An Experimental Investigation in Hard Turning of AISI 4140 Steel

There is a growing demand for new and special alloys like nickel alloys, chrome- molybdenum alloys due to their special properties like high strength, light weight, and corrosive resistance. The present work is based on the experimental investigation of chrome-molybdenum alloy to study the effect of process parameters like cutting velocity, feed, and depth of cut on the output responses like force, surface roughness, tool wear. A full factorial design with 33 lay out with total 27 numbers of runs were carried out and optimum cutting condition for all three output responses was found out using grey relational analysis method. White layer formed in a hard turned component is mainly influenced by the abrasive wear of the tool. It has immense response on the performance of product so it is necessary to find out the white layer thickness. To investigate the machined surface properties like white layer and micro-hardness, the sliced machined surface was observed under scanning electron microscope (SEM) and micro-hardness tester respectively. It has been found that the as speed increases, the thickness of white layer increases due to increase in flank wear. Finally, a thermo-mechanical 2D model using finite element method available in Deform 2D TM has been prepared to investigate the output responses like force. Further, the model has been validated comparing the results of simulation with the measured results

Experimental investigation on flank wear and tool life, cost analysis and mathematical model in turning hardened steel using coated carbide inserts

Turning hardened component with PCBN and ceramic inserts have been extensively used recently and replaces traditional grinding operation. The use of inexpensive multilayer coated carbide insert in hard turning is lacking and hence there is a need to investigate the potential and applicability of such tools in turning hardened steels. An attempt has been made in this paper to have a study on turning hardened AISI 4340 steel (47 ± 1 HRC) using coated carbide inserts (TiN/TiCN/Al2O3/ZrCN) under dry environment. The aim is to assess the tool life of inserts and evolution of flank wear with successive machining time. From experimental investigations, the gradual growth of flank wear for multilayer coated insert indicates steady machining without any premature tool failure by chipping or fracturing. Abrasion is found to be the dominant wear mechanisms in hard turning. Tool life of multilayer coated carbide inserts has been found to be 31 minute and machining cost per part is Rs.3.64 only under parametric conditions chosen i.e. v = 90 m/min, f = 0.05 mm/rev and d = 0.5 mm. The mathematical model shows high determination coefficient, R2 (99%) and fits the actual data well. The predicted flank wear has been found to lie very close to the experimental value at 95% confidence level. This shows the potential and effectiveness of multilayer coated carbide insert used in hard turning applications

