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New stricter regulations on lead (Pb) content in brass for use in certain applications is driving the industry from traditional leaded brass towards Pb-free alloys. However, machining induced surface integrity for such Pb-free alloys and related corrosion resistance are largely unknown. Two Pb-free brass alloys, CuZn38As and CuZn21Si3P, approved for use in drinking water applications, were machined under different cutting conditions, tool geometries and tool wear states. The resulting surface integrity and sub-surface deformation was characterized using nano-indentation, scanning electron (SEM) and ion microscopy, and electron backscatter diffraction (EBSD). The materials resistance to stress corrosion cracking (SCC) was assessed by exposing the machined samples to a corrosive substance in accordance with SIS 117102. The results show that tool wear is the most influencing parameter leading to stronger sub-surface deformation. This was especially pronounced for alloy CuZn38As, where for equivalent depth of deformation, the material exhibited higher degree of work-hardening compared to the other tested alloy. Subsequently, substantial stress corrosion cracking was registered for machined CuZn38As samples.

Lead has traditionally been added to brass alloys to achieve high machinability, but the exact mechanisms at work are still debated. Lead-free brass alternatives could be developed if these mechanisms were better understood. Accordingly, machinability characteristics were investigated for two brass alloys with similar mechanical properties and phase composition, but with very different machining characteristics because one has 3 wt.% lead (CuZn38Pb3) while the other has only 0.1 wt.% (CuZn42). The effect of the lead was investigated using infrared temperature measurement, electron microscopy, secondary ion mass spectroscopy, quick-stop methods, and high-speed filming. Neither melting of lead nor its deposition on the tool rake surface takes place during machining, thus confirming its limited lubrication and tribological effects. Instead, the main role of lead is to promote discontinuous chip formation. Lead deforms to flake-like shapes that act as crack initiation points when the workpiece material passes through the primary deformation zone. This effect prevents the development of stable tool–chip contact, thus lowering cutting forces, friction, and process temperature.

Future Ni-base superalloys are designed to deliver outstanding mechanical behaviour at high temperatures, which may translate in significant machining challenges. In this work, a paradigm is presented by which is proven how machining of these materials could benefit from increased cutting speeds and temperatures provided that they are able to promote shear localisation and thermal softening in the chip deformation zones, whilst retaining high-temperature strength within the machined surface. In this way, thermal control of chip formation leads to both lower cutting forces and energies, as well as enhanced surface integrity with lower levels of microstructural reconfiguration.

Conventional cemented carbide is recommended for machining Ti6Al4V. However, polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (pcBN) also show promise. Demands for higher productivity accelerate diffusional dissolution and chemically driven wear mechanisms in these tool materials. This study investigates active wear mechanisms by studying the interactions between Ti6Al4V and PCD, pcBN, and cemented carbide tools in diffusion couples at temperatures from 900° to 1300°C. All tool materials suffered from diffusion to varying degrees, and different chemical reactions occurred. Titanium carbide with minor vanadium alloying (Ti,V)C reaction products act as diffusion barriers when using PCD and cemented carbide, while the reaction products acting as diffusion barrier in pcBN is (Ti,V)B2. The presence of Mo and W in binder sites of pcBN reduces diffusional dissolution of cBN. Diffusion simulations agreed well with microscopy investigations and were enabled by the known temperature and pressure conditions of the static diffusion couples. QC 20221025

A novel and effective approach for determining mechanics and residual stress when turning a component with curved surfaces is presented in this paper. This predictive approach is based on a three-dimensional analytical model to study the distributed mechanics and residual stress caused by vary cutting condition during the machining process. The variation of uncut chip area in this process can be divided into several stages based on different tool-workpiece contact and the discretization of cutting edge is conducted at an arbitrary tool position. The chip flow direction is calculated through the equilibrium of the incremental interaction forces. The cutting force can be determined by integrating the force components along the cutting edge, with each incremental force component obtained based on a fully analytical model. Distributed heat source intensity is considered to model the temperature rise at an arbitrary point in workpiece. The residual stress in curved surface machining is obtained considering the loading-unloading-relaxation procedure at the engagement of cutting edge and machined surface. Finally, Finite Element (FE) modeling and experiments are performed to validate the correctness and robustness of the analytical model proposed in this paper. The results of predicted chip flow direction, cutting force, temperature, and residual stress show good agreement with the simulated and measured results.

