Sintered ceramics are recognized as promising materials for high-precision and advanced applications, such as orthopedic grafts implants, owing to their superior mechanical performance and biocompatibility. The fabrication of complex or intricate geometries often necessitates post-processing, for which micro-milling is frequently utilized. This paper focuses on the micro-milling of zirconia-toughened alumina (ZTA), a high-performance ceramic widely used in the medical industry for joint implants and rehabilitation components. The study investigates the surface formation mechanisms, size effects, and chip thickness characteristics associated with the process. In addition, the performance of cemented carbide micro-milling tools coated with a multi-layer HF-CVD diamond film is evaluated to assess their suitability for precision machining of ZTA ceramics. The tool wear mechanisms were systematically investigated, with particular attention given to the main failure modes occurring during the micro-milling process, including coating deterioration of the cutting tool. The surface formation and damage behaviour of ZTA under various cutting conditions were analysed in detail. Experimental results demonstrate that ZTA can be efficiently machined by micro-milling under controlled cutting parameters, achieving high surface quality and an industrially relevant tool life. The micro-milling of sintered ceramics remains challenging due to their inherent high strength and brittleness. Attaining the desired surface integrity and dimensional accuracy requires further optimization of machining parameters and strategies. Key aspects include the control of ductile-regime machining and the reduction of cutting near the tool center, both of which are critical to achieving improved performance.

Machining Inconel 718 remains a challenge for various industry sectors, causing high levels of tool wear only after a few minutes of machining, making it a hard to process material. Furthermore, Inconel 718 parts are crucial for sectors such as the aeronautical and aerospace, with these components being required to have high-quality and tight tolerances. This makes the machining of this alloy even more challenging, as guarantying these pre-requisites requires a high number of tool changes, ensuring that are always in good condition. To mitigate the problems associated with the machining of this alloy, many researchers and manufacturers use of coated tools, with the WC-Co tools still being widely used in this regard. However, since processing this alloy remains a challenge, there is a wide variety of studies focusing on finding even more solutions, by developing novel machining strategies, coatings and employing different tool materials. Lately there has been a focus on the study of ceramic tool materials to machine this alloy, as these materials exhibit high levels of hardness and wear resistance. Moreover, ceramic tools can be used at much higher cutting speeds than standard WC-Co tools, not only mitigating sustained wear, but also being more productive than their competitors. In the present review study, recent research papers were analysed, focusing on the milling of Inconel 718 using WC-Co tools and ceramic tool materials, particularly, SiAlON. The recent research trends and directions will be presented, as well as a comparison of the productivity and surface quality obtained with milling tools made of these tool materials. Regarding the comparison, the selected research studies focus on applications that can be replicated in industrial settings, thus facilitating this comparison. It was found that these ceramic tool materials show tremendous potential when applied to milling of Inconel 718, particularly for roughing operations, exhibiting material removal rates of up to ten times higher than standard WC-Co tools. However, the production quality is still not up to par with WC-Co tools.

Characterization methods constitute a fundamental path of determining the properties of a machining tool coating before experimental works are undertaken, so that its fitness for a certain operation is studied beforehand. When the requirement is to machine fibre metal laminates, this is even a more important matter, since the coating is expected to withstand several challenging solicitations, which most of the times result in an excessive tool wear resultant from the composite fibres’ abrasiveness and the dissimilar materials distinct cutting patterns. Nevertheless, this problem can be avoided through a correct characterization of the coating, which will both make it possible to avoid early tool wear and increase its lifetime, resulting in huge economic savings and lower waste, making the overall process much more sustainable. Machining tool coatings can be characterized following diverse physical, mechanical and tribological techniques. The most frequent characterized methods used for this application are the atomic force microscopy (AFM), the scanning electron microscopy (SEM), the x-ray diffraction (XRD), the Raman spectroscopy, the nano/microindentation, the scratch test, the pin-on-disc test and the micro-abrasion. This paper consists of a narrative review containing the state-of-the-art of the literature using these methods, with several combined in some cases for a complete coating characterization, in addition to a SWOT analysis for each methods group. Accordingly, this article’s main objective is to collect the important findings regarding machining tools’ coating characterization studies performed in the literature from 2020 to 2026 to highlight their differences and the best for each determined application.