Hard turning of martensitic AISI 440B stainless steel

Hard turning has been in use for some time to achieve close dimensional tolerances to eliminate time consuming and costly grinding operations. The most widely used cutting tools for finish machining of hardened steels under dry cutting conditions are the ceramics and PcBN cutting tools. The purpose of this study was to investigate the machinability of hardened martensitic AISI 440 B stainless steel (HRC 42-44) using commercially available cutting tools: alumina based ceramic and PcBN, by hard turning under different machining conditions, by providing an in-depth understanding of wear mechanisms of these cutting tools. The study also developed a serrated chip formation mechanism of the workpiece and provided a deep understanding of the chemical interaction between workpiece and cBN cutting tools, through microstructural analysis of the adhered layer on the worn cutting tool. Experimental studies on the effects of cutting parameters on the tool wear mechanism, cutting forces; surface roughness, dimensional accuracy, and chip formation mechanism were investigated. The characterization of the workpiece, cutting tools, chips and wear scars on the cutting tools was performed using an X-ray diffractometer, and optical, scanning and transmission electron microscopes, as well as an energy dispersive spectroscope (EDS). The cutting speeds selected for testing the cutting tools were in the range of 100 m/min and 600 m/min, depending on the type of parameter investigated. Two depths of cut, 0.1and 0.2 mm, and three feed rates, 0.05, 0.1 and 0.15 rev/min, were selected for the experiments. Experimental results showed that the flank wear in the PcBN cutting tool is lower than that of the mixed alumina, with PcBN showing better wear resistance at all cutting conditions (about five times longer in some instances). Apart from the cutting speed, the feed rate was found as a parameter that directly influences the flank wear rate of the cutting tool. The wear mechanism for the ceramic cutting tool is predominantly abrasive wear, and for PcBN tools it was adhesive wear and abrasive wear. The abrasive wear was caused by hard carbide particles in the workpiece material resulting in grooves formed on the flank face. There was formation of a transferred layer followed by plastic deformation of the workpiece material on the rake face of the PcBN tool when cutting at low cutting speed and feed rate. At much higher cutting speeds, some form of chemical wear preceded by adhesion and abrasion was the main tool wear resulting from the chemical affinity between the PcBN tool and the workpiece. Better surface finish (Ra) was recorded for mixed ceramics but with deteriorating surface topography. The increase in the cutting speed results for improvement in the surface finish produced by both cutting tools was investigated. The final part, using the PcBN cutting tool, produced better dimensional accuracy resulting from its better wear resistance at the flank face. The results also show that good dimensional accuracy can be achieved with cBN tools using a CNC machine with high static and dimensional stiffness coupled with high precision hard turning. The influence of cutting conditions on the chip formation showed production of continuous chip at a cutting speed of 100 m/min and segmented chip at higher cutting speeds above 200 m/min by both cutting tools. The increasing cutting speed affects the formation of shear localised chips with rapid increase in shear strain rate and degree of segmentation at cutting speeds higher than 200 m/min. The microstructure of the chip produced shows the distinct carbide grain in the martensite of the work material with intense shear localisation in the primary deformation zone of the cutting tool and formation of white layer in the secondary deformation zone. The microstructure of the crater of the worn PcBN cutting tool at cutting speeds of 100 m/min and 600 m/min were studied in detail. A situ lift-out technique, in a Focused Ion Beam/SEM instrument, was used to produce thin foil specimens, which were taken out of the crater face of the PcBN tool and observed using SEM and TEM. The SEM and TEM study showed evidence of chemical interaction between the work material and the PcBN tool. Fe from the work material was found in the vicinity of TiC and AlB grains of the PcBN tool, with TiC having greater affinity for Fe. Oxidation of the elements was common in all Fe-rich areas. The microstructure of the worn PcBN cutting tool at the cutting speed of 600 m/min showed deeper penetration of Cr and Fe into the cBN tool, which was not easily detected by SEM at the cutting speed of 100 m/min. The hard turning operations using the PcBN cutting tool for substituting traditional machining operations was successfully performed in the industrial environment. The overall surface finish and dimensional accuracy generated during the application of CBN-100 for machining within the industrial environment on specified mass produced shape showed a component acceptable tolerance range with good surface finish similar to that of the grinding operation

A Comprehensive Review on AISI 4340 Hardened Steel: Emphasis on Industry Implemented Machining Settings, Implications, and Statistical Analysis

Turning of hardened AISI 4340 steel is regarded as one of the demanding challenges in machining sectors where precision tolerances are essential for automobile parts. The AISI 4340 steel is broadly utilized in forged steel automotive crankshafts systems, hydraulic forged and additional machine tool purposes because of their improved characteristics.  Moreover, one of the keys confronts in the machining of hard 4340 steel is the comparatively deprived machining behavior that reduces the functionality of the material and further leads to component  rejection at the final inspection stage. In addition, accelerated tool wear necessitates for repeated changing of cutting tool that results in higher machining and tooling costs. This comprehensive review aimed to present in-depth features on the development of machining performances using various cutting tools. This review focus is to provide a broad perceptive of the role of controllable variables during machining of hardened steel. This review analysis examines the response variables and its advantages on chip morphology and heat generation. The comprehensive overview of machining settings, key machinability indicators and statistical analysis for AISI 4340 steel has been presented. This overview will provide academic, industrial and scientific communities with benefits and shortcomings through improved conceptual understanding towards further research and development