Most of the studies on cutting mechanisms and surface integrity in turning are investigated with a straight tool path (longitudinal/end face turning) while few contributions have been done in curved surface turning. This work explores the evolutions of cutting force, chip morphology and surface integrity when turning a curved surface, using fillet surface machining of AISI 304 stainless steel. The varying cutting conditions caused by the presented turning are revealed by detailed geometric analysis and employed as indicators for further discussions on cutting force, chip morphology, and machined surface integrity (including surface roughness, microhardness, microstructure, and residual stress). Apart from the difference of cutting force components in tangential, radial, and cutting speed directions along the fillet surface, wider and thinner chips are obtained from end face turning. The measured microhardness, microstructural alternation, and stress condition results comprehensively illustrate a reduction of severe plastic deformation from the outer face to the end face. (Less)

Adequate setting of the boundary conditions for the heat equation when modeling the temperature distribution in the cutting tool is one of the key points. The boundary conditions on the tool surfaces can be divided into two groups: conditions that describe heat losses (heat exchange with the environment) and conditions that characterize the heat source that heats up the tool (heat flux from the cutting zone). Additional complexity in modeling is provided by the fact that during cutting the surface on which the heat source acts changes, for example, due to wear on the flank surface. In this paper, a method is proposed for measuring the power of a heat source acting on the flank surface. The hardware of the method includes a sensor equipped tool and specially manufactured inserts that imitate the geometry of worn flank surface. In turn, the software is based on the method of solving the inverse heat conduction problem in metal cutting, which allows restoring the heat flux flowing into the tool by measuring temperature with sensors installed in the toolholder. The experimental plan included inserts with negative and positive rake, different cutting speeds (190, 235, 280 m/min), and feeds (0.15, 0.3, 0.45 mm/rev).

Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al2O3 and (Al,Cr,Ti)3O4 spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining.

Machining is often the most expensive manufacturing process step when producing titanium alloy components. With a move towards higher metal removal rates to meet aircraft orders, it is important to develop rapid, low-cost methods that assess the machinability of titanium alloys and cutting tool combinations. A cost-effective, small-scale methodology has been developed and validated on the industrial scale using high-speed turning to inform on the machining characteristics of commercial and emerging titanium alloys to aid companies in future developments of new titanium alloys and cutting tool materials. The article demonstrates, using the titanium alloys Ti-6Al-4V (Ti-64) and TIMETAL 407® (Ti-407), that a series of early stage, small-scale methods can identify key machinability characteristics including chip form, tool wear, cutting force and surface damage. It can be concluded using these low-cost machinability assessment methods that Ti-407 exhibits better machining properties to Ti-64 for the aspects of machinability focused on cutting forces and tool wear, whereas the contrary is found for subsurface microstructural features and chip control.

Additively manufactured (AM) components possess microstructures different from conventional forms in the same material and as a consequence, the mechanical properties and machinability of components produced using these technologies differ. Also, the microstructures from these processes are often anisotropic and as such different regions possess varying properties and hence varying response during post process machining. An adaptive control (AC) machining system for addressing this variation in microstructures during post process machining is developed here and its use demonstrated in this paper. The adaptive control system is used in milling and drilling trials for machining components manufactured by Directed Energy Deposition (DED). Surface roughness and residual stress analysis in the ‘as built’ state and after post process machining with the prevailing cutting forces are also presented here. Microstructures of the deposited material and the subsurface effects at the machined region due to the action of the cutting tool is also analysed. Milling trials are investigated from the standpoint of the use of adaptive machining for the removal of the outermost layer of DED produced Ti6Al4V and in the machining of bulk regions after preliminary machining of the undulating layer. Drilling experiments are carried out for investigating the effects of the machining process on the resulting surface condition, comparing the process with and without adaptive control. The effects of variation in cutting forces during drilling through the different material systems comprising of the DED region and the wrought substrate is also discussed. The effect of periodic changes in cutting forces during machining due to the variation in microstructure along the build direction is analysed and discussed. The use of adaptive control machining for post processing is shown to improve surface finish as it reduces the initiation and generation of chatter marks on the machined surface resulting from material anisotropicity.

