In recent years, manufacturing technologies have been progressing with the high demands of industry. In the automobile and aircraft industries, for example, the manufacturing processes have been requiring for technologies that allow for high machining rates of lightweight and/or difficult-to-cut materials. Medical device production includes the machining of biocompatible materials that have high mechanical strength. Information devices require high quality in ultra-precision manufacturing processes. Measurement and characterization technologies in manufacturing have also been essential in the progress. Along with evolution of manufacturing technologies, scientific studies have been done on manufacturing phenomena and the control of processes, based on physical and/or mathematical aspects.
This special issue is promoted by the International Conference on Leading Edge Manufacturing/Materials & Processing (LEM&P2020), which was canceled to protect the health and wellness of our community from COVID-19, and by the Research Committee of Cutting Technologies in the Japan Society for Precision Engineering.
This special issue includes 17 papers that detail progress and innovations in the following areas:
- Characterization of materials
- Fundamental study and modeling of material removal process
- Manufacturing control and optimization
- Manufacturing processes for new/hard materials
- Micro-/Nano-scale manufacturing
- Tool manufacturing and performance
- Metrology and evaluation
- Surface characterization
This special issue also includes not only technical but also scientific discussions, suggesting new key technologies for future manufacturing. We hope this will help the readers to understand the manufacturing processes and improve their operations.
We thank the authors and the reviewers for their generous cooperation and the editing staffs for their many contributions.
The microstructure and mechanical properties of the AlSi12CuNi alloy fabricated by the additive manufacturing technique, laser powder bed fusion (L-PBF), were investigated. Several laser irradiation conditions were examined to optimize the manufacturing process to obtain a high volume density of the fabricated alloy. Good fabricated samples with a relative density of 99% or higher were obtained with no cracks. The fabricated samples exhibited significantly good mechanical properties, such as ultimate tensile strength, breaking elongation, and micro-hardness, compared to the conventional die casting AlSi12CuNi alloy. Fine microstructures consisting of the α-Al phase and a nano-sized eutectic Al-Si network were observed. The dimensions of the microstructures were smaller than those of the conventional die-casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification in the L-PBF process. Furthermore, the influence of the building direction on the mechanical properties of the fabricated samples was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction; mechanical properties parallel to the roller moving direction were significantly better than those perpendicular to the roller moving direction. In conclusion, AlSi12CuNi alloys with good characteristics were successfully fabricated by the L-PBF process.
Clamp force errors in bolted joints often cause accidents in various mechanical structures. Therefore, the clamp force must be controlled accurately and maintained for securing the reliability of mechanical structures such as vehicles. However, the clamp force cannot be controlled easily during tightening. Moreover, it is difficult to detect the clamp force after tightening. We previously proposed a method to easily detect the clamp force of a bolted joint that has been tightened. In that method, the bolt thread protruding from the nut is pulled while the nut’s upper surface is supported. The relationship between tensile force and displacement at the pulling point where the tensile force is applied differs before and after the tensile force reaches the clamp force. The method detects the tensile force at the point, where the relationship changes, as the clamp force. In this study, we investigate the influence of squareness error on the bearing surface of the clamped part in a bolted joint on the detection error of the method using experiments and finite element (FE) analysis. The experimental results show that the squareness error has an influence on the detection accuracy. The average detection error in the experiments increases by approximately 10% with an increase in the squareness error. To understand the cause of this phenomenon, we investigate the effects of backlash between mating thread surfaces of bolts and nuts on the detection error. The results show that the error decreased because of the backlash. Consequently, it is assumed that the error is caused by the non-separation of the mating thread surfaces when the tensile force reached the clamp force. Furthermore, the FE analysis results show that the squareness error on the bearing surface of the clamped part has an influence of the squareness error on the detection accuracy. The results indicate that we should control the tolerance of squareness errors on the bearing surface of the clamped part when the clamp force detection method is applied to bolted joints.
Many mechanical parts used for various purposes, including medicine and information communication, have complicated and thin shapes owing to their functions and designs. To machine thin parts with high accuracy, it is necessary to reduce the cutting force induced on the workpiece or clamp the workpiece in an optimal manner. In this study, a support method capable of supporting the strength by using a magnetic elastomer is proposed. To test the effectiveness of the proposed support method, the use of the approach when applying a magnetic elastomer was compared with a method using a core, the low-melting point alloy, the low-melting point alloy and the elastomer. The effectiveness of the proposed method was clarified experimentally.