Process limits in high-performance peel grinding of hardened steel components with coarse CBN grinding wheels

Recent developments in the production processes for cubic boron nitride (CBN) abrasive grains have led to commercially available grain sizes larger than lg > 300 µm. These superabrasive grains allow higher material removal rates during grinding of hardened steel components. Currently, these components are pre-machined by turning processes before being hardened and eventually finished by grinding. However, the turning process can be substituted by grinding with coarse CBN-grains since higher depths of cut are achievable when machining hardened components. This paper investigates the process behaviour of vitrified and electroplated grinding wheels with large grain sizes during the machining of hardened steel components. Process forces, wear behaviour and workpiece surface roughness are investigated for three different grain sizes, and the process limits of both bond types are examined. The investigations show that vitrified tools do not fully suit the demands for peel grinding process with high material removal rates since wear by bond breakage occurs. The electroplated tools on the other hand are capable of very high material removal rates. Their wear behaviour is characterized by clogging of the chip space if the process limit is reached. Even so, both tools outperform a standard hard-turning process in terms of process time by 74% and 94% respectively. This process time reduction in combination with the possibility to use the same (machine) tool to machine both soft and hard sections of a workpiece adds flexibility to current process chains

Morphology Analysis and Characteristics Evaluation of Typical Super Abrasive Grits in Micron Scale

Distribution characterization of geometry shape and size of abrasive grits with high quality in tight size band and exact pattern is crucial for modern tool manufacturer to make fine powder abrasive tool and other powder tools, but complex to be classified and evaluated accurately due to the lack of scientific method. In contrast to industrial methods with sieving mesh size or simplified projection criteria with circumscribed (inscribed or escribed) circle or rectangle, a set of new systemic criteria is developed and validated by measuring three representative grits samples in micron scale under 2D/3D microscopy platform. The features of micron abrasive grits under morphology classification include total four groups, six subgroups and eighteen sub-types in consideration of spatial geometry and statistical size distribution. For grinding performance analysis and simulation, it would be better to use a set of dominant volumetric geometries rather than use single simple geometry. Furthermore, the significance of abrasive grits geometries in grinding performance is discussed

Surface defect machining : a new approach for hard turning

Hard turning is emerging as a key technology to substitute conventional grinding processes, mainly on account of lower equipment cost, short setup time, and a reduced number of process steps. This is, however, being impeded by a number of challenges required to be resolved, including attainable surface roughness, surface deteriorations, surface residual stresses and metallurgical transformations on the machined steel surface (white layer). In this thesis, a novel approach named Surface Defect Machining (SDM) is proposed as a viable solution to resolve a large number of these issues and to improve surface finish and surface integrity. SDM is defined as a process of machining, where a workpiece is first subjected to surface defects creation at a depth less than the uncut chip thickness; either through mechanical and/or thermal means; then followed by a normal machining operation so as to reduce the cutting resistance. A comprehensive understanding of SDM is established theoretically using finite element method (FEM). Also, an experimental study has been carried out for extensive understanding of the new technique. A good agreement between theoretical and experimental investigations has been achieved. The results show very interesting salient features of SDM, providing favourable machining outcomes. These include: reduced shear plane angle, reduced machining forces, lower residual stresses on the machined surface, reduced tool-chip interface contact length and increased chip flow velocity, as well as reductions in overall temperature in the cutting zone and changing the mechanism of chip morphology from jagged to discontinuous. However, the most prominent outcome is the improved attainable surface roughness. Furthermore, SDM shows the ability to exceed the critical feed rate and achieve an optical surface finish upto 30 nm. A scientific explanation of the improved surface roughness suggests that during SDM, a combination of both the cutting action and the rough polishing action help to improve the machined surface. Based on these findings, it is anticipated that a component machined using the SDM method should exhibit improved quality of the machined surface, which is expected to provide tremendous commercial advantages in the time to come