Machining-induced white layers and severely deformed layers are undesirable surface integrity features which can be formed when machining high-strength aerospace alloys. An orthogonal milling process has been designed and performed to assess the impact of cutting speeds, tool wear, cutting edge radius and climb vs conventional milling on white layer formation and plastic strain distribution. The plastic deformation in the machined surface associated with the formation of white layers in Ti-6Al-4V has been quantified using micro-grids of different length scales printed using the electron beam lithography technique. It was found that white layers formed via the severe plastic deformation mechanism, at equivalent plastic strain values in excess of 1.2 and in regions of the cutting arc with the instantaneous chip thickness of less than the cutting-edge radius and ploughing and rubbing being the dominant mechanisms. The results indicated that the magnitude of the measured strains and the depth of plastically deformed material was greater at lower cutting speeds, during climb milling and when machining with a larger cutting edge radius and tool flank wear land.

Additive manufacturing (AM) is characterised by several unique advantages, such as (freedom of) design, capability of fusing dissimilar materials, near-net-shape, and achieving a more sustainable production. While the increased precision of metal AM in recent years reduced the needed amount of post-processing to meet dimensional tolerance, the requirements for functional surfaces necessitate a well-understood post-processing, ranging from heat treatment to machining and finishing. The inherently rough initial (as-built) surface topography next to complex material microstructure affects the capability of post-processing/finishing operations to smooth the surface texture and obtain a favourable surface integrity. In this respect, a more fundamental understanding of the effects of material properties on post-processing/finishing is needed. Therefore, this review paper aims to establish the relationship between the characteristics of different AM technologies, microstructural properties of materials in as-built and heat-treated conditions, and the physical properties influencing the response of additively manufactured materials during post-processing/finishing operations. In particular, emphasis is placed on the physics-based understanding of how the microstructural characteristics of 316L, Ti6Al4V and Alloy 718 produced using the two principal technologies, Powder Bed Fusion (PBF) and Direct Energy Deposition (DED), influence their mechanical properties like tensile strengths, hardness and ductility. These properties are among the key factors influencing the response of material during post-processing/finishing operations involving material removal by shear deformation. This review paper also discusses the role of post-processing/finishing on fatigue performance, tribological behaviour and corrosion resistance of investigated AM materials. The paper summarises the state-of the art of post-processing/finishing operations and future research trends are highlighted. QC 20221206

This study investigates machining superalloy Inconel 718 with polycrystalline cubic boron nitride (pcBN) tooling both numerically and experimentally. Particular attention is given to mechanical and thermal stresses in the cutting tool arising from segmented chip formation and associated forces and temperatures. The temperature dependence of the mechanical properties of pcBN has been investigated and incorporated into a numerical model. In order to capture the dynamic loads due to a serrated chip formation, the Johnson–Cook damage model has been used. The extreme deformations during a machining process often results in a numerical difficulties due to a distorted elements. This paper uses the coupled Eulerian–Lagrangian (CEL) formulation in Abaqus/Explicit, where the workpiece is modelled with the Eulerian formulation and the cutting tool by the Lagrangian one. This CEL formulation enables to completely avoid mesh distortion. The finite element simulation results are validated via comparison of the modelled static and dynamic cutting forces and thermal loads induced into the cutting tool. The numerical model predicts a temperature of 1100–1200 ∘C at the cutting interface, which is in line with experimental determined data. The principal stresses at the rake up to 300 MPa are recorded, whereas higher level of stresses up to 450 MPa are found in the notch region of the tool, well correlated with experimental observation.

Machining-induced white layers are an undesirable surface integrity feature which, due to their physical properties, can have a direct effect on the in-service performance of aero-engine components. Typically, destructive methods such as cross-sectional microscopy are used during inspection to identify white layers. This is costly, both in terms of parts sacrificed and time-consumed. A non-destructive evaluation method could speed-up inspection and allow all parts to be inspected before entering service as well as throughout the component life cycle. The present work covers the quantitative characterization of machining-induced white layers in super chrome molybdenum vanadium steel through destructive methods in addition to Barkhausen noise non-destructive testing of the same surfaces. White layers formed by machining with severely worn inserts were measured to be up to 50% harder than the bulk material, possess nano-scale grains and can have an associated compressive residual stress state of up to -1800 MPa. Barkhausen noise testing was used to show that surfaces with a white layer formed by SPD could be detected by measuring shifts in the peak frequency of the Barkhausen noise signal, caused by the compressive near-surface residual stress state associated with the formation of white layers of this type.

