Cutting technologies are utilized in many industrial sectors, such as automobile, aircraft, and medical-device manufacturing as well as dies and molds. Thus, the requirements for higher geometric accuracy, better surface integrity, and longer component service lifetimes have substantially increased. In addition, maintaining high machining efficiency while simultaneously reducing power consumption and CO₂ emissions during machining is important for sustainable development.

This special issue features 11 papers on the most recent advances in cutting technologies for metals and composite materials.

- Reverse finishing characteristics of drilling surfaces

- Machining error simulation for end milling

- Visualization of cutting phenomena using a single-crystal diamond tool

- Milling of TiB₂ particle-reinforced high-modulus steel

- Electrodischarge-assisted turning of carbon fiber-reinforced polymers

- Suppression of chatter vibration during double-insert turning

- Prediction of surface roughness components during turning

- Microtome blades for high-precision tissue sectioning

- Boiling of coolant near the cutting edge in high-speed machining

- Residual stress during drilling of aluminum alloy

- Effect of strain hardening on burr control during drilling

This issue provides an understanding of recent developments in cutting technologies, aiming to inspire further research in this field.

We deeply appreciate the careful work of all the authors and thank the reviewers for their diligent efforts.

Aluminum alloys are often used in automobile and aircraft parts that require higher dimensional accuracy and durability. Drilling is often used in the machining process of these products and accounts for about 60% of the machining performed on these products. Deterioration of finishing surface accuracy in drilling causes problems such as decreased tool life due to wear and increased cost due to the introduction of the finishing process. The objective of this study is to evaluate the finished surface characteristics in the drilling of aluminum alloys using reverse finishing, with a focus on the cutting direction of finishing, with respect to the roughing direction. The torque and thrust force are smaller in reverse finishing than in forward finishing. The reduction effects of cutting force in reverse finishing were more significant when the finishing depth of cut was smaller in relation to the roughing-affected layer. Under conditions where the finishing depth was equal to or greater than the roughing-affected layer, it was possible to reduce cutting forces and improve surface roughness while obtaining compressive residual stresses equivalent to forward finishing.

Depending on cutting conditions, unacceptable machining errors are caused by tool deflection in end milling operations. Many studies have proposed methods for predicting the machining error owing to the tool deflection to achieve the theoretical optimization of the cutting conditions. However, the conventional machining error simulation is not practically utilized to determine the optimal cutting conditions. Tool system stiffness parameters and cutting coefficients must be identified in advance to simulate machining errors. However, dynamometers and displacement sensors are required for parameter identification. Therefore, it is impossible to identify the required parameters in typical factories, which do not possess such special equipment. In this study, a practical method was developed to identify the stiffness parameters that can be determined in factories. The proposed method employs on-machine measurement and sensor-less cutting force monitoring to achieve practical parameter identification. In the proposed method, the profile milling is first conducted. During the milling operation, the cutting force and cutting torque are monitored through a controller based on the sensor-less monitoring technique. After the operation, the machining error distribution on the machined surface is measured on machine using a touch probe. The required parameters are identified by minimizing the differences between the measured and theoretical forces, torques, and machining error distributions.

Analysis of cutting phenomena has been conducted for a long time and many researchers have elucidated the phenomena that may occur at the cutting-edge during machining; for example, built-up edges and welding phenomena on cutting edge. However, the existing research has focused on observing the tool and chips after machining, when the tool and work material have been cooled, and are under atmospheric pressure. Therefore, we consider that it is different from the phenomenon that occurs during cutting. Because the cutting edge of a tool is in a high-temperature and high-pressure environment during machining and is released from such an environment after machining, the cutting edge must be visualized to discuss the actual cutting phenomena. There have been research reports in the past that have visualized the backside of cutting chips; however, that experiment was far from actual cutting phenomena and was conducted at significantly low cutting speed. Thus, the visualization of the cutting phenomenon is physically extremely difficult at the cutting edge. Under such circumstances, this study developed a device that observed the behavior of the boundary surface between cutting chips and the rake face in real time from the backside of the rake face during machining. By using the developed device, we could visualize this phenomenon to acquire the data directly and visually, which can otherwise be grasped only indirectly. In this device, a camera was mounted on a tool holder, and a cutting tip made of a transparent material was used to observe rake face, cutting edge, and flank face which can be visualized during machining from the backside of the rake face within one field of view. This paper reports on the outline of the developed device, its method, and the results of experimental observation of the state of two-dimensional cutting using a lathe.