Pulse laser grinding (PLG), an edge-shaping process, was developed previously to implement high-performance cutting tools. In this study, two femtosecond (fs) lasers with wavelengths of 1045 nm and 257 nm were used to conduct PLG on chemical vapor deposited (CVD) diamond-coated tool edges, as the fs laser is reported to have less thermal impact and the potential to improve the material crystallinity. We investigated the effects of the laser parameters on the tool edge formation and microstructural changes. The results show that although the infrared fs laser could – compared to the conventional nanosecond (ns)-laser PLG – naturally suppress surface thermal damage, the roughness of the processed surface remained relatively high with an Rz of 0.21 μm. However, under the optimal laser parameters proposed in this paper, an ultraviolet fs-laser PLG was used to obtain a much smoother edge, reducing Rz to approximately 0.08 μm. Moreover, scanning electron microscopy images indicated that the longitudinal machining marks on the ns-laser-processed surface were significantly reduced, with virtually no attached debris on the surface. Furthermore, from the Raman spectra, a significant increase in the diamond peak intensity was observed, indicating that the crystallinity of the CVD diamond (CVDD) was improved following ultraviolet-fs-laser PLG. These results demonstrate that edge shaping and structural modification of polycrystalline CVDDs can be integrated into ultraviolet-fs-laser PLG.
In this study, the “surface tension defined from stress” was used to predict the change in the cutting edge radius in the tool’s initial-stage wear regime. An analysis of the “surface tension defined from the stress” between solids showed that the flow of the material and the adhesion phenomenon must occur simultaneously at the interface. From the experimental and simulation results, it was confirmed that the proposed model can be used to predict the stress distribution acting on the cutting tool and evaluate the “surface tension defined from the stress” at the tool and workpiece interface. It was also verified that the cutting-edge radius under a state of equilibrium changes based on the cutting condition. These results indicate that simply using a cutting tool with a smaller cutting-edge radius will lead to a rapid increase in the cutting-edge retreat at the beginning of the cutting. For the unmanned operation of the cutting processes, it is desirable to use a cutting tool with a cutting-edge radius under a state of equilibrium at the beginning of the cutting to improve the cutting efficiency and reduce the cutting cost.
This paper presents an analytical model to study the influence of the thickness of the built-up layer (BUL) / built-up edge (BUE) on its protective effect during cutting. A new elastic-plastic contact model at the tool-chip interface is proposed to analyze the sliding contact problem with a layer of adhesion (including the BUL and BUE). The equivalent inclusion method (EIM) is utilized to analyze the stress disturbance caused by the adhesion and to evaluate the protective effect of the adhesion. In this method, the adhesion is considered as an equivalent elliptical inclusion at the tool-chip interface. The protective effect of the adhesion and the influence of the adhesion thickness on its protective effect can be evaluated. The proposed analytical model was verified based on experimental data obtained from dry cutting of SUS304 stainless steel. From the results, it can be confirmed that BUL/BUE can protect the cutting tool by affecting the stress distributions in the tool, the positions of yield initiation, and the tangential force acting on the tool. It can also be concluded that a greater thickness improves the protective effect of the BUL/BUE. Furthermore, the proposed model can also provide a clear understanding of the BUL/BUE formation phenomenon.
In recent years, magnesium-based materials have become expected to replace conventional engineering plastics as next-generation industrial materials to protect the global environment. However, in the production technology, problems of cracking and unstable accuracy in drilled hole shapes persist in plastic molding and machine tool processing; many studies have been conducted to address these problems. In dry machining ignition can be caused by the material, so wet machining is the prevalent method. However, it is necessary to establish a machining method with improved environmental parameters, considering the impact of oil mist and waste oil treatment on woks. In this study, the relationship between machining temperature and the accuracy of hole shapes in magnesium alloy AZ31 is investigated with four types of drills: high-speed steel, cemented carbide (K-Base), diamond-like carbon (DLC; K-Base), and TiN-coated cemented carbide (K-Base). The drill tip angle is set to 116°, 118°, or 120°. The work material used is the extruded AZ31 magnesium alloy. To evaluate the hole shape accuracy, squares of 80 × 80 mm are used. The cutting temperature is measured over an area of 12 × 30 mm. The work material is drilled using a dry method with a 3-mm-diameter drill having the aspect ratio (L/D) of 10. The tool protrusion length of 50 mm and cutting speed of 20 m/min are fixed, and the tool feed rate and drill step amount are changed. The experiment is repeated 3 times. The burr generated around the loophole on the back surface of the test material after the test is evaluated with a criterion burr height H of 0.02 mm. Furthermore, the average roughness (Ra) of the centerline is measured on the inner surface of the hole with a contact-type roughness meter. The results show that when using the three drill point angles of 116°, 118°, and 120° in the drill step, no burrs form at the exit of the drill hole. Carbide tools form burrs when the feed rate exceeds 30 mm/min and the step amount exceeds 20 mm. TiN tools are highly accurate up to a tip angle of 118°, while DLC tools have lower cutting forces and yield better finished surfaces than the other tools.
