Subtractive Manufacturing Processes Research Articles

Robot path planning for metrology in hybrid manufacturing

The objective of the wire arc additive manufacturing (WAAM) hybrid cell is to significantly reduce lead time associated with large scale parts. The WAAM process utilizes a 6 degree-of-freedom (DOF) robot manipulator in addition to a 2 DOF part positioner. After printing, the part is translated into position for scanning to inform the subtractive manufacturing process. Scanning in a manual setting can be a long and arduous process to generate scans of sufficient quality for the basis of informed machining. Effective path planning for scanning with the intent to reduce scanning time, increase quality of scans, and move toward a full automation of the hybrid manufacturing cell is investigated in this paper. Simulation software is used to create and verify path plans prior to importing and implementing on a 6 DOF robotic manipulator to which a GOM ATOS Q 3D scanner is mounted. The quality, amount of time necessary to produce, and number of scans required to produce a sufficient representation for machining are compared using three methods. The first method is a manual scanning configuration, the second is using a generalized path plan, and the third is using a geometry-based path plan.

Measuring thermomechanical response of large-format printed polymer composite structures via digital image correlation

Large-format additive manufacturing (LFAM) is a branch of additive manufacturing (AM) research with the ability to create large structures typically measuring several meters in scale. LFAM is advantageous for tooling applications, not only because it offers the ability to create complex geometries not easily made using subtractive manufacturing processes, but the cost savings of pelletized feedstock used by these systems result in larger parts printed at faster speeds than traditional AM systems. Fiber reinforced polymer (FRP) is a commonly used feedstock material in LFAM structures because it reduces the distortion experienced during printing. However, FRP introduces highly anisotropic thermomechanical properties and contributes to a nonhomogeneous microstructure that can result in critical distortion of dimensions during tooling. Measuring the global thermomechanical response of LFAM structures requires a more representative method that accounts for not only anisotropic properties but also the nonhomogeneous nature of the final part. This is where traditional techniques to measure thermomechanical response, such as thermomechanical analysis (TMA), fall short as they assume homogeneity. This study evaluated the coefficient of thermal expansion (CTE) of LFAM structures as measured by TMA as compared to a novel digital image correlation oven (DIC Oven) system. The LFAM structures were made from 20 % by weight carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS). TMA measurements showed significant variations in CTE across a single LFAM bead, confirming the need for a global technique that captures overall thermomechanical response. The CTE values measured using the DIC Oven compared well to average TMA values obtained from localized measurements across the sample. The DIC Oven was also used to quantify the effects of different layer orientations on thermomechanical properties, which cannot be easily captured using TMA. A predictive model was also developed by using localized TMA values across an LFAM bead to predict the overall thermomechanical response of an LFAM structure.

Fabrication of a Low-Cost Fused Filament Fabrication-based 3D Printer and Investigation of the Effect of Process Parameters on Mechanical Properties of 3D-Printed Samples

Additive Manufacturing (AM) techniques add material layer-by-layer to fabricate parts or products, compared to subtractive manufacturing processes, where the material is removed to obtain the final product. The most common method among AM techniques is fused filament fabrication (FFF), which uses filament material to print objects into end products. The present study's aims include designing and fabricating a custom FFF-based 3D printer and investigating the effects of three process parameters on the tensile properties of the 3D-printed samples. Initially, the 3D printer was successfully fabricated. The locally fabricated 3D printer uses Marlin Firmware 2.0 as programming code to control different functionalities of the printing processes. After fabrication and calibration, the printer 3D-printed a few samples successfully. Moreover, a design of experiments plan was formulated to print tensile specimens based on the levels of the process parameters. Tensile testing was performed, and the analysis of variance (ANOVA) confirmed that the process parameters significantly affected the tensile strength. The effects of the process parameters were then analyzed, along with the defect formation and microstructure analysis. Finally, optimum parameters for printing PLA parts with better tensile properties were figured out for the designed 3D printer.