TiB₂ particle reinforced high-stiffness steel is one of the composite materials that aim to improve Young’s modulus by compositing TiB₂ particles into a stainless steel base phase. This material is designed to exhibit higher rigidity and strength than conventional iron-based materials by using TiB₂ particles as the reinforcing phase, and is expected to reduce the weight of high-load components in engines. For this reason, tool life is very short when machining this material. Therefore, high Young’s modulus steel containing TiB₂ particles is known to be one of the most difficult-to-cut materials. The purpose of this study was to investigate how to extend tool life in the milling of high-Young’s-modulus steel. Cutting speed dependence of tool life was investigated by end milling using a binderless CBN tool with excellent hardness and bending strength. In addition, the tool damage mechanism was also investigated. The results showed that tools composed of binderless CBN tool have a longer life than conventional CBN tool. In this type of binderless CBN tool, the tool wear rate tended to increase with increasing cutting speed. In addition, the longest tool life was obtained at a cutting speed of 1.25 m/s, though wear rate increased at a boundary cutting length of 1300 m. The wear rate was found to increase with increasing cutting speed. Temperature measurement results indicate that the primary cause of tool damage was mechanical wear, as the temperatures were much too low for a reaction between cBN and Fe. Friction tests revealed scratch marks on the tool originating from crushed cBN particles produced by the crushing of the cutting edge. This indicates that wear is accelerated by the high frictional energy of the cBN powder rubbing against the flank face.

The demand for carbon fiber reinforced plastics (CFRP), classified as functional resins, has increased for micromachined products that are manufactured using lathes and used in the medical field. However, the problems with machining CFRP include the occurrence of burrs and deterioration of the finished dimensions owing to the significant tool wear caused by the carbon fiber. To turn CFRP and maintain high dimensional accuracy, the authors proposed a novel combination of conventional turning and electrical discharge-assisted turning (EDAT). In this study, the capability to control the machinability of EDAT under low-voltage conditions was experimentally investigated. The relationship between the discharge voltage, frequency, and depth of discharge influence of the carbon fibers was clarified.

A novel cutting manner is presented to control regenerative chatter vibration in double inserts cutting, in which the forward and the backward inserts cut workpiece simultaneously with phase difference in the modulation of finished surface. In double inserts cutting, the forward insert is clamped above the backward insert. Both the inserts are positioned symmetrically with a height offset with respect to the workpiece rotation center. The forward insert mainly removes the material; while the backward insert cuts a part of the inner modulation to lose the regular excitation. The exciting force is also reduced with the cutting thickness of the forward insert after a workpiece revolution. Because the theoretical position offset of the inserts in the feed direction is small, the side cutting edges of inserts are aligned in the same position. The process parameters are determined by estimating the removal volume of the backward insert with the phase shift. The range of the cutting speed and the height offset are given by the frequency of the chatter vibration, which is nearly the same as the natural frequency of the workpiece in single degree of freedom. The proposed cutting manner is validated using comparison between the single insert and double inserts cuttings.

Surface roughness is affected by the tool geometry, feed rate, overcutting by built-up edge, and tool vibration in the depth of the cut direction. However, dividing the roughness value into each component is difficult. Therefore, a new prediction method for the position of the tool contour on the roughness curve is proposed to divide the measured roughness value into components. This proposed method consists of two processes. In one, the roughness curve is divided into the roughness curve formed during each revolution of the work material regardless of the clarity of the feed marks. The other is the process that predicts the vertical position of the tool contour. If the vertical position of the tool contour can be predicted, the vibration and overcutting components of roughness can also be predicted. In this study, the transition of roughness components such as the theoretical roughness, vibration width, and overcutting is studied with the increase in the cutting distance in the turning of chromium molybdenum steel, JIS SCM435. When supplying a 10% emulsion mist, the measured R_z is smaller than that of the dry condition. In both the dry and mist supply conditions, the measured R_z increases from the beginning of cutting then decreases and then increases again with the increase in the cutting distance. The largest component of the total roughness in both the dry and mist supply conditions is the theoretical roughness R_th. The ratio ranges between 50.3% and 78.7%. Regardless of the cutting conditions, the vibration width in the depth of the cut direction is relatively constant. The overcutting slightly increases after the start of cutting, then decreases when the maximum contact length exceeds approximately 0.1 mm. The proposed method verifies the ratio of the surface roughness components and is an effective method for improving the surface roughness.

