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Directed energy deposition is an additive manufacturing process which produces deposits by irradiating laser beam on the baseplate and supplying material powder to the meltpool. Although the material powder is generally conveyed with carrier-gas flow, the powders diffuse and some of them do not reach to the meltpool. In order to suppress the waste of materials, the particle movement should be analyzed and modified not only from the viewpoint of deposition conditions but also the nozzle design. Against this background, this paper presents analytical and measurement results of powder distribution under the nozzle and proposes a nozzle design to reduce the waste of material powder based on a gas-solid multiphase-flow simulation. The experimental result of designed nozzle certainly shows high powder supply efficiency of 74.8%, whereas that of the conventional nozzle is 52.6%.

Generally, manufacturing process of optical glass lenses, which are used for single lens reflex cameras, is classified into grinding and polishing for removing cracks generated by grinding. Thus, it is desired not to generate the cracks in grinding as much as possible. Because grinding condition with cracks differs depending on the material properties of the workpiece, suitable grinding condition needs to be selected based on a lot of experimental verifications. In addition, the controller’s gain of the tool spindle with grinding wheel may be intentionally set to low value in ultra-precision grinding. Thus, the spindle speed may decrease even under servo control because of grinding load. In this study, the influence of servo characteristics on crack generation is evaluated in ultra-precision grinding of optical glass lenses. Concretely, an optical glass lens was machined using an ultra-precision 5-axis grinding machine and servo information of tool spindle was monitored during the process. Comparison of the obtained servo information and the surface observation of the workpiece revealed that the spindle speed decreased and the number of the cracks increased at the outside of the workpiece. The experimental results suggested the possibility of estimating the grinding load and predicting the surface quality by monitoring the variation in the spindle speed.

Tool collision must be detected with high response and reliability to reduce damage on machine-tool components. Several researches have proposed tool collision detection methods by monitoring a fluctuation in acceleration or force in collision direction with additional sensors. However, the installation of additional sensors is not desirable due to cost, machine-tool stiffness and failure rate. Moreover, these approaches do not focus on practical use of information in the other directions, although the collision-induced fluctuation can be observed not only in collision direction. This paper presents a tool collision detection method by applying disturbance observer theory and integrating the estimated collision force information in two axes. Furthermore, hotelling's T2 statistic is employed as a multivariate statistical process to the estimated collision force in the two directions. The proposed method successfully detects tool collision with higher response and reliability than that using only information in collision direction.

High-precision and wideband sensorless cutting force monitoring is one of the important technologies for tool condition monitoring. Particularly in milling, not only the fundamental frequency component of cutting force, but also harmonics need to be monitored, because they could result in the development of chatter. In this study, a process monitoring technique was proposed by the estimation of cutting force components in rigid body mode and vibration mode coordinate systems independently, which was based on multi-encoder based disturbance observer. From milling test results, cutting force including higher harmonics components yielded accurate estimation in the vibration mode without exciting the components that are closer to the resonance frequency.

Optical micro-resonators attract interests as essential components to develop optical signal processing circuits which can reduce energy loss. Single-crystal calcium fluoride (CaF2) could be the most suitable material from a viewpoint of optical property. To satisfy high form accuracy and surface roughness, ultra-precision cylindrical turning (UPCT) is a feasible fabrication process. In previous research, it was indicated that the tool with sharper nose radius could make UPCT more stable and reduce subsurface damage. In this study, the tool with much smaller nose radius 0.01mm was applied, then, the influence on surface integrity was investigated by TEM observation.

Although chatter stability analysis is necessary to enhance cutting accuracy and efficiency, a reliable prediction is difficult to achieve because of the analysis error of frequency response function. Therefore, the investigation proposes an experiment-based identification method for stable spindle rotations in milling by gradually changing the spindle rotation and capturing chatter frequency shift from servo information. In order to evaluate the identification accuracy, this paper presents theoretical approaches to analyze time-dependent variation in chatter and the expected identification error of proposed method by using a time-domain simulator and a frequency-domain model considering amplitude ratio between inner and outer modulations of the chip.