The emergence of metal additive manufacturing (AM) processes offer manufacturers a promising alternative to traditional forging and casting techniques for the production of near net shape titanium alloy components. However, limitations in both the surface finish quality and the geometric accuracy of parts produced by AM means that post-build finish machining of the part remains to be a requirement to produce high precision components. Furthermore, the fatigue performance of material produced directly by these processes is often limited by both the poor surface finish and porosity related defects which occur within the material. This study investigates the implications of machining stock allowance on the surface integrity of Ti-6Al-4V specimens produced by selective electron beam melting (SEBM) followed by post-build finish machining. The study revealed that the exposure of porosity related defects on the newly machined surface varied depending on the depth of material removed from the as-built specimen surface during machining. Four point bend fatigue testing of the specimens was carried out to determine the effect of the exposed surface defects on the fatigue performance of the material. This study highlights that the non-uniform distribution of pores within SEBM Ti-6Al-4V means that careful considerations must be given regarding machining stock allowance in the design of these components due to the implications of material removal depth on surface integrity.

Broaching is a unique machining process with high accuracy and surface quality, which is employed in mass and batch production for the manufacture of components with highly complex geometries. It involves the use of multiple-edged complex tools in which the cutting edges are arranged with an offset also known as “rise per tooth” that determines the depth of cut per tooth. This paper presents the state-of-the-art of both the experimental and modelling aspects of broaching, and identifies the most important features related to this machining process. This includes a critical assessment of specifically designed broaching setups and their applicability and/or limitations compared to the machines used in industry. Contributions from academia and industry are included to support a comprehensive report of recent advances, as well as a roadmap for future developments.

The present work aims at improving tool wear simulation in orthogonal turning operations by considering local wear properties at the scale of the coating. A multi-step procedure developed in previous studies is first employed to predict cutting tool wear by combining a pure thermal model to an Arbitrary-Lagrangian-Eulerian (ALE) thermomechanical sub-model in order to predict the thermomechanical loadings applied onto the tool. The tool geometry is updated by moving the tool nodes, taking into account the local contact pressure, sliding velocity and temperature. The key improvement of this paper is to implement a specific wear model for each of the coating layer and substrate depending on the current position of each node at the contact interface. A comparative study is performed between the homogenous wear equation and the improved multi-layer model. This work highlights that an adaptive wear rate calculation based on nodal position has to be considered to achieve an actual predictive model.

Porosity related defects within metal additive manufactured components has made it challenging to certify their use in fatigue critical applications. In this study, the fatigue behaviour of selective electron beam melted (SEBM) Ti-6Al-4V specimens following hot isostatic pressing (HIP’ing) and finish machining has been investigated. Employing a sufficient material removal depth during machining was shown to significantly improve fatigue performance. This was attributed to be a direct result of removing material rich in lack-of-fusion defects, concentrated in the sub-surface. HIP’ing was shown to enhance fatigue performance to a lesser degree, as the treatment was only effective at reducing gas porosity.

Tool wear remains of high interest for industry, as it influences process costs and part’s surface integrity. Although experimental and analytical investigations have been the main ways to investigate wear, the growing development of computational power enables predicting tool wear based on chip formation simulations. If this has been quite successful in turning, developments in milling are still limited due to the specific nature of this machining operation characterized by an interrupted cutting process leading to mechanical and thermal cyclic loadings onto the cutting tool. Wear modes are often not well characterized and become even more difficult to model as far as hard to machine material such as martensitic stainless steels are concerned. The present work propose to investigate wear in orthogonal milling of a 15-5PH martensitic stainless steel. An experimental campaign is first performed to identify the wear modes when cutting this material with uncoated and coated carbide tools. Milling forces, tool wear and material transfer are especially studied. A multi-scale numerical procedure is then developed by combining an Arbitrary-Lagrangian-Eulerian (ALE) thermomechanical model to a pure thermal sub-model in order to predict the thermomechanical loadings withstood by the tool. The thermal sub-model is applied at the scale of the coating in order to extract the thermal gradients generated by the interrupted cutting. These loadings are finally compared to the reported wear modes to identify a correlation and improve their understanding.

The grain boundary network of WC in WC-Co is important, as cracks often travel intergranularly. This motivates the present work, where we experimentally measure the fracture energy of Σ2 twist grain boundaries between WC crystals using a double cantilever beam opened with a wedge under displacement control in a WC-10wt%Co sample. The fracture energy of this boundary type was compared with cleaving {$$10\overline{1}0$$ 10 1 ¯ 0 } prismatic planes in a WC single crystal. Fracture energies of 7.04 ± 0.36 Jm−2 and 3.57 ± 0.28 Jm−2 were measured for {$$10\overline{1}0$$ 10 1 ¯ 0 } plane and Σ2 twist boundaries, respectively.