The aim of this study is to investigate the dynamic phenomenon of ultrasonic vibration-assisted cutting by utilizing a stress distribution visualization system. The vibrating cutting-edge is considered to be a cause of dynamic changes in the cutting force at ultrasonic frequencies. However, many researchers have explained the effect of ultrasonic vibration-assisted cutting by evaluating the time-averaged cutting force, because existing dynamometers are unable to measure the dynamically changing cutting force at ultrasonic frequencies. There are some reports that the vibration direction of cutting edge strongly affects tool wear. However, in practical ultrasonic cutting, the vibration of the cutting edge has yet to be measured in a production environment. In this study, the instantaneous stress distribution on the workpiece was visualized by a photoelastic method that combines a pulsed laser emission synchronized with tool vibration. The developed photographic system can capture 360 frames in one ultrasonic vibration period. The dynamic cutting force was calculated by Flamant’s stress distribution theory. It was experimentally confirmed that the stress distribution under vibration-assisted conditions showed periodical changes synchronized with vibration. Because these results are compatible with well-known vibration-cutting theories, the imaging system was able to show the periodic changes in stress distribution in the ultrasonic frequency band. This indicates that the dynamic change in cutting force during the ultrasonic vibration period affects intermittent cutting conditions. In this report, the vibration direction was adjusted from −9.5° to +9.5° along the cutting direction. When the tool moved in upwards for the cutting phase and downwards for withdrawal phase, the stress distribution was continuously observed over one tool vibration period; no intermittent cutting was observed. The locus of the cutting force vector was affected by the ultrasonic vibration direction and rake angle of the cutting tool. A negative rake angle showed that the direction of the cutting force vector shifted toward the workpiece side near the most advanced position of the cutting edge.
Carbon fiber reinforced plastic (CFRP) is increasingly used in aerospace, automobile, and other industries. With the improvement of carbon fiber reinforced thermoplastic molding technology using thermoplastic resin, it is expected that the applications of CFRP will be expand further. Because of the following issues, CFRP is known as a difficult-to-cut material. i) Machining CFRP is difficult. ii) Its finished surface deteriorates due to delamination and uncut fiber. iii) It has a shortened tool life due to severe tool wear. In addition to these issues, we has been problem presentation of fine cutting chips generated by machining. Because these fine cutting chips may scatter in the atmosphere and adversely affect the human body and machine tools, we have established a chip disposal technology that suppresses these issues to improve the processing environment. A previous study reported that shape of the tool edge is responsible in suppressing the generation of fine cutting chips. Here, we experimentally investigated the effects of tool edge shapes on the chip collection rate and tool life. An attempt was made to determine whether the same effect can be obtained by using the outside dust-collection method which is known that the dust collection efficiency is low. We revealed that the chip collection rate increases if a tool that suppresses the generation of fine cutting chips is used instead of a conventional tool; furthermore, the tool life is insensitive to coating. In contrast, a comparison of our results with previous findings indicates that the tool with a sharpened cutting edge has a longer tool life than the conventional twist drill with honing. A high cutting chip collection rate was obtained, even with the outside dust-collection method, which led to an improvement in the working environment.