Application of Nonlinear Analysis in Evaluating Additive Manufacturing Process for Engineering Design Features: A Study and Recommendations

In today’s world, Additive Manufacturing (AM) is quickly becoming the dominant manufacturing technology. Massive development has occurred in recent decades, and it is occurring at a much faster rate. It has also progressed from simple prototype to actual end-use items and manufacturing tools. Various manufacturing processes, such as SLS, LENS, FDM, PolyJet, SLA, LTP, DMLS FDM, and binder jet printing, are produced using additive manufacturing techniques. Layer by layer material deposition/addition is a critical component in all these operations, which is why this technology is known as additive manufacturing. Rapid prototyping, 3D printing, digital manufacturing, and other such names are used. Automotive, Aerospace components, medical equipment parts, consumer goods and gadgets, fashion sector, jewelry, and other industries employ additive manufacturing.Currently all designed parts can manufacture using either subtractive or additive manufacturing processes. However, distinct design elements established for production provide additional manufacturing obstacles in metal substation and metal addition manufacturing procedures. As the number of parts made directly utilizing additive manufacturing techniques grows, it is critical to compile a list of the best design for manufacturing principles applicable for various additive manufacturing procedures. This will assist the design community in ensuring that items are developed for additive manufacturing rather than generic strategy and produced.The primary goal of this effort is to evaluate and comprehend the various additive processes and choose the optimal design for manufacturing procedures to be used. As a result, one should be prepared to select a suitable additive manufacturing process for printing based on the design aspects of the component to be produced.

Effect of additive and subtractive sequence on the distortion of cone-shaped part during hybrid direct energy deposition

Hybrid manufacturing combines additive manufacturing (AM) and subtractive manufacturing processes to achieve simultaneous benefits. Unlike traditional AM, it allows for interleaved subtractive steps, enhancing machining tool access for parts with high aspect ratios. However, optimizing the printing sequence remains as an area of exploration. In this study with two conical shapes, one exhibited a geometrical mismatch at the interface between two printing sections, while the other did not. 3D laser scanning, finite element simulation, and methodical analysis were used to understand this issue. Printing support structure before machining improved dimensional accuracy, with 0.5 mm reduction in distortion achieved, corresponding to 50 % of the final wall thickness. However, the absence of a feedback mechanism to track wall distortion after the additive process resulted in non-uniform wall thickness with a constant depth of cut during the machining operation. This research highlights the importance of process sequencing in hybrid manufacturing for achieving desired geometry.

The influence of deformation affected region on microstructure and mechanical property of 316L fabricated by hybrid additive-subtractive manufacturing

The hybrid of additive manufacturing and subtractive manufacturing is promising in producing high-quality and high-accuracy parts made of hard-to-machine metallic materials with complex geometries. However, few studies have been conducted to analyze the influence of responses from subtractive manufacturing, especially the plastic deformation region induced by mechanical cutting, on the following additive manufacturing processes. This paper comprehensively investigates the impact of finishing milling on the mechanical properties and quality of 316L fabricated by hybrid additive-subtractive manufacturing. The whole manufacturing process consisted of a two-stage micro selective laser melting μSLM process with three scanning speeds and one finishing milling process. Typical machining responses including phase, cutting force, surface roughness at different manufacturing stages were analyzed; the mechanisms of how the deformation-affected region induced in subtractive manufacturing process affects the microstructure, hardness, and mechanical properties after the second-stage additive manufacturing were explored. Fine grains were formed after the second-stage μSLM in the connected region, because of the lower G/R ratio and the higher G × R value, whereas the hardness in this region was lower than the bulk material consisting of coarse grains, caused by the thermal softening effect induced in mechanical cutting. The elongation rate was increased due to the existence of the grain-boundary-rich connected region.

Comparing the Performance of Rolled Steel and 3D-Printed 316L Stainless Steel.

Three-dimensional printing is a non-conventional additive manufacturing process. It is different from the conventional subtractive manufacturing process. It offers exceptional rapid prototyping capabilities and results that conventional subtractive manufacturing methods cannot attain, especially in applications involving curved or intricately shaped components. Despite its advantages, metal 3D printing will face porosity, warpage, and surface roughness issues. These issues will affect the future practical application of the parts indirectly, for example, by affecting the structural strength and the parts' assembly capability. Therefore, this study compares the qualities of the warpage, weight, and surface roughness after milling and grinding processes for the same material (316L stainless steel) between rolled steel and 3D-printed steel. The experimental results show that 3D-printed parts are approximately 13% to 14% lighter than rolled steel. The surface roughness performance of 3D-printed steel is better than that of rolled steel for the same material after milling or grinding processing. The hardness of the 3D-printed steel is better than that of the rolled steel. This research verifies that 3D additive manufacturing can use surface processing to optimize surface performance and achieve the functions of lightness and hardness.