The mechanics of large-strain deformation in cutting of metals is discussed, primarily from viewpoint of recent developments in in situ analysis of plastic flow and microstructure characterization. It is shown that a broad range of deformation parameters can be accessed in chip formation—strains of 1–10, strain rates of 10–105/s, and temperatures up to 0.7Tm—and controlled. This range is far wider than achievable by any other single-stage, severe plastic deformation (SPD) process. The resulting extreme deformation conditions produce a rich variety of microstructures in the chip. Four principal types of chip formation—continuous, shear-localized, segmented, and mushroom-type—as elucidated first by Nakayama (1974, “The Formation of ‘Saw-Toothed Chip’ in Metal Cutting,” Proceedings of International Conference on Production Engineering, Tokyo, pp. 572–577) are utilized to emphasize the diverse plastic flow phenomena, especially unsteady deformation modes that prevail in cutting. These chip types are intimately connected with the underlying flow, each arising from a distinct mode and triggered by an instability phenomenon. The role of plastic flow instabilities such as shear banding, buckling, and fracture in mediating unsteady flow modes is expounded, along with consequences of the flow modes and chip types for the cutting. Sinuous flow is shown to be the reason why gummy (highly strain-hardening) metals, although relatively soft, are so difficult to cut. Synthesizing the various observations, a hypothesis is put forth that it is the stability of flow modes that determines the mechanics of cutting. This leads to a flow-stability phase diagram that could provide a framework for predicting chip types and process attributes.

International audience; This paper deals with the determination of the constitutive model coefficients used in machining simulations. An optimization-based procedure is developed and applied to constitutive model coefficients determination of Ti6Al4V titanium alloy. The procedure is implemented in LS-Dyna/LS-Opt software, coupled with Abaqus/Explicit to calculate the force-displacement curve at each iteration, which is required for the optimization-based procedure. The robustness of the procedure to determine the constitutive model coefficients is evaluated by comparing the predicted and measured plastic strain distributions in the samples.

Machining of carbon fibre reinforced polymers is part of the production process that introduces several challenges due to inherent characteristics of CFRPs such as non-homogeneity of their mechanical properties. A comparative analysis of conventional milling and abrasive water jet (AWJ) cutting is performed to quantify the effects of machining induced damage on flexural strength of woven CFRP laminates. The machined surfaces quality is characterized using optical and scanning electron microscopy methods prior to flexural mechanical testing. High-speed Digital Image Correlation technique is also used to measure deformation evolutions and determine fracture mechanisms in relation to the applied machining operation and produced machined surfaces. The effect of machining induced damage on strength of milled samples was less than expected with the AWJ processed samples having the least mechanical properties. The surface morphology analysis revealed that the entry and exit point of the water jet introduced severe surface and subsurface damage across the full thickness. The failure initiation sites were determined by strain distribution maps indicating that machining induced damage promotes failure of the tested CFRPs away from maximum compressive stress observed under the loading points.

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.

We examine segmented chip formation and associated flow dynamics in cutting of metals of low-to-moderate workability using high-speed imaging. Segmentation is initiated by a surface instability – formation of a ductile crack in a prow – on workpiece surface ahead of the tool, this crack then propagates towards the tool tip. Prow-crack initiation occurs at a critical strain ˜0.75 that is independent of material and deformation geometry. This ductile failure is analyzed in terms of local hydrostatic stress state and stress triaxiality. Material-agnostic methods to suppress and enhance segmentation using constrained cutting and a mechanochemical effect are demonstrated.

Critical raw materials (CRM) are extensively used in tools for metal cutting, such as in cemented carbide tools (cobalt and tungsten), because they provide desired characteristics of high fracture toughness and wear resistance. Both academia and industry are examining CRM-free material alternatives, such as tools based on polycrystalline diamond (PCD) or ceramic materials. These materials are generally more cost intensive as compared to cemented carbide but could also provide higher efficiency in terms of material removal rate. Material removal rate and tool costs have a substantial influence on the final part cost. When deciding on tool material, the manufacturing industry is either looking for the most cost effective alternative or the alternative providing the highest productivity output. The purpose of this paper is to provide industry with decision support for selection of tool and cutting data that provide the financial most sound production set-up. This work aims to present a novel methodology combining the Colding tool life model and a previously presented model for cost performance ratio. A previous publication provided a method to assess technological solutions and investments based on final part cost. The developed methodology in this article combines cutting performance and production performance to allow a comprehensive cost assessment for a production process. The assessment includes cutting data, tool life and costs of tooling, quality rejections, process availability, equipment investment, personnel and facility. A case study based on experimental data is presented to verify the proposed methodology.