Cellulose nanofiber (CeNF)-reinforced polymer composites have wide potential applications in the manufacturing of optical and mechanical parts owing to their light weight, high mechanical strength, and optical transparency. In this study, CeNF-reinforced homogeneous polypropylene (PP-CeNF) was machined under various conditions by ultraprecision diamond turning, and the results were compared with those of pure PP without CeNF addition. The influence of CeNFs on material removal was investigated by examining the surface topography, chip morphology, cutting forces, and cutting temperature. It was found that the surface defects in pure PP cutting were surface tearing, while the surface defects of PP-CeNF were surface tearing and micro-holes induced by the pulling-outs of CeNFs. Surface tearing increased with cutting speed; pulling-outs of CeNFs were slightly affected by cutting speed but strongly dependent on the tool feed rate. Under a small tool feed rate, the surface roughness could be reduced to ∼10 nm Ra for PP-CeNF. The thermal effect was insignificant in the experiments, whereas the effect of strain rate-induced material hardening was dominant for both workpiece materials at a high cutting speed. This study helps to understand the mechanisms for ultraprecision cutting of CeNF-reinforced polymer composites and provides guidelines for improving the machined surface quality.
In laser cleaving, the thermal stress caused by laser heating and water-jet cooling propagates previously induced cracks in the workpiece material. The laser-cleaving conditions affect the quality of the fracture surface, and therefore, elucidating the relationship between the cleaved surface, cleaving conditions, and crack propagation is essential. Against this backdrop, in this study, we investigated the morphology of the cleaved surface and visualized the crack propagation and stress in situ using a high-speed polarization camera. The distance between the glass edge and cleaved surface was varied. When the laser-cleavage line was close to the glass edge, twist hackles were formed on the cleaved surface. The area in which the twist hackles formed on the cleaved surface coincided with the lagging section of the crack front. Furthermore, the twist hackle reached the specimen surface, and the edge of the surface exhibited a sawtooth shape. Observations with the high-speed polarization camera revealed that the internal stress was asymmetric with respect to the crack when the twist hackles were formed.
In the recent period of the miniaturization of devices, there has been a high demand for high-resolution, flexible, and fast machining technique to accommodate high production volumes. Conventional laser machining with a focused laser beam has been widely used to fabricate small devices for various applications. However, this process is limited by the optical diffraction limit of the laser beam. Therefore, the photonic nanojet (PNJ) machining technique is a promising solution to tackle this problem. This technique is based on the near-field focusing of light waves with a high-energy laser power below the surface of an irradiated dielectric microsphere. We introduce water as a medium in the proposed PNJ machining technique so that the pattern could be fabricated more efficiently, faster, and with better quality. We evaluate the characteristics of the generated PNJ in water; further, we estimate the PNJ machining results numerically using the FDTD method and confirm them experimentally. To the best of our knowledge, this is the first ever to do so. All the holes obtained from the PNJ machining experiment were consistently in the sub-micrometer order and below the optical diffraction limit value of the constructed setup.
Superconductive assisted machining (SUAM) is a novel machining method that eliminates tool interference via magnetic levitation tools. In our study, we developed a double magnet system (DMS) to increase the maximum power of the holding force and stabilize the magnetic rotation during polishing via the higher magnetic flux compared to a single magnet system (SMS). The maximum magnetic flux density of the DMS was approximately 100 mT higher than that of the SMS. In these cases, the entire holding force increases as the distance between the superconducting bulk and lower magnet decreases. The attractive forces are maximum around a displacement of 6 mm, although the repulsive and restoring forces increase spontaneously. The polishing performances of the DMS on the SUS304 and A1100P plates were evaluated using water-based diamond slurries, for equal levitation amounts. The amount removed by the DMS increased for the A1100P and SUS304 substrates compared to that by the SMS. In this case, we observe that the deviation of the polishing area on the DMS decreases compared to that of the SMS, reflecting a more stable rotation and movement due to the higher holding force.
High quality surfaces with transparency are required for manufacturing of plastic products. In cutting of polymer materials, surface quality is sometimes deteriorated by tarnish and/or unequal spaces of area on a surface. The cutting parameters should be determined through understanding of surface finish characteristics. This paper presents an optimization approach in milling of polycarbonate with polycrystal diamond tools in terms of the surface finish. Surfaces are finished with changing the feed rate and the clearance angle of the tool. The surface finishes, then, were observed to classify the deterioration type into welding, adhesion, and the unequal space of cutter marks with measurement of the surface profiles. The measured surface roughnesses are decomposed into the theoretical/geometrical term and the irregular term induced by the thermal and the dynamic effects. A map is presented to characterize the irregular term for the feed rates and the clearance angles. Because the surface roughnesses are measured at discrete sets of the cutting parameters in the actual cutting tests, the process design cannot be conducted to optimize the operation parameters. Therefore, a neural network is applied to associate the cutting parameters with the irregular term in the map. An approach is presented to determine the number of hidden nodes/units in the design of the neural network. Three prominent areas of welding, adhesion, and unequal spaces of the cutter marks, appear in the map of irregular roughness. The map of the surface roughness is made to optimize the cutting process. The applicable feed rates and clearance angles are determined for the tolerable surface roughnesses. The gradient information in the map is used to evaluate the stability/robustness of the surface quality for changing the parameters. The optimum parameters were determined to minimize the gradient information in the applicable feed rates and clearance angles.