A novel laser cladding AlMgZnCuErZr alloy: Material genetic design, strengthening andtoughening mechanisms

Aluminum alloy with high strength, toughness, and corrosion resistance is one of the new materials for laser additive manufacturing of lightweight high-speed train brake discs. However, due to the non-equilibrium solidification characteristics during the laser melting process, the commercial Al alloys with high performance and laser formability face several bottlenecks in alloy composition design and preparation. This paper employs a material genetic design method to develop a novel laser cladding Al14Mg9Zn6Cu2Mn0.5Si0.6Er0.4Zr alloy, which exhibits excellent laser formability and better strength, toughness, and corrosion resistance under an optimized laser energy density of 1157 J/mm3. Specifically, an in-situ generated T-AlMgZnCuZrEr genetic phase with internal cell-like α-Al was first discovered, which significantly improves the properties of the alloy. The alloy sample demonstrates a remarkable compressive strength of 663 MPa along with a deformation of 15 %. The compressive strength and deformation product of the laser cladding sample reaches 9.9 GPa%, which is 13.44 % higher than that of the high-strength AlZnMgCu alloy prepared by other subtractive manufacturing processes. The mechanisms of matching strength-toughness and corrosion resistance of the alloy have been elucidated. This study provides a feasible material design and preparation pathway for laser additive manufacturing of high-performance and lightweight Al alloy high-speed train brake discs.

Evolution of surface quality in micromilling Ti-6A1-4V alloy with increasing machined length

Micromilling is a subtractive manufacturing process that presents challenges due to scale effects and rapid tool wear. To understand the evolution of surface quality when increasing the machined length during the micromilling process, this study assessed the surface roughness, topography, and defects of slots micromilled on Ti-6A1-4V. For the experiments, 1 mm diameter flat end mills were employed, and the cutting parameters were varied using a full factorial design. Subsequently, the surface texture field parameter Sa was assessed every 20 mm, up until the machining length of 260 mm. The analysed results led to the conclusion that, for the adopted set of parameters and the machining length of up to 260 mm, surface roughness was not significantly correlated to the machined length in the micromilling process of Ti-6A1-4V, as the Pearson coefficient, obtained from the correlation analysis, was -0.052. However, the surface roughness was mainly influenced by feed rate (Pearson coefficient of 0.82), with higher feed rates leading to roug surfaces (up to Sa = 0.4 µm) duhere to the tool load increase that causes wider feed marks on the surface. Regarding the feed marks, they were affected by the tool rotational frequency due to system vibration. Additionally, surface defects of adhered material, smearing, tearing and side flow were observed. For lower feeds, material adhesion was the main type of defect observed, while higher feed rates favoured the side flow phenomenon.

Environmental Assessment of Metal Chip Recycling – Quantification of Mechanical Processing's Global Warming Potential

Material recycling is an essential lever for improving the sustainability of production processes. One way of reusing metal chips that occur as waste in machining or other subtractive manufacturing processes is to mechanically pretreat and remelt them. In mechanical pretreatment, the chips are separated from the cutting fluid by a centrifuge and then briquetted directly on site. This simplifies the handling and makes the transport and subsequent remelting more efficient than in thermal processing alone. The main objective of this work is to quantitatively assess the environmental impacts of the described recycling process, focusing on the global warming potential. Furthermore, recycling by means of mechanical chip processing is compared with alternatives such as thermal drying and primary material extraction. A parametric life cycle assessment (LCA) model has been developed for this purpose. The model considers equipment, material, throughput and location variations to analyze different use cases. The results of the LCA of an exemplary use case show that environmental benefits result from a higher bulk density during transport and a lower energy input during remelting due to a lower liquid content.