Additive manufacturing (AM) technologies offer new processing routes for functionally graded materials. At present, parts built using these processes often require additional processing as a result of the characteristic surface finish limitations synonymous with AM processes. A difficulty thus arises in the post processing of these components as volumes within the part have differing material properties by definition and will therefore exhibit variable machinability. In this study, machining of functionally graded Ti6Al4V/ WC components consisting of a metal matrix composite (MMC) region and a single alloy region produced via direct energy deposition using commercially available tooling is explored. The influence of post processing on surface integrity is investigated and reported. The effect of material variation on cutting forces and tool response along the component is also analysed and reported. Cutting forces within the MMC region are found to increase by as much as 40% which has been subsequently related to the periodic changes in microstructure generated by the layer by layer build strategy. Tool wear mechanisms are investigated and the influence of material pull out on surface integrity of both MMC and single material regions is explored. This study provides an insight into how the layer building strategies, particularly with multiple materials and the resulting variation in microstructure influences the machining of resulting components.

The presence of machining-induced white layer in the near-surface of critical aeroengine alloys has a detrimental effect on the lifetime of a component. Present techniques for identifying and characterizing white layer, such as optical microscopy and hardness testing, whilst effective, are destructive, costly and time-consuming. Non-destructive testing methods may, therefore, offer improvements to the process of white layer detection. This paper discusses the formation mechanisms and the defining physical properties of machining-induced white layers before offering a comprehensive review of the current state-of-the-art in both destructive and non-destructive testing methods for detecting this anomalous surface feature.

The novel wrought nickel-based superalloy, AD 730™, is a good candidate material for turbine disc applications at high temperatures beyond 650 °C. The present study focuses on the machining performance of this newly developed alloy under high-speed turning conditions with advanced PCBN tools. Meanwhile, the machined surface integrity as influenced by cutting speed and feed rate was also investigated. The surface integrity was thoroughly characterized in terms of surface roughness and morphology, machining-induced plastic deformation, white layer formation, and residual stresses. It has been found that the cutting speed and feed rate had a strong effect on the cutting forces and resultant surface integrity. The cutting forces required when machining the alloy were gradually reduced with increasing cutting speed, while at 250 m/min and above, the flank tool wear became stronger which led to increased thrust force and feed force. A higher feed rate, on the other hand, always resulted in higher cutting forces. Increasing the cutting speed and feed rate in general deteriorated the surface integrity. High cutting speeds within the range of 200–250 m/min and a low feed rate of 0.1 mm/rev are preferable in order to implement more cost-effective machining without largely reducing the surface quality achieved. The formation of tensile residual stresses on the machined AD 730™, however, could be of a concern where good fatigue resistance is critical.

This study aims to provide a fundamental understanding of the role of microstructural characteristics influencing tool wear when machining Alloy 718 fabricated using Powder Bed Fusion (PBF). The effects of preferred crystallographic orientation (texture), shape and distribution of grains, local misorientation, type and amount of precipitates as well as the type, size and amount of abrasive carbides, nitrides and oxides on tool wear are investigated in as-built condition and after the standard solutionising and double-aging treatment. The microstructures of workpiece materials and the surfaces of worn tools were examined using different material characterisation techniques, including Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). A dislocation-based approach was used to reveal the cumulative effects of the microstructural characteristics on deformation behaviour and the thermo-mechanical loads on the tools during cutting. The analyses suggest that texture and the extent of material work-hardening prior to the onset of crack formation markedly influence the amount of plastic work and thus heat generation when machining Electron Beam Powder Bed Fusion (EB-PBF) material. The higher heat generation in the cutting zones provokes thermally-induced wear mechanisms like diffusion-dissolution and oxidation. In addition, the larger amount of hard oxide inclusions present in EB-PBF material leads to higher wear by abrasion. In contrast to the prevailing experimental approaches in this field, the present investigation is built on a physics-based framework to understand the fundamental aspects that govern material deformation and heat generation in cutting and, consequently, tool wear mechanisms. This framework can be used for machinability assessment of any alloy manufactured by different additive manufacturing (AM) technologies and for optimising the process-chain, including printing strategies and thermal post-treatments, to improve the machinability of AM alloys by tailoring their microstructure.