Milling Inconel 718 remains a significant challenge leading to accelerated tool wear and premature tool failure. Consequentially, milling Inconel 718 with conventional tooling, namely WC-Co, requires conservative cutting parameters and use of flood cooling/lubrication. These practices compromise process sustainability, resulting in high energy consumption, prolonged machining times and multiple tool changes. To mitigate these problems, alternative tool materials and more sustainable machining strategies are required. In this study, SiAlON and WC-Co cutting tools were evaluated in Inconel 718 face-milling operations for four cutting parameter combinations. The process was monitored through cutting force measurements, tool wear analysis and machined surface quality evaluation. Results show that SiAlON tools improve both productivity and sustainability compared to WC-Co tools. Although SiAlON alone may not fully meet all surface quality requirements, its integration into machining strategies offers a promising approach to mitigate excessive tool wear and lower the environmental impact of machining Inconel 718.

The digitalization of machining processes is increasingly recognized as essential for achieving higher productivity, reliability, and traceability. However, access to reliable in-process sensor data remains limited, particularly in multi-axis CNC machining, where dimensional accuracy and surface integrity strongly depend on stable and optimized process conditions. This study investigates sensor-based monitoring as a practical approach for evaluating process performance in five-axis CNC milling. Electric current and vibration signals were acquired during three machining operations, under distinct cutting parameters, using current clamps and a plug-and-play MEMS accelerometer. The signals were processed using the root mean square method to assess the correlation between sensor data and machining conditions. Dimensional inspection of each workpiece was carried out to verify geometric conformity. The results show that spindle current measurements exhibit a strong linear correlation with material removal rate and cutting power, supporting their use as indicators of cutting forces and energy consumption. Vibration signals revealed pronounced dynamic behaviour for specific tool orientations, particularly in transverse to tool axis direction. The proposed methodology provides a simple and low-cost framework for integrating sensor-based monitoring into five-axis CNC milling, particularly relevant for semi-roughing operations, and offers a basis for future studies on process optimization and real-time condition monitoring.

Metal cutting involves extensive plastic deformation as the workpiece material flows through the shear plane, promoting mechanisms of initiation, coalescence, and propagation of cracks. This the largest plastic deformation that it can withstand, above those of tensile and compression tests. Such condition ultimately leads to the onset of an ever-present crack just ahead of the cutting edge that provides the separation mechanism necessary to form the chip. However, it is neither easy nor simple to measure the fraction of the total energy involved in the material separation mechanism and its correlation with operating conditions.In this research, a new design of a multiaxial tool for determining mode II ductile fracture toughness is proposed. This testing tool is composed of several hydraulic and pneumatic actuators that allow a shearing punch to act against double-notched prismatic specimens with superimposed orthogonal load, yielding a wide range of stress triaxialities. This load can vary from the compressive to tensile yield stress of the material. Thus, allowing the influence analysis of the stress state on the mechanical response of ductile materials, like that experienced on the shear plane of metal cutting due to rake face angle variation. Experiments performed in AISI 1045 give support to the presentation and allow a better understanding of the influence of the superimposed pressure on fracture toughness of ductile metals.