Tribological Properties of Additively Manufactured Al-Si Alloys and Steels

Metals are prone to wear through the separation of wear debris particles as well as the plastic displacement of surface and near-surface material. Particle sizes range from millimetres to nanometres. Erosion is the gradual, layer-by-layer destruction of a metallic object's surface brought on by mechanical pressure or electrical discharges. Metals erode as a result of surface friction, wear, cavitation, and the influence of powerful gas or liquid currents on a surface. Jet engines, nuclear reactors, steam turbines, and boilers might all suffer damage from erosion. By enhancing process technology or unit design, using better materials, and applying heat treatment, it is possible to strengthen the resistance of components against erosion. AlSi10Mg is a hypoeutectic alloy that may be additively manufactured due to its limited solidification range, which reduces hot cracking susceptibility during cooling. Complex bulk and open-cell structures with outstanding strength ratio (strength-to-weight ratio) and good formability may be created using additive manufacturing of aluminium alloys, particularly AlSi10Mg. Carbon, manganese, sulphur, silicon, phosphorus, chromium, nickel, copper, and niobium are all present in the pH grade of 17-4. This combination of high strength and corrosion resistance benefits a 17-4 PH stainless steel grade. It may be utilised effectively in a variety of applications due to its high tensile strength and exceptional corrosion resistance.Powder bed fusion is one of the most mature metal additive methods, and as such, it benefits from decades of industrial expertise. PBF can satisfy demands of creating a new component and need to iterate on ideas quickly or are searching for a more efficient procedure to produce sophisticated components. Material waste is reduced because building the part layer by layer reduces the majority of the waste associated with subtractive manufacturing processes. Any surplus powder is collected and recycled when the item is finished. This review researches about the wear and erosion behaviour of Al-Si Alloy and steels printed using additive manufacturing methods. Finally, the findings of this review are summarised, and recommendations are made for future research aimed at resolving current issues and advancing technology.

Prediction of residual strain/stress validated with neutron diffraction method for wire-feed hybrid additive/subtractive manufacturing

Hybrid manufacturing integrates additive manufacturing (AM) and subtractive manufacturing in the same machine. The integration of the two processes enables the creation of complex geometry, further reduces material waste, and decreases lead time. Moreover, this in-envelop method enables an interleaved printing strategy in which the part is partially AM printed and then machined repeatedly. This method is not available in either traditional manufacturing or AM technologies. Nevertheless, measuring and controlling of distortion and residual stress are still challenging due to highly varying process conditions and limited access to the machine during hybrid additive/subtractive manufacturing processes. Moreover, the residual stress measurement is ex-situ process, so it only gives information at the final stage of stress evolution. Therefore, it’s nearly impossible to know the AM induced residual stress distribution before the machining process in hybrid additive/subtractive process. In this prospective, numerical modeling can be an effective tools to overcome those challenges. However, the modelling/simulation methods for fully-coupled additive and subtractive operation has not reported to the best of our knowledge. In this work, we developed a comprehensive simulation method using finite element method (FEM) for fully-coupled additive and subtractive manufacturing process. The results were validated with strain measurements by neutron diffraction in two different machining conditions: hot-machining and cold-machining. The validated model was used to investigate how machining affects part distortion and evolution of residual strain/stress during fabrication. Alternating tensile-compression longitudinal (ε11, x-direction) strains and stresses along the build direction showed the physical interaction of additive and subtractive steps in the interleaved strategy. The alternating pattern was found in both the model and neutron diffraction measurements. This work’s findings can be used to develop strategies to control of part distortion and residual stresses in the hybrid additive/subtractive manufacturing process.

Status of 3D Printing Technology for Preparing Bioceramic Materials

3D printing technology has great advantages in small batch and personalized customization, so it has attracted much attention in the biomedical field. The consumables available for 3D printing include polymer, metal, ceramic and derived materials. Biomedical ceramics, with high melting point and poor toughness, are the most difficult materials to be used in 3D printing. The progress of 3D printing ceramic preparation process using ceramic powder, ceramic slurry, ceramic wire, ceramic film and other different raw materials as consumables are reviewed, and the surface roughness, size, density and other parameters of ceramics prepared by SLS, 3DP, DIW, IJP, SL, DLP, FDM, LOM and other different processes are compared. The study also summarizes the clinical application status of 3D printed bioceramics in the field of hard tissue repair such as bone tissue engineering scaffolds and dental prostheses. The SL ceramic additive manufacturing technology based on the principle of UV polymerization has better manufacturing precision, forming quality and the ability to prepare large-size parts, and can also endow bioceramics with better biological properties, mechanical properties, antibacterial, tumor treatment and other functions by doping trace nutrients and surface functional modification. Compared with the traditional subtractive manufacturing process, the bioceramics prepared by 3D printing not only have good mechanical properties, but also often have better biocompatibility and osteoconductivity.