In this study, the durability of microtome blades, used for sectioning paraffin blocks, was evaluated with the goal of improving the quality of sections in pathology tests. First, for the durability test of microtome blades, a sectioning test device that realizes stable sectioning operations was developed. This device comprised precise stages supported by cross-roller guides, achieving sufficient rigidness. This device allowed automated repetitive sectioning and simultaneously measured the principal and thrust cutting forces. Samples embedding porcine kidney and rib tissues were used for the durability test. Two types of blades with different blade edge angles were used. Additionally, the rake face and cross-section of blades, as well as H&E-stained sections, were observed. In the durability test with porcine kidney tissue, good quality sections were obtained even after 100 times of sectioning with both microtome blades, showing sufficient durability. However, in sectioning porcine rib tissue, the microtome blade with a large blade edge angle produced good-quality sections in the initial phase of the durability test; however, defects such as overlapping of folds were observed after 100 times of sectioning. Meanwhile, the microtome blade with a small blade edge angle experienced blade damage from the early phase of the durability test, resulting in the production of unsuitable preparations for pathology tests. These results indicated that the microtome blade with a small blade edge angle lacked durability against hard tissues such as porcine ribs.

This study investigates film boiling of coolant as a cooling inhibitor in a narrow wedge-shaped space between the tool flank face and the machined surface of a workpiece, observed during high-speed turning of stainless steel SUS304 and nickel-based superalloy Inconel 718. The boiling, likely triggered by high surface temperatures at both the face and surface close to the cutting edge, impedes coolant access to the tool tip area and efficient cooling. Therefore, the impact of coolant pressure on the boiling zone size was initially explored across pressures ranging from 0.1 to 20 MPa. A burn mark band due to coolant boiling, distinctly visible on the flank face of an insert with a yellow hard coating, expanded over cutting time. The film boiling area width, or the distance from the flank wear area to the band, decreased with increasing coolant pressure, reflecting the enhanced cooling ability and tool life with high-pressure coolant. Applying Boyle–Charles’ law to film boiling indicated that vapor pressure was directly related to coolant velocity rather than pressure. In contrast, the boiling area width increased with increasing cutting speed.

Residual stress is one of the critical evaluation factors as well as machining accuracy and surface finish in cutting. From the perspective of the fastening strength of parts, residual stress in drilling has an influence on the product or part life. Especially in the aircraft manufacturing, the tensile residual stress is crucial as it can cause major accidents. However, few studies have focused on residual stress in drilling so far. Most of them investigated the characteristics of residual stress based on the experimental data. This paper discusses residual stress in drilling in terms of its mechanical effect. The residual stresses in the inner surfaces of holes were measured in the depth direction from the top of the plate. The change in the residual stress has good correlation with the chip flow direction and the load applied to the inner surface, which acts as a counter force to the cutting force near the outermost ends of the lips. The cutting force is determined using an analytical model based on the minimum cutting energy. The correlation between the residual stress and the direction of the load applied to the inner surface depends on the margin width and back taper on the peripheral sides of a drill. The effect of the margin contact on the residual stress is characterized by linear regression analysis. Finally, an analysis-neural network hybrid system was developed to estimate the residual stresses in drilling. In the system, the mechanical effects of the drilling process, which are the magnitude and direction of the load applied to the inner surface, are obtained through analytical simulation. Meanwhile, the margin effects are expressed as the coefficients in the linear functions, which are associated with the margin width and back taper angle by a neural network. Then, another neural network, working as a post process, estimates the residual stresses using the information of mechanical and margin effects. The developed system is validated by presenting a comparison between the estimated and the actual residual stresses.