The machining process remains relevant for manufacturing high-quality and high-precision parts, which can be found in industries such as aerospace and aeronautical, with many produced by turning, drilling, and milling processes. Monitoring and analyzing tool wear during these processes is crucial to assess the tool’s life and optimize the tool’s performance under study; as such, standards detail procedures to measure and assess tool wear for various tools. Measuring wear in machining tools can be time-consuming, as the process is usually manual, requiring human interaction and judgment. In the present work, an automated offline flank wear measurement algorithm was developed in Python. The algorithm measures the flank wear of coated end-mills and slot drills from Scanning Electron Microscopy (SEM) images, according to the ISO 8688 standard, following the same wear measurement procedure. SEM images acquired with different magnifications and tools with varying machining parameters were analyzed using the developed algorithm. The flank wear measurements were then compared to the manually obtained, achieving relative errors for the most common magnifications of around 2.5%. Higher magnifications were also tested, yielding a maximum relative error of 13.4%. The algorithm can measure batches of images quickly on an ordinary personal computer, analyzing and measuring a 10-image batch in around 30 s, a process that would require around 30 min when performed manually by a skilled operator. Therefore, it can be a reliable alternative to measuring flank wear on many tools from SEM images, with the possibility of being adjusted for other wear measurements on different kinds of tools and different image types, for example, on images obtained by optical microscopy.

Multi-materials are increasingly used in the automotive and aeronautical industries owing to their high strength-to-weight ratio, besides the high strength and stiffness of metals allied to the lightweight, corrosion resistance, impact, fracture and fatigue properties of composites. Despite being manufactured in near-net shapes, the drilling process remains necessary for component assemblies. However, this process presents significant challenges due to the high abrasiveness of composite fibres and the requirement for tools to cut through different materials simultaneously. These factors contribute to hole damage and rapid tool wear, hindering the efficiency of the machining process. In this paper, multi-material stacks composed of carbon fibre reinforced polymer and aluminium layers were drilled with chemical vapour deposition diamond coated tools to infer on parameter combination (feed and cutting speed) and conditions required to improve the process, as well as reduce/mitigate delamination. A fracture characterization campaign, through the double cantilever beam testing, was performed to correlate the composite's fracture toughness with the maximum force on the onset of delamination, to prevent hole and surface damage. For that the identification of a fracture mechanics peel-up model and its numerical-experimental validation has been performed. Future research includes adding the full fracture envelope (instead of solely pure mode I) as an input to the delamination model, for more accurate portrayal of real conditions.

The use of carbon fibre reinforced polymers (CFRP) has transitioned towards applications with large-scale manufacturing with specific desired material characteristics, such as in the aerospace and automotive industries. Despite being manufactured in a near-net shape, machining of CFRP is often necessary to meet dimensional tolerances. The requirement to improve both the processing capability and production cost is heightening given the challenging cutting operations of CFRP, with common issues arising such as machining-induced delamination, poor surface finish and increased tool wear. Sharp polycrystalline diamond (PCD) tools are often employed during CFRP milling, however these are not economically practical due to their high cost, geometric construction limitation and inherent weakening of their geometry (due to relative low toughness and very sharp edges), leading to decreased tool longevity. Sharp diamond-coated carbide tools represent a cost-effective alternative to PCD tools. A novel approach is presented utilizing a high-thickness HF-CVD (Hot-Filament Chemical Vapor Deposition) diamond coated carbide milling tool, with laser sharpened edges, which was used for investigating the effect of coating on cutting force and surface quality of fibre reinforced composites. This paper is an introductory exploration of laser sharpened tools, focusing on their durability and performance. Instrumented experimental tests in contour milling operations demonstrated the increased cutting performance for achieving well-finished surfaces, with negligible rounding of the coated cutting edge. Future studies will compare these tools with standard PCD coated tools without laser sharpened edges to evaluate their relative advantages in machining applications during extensive tool wear tests, when machining abrasive materials, such as CFRP.

Inconel 718 is used in many industry sectors, particularly, in the aerospace, automotive and energy industries. This alloy is selected due to its excellent mechanical properties and stability at high temperatures. However, this material is considered difficult to machine. Its high-strength, low thermal conductivity, and tendency to work-hardening, makes the machining of this material quite challenging, generally causing high amounts of tool-wear. To surpass these processing problems, usually, coated tungsten carbide tools are used for machining Inconel 718, due to their high-hardness and wear resistance. In the present work, finishing turning experiments were conducted on Inconel 718 alloy, using TiAlSiN coated WC-Co tools at different cutting parameters. Different values of feed and cutting speed were used. Tool-wear was assessed and characterized, as well as the machined surface quality. Additionally, cutting forces were measured and evaluated, trying to establish relations between the cutting forces and observed tool-wear. It was found that for lower cutting speeds the registered force values were higher, particularly for worn tools. Tool-wear also seemed to increase these cutting force values. Furthermore, numerical simulations of the cutting process, using finite element method, was performed. These simulations were conducted aiming for the prediction of tool-wear and to compare the developed cutting forces with the obtained through this method. A low error value was obtained for the comparison of the force values, and an accurate tool wear distribution was obtained.