Micromachining techniques for manufacturing high aspect ratio microelectrodes: A review

The advancement in micromanufacturing techniques has increased due to the demand for microtools used in biomedical engineering. The development of tailored micro-sized components has advanced significantly as manufacturing accuracy has improved. Although the machining of smaller dimensions is not new, difficulties arise when features are reduced to tens or hundreds of microns in size. Micro-machining technology is progressing towards the production of complex 3D parts. The creation of very precise equipment is essential to achieving productivity goals in terms of effectiveness, adaptability, robustness, and accuracy. Since even a minor modification can have a significant impact on machining performance, precise control over the machining variables is essential. This review paper describes the literature of subtractive micro manufacturing processes (traditional and advanced). In addition to subtractive processes, an overview of various micro machining techniques such as additive, mass containing and joining processes has been studied. In this paper, various micromachining techniques for fabricating high aspect ratio microelectrodes are studied and evaluated to find the suitable machining process to fabricate micro electrodes. The growing demand in the micro sector has attracted attention to the fabrication of high-aspect micro tools with diameters below 100 μm and high accuracy and precision.

Blended structural optimization of steel joints for Wire-and-Arc Additive Manufacturing

Metal Additive Manufacturing, and in particular Wire-and-Arc Additive Manufacturing (WAAM) has proved to be a great and efficient alternative to the common subtractive manufacturing processes to realize complex-shape members and connections for construction. With reference to complex spatial structures such as gridshells, the connections play a crucial role both in the design and the construction processes. Novel computational design tools allow designers to conceive optimized joint solutions while minimizing the material use, resulting in difficult geometries to be fabricated with conventional methods. The present work aims at providing an innovative integrated design and fabrication framework to efficiently apply topology optimization algorithms to improve the efficiency of steel joints in complex spatial structures. The framework is based on the so-called “blended” structural optimization approach aimed at incorporating manufacturing constraints, basic principles of conceptual structural design and structural requirements into topology optimization to design ready-to-fabricate complex steel joints. The designs are suitable for fabrication with the WAAM process. The approach is applied to a case study to re-design the joint connections of the world’s renowned British Museum gridshell rooftop structure. From a catalogue of various designs for each unique joint, one selected design is optimized and then checked for structural requirements in terms of strengths and stiffness. Then the optimized joint is validated for fabrication with WAAM process.

3D printing of ultra-thin veneers made of lithium disilicate using the LCM method in a digital workflow: A feasibility study.

This article highlights the feasibility of the additive fabrication of ultra-thin veneers made of lithium disilicate using the lithography-based ceramic manufacturing (LCM) method. An esthetical appealing restoration of anterior teeth with thin ceramic veneers is considered one of the ultimate challenges in restorative dental prosthetics. These sophisticated restorations can be fabricated in different ways. Both analog and digital subtractive manufacturing processes have been used to date. Either of the methods is highly demanding for the dental technician and dental engineering due to the required low ceramic layer thickness. Modern additive manufacturing methods, for example LCM technology, enable the production of ultra-thin lithium disilicate veneers with layer thicknesses of down to 0.2 mm and could therefore represent a viable alternative for this indication in the future. Digital technologies can help streamline workflows, make the outcome more predictable and reproducible, and even further optimize therapeutic restorative options such as highly esthetic veneers for anterior teeth. The reduced material thickness allows for a true non-prep solution or minimally invasive preparation.

316L Stainless Steel Thin-Walled Parts Hybrid-Layered Manufacturing Process Study.

Additive manufacturing technology overcomes the limitations imposed by traditional manufacturing techniques, such as fixtures, tools, and molds, thereby enabling a high degree of design freedom for parts and attracting significant attention. Combined with subtractive manufacturing technology, additive and subtractive hybrid manufacturing (ASHM) has the potential to enhance surface quality and machining accuracy. This paper proposes a method for simulating the additive and subtractive manufacturing process, enabling accurate deformation prediction during processing. The relationship between stress distribution and thermal stress deformation of thin-walled 316L stainless steel parts prepared by Laser Metal Deposition (LMD) was investigated using linear scanning with a laser displacement sensor and finite element simulation. The changes in stress and deformation of these thin-walled parts after milling were also examined. Firstly, 316L stainless steel box-shaped thin-walled parts were fabricated using additive manufacturing, and the profile information was measured using a Micro Laser Displacement Sensor. Then, finite element software was employed to simulate the stress and deformation of the box-shaped thin-walled part during the additive manufacturing process. The experiments mentioned were conducted to validate the finite element model. Finally, based on the simulation of the box-shaped part, a simulation prediction was made for the box-shaped thin-walled parts produced by two-stage additive and subtractive manufacturing. The results show that the deformation tendency of outward twisting and expanding occurs in the additive process to the box-shaped thin-walled part, and the deformation increases gradually with the increase of the height. Meanwhile, the milling process is significant for improving the surface quality and dimensional accuracy of the additive parts. The research process and results of the thesis have laid the foundation for further research on the influence of subtractive process parameters on the surface quality of 316L stainless steel additive parts and subsequent additive and subtractive hybrid manufacturing of complex parts.