In general, NC programs for machining free-form surfaces using a computer numerical control (CNC) machine tool are generated using a computer-aided manufacturing (CAM) system. The tool paths (CL data) generated by a CAM system are approximated straight-line segments based on tolerance (allowable error). As a result, the tolerance affects the machining accuracy and time. If the tolerance is set to a small value, the lengths of the segments are shortened, and the machining accuracy is improved. The process in which a CNC machine tool reads and analyzes an NC program and controls the motors requires a minimum processing time of an NC program block (block-processing time). Therefore, if the lengths of the approximated straight-line segments are too small, it will be impossible to reach the indicated feed speed, and the machining time will be longer. In this study, by identifying the block-processing time of a CNC controller and deriving the appropriate length of the approximated straight-line segment based on the block-processing time, a CL data creation method that is capable of high-speed and high-accuracy free-form surface machining is proposed. In addition, experimental verification tests of the method are conducted.
Confocal probes have been widely adopted in various industries owing to their depth-sectioning effects. A dual-detector differential chromatic confocal probe using a mode-locked femtosecond laser source is proposed herein, and the measurement range expansion of the probe using a supercontinuum light source is discussed. Supercontinuum light has an extremely wide spectrum. A simulation based on wave optics is performed to evaluate the detection sensitivity and measurable range by considering the chromatic aberration of the lens materials. Additionally, an experimental setup is constructed using a supercontinuum light source, and its feasibility is validated. A measurable range of 200 μm is adopted in the experiment, and three-dimensional surface profile measurements are performed. However, the developed confocal probe has not been used for surface topography measurements. Experiments are conducted to verify the performance of the developed probe.
In electric power stations, precision surface roughness measurements are performed for environmental loading reduction, quality assurance, and safety. These measurements are performed manually at high places, narrow places, uncomfortable environments, etc. Therefore, workers in power stations experience a lot of hardship and are exposed to danger. To solve these issues, this study researched and developed a crawler-type robot with high measurement accuracy. Conventionally, robots that supply workpieces for surface roughness instruments have been developed. However, to the best of our knowledge, robotization and self-propelled precision measurement instruments have not been developed. Usually, a precision measurement instrument is designed for increased stiffness and stability because high measurement accuracy is the highest priority. However, if the stiffness and stability of the robot are as high as those of the precision measurement instrument, a problem occurs in the robot operation. Therefore, we propose a precision measurement unit using electromagnets and a crawler-type self-propelled robot to equip the unit. In a previous study, vibration analysis experiments using the impulse response method were performed on a precision measuring robot. In this study, the relationships between the voltages applied to the electromagnet and the reductions in the vibration magnitudes were determined by analyzing the vibrations of the robot during measurement. Furthermore, an optimal voltage of the electromagnets of the precision measuring robot to reduce vibrations was determined. From the results of the vibration analysis, the authors demonstrated that the optimal voltages were 9 and 12 V, and the precision measurement unit confirmed the effectiveness and validity of vibration reduction and improved measurement accuracy.
Automatically controlled machine tools have been used extensively in the industrial field, and fault analysis methods have garnered increasing attention. This paper first describes the software and hardware design of a machine tool and then presents a fault analysis of the machine tool. The fault types of machine tools are analyzed. A signal is obtained from a vibration sensor, the characteristic value is extracted, and the fault is analyzed using a back-propagation neural network (BPNN). The experimental results show that the BPNN yields the best performance when the structure is 8-9-8, and its recognition rate is 97.22% for different types of faults. Meanwhile, the recognition rate of naive Bayes is only 76.73%, and that of a support vector machine is only 85.55%, which is significantly lower than that of the BPNN. The results show that the BPNN is effective in fault analysis and can be promoted and applied more extensively.