Due to the high abrasiveness and anisotropic nature of composites, along with the need to machine different materials at the same time, drilling multi-materials is a difficult task, and usually results in material damage, such as uncut fibres and delamination, hindering hole functionality and reliability. Image processing and analysis algorithms can be developed to effectively assess such damage, allowing for the calculation of delamination factors essential to the quality control of hole inspection in composite materials. In this study, a digital image processing and analysis algorithm was developed in Python to perform the delamination evaluation of drilled holes on a carbon fibre reinforced polymer (CFRP) and aluminium (Al) multi-material. This algorithm was designed to overcome several limitations often found in other algorithms developed with similar purposes, which frequently lead to user mistakes and incorrect results. The new algorithm is easy to use and, without requiring manual pre-editing of the input images, is fully automatic, provides more complete and reliable results (such as the delamination factor), and is a free-of-charge software. For example, the delamination factors of two drilled holes were calculated using the new algorithm and one previously developed in Matlab. Using the previous Matlab algorithm, the delamination factors of the two holes were 1.380 and 2.563, respectively, and using the new Python algorithm, the results were equal to 3.957 and 3.383, respectively. The Python results were more trustworthy, as the first hole had a higher delamination area, so its factor should be higher than that of the second one.

Machining in ductile mode is usually applied for finishing precision parts of hard materials, such as cemented carbide parts, medical ceramic components or glass material applications. Thus, the study of ductile mode cutting of brittle materials has been attracting more and more efforts. The possibility of applying predominant plastic-flow cutting (ductile mode), using ultra-precision machines, in hard/brittle materials has been previously linked to the careful selection of operational conditions, regarding the brittle-to-ductile threshold. This threshold, also known as the critical depth of cut, relates with material specific properties (i.e., elastic modulus, material hardness and fracture toughness) as is widely employed in grinding processes control. In the present work, micro-milling of WC-15wt.%Co sintered samples was performed with diamond coated end mills, confirming the influence of a ductile-to-brittle threshold on the cutting regime. Critical scale effects and structure-related behaviour were also confirmed. A positive impact on machined surface quality was observed when ductile mode was applied. Scanning electron microscopy was used to evaluate the microstructure features after different machining conditions.

The automotive industry encounters daily challenges as it navigates through new design trends and technological developments, which drive companies to rapidly develop new models. This scenario paves the way for new manufacturing approaches such as additive manufacturing (AM) which is transforming the manufacturing industry by enabling the production of complex geometries while minimizing material usage. Regarding the cutting tools sector, AM enables the resource-efficient generation of shapes and features that are not possible with conventional subtractive processes. This work explores the feasibility of AM, specifically Laser Powder Bed Fusion (LPBF), in the creation of a complex milling tool geometry with enhanced machining efficiency and increased durability in cutting applications. The final developed tool incorporates internal conformal channels, high teeth number (relatively to tool size) within a hollow interchangeable body. The combination of (post-AM) brazed PCD (PolyCrystalline Diamond) inserts, which is the hardest cutting tool material available, with enhanced tribological conditions at the cutting zone (improved cooling and lubrication of the cutting edge) and increased number of teeth is expected to promote ideal cutting conditions, therefore extending tool lifespan, which is particularly relevant in the automotive industry, where lightweight design dictates the usage of metals such as aluminium. The remarkable durability of PCD in aluminium machining makes them an ideal choice as the active cutting zone for AM produced milling tool bodies. The typical relative small series of tooling (as compared to parts produced) supports the usage of AM, which in turn boosts efficiency and cost effectiveness of these cutting tools. The demand for aluminium parts is rapidly increasing as the automotive industry accelerates towards light weighting and electrification, creating a favorable opportunity for the implementation of the developed tool within the automotive industry.