Development and Production of Artificial Test Swarf to Examine Wear Behavior of Running Engine Components-Part 2: Experimentally Derived Designs.

In subtractive manufacturing processes, swarf, burrs or other residues are produced, which can impair the function of a tribological system (e.g., journal bearings). To prevent premature engine damage, cleanliness requirements are defined for production processes. Damaging particle tests are an experimental approach for validating these defined cleanliness requirements. This methodical approach is not yet widely used. For one, the test setup must be developed and proven for the respective application. For another, in order to carry out the tests in a systematic manner, defined test particles with properties similar to those of the contaminants encountered in reality are required. In the second part of the paper, the process chain for manufacturing artificial test swarf by micro powder injection molding (MicroPIM) is described. The size and shape of the swarf were derived from real swarf via several abstraction processes. Although certain design guidelines for MicroPIM parts could not be taken into account, the targeted manufacturing tolerances were achieved in most cases. During demolding, it became apparent that the higher ejection forces of the free-formed geometries must be taken more into account in the design of the mold. The experiments on the test setup also revealed that the artificial test swarf was unexpectedly brittle and was therefore ground up in the bearing gap without causing any substantial damage to the bearing. Thus, the artificial test swarf in its current sintered state is not a suitable substitute for micromilled swarf. However, MicroPIM could still be used to manufacture test particles in applications involving lower mechanical forces.

What alternatives to computed tomography for inspection of additive manufacturing parts with channels

Non-destructive inspection of parts with small diameter channels is a major challenge. Additive Manufacturing (AM) offers many advantages compared to the traditional subtractive manufacturing process for the manufacturing of these complex structures. Thales, Safran and ArianeGroup joined forces to find a way to inspect parts with small diameter channels by technics other than X-ray computed tomography. LNE and Institut de Soudure (French welding institute) worked with them to identify, propose and test non-destructive techniques capable to detect flaws and cavities containing unfused powder unique to the powder-bed fusion AM process category. This paper will present some results of this project called FA- Canalsafe®. Artificial defects created on mock-ups will be described. Some results and limitations on eddy current testing and on visual endoscopy will be discussed. Finally, some recommendations on NDT implementation will be proposed.

Achieving clean production with nanostructured coated milling tools dry machining low carbon steel

The advancement of clean production using nanostructured materials in subtractive manufacturing processes has focused on replacing the use of liquid lubrication with solid lubricants coated to conventional cutting tools machining low carbon steel (∼0.2 wt % carbon). However, little is known about the wear mechanisms that dominate such tools when coated with functional graded nanostructured coatings. The present study follows an international standard for characterizing such wear (ISO 8688) but uses advanced measurement techniques such as x-ray fluorescence technology to measure the diffusion of chemical species from tool to workpiece and vice versa, that contributes to tool wear with the view to enhance the principles of cleaner production. The results show that when commercially-available tools coated with the appropriate functionally graded industrial coating, diffusion does not take place and creates an effective chemical barrier during machining. The experimental methods used in the study include machining workpieces using a CNC milling machine, tachometer for measuring spindle speed, dynamometer for measuring cutting forces, infra-red camera for measuring cutting temperatures, chemical species diffusion wear using x-ray fluorescence detector, and an optical microscope for measuring tool wear. Coupled with the physical measurement of wear, it is concluded that mechanical wear dominates the milling of a low carbon steel and that thermal properties of the coatings do not correlate with such wear. It is also concluded that flank wear as a function of volume of workpiece removed and machining duration (machining index) is a sound method for assessing the transition of the stages of wear during clean machining operations. The present study not only has implications for the design of better cutting tools, but also advances dry machining processes that eliminate the use of liquid lubricants making subtractive production processes cleaner. The main conclusions drawn from this study show that coated tools have a longer life under dry conditions compared to uncoated tools and that there is no correlation between coating properties and tool wear. Diffusion of chemical species into the cut chips did not occur because of the lack of thermally induced chemical wear of the cutting tool and that wear is caused by the gradual erosion of the flank face due to the chip abrading the cutting tool.