Austenitic stainless steel has been widely used in various industries, such as aerospace, medical, and hydrogen energy, due to its high strength over a wide range of temperatures, corrosion resistance, and biocompatibility. However, stainless steel is a difficult-to-cut metal because its ductility and low thermal conductivity induce a strain hardening with significant plastic deformation at high temperatures. Burr formed at the back side of a plate is a critical issue which deteriorates the surface quality, especially in drilling. Burr removal operation, therefore, should be done in the machine shop. This study discusses the effect of strain hardening of austenitic stainless steel, SUS 316L, on burr formation. Hardness and cutting tests were conducted to compare the strain hardening effect for three types of workpieces: as-received, pre-machined, and tensile treated specimens. In the employed specimens, the tensile treated specimen is harder than the as-received specimen. Those specimens have uniform hardness in the depth direction from surfaces. Pre-machined specimen, in which the back side of the plate was finished by face milling, has a distribution of hardness in the depth direction from a surface. The highest hardness appears in the subsurface of the pre-machined specimen. The cutting forces in the steady processes, in which the entire edges remove material, were nearly the same as the tested specimens each other. However, remarkable differences were confirmed in the chip thickness and burr formation. The higher strain hardening of the tensile treated specimen is effective to suppress burr formation. The cutting characteristics are then identified to associate burr control with the shear plane model of orthogonal cutting using an energy-based force model. The shear stresses, shear angles, and friction angles of the tensile treated and as-received specimens are compared to discuss the effect of strain hardening on reduction of burr formation.

Because edge-aware filtering has been widely used for image-based automation technologies, developing a practical, fast algorithm for its use is important. This letter proposes a simple and fast computational method for edge-aware image filtering based on bilateral half-box regions. Our filter consists of a weighted average of only eight color sums within each half-box region adjacent to a given pixel, where the tonal weights are similar to those obtained with bilateral filtering. The eight sums are efficiently obtained by a single fast box filter using the relative coordinate relationship between the pixel and each half-box center. We examined the performance of our filter based on comparisons with conventional methods.

Although, three-dimensional printing has several advantages, however there are currently many limitations. In particular, printed products using composite materials such as fiber-reinforced plastic have yet to achieve the same mechanical properties as those obtained from conventional manufacturing methods. In addition, fabricating thin plates or thin shell shapes with sufficient strength is challenging. Incremental forming enables high-mix, low-volume production of thin sheets. This method applies incremental deformation to thin sheets, the desired shape is obtained by accumulating the deformation, and no dies are required. Carbon-fiber-reinforced plastic (CFRP) materials have high specific strength. Discontinuous-fiber CFRP is capable of large plastic deformation under appropriate conditions due to the discontinuity of the reinforcement, and its mechanical properties are nearly isotropic due to the random fiber arrangement. The authors focused on this property and studied the application of single-point incremental forming to discontinuous carbon-fiber-reinforced polyamides. In this study, the workpiece was formed by heating it locally to a deformable temperature by the frictional heat between the rotating tool and the workpiece. The forming experiment was also conducted in an oil bath to keep the entire material at a suitable forming temperature. The results showed that the spindle speed affected forming results even in an oil bath and that heating using an oil bath suppressed deviations from the sine law for thickness and wall angle due to elastic deformation.

A five-axis machining center (5MC) is capable of synchronous control, which makes it a feasible tool for quickly and accurately machining complicated three-dimensional surfaces, such as propellers and hypoid gears. Recently, the necessity of improving both the machined shape accuracy and the machined surface roughness of free-form surfaces is growing. Therefore, in our previous study, we aimed to maintain the feed speed vector at the end-milling point by controlling two linear axes and a rotary axis of the 5MC to improve the quality of the machined surface. Additionally, we developed a method for maintaining the feed speed vector at the end-milling point by controlling the three axes of the 5MC to reduce the shape error of the machined workpieces (referred to as the shape error herein), considering the approach path of the tool determined via calculation. However, a high machining force at the start of the workpiece cutting was observed and the factor contributing to this phenomenon was not determined, although this phenomenon leads to a shape error to a certain degree according to the machining condition. In this study, the main objective is to suggest a method to reduce the machining force at the start of the workpiece cutting and shape error. Hence, we develop a theoretical method to estimate the machining force by using an instantaneous cutting force model, which considers the synchronized motion of two linear axes and a rotary axis of the 5MC. Subsequently, we determine the most suitable approach path of the tool considering the prediction of the machining force. The results of this study indicate that the machining force can be estimated by applying an instantaneous cutting force using the feed per tooth and machining angle, and that both a high machining force at the start of the workpiece cutting and shape error reduction can be realized by using the proposed approach path of the tool.