Achieving a mirror-like finish surface quality in plastic injection molds and dies is necessary for the manufacture of optical components in the automotive industry. Any defects present on the mold surface will be evidenced on the injected part, compromising the functionality of the final product. Moreover, the typically employed finishing techniques (milling and polishing) in mould steels can be excessively time-consuming. The identification of machining and polishing combinations that meet the demanding surface requirements while minimizing time and material resources is therefore essential for ensuring the efficiency and cost-effectiveness of the mould-making process. In this work, an experimental study was conducted on the milling of hardened tool steel using a 6 mm two flute ball nose end mill. Distinct configurations of axial and radial depths of cut as well as feed per tooth were considered and their impact on the pre-polishing surface roughness was analysed. A methodology for the parametrization of polishing conditions was developed, ensuring consistency of speed and pressure. Further tests were conducted to evaluate the relation between post-polishing surface quality and the total duration of the combined finishing approach. The polishing stage consisted on submitting the milled samples to SiC paper (800 and 1000 grit) and diamond cloth (6 and 3 µm) polishing. The method provided enhanced control of the polishing operation and revealed milling/polishing improved sequences for attaining surface roughness technical requisites.

Multi-Component Molding (MCM) enables the combination of different materials and components in a single manufacturing process, allowing the creation of complex and functional products. Still, inherent challenges related with distinct physical and mechanical properties of the materials tend to arise, namely the adhesion of the involved materials. The development of strategies to improve polymer-polymer and polymer-metal adhesion is of great importance to ensure the integrity of final parts. In this work, an experimental campaign covering different operational conditions of that moulding process was conducted in order to infer on the adhesion quality of the injected parts. The Influence of a coupling agent, maleic anhydride-modified high-density polyethylene (MAMHDPE), on the adhesion quality between PA6 reinforced with 30% (weight) glass fibers (PA6-GF30) and HDPE has been investigated on overmoulded parts. Furthermore, different thermal (mould pre-heating temperature) and surface conditions (simplified flame treatment and mechanical abrasive sanding) were applied to improve the adhesion between a silver-plated bronze insert and HDPE (insert molding). Adhesion tests on the polymer-polymer show an increase of materials’ adhesion when using the coupling agent. Moreover, scanning electron microscopy (SEM) imaging reveals a lower tendency towards defects occurrence at the polymer-metal interface for higher processing temperature in the insert moulding process.

A maquinagem de superligas termorresistentes promove a elevada geração de calor, o rápido desgaste das ferramentas de corte e alterações superficiais nas superfícies geradas, mesmo com taxas de remoção de material conservadoras. O principal objetivo deste estudo é avaliar, através de uma metodologia experimental e numérica, a maquinabilidade da liga IN718 utilizando ferramentas de fresagem em SiAlON. O trabalho centra-se em operações de fresagem, com foco específico na evolução do desgaste e sua correlação com dados do processo, como as forças e binários de corte, temperatura e o movimento relativo entre rotação e avanço (concordante vs. discordante). A rugosidade superficial e alterações microestruturais das superfícies maquinadas, foram também objeto de estudo. Adicionalmente, foram construídas simulações numéricas do processo para evidenciar o mecanismo de corte, com o objetivo de identificar as condições de funcionamento ideais para aplicações industriais. As ferramentas de corte cerâmicas constituem uma alternativa viável a soluções convencionais compósitas de carbonetos cementados (i.e., WC-Co) especialmente porque permitem alcançar taxas de remoção muito elevadas.