Surface Roughness Prediction in Grinding Ti using ANFIS Hybrid Algorithm

Intelligent manufacturing is needed, and many techniques and tools have been developed with this in mind. Over time, many of these techniques have been combined, and hybrid approaches have provided better results in shorter times, leading to a more precise prediction of outcomes when compared to the use of individual tools. This research focused on grinding Ti-6Al-4V workpiece material with a Carbon nanotube (CNT) incorporated grinding wheel. The Adaptive Neuro-Fuzzy Inference System (ANFIS) was used to predict surface roughness which was taken as the output of choice for this study. A new hybrid of ANFIS with Genetic Algorithm (ANFIS-GA) was then proposed to see if this prediction method could obtain greater precision. The regression analysis predicted the experimental model’s linear relationship to surface roughness, and the effect of grinding process parameters on surface roughness was analysed using the sensitivity analysis method

ENHANCEMENT OF TOOL-LIFE OF HARD TURNING PROCESS VIA CRYOGENIC COOLANT AND MICROPATTERNED INSERT

Department of Mechanical EngineeringHigh hardness and high strength of materials are essential for advanced engineering applications to guarantee the safety and durability of the manufactured products. The hard turning process enables the machining of hardened materials which makes it one of the most widely used operation in automobile and heavy machinery industries. However, the problem with the hard turning is extreme machining conditions such as high cutting force and temperature generation leading to accelerated tool wear. Cubic boron nitride (CBN) is the essential insert of the hard turning operations. However, due to the higher production cost of CBN cutting tool, its performance should be maximized to achieve the higher machining and economic efficiency. The cryogenic liquids were mainly applied to machining of difficult-to-cut materials. The cryogenic liquids such as liquid nitrogen and carbon dioxide have been used as the cutting fluids to remove the heat generated in the cutting zone. Furthermore, some researchers have found that the textured (or patterned) functional surfaces can improve the frictional and tribological conditions between the two contacting surfaces. Hence, a proper development of the textured surfaces on the cutting tool can enhance the machining performances in the hard turning process. This dissertation presents a framework for the development of a numerical model and experimental investigations for enhancing the performance of the hard turning process using a cryogenic coolant and micropatterned tool. The first of this research presents the developed cutting model based on the modified Oxley???s theory. The cooling effects of cryogenic coolant were included in the model by implementing the proper heat transfer coefficient. Thermal effects generated in the primary and secondary zones were also modeled using the moving heat source technique. The model provides the predictions of cutting force, temperatures and tool wear, which were validated by experimental works. It was found that the use of LN2 coolant can reduce the effect of thermal softening in secondary deformation zone, which in turn increases the cutting forces. However, the cryogenic cooling mainly contributed the decrease in the diffusive and abrasive wear mechanisms to the improvement of tool life. The tool wear of CBN cutting tool was reduced by 20~34% in cryogenic cooling condition as compared to dry condition. Furthermore, finite element method (FEM) simulations were used to analyze the various pattern geometries and dimensions of micropatterned inserts. The simulation results showed that the micopatterned tool can decrease the stress distribution, force, and friction in the tool-chip interfaces. When the perpendicular and parallel type micropatterned tool having 100 ????m edge distance, 100 ????m pitch size and 50 ????m in height was used, the force and the friction was reduced by 6% and 25%, respectively. The experiments were conducted using micropatterned tool for the hard turning process and the variations in the chip morphology, cutting force, friction, and tool wear were analyzed. The results showed that the micropatterned tool was able to reduce the forces by 18.7%, friction by 34.3% and tool wear by 11.4% within the given ranges of experimental conditions. The model and the experimental findings of this research can be beneficial for the enhancing efficiency of the hard turning processes used in different industries. The techniques developed in this work can be further extended to see its applicability in other cutting operations such as drilling and milling.ope

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

AbstractAmong the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiCp/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiCp/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiCp/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiCp/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiCp/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications