The increasing demand for machined components of superior quality at competitive costs has driven machine and cutting tools manufacturers to innovate in machine tool technologies and cutting tools materials. Consequently, optimizing the machining process becomes an important subject of research. Particularly, optimizing machining parameters like cutting speed, depth of cut and feed rate stands out. Literature review highlights that optimization considers various “objective functions” such as minimum production cost, maximum production rate, and minimum energy consumption. However, one aspect not objectively considered is the customer's demand within a specific timeframe, known as takt time. The relevance, originality and contribution of this work is the development of a method that, considering the current machining parameters and the takt time for a given machining stage, defines the optimized cutting speed for each cutting tool to meet the takt time at the lowest production cost. An algorithm based on classical equations for calculating machining times and costs for machining processes with multiple cutting tools was developed. A software in Excel receives process data, “x and K” coefficients from Taylor’s life equation and calculates the optimized cutting speeds. The present method was applied in a heavy machining industrial environment using actual production data and machining parameters. Taylor coefficients x and K were obtained through cutting tool life tests carried out on the part under analysis. Results showed potential machining cost savings of up to 6.2

Various means of lubrication and/or cooling, as well as different ways of applying these fluids have already been implemented in machining in order to try to save costs during the manufacturing process, as well as not exposing the operator's health to irreversible damage by inhaling the vapor of these fluids. This work aims to study two new lubrication and cooling methods, never tested before: milling with the part submerged in neat oil and milling with the part submerged in aqueous fluid. The motivation for this study is to minimize the thermal cyclic variation of milling, which accelerates wear of the cutting tool and which should be reduced by submerging the part in these fluids. Machinability was then evaluated in terms of tool life, surface roughness and cutting power among 6 lubrication-cooling processes, namely, submerged with neat oil, submerged with aqueous fluid, abundant aqueous fluid (conventional machine jet), minimum volume of oil (MVO), minimum quantity of fluid with compressed air (MQF) and dry cutting. The above processes were also evaluated under different cutting speeds and different cutting widths (ae). The results showed that the submerged process with neat oil was the one that provided the greatest chip removal per tool life, followed by the submerged process with aqueous fluid, which fully met the expectations of this research. The mechanisms causing tool wear were attrition, abrasion and thermal cracks which were predominant in processes with aqueous fluid.

During machining, the workpiece material tends to undergo mechanical and thermal transformations. Machining Inconel 625 is a challenging task since this material has low thermal conductivity, rapidly work hardening and maintains its strength even at high temperatures. This superalloy is used extensively by the aerospace and oil and gas industries due to both its corrosion and heat resistance. All these characteristics influence tool life, cutting forces, and the integrity of the machined surface, which, in turn, significantly impacts the fatigue life of the components. It is therefore important to understand the surface integrity induced during milling. Although many reports have been published about tool wear and surface integrity studies for Inconel alloys, especially on the effect of the tool condition on the surface and subsurface which address residual stress, corrosion, and deformed layers have not been investigated so far. This study highlights the importance of assessing the surface integrity of Inconel 625 clad workpieces milled with both fresh and worn tools at different cutting speeds and feed rates. The results show that the best conditions for maintaining surface integrity among the conditions tested are vc=55 m/min and fz=0,10 mm/tooth. The workpiece milled with a fresh tool presented better corrosion resistance, whereas the worn tool produced more compressive stress, indicating that such conditions would improve the fatigue life of the part.

In the manufacturing of dies and molds, vibrations may represent serious problems, since the finishing tool used is usually slender (high length/diameter ratio) in order to machine deep cavities with complex geometries, typical of these products. Vibration is an undesirable phenomenon in any machining operation as it can lead to poor surface finish, low material removal rate, and high tool wear rate. Impact dampers have been put into the tools as a method for reducing vibration in machining processes. Damping occurs through energy dissipation and linear momentum exchange during intermittent collisions between the main structure (in this case the milling tool) and a free mass (spheres or cylinders placed within a tool cavity). Although efficient, these types of dampers are highly nonlinear. Thus, the aim of this work is to analyze the effect of different materials and geometries (steel spheres, tungsten spheres and steel cylinders) acting as impact damper elements inside a ball nose end milling tool. To perform this task, a comparison of commercial tool holders and dampened tool holders was done in the milling of a convex D6 steel surface, comparing commercial tool holders with dampened ones. The results showed that the tools with impact dampers generated lower values of roughness in the workpiece (around 30% of the value observed in the conventional steel tool holder for the case of steel cylinders and around 40% for both spheres) and presented lower levels of vibration when compared to the same tool without the impact damper, mainly in the machining of workpiece regions where radial and tangential forces are predominant. The tool which used tungsten spheres as damper elements generated roughness surfaces similar to those obtained with steel spheres, while the tool which used steel cylinders only generated lower roughness in the regions where the axial force component is not predominant, which shows that its performance is highly dependent on the resulting force direction.

Nickel-based alloys are used widely in aerospace components and the oil and gas industry, operating in an extremely adverse environment. These alloys are characterized as difficult-to-machine materials due to their high hardening rate, low thermal conductivity, and superior hot hardness. Since the material and its machining are very expensive, it is important to evaluate how the machining processes deteriorate the surface integrity to prolong the service life of the Inconel components as long as possible. In order to reach this goal, the influence of tool geometry, feed rate, and cutting speed on surface integrity was evaluated for the milling process of Inconel 625 cladding. Qualitative and quantitative mechanical and metallurgical analyses on the surface and subsurface were performed using 3D optical microscopy, scanning electron microscopy (SEM), instrumented indentation, X-ray diffraction for residual stress measurements, and corrosion tests. The results indicate that cutting speed has the greatest influence on specific cutting pressure. The cutting speed and feed rate were the main factors that affected the thickness of the deformed layer. The results suggest that surface and subsurface alterations after machining are driven by mechanical-thermal loadings and cause beneficial results related to corrosion resistance and compressive residual stress.

Regarding milling of dies and molds, there are several geometric requirements, and it is absolutely not trivial to machine complex either concave or convex surfaces. Since the contact between tool and workpiece changes all the time, making the components of the milling forces also to change, it is fundamental to find the correct milling strategies which cause the smallest variation of cutting forces (amplitude and sense) in order to obtain the best possible workpiece surface quality. In this work, four different machining strategies for finish milling of D6 tool steel were studied. They were compared in terms of surface roughness, cutting force, and tool wear at the end of tool life. Results show that lower surface roughness was obtained using descending down milling and ascending up milling because the sense of the cutting force components, specially the one that is normal to the machined surface on the most critic region of the workpiece, pulled the workpiece against the tool and the tool against the workpiece. On the other hand, descending up milling and ascending down milling did not present good results because the sense of the force components was responsible for excessive tool bending moving the tool and workpiece apart.

Milling is a very important machining process for many industry fields. In rough milling, changing the tool in the correct moment is an important task, since both, the tool (which is usually big and with many teeth) and the machine used are very expensive. Several studies were carried out mainly during the 1980s and 1990s, seeking to establish criteria for the end of tool life, as well, methods that could indicate the ideal time for tool change in real production. Nevertheless, according to an extensive literature review based on publications in manufacturing technology journals, university research, and benchmarks with industry developments, it was not possible to find out publications that confirms the usage of automatic definition for the end of tool life under heavy roughing five-axis milling in a production environment. Based on this context, the relevance, originality, and contribution of the present work for the scientific community is grounded in developing an automatic tool change process completely independent of the cutting parameters and inside a production environment, that can be replicated for many other machining operations by using state of art technologies (Industry 4.0–The Digital Age), in order to take out of the machine operator’s hands the important decision to establish the end of tool life. Aiming this goal, several rough milling experiments were conducted in a real production of hydraulic turbines. The main conclusion was that, in rough milling process, where the admissible flank wear is very high, both, the power consumption of the machine and the cutting temperature at the end of tool life are independent of the cutting conditions (vc and fz) and, consequently, a specific value of power and temperature can be established to determine tool life end.

The increasing use of titanium and its alloys in the manufacture of implants results from the simultaneous presence of excellent biocompatibility, relatively low density, high mechanical properties, and corrosion resistance. Unlike the excellent application characteristics, titanium is classified as a difficult-to-machine material. Therefore, one constant challenge for implant manufacturers is to correctly choose turning tools for each application. This work aims to compare the useful life of the uncoated insert with other three types of coatings on carbide tools, titanium aluminum nitride (TiAlN), aluminum chromium nitride (AlCrN), and titanium nitride/titanium carbonitride multilayer coating (TiN + TiCN). Turning experiments were performed using grade 4 commercially pure titanium (typically used in dental implants), testing two cutting speeds for each tool used. The tests were carried out in a CNC rotary head lathe, using cutting fluid in abundance. The results showed that the uncoated insert achieved the shortest life due to its worst properties (lower surface hardness, higher friction coefficient, and lower maximum working temperature), even with its supposedly higher chemical stability with titanium. On the other hand, the tool with the TiN + TiCN multilayer coating obtained the longest tool life among the four tested inserts. The main novelty of this work is that the tool that showed the longest life (TiN + TiCN coating) did not have the best properties among the tested coatings. In fact, it had both the lowest hardness and working temperature. However, this tool has a low coefficient of friction and a multilayer structure coating, which increases its resistance against the wear mechanism that occurred predominantly in this application, which was attrition. Even with the increased cutting speed, this coating also achieved the best result. Therefore, during the machining of titanium, the most important characteristics of the tool are low coefficient of friction and resistance against the pull out of particles.

The increasing market demand for smaller products requires the development of micromachining processes. This, in turn, enhances the importance of knowledge about the phenomenon of chip formation and its characteristics at the microlevel. Conventional machining generally assumes that the tool cutting edge is perfectly sharp, and that it usually does not affect the chip formation process. However, in micromachining, the magnitude of the edge radius (r(e)) is often the same as that of the chip thickness, thus significantly affecting the process. Moreover, the study of chip formation at the microlevel is even more complex. In micromachining, as the chip thickness decreases, it reaches a minimum thickness at which a chip is still formed, called the minimum uncut chip thickness (MUCT). Therefore, the purpose of this work is to use an experimental method, based on milling, to reach the MUCT (h(min)) by simulating a micromilling operation. AISI H13 steel was used in two conditions: hardened and as received, with around 60 and 25 HRc, respectively. The experiments were performed according to a novel method simulating end milling in orthogonal cut. It was found that h(min) varied from 0.56r(e) to 2.5r(e), and that this range depends not only on r(e) but also on the material being machined and on the mechanical compliance of all the equipment used in the test. Based on the theory of contact mechanics, it was possible to explain that a chip is formed only after the cutting edge has attained the necessary stresses to cause failure of the material being tested, and this knowledge is fundamental to understand the occurrence of h(min). In addition, the method used here was successful in reaching h(min) values typically obtained in milling conditions. Using the same method proposed herein, future studies of MUCT can be performed employing even conventional machine tools.

Turning operations, especially those performed in deep holes, are associated with significant problems related to chatter, which have considerable influence over some productivity factors, production costs, etc. In pre-roughing operations, the drill marks leave great irregularities on the part’s surface. Those cause chatter during the internal turning process, especially during finishing operations, which are used to obtain internal diameters of better accuracy. The vibration is even more accentuated in the machining of hard materials, that requires more intense cutting forces and reach higher cutting temperatures. In such cases, the use of Cubic boron Nitride (CBN) tools is necessary to improve the performance during the machining operation. This work aims to verify the influence of vibration over tool life in long overhangs. To that end, the tests consisted in collecting acceleration signals determined from the Fast Fourier Transform (FFT) and monitoring the tool wear process using optical microscopy, so that the lifespan of the tool could be verified. The tool overhang was varied until it reached a limit (the deepest hole it could machine). The results show that, when the tool overhang is within its stability range, the tool vibration amplitude is greater in the beginning of tool life than in its end, and the surface roughness of the machined part is not affected. Also, the flank wear of the tool is accentuated when the tool overhang outreaches its stability limit.

Surface texture of stamping tools affects the performance of the tool, tool life, and surface quality of the stamped product. In this work, punch samples were machined after heat treatment by milling and turning strategies in super finish processes and part of the punches were submitted either to plasma nitriding or nitrocarburizing treatment before the experiments using hot stamping of washers, which were made in two stages. Based on roughness results, for non-treated punches, most of the milled punches presented more intense surface damage than turned punches after hot stamping process, possibly due to the marks left by machining processes, affecting mechanical obstacles to wear evolution and lubricant retention on punch surface. For nitrided punches, surface damage was less intense than it was on non-treated punches. Parallel contours strategy and turning upward strategy presented less intense surface damage after the hot stamping process. For nitrocarburized punches, surface damage was less intense than it was to non-treated punches, mainly for milling strategies. SEM images of nitrided and nitrocarburized punches suggested alveolar corrosion occurrence during hot stamping process for circular upward strategy.

Eco-efficiency solutions have been more and more proposed by researcher and industry around the world in latest years in order to become the manufacturing systems cleaner and greener. This action is related to the global warning about the generation of greenhouse gases (GHGs), like CO2, as reported by Intergovernmental Panel on Climate Change (IPCC) . One of the most hazardous issue related to environmental risk in machining process is the application of metalworking fluids (MWFs), especially in grinding process in which MWFs are pivotal to control high generation of heat and avoid workpiece surface burns and microstructural changes. The minimum quantity lubrication (MQL) was broadly reported in the literature as a potential alternative lubri-cooling technique to the conventional technique (flood F). However, the main drawback of MQL grinding is related to high generation of clogging phenomenon produced by the chips lodged on the grinding wheel active surface (GWAS) due to the low oil volume and consequently the low lubricating and cooling action. In order to propose improvements on MQL technique, increase its efficiency and viability and develop a potential greener lubri-cooling technique, this work aims to propose and evaluate the application of hybrid HMQL + WCJ technique combined oil and water at 1:5 oil-water in the Al2O3 grinding process of AISI 4340 steel. This technique was compared to flood F and the pure PMQL + WCJ (pure oil) techniques. Both MQL techniques (hybrid and pure) employed at 30, 60 and 120 mL/h. The PMQL + WCJ technique produced the worst results irrespective of the flow rate. The HMQL + WCJ at 120 mL/h (highest flow rate) presented similar performance to the F technique in terms of surface roughness, microhardness, clogging behavior on GWAS, workpiece form deviation, grinding power, generation of CO2 during the process and acoustic emission (AE) and outperformance in terms of G ratio. This indicates the eco-efficient potential to be widely employed in manufacturing industry and mitigate the environmental impact and carbon footprint of hybrid MQL + WCJ technique. (C) 2020 Elsevier Ltd. All rights reserved.

In grinding, the viability of the minimum quantity lubrication (MQL) technique is still limited, due to the frequent occurrence of overheating and wheel clogging. Thus, MQL improvement is essential to allow its extensive application in grinding processes. This work evaluates a cooled wheel cleaning jet (CWCJ) under different temperatures, applied simultaneously to the MQL in grinding of AISI 4340 hardened steel. Tests with the conventional, MQL, and MQL + WCJ methods were also performed for comparison. The assessed output parameters were workpiece surface roughness, microhardness and roundness deviation, diametrical wheel wear, and grinding power. The machined surfaces and the chips were evaluated through scanning electron microscopy. The application of the CWCJ enhanced the performance of the MQL technique.

Minimum Quantity of Lubricant (MQL) has been used in the grinding process to make the process eco-friendlier. On the other hand, it brings some technical problems to this process: the clogging phenomenon, i.e., chips adherence on the wheel cutting surface. Although this phenomenon yields widely known negative effects on productivity and workpiece quality, few studies exist about clogging in MQL grinding. Thus, this paper aims to explain the clogging formation and evaluate its effects on workpiece finishing and geometrical tolerances. External cylindrical plunge grinding tests in quenched and tempered AISI 4340 steel with CBN wheel, varying lubri-cooling conditions were carried out. Clogging affects the cutting ability of the grinding wheel and impacts on the chip formation. The addition of water in the MQL flow reduced the clogging occurrence in 40%, which corroborated to a reduction of 51% the surface roughness and 58% the roundness error.

Superalloys are high-performance materials which combine high tensile, creep and fatigue strength, besides good ductility, toughness and resistance to corrosion, properties that are also responsible for their low machinability. The VAT 30® alloy contains an austenitic stainless steel base with additions of chromium, nickel, titanium and aluminum, and it is mainly applied on the manufacture of valves of combustion engines, due to its advantageous characteristics. This alloy exhibits both high ductility and abrasiveness, features that may promote both attrition and abrasion wear mechanisms on the tool used to cut it. This work contains some investigations about the effect of cooling condition, tool rake angle and cutting speed on the machinability of Ni-30 alloy in terms of cutting power consumption, surface roughness and tool life, besides the tool wear mechanisms. Conventional and high-pressure coolant injected toward the tool rake face was compared, as well as negative rake angle and neutral tooling, besides two different cutting speeds. Results show that high-pressure coolant may reduce cutting power consumption and even increase the volume of material removed during tool life up to 45% in some cases, but this same influence has not been verified regarding the workpiece arithmetical mean roughness value. Negative and neutral rake angle tools did not present very different results in terms of power and roughness, but negative tools provided considerably higher volume of material removed per tool life (up to 75% in one condition). Cutting speed showed strong effect on the cutting power, as expected, but no reasonable effect on workpiece surface roughness; regarding tool life, the cutting speed increase typically reduced the volume of material removed per tool life with conventional cooling, but when high-pressure coolant was used, this effect was attenuated. Abrasion and attrition were the main tool wear mechanisms in any tested condition.

Iron-based superalloys are difficult to machine because of their thermal and mechanical properties provided by alloying elements as nickel, chromium, titanium, and aluminum. However, parts made with this kind of material has to be machined during their production processes. In this work, two different automotive engine valve steel grades, VAT 30® and VAT 36®, were compared in terms of machinability, considering cutting power consumption, roughness of the machined surface, and tool life, besides the identification of the main tool wear mechanisms that have led to the end of tool life. The main goal of this work is to understand the difference in these machining outputs based on the thermal and mechanical properties of these two materials. In order to reach this goal, turning tests were held using two different cooling conditions, conventional and high-pressure coolant. Also, two PVD-coated carbide inserts were applied, one with negative rake angle and another neutral. Finally, cutting speed was tested in two levels, providing a full 2 4 factorial planning. Results show that VAT 30® has shown higher machinability in terms of tool life in almost every condition, although this steel presents higher hardness, mechanical strength, and strain hardening coefficient, besides lower thermal conductivity. However, it also presents lower ductility and abrasiveness, features that retarded abrasion and attrition as tool wear mechanisms, in such a way that tool life could have been lengthened.