL® 54M, TMETAL® 407) without compromising titanium’s excellent mechanical properties. Increasing the tool life by a factor of minutes can have a dramatic effect on machining cost. Unlike steels, the same tool grade is used for all titanium alloy types from alpha to beta rich, with the latter being more difficult to machine. Diffusion dominated crater wear is the primary tool wear phenomena which has yet to be fully understood. This thesis demonstrates the application of a low cost diffusion couple technique which gives a strong indication of the complex reaction mechanisms occurring at the tool-chip interface during the machining of titanium alloys. These small scale tests have been validated with large scale dynamic machining trials and strong agreement has been observed. The results have allowed for hypotheses to be made over the reaction mechanisms behind tool crater wear underpinned by key observations in the literature. Such a testing regime can be incorporated into alloy design approaches to inform the industry e.g. TIMET and Rolls-Royce about the ‘machinability’ qualities at a much earlier stage before costly machining trials. Such a method will also aid tool manufacturers to tailor tool carbide grades as well as new coatings to specific alloy chemistries. This is the first time that small scale testing such as this has shown why different alloy chemistries exhibit different tool wear characteristics. The technique is now being developed further by the aerospace manufacturing supply chain including tool manufacturers and titanium alloy producers. It will be used to; (a) develop more machinable alloys at an earlier stage in the alloy design development and (b) match different titanium alloys to more appropriate tool materials and new coatings. As such this thesis should be of interest to a broad readership including mechanical engineers and materials scientists as well as the machining and manufacturing community

A Methodology For Coronary Stent Product Development: Design, Simulation And Optimization

Coronary stents are slotted tubes made of metals, alloys, or polymers. They are deployed in human arteries, which are blocked by calcified plaque, to keep the arteries open and allow the blood to flow with ease. Coronary stents have been proven as an effective treatment device for heart diseases such as acute myocardial infarction. Design plays an important role for coronary stents to perform the clinical functions properly. Various parameters such as materials, structures, dimensions, and deployment methods etc., need to be considered in the design of coronary stents. There are numerous studies on design of coronary stents and many significant manufacturing methods have been reported in the past two decades. However, there is no comprehensive methodology for the product development of coronary stents in terms of design, simulation, and manufacturing. The objective of this research is to develop a methodology for coronary stents product development that focuses on design, simulation, and manufacturing. The methodology brings together insights from numerous engineering design disciplines with the aim of making coronary stent development more flexible and more cost-efficient The product development methodology for coronary stents is executed through modeling and analyzing stent designs with details of design, simulation, and optimization methods. Three innovative stent designs are modeled using engineering design software (SolidWorks) and mechanical performances are simulated, evaluated, and optimized with the help of advanced engineering simulation software (ANSYS). In this study, the performance of stents based on stress, strain, and total deformation during deployment are analyzed and compared with commercially available optimal design i.e., Cypher (J & J Co.) stent, which acts as a benchmark design

Machining of biocompatible materials: Recent advances

Machining of biocompatible materials is facing the fundamental challenges due to the specific material properties as well as the application requirements. Firstly, this paper presents a review of various materials which the medical industry needs to machine, then comments on the advances in the understanding of their specific cutting mechanisms. Finally it reviews the machining processes that the industry employs for different applications. This highlights the specific functional requirements that need to be considered when machining biocompatible materials and the associated machines and tooling. An analysis of the scientific and engineering challenges and opportunities related to this topic are presented

Influence of CVD multilayer coating on machinability characteristics of aerospace grade stainless steel

In the recent years, aeroengine superalloys have gained high amount of research interest owing to their wide engineering application particularly in strategic environment.17-4PH (precipitation hardened) stainless steel (SS) is one such grade of aerospace alloys used to manufacture mostly small parts and mainly stator of aircraft engine in place of Titanium alloy for material cost saving.17-4PH SS falls under the category of difficult-to-cut material because of its low thermal conductivity and high ductility. Although most of the research work was concentrated on machinability of Nickel-based and Titanium based superalloy, no such work on the 17-4PH has been reported so far. Today different coated tools are widely used in machining industries. Therefore it is also essential to select suitable coating material for machining such aeroengine alloys. In order to achieve some of the objectives, the research work has been under taken aiming at investigating the influence of cutting speed (100, 140 & 190 m/min) and feed rate (0.16, 0.20 & 0.24) on various machining characteristics like chip morphology, chip reduction coefficient, tool wear, cutting force, cutting temperature and machined surface roughness. The machining operation was carried under constant depth of cut 0.5 mm and at dry environment.CVD multilayer coated (TiN/TiCN/Al2O3/ZrCN) cemented carbide (ISO P30 grade) insert has been chosen for the current study. The performance of the coated tool has also been compared with that of uncoated carbide insert of similar grade and geometry in order to understand the effectiveness of CVD multilayer coated tool during dry machining of 17-4 PH stainless steel