In recent years, promising solutions have emerged to address the need to reduce structural weight in the modern transportation (aeronautical and automotive) industry, namely multi-material assemblies combining fibre-reinforced polymers and aluminium alloys. Given the distinct mechanical and thermal characteristics of each component, the drilling process, fundamental for creating holes in riveted or bolted assemblies, presents significant challenges in achieving damage-free holes with precise tolerances. This is due to defects formation, such as metal burrs, incomplete fibre cutting, delamination, and tool wear. Consequently, meticulous selection of cutting conditions and tools becomes imperative to mitigate these issues effectively. In this work, the drilling process of two types of multi-material laminates (with alternate CFRP and Al2024 layers) using two distinct geometries of CVD diamond coated WC-Co single-shot drilling tools, was studied to find the ideal operating conditions. Different levels of feeds and cutting speeds were considered and an additional wear inspection experimental campaign was carried out. Results revealed considerably higher thrust force and torque in the aluminium layers, when compared to the CFRP, which suffered some delamination, contrarily to the burrs present in the aluminium. The feed was the parameter which most contributed to the appearance of defects. After an approximate drilling distance of 1550 mm in both types of plates, a slight abrasive wear was detected for multi-material type I and some aluminium adhesion on the cutting edge for type II, indicating a potential wear tendency (associated with built up edge) for this specific configuration. Nevertheless, no major wear was verified overall.

Micro milling of cemented carbides is a challenging task due to their high hardness, low toughness and high wear resistance. Ensuring good surface quality and dimensional accuracy is crucial for extending parts service life, which in turn enhances economical and environmental sustainability. This paper is mainly focused on evaluating surface formation mechanisms, scale effects, fracture behaviour and chip formation using distinct cemented carbide micro milling tools with multi layer diamond HF-CVD. In order to achieve higher precision and more efficient micro milling operations on WC-15Co and WC-10Co, a systematic experimental approach has been carried out. The influence of cutting parameters, achievable surface quality and defects occurrence were thoroughly examined. Experimental results evidence the influence of operational conditions on the chip formation of cemented carbides as well as an important impact of the utilized cutting tool. Micro pits, cracks, thin ploughing layer and fractured workpiece edges are amongst the observed surface damage mechanisms. A ductile cutting regime of the high-hardness composite material is confirmed, exhibited by the plastic deformation even when small depths of cut are considered.

The drilling process of composite materials, such as the carbon fiber reinforced polymer (CFRP), constitutes a challenging task due to their inhomogeneous and anisotropic characteristics, besides the highly abrasive wear behaviour of their fibers. Accordingly, machining parameters should be carefully studied to optimize the process, leading to a better surface quality (avoiding defects in the CFRP) and to a lower wear behaviour of the cutting tool. This study proposed to test the drilling of a CFRP with a thermoplastic matrix using two different tool geometries (conventional and double-point angle drill) and varying two parameters, feed (f) and spindle speed (n), each one with two levels. It was concluded that the double-point angle drill with lower spindle speeds generates lower thrust force and torque values, as well as better hole quality. Higher spindle speeds combined with lower feeds result in fractured chips, in contrast with continuous chips for the other combinations.

Metal additive manufacturing (MAM) currently allows the production of mechanical components with technical specifications suitable for structural applications with a high level of complexity. Despite the most recent technological developments, additively manufactured parts may still lack the geometrical and dimensional accuracy as well as surface integrity required for precision mechanical assemblies and system reliability. These requirements often lead to post-processing operations through precision machining technologies. The present work focuses on the machinability study of 18Ni300 maraging steel obtained by laser powder bed fusion and its comparison with the conventional counterpart. Milling tests were carried out covering a wide range of cutting parameters, aiming at understanding their influence and comparing the obtained results in terms of cutting force, specific cutting pressure, roughness and chip morphology. In depth residual stresses have been measured for different operational and metallurgical conditions and their comparison was performed. A more significant effect of the feed parameter on the analysed data is noticed, particularly regarding the affected layer depth of the residual stresses due to cutting. Moreover, the higher mechanical strength of the additively manufactured alloy does not translate into an equivalent increase in the required average specific cutting pressure.