To achieve maximally efficient signal processing, an electrical signal processing circuit needs to be replaced with an optical one. Optical micro-resonators, storing light at certain spots, are essential for optical signal processing. Single-crystal Calcium Fluoride (CaF2) is the most suitable material for highly efficient optical micro-resonators, and a resonator made of CaF2 can be manufactured by ultra-precision machining. However, the performance of such optical micro-resonators depends on its surface integrity. In this study, the relation between the crystal anisotropy and surface integrity after ultra-precision cutting was investigated. The most difficult point in the cylindrical turning of a crystalline material is that the crystalline plane and the cutting direction constantly vary. We analyzed crack initiation and surface integrity of the entire machined surface from the perspective of slip system and cleavage. Subsurface damage was also observed by using the TEM and X-ray analyzers for more efficient manufacturing of optical micro-resonators.

Carbon fiber reinforced plastics (CFRP) have been used for various applications such as aerospace, automobiles, and sporting goods due to their superior properties, and the demand for through-hole drilling of CFRP is increasing. A novel hybrid helical milling technique applying ultrasonic vibration and cryogenic tool cooling method is proposed in this paper, as an effective machining method for CFRP. To investigate the effects of ultrasonic-vibration-assisted machining and cryogenic tool cooling method, cutting performance evaluations based on thrust force, machining accuracy, and tool wear were conducted in this study. The results of the cutting tests clearly indicated that the proposed cutting method provides reductions in thrust force, and suppresses delamination at the machined surface.

The on-machine measurement of a machined workpiece has numerous advantages such as reducing the man-hours and operator-dependent measurement errors, and improving work-efficiency. In this paper, we propose an external sensor-less on-machine measurement system by only utilizing internal servo information in order to add a workpiece-measurement function to ultra-precision machine tools without increasing the cost. The cutting force observer developed for monitoring the process has the ability to estimate the external force with a resolution of 0.05 N based on servo information. Sensor-less contact force control with the cutting force observer is applied to an on-machine measurement system. To evaluate the performance, several tests are carried out. The results show that the proposed on-machine measurement system is effective at measuring the accuracy of the machined form.

Detection of tool fracture is important to avoid tool breakage and ensure cutting accuracy. Though additional sensors are generally used for monitoring a tool condition, installing them causes high cost and increase of failure rate. In this study, a novel in- process method to detect a tool fracture is proposed on the basis of a disturbance observer theory. It uses only servo information in a ballscrew driven stage and never requires external sensors. Furthermore, a rotational digital filter is invented and applied to drilling tests to improve the detection accuracy. A tool fracture is successfully detected by the proposed method.

This paper deals with the use of two types of ultrasonic-assisted micromachining methods for obtaining longer tool life and higher machining efficiency in the micromachining of hard and brittle materials. USV drilling is drilling that is aided by ultrasonic vibration in the direction axial to the tool. Cavitation machining is a method is aided by ultrasonic vibration of the cutting fluid. We investigated the effects of USV, cavitation, and their combination on the micro drilling of SiC. Experimental results clearly showed an improvement in tool life and a reduction in tool wear. Furthermore, the accuracy was improved.

Precise tool length measurement and work coordinate setup is technically a difficult operation which generally requires a manual adjustment and takes long time. Contact of cutting edge of a micro tool is conventionally detected by laser, vision sensor, acoustic emission sensor (AE sensor) and so on. However, those techniques are necessary to install additional sensors and equipments to a machine tool. In addition, tool setting technique depends on an engineer's skill. Therefore, skill-independent technology of tool setting is desired. In this study, we propose an automatic detection methodology of the tool contact by cutting force observer. Moreover, applying the developed detecting technique of the tool contact, automatic micro drilling system without tool setting is developed. Its validity is verified through glass micro drilling tests.

Chatter vibration can be monitored by using external sensors such as acceleration sensors and dynamometers. However, from the viewpoint of reliability, using external sensors leads to an increase in failure rate. Therefore, we developed a disturbance observer theory–based method for the detection of chatter vibration, and confirmed its validity experimentally. The developed method does not require the use external sensors. In this study, a system for the in-process suppression of chatter vibration is developed by applying the abovementioned detection method. In a milling test, conducted to verify the developed system, it was found that chatter vibration was successfully suppressed by automatic adjustments to the cutting conditions.

It is important to take countermeasures against tool collision to avoid serious damage to the machine tool. Though rapid collision detection is needed, the introduction of additional sensors to a machine tool is not desirable owing to cost, machine-tool stiffness, and failure rate considerations. In this study, a sensor-less tool collision detection method is proposed on the basis of the disturbance observer theory. It only uses the servo information of a ball-screw-driven stage and does not require external sensors. The proposed method successfully detects the collision between a tool and a workpiece in less than 3 ms with a feed rate of 50 m/min.