Mitsugu Yamaguchi

On-Demand Infrared Laser Sintering of Gold Nanoparticle Paste for Electrical Contacts

This paper discusses the formation of a conductive film from noble metal nanoparticles as an alternative to conventional electroplating for electrical components, such as connectors, switches, and memory cards. The proposed method consists in dispensing with nanoparticle paste followed by laser sintering. The aims are fourfold: 1) to establish sintering technology for gold nanoparticles placed on a nickel-electroplated phosphor-bronze substrate; 2) to characterize the laser-sintered film; 3) to discuss the laser sintering mechanism; and 4) to examine applicability to industry. The major results obtained are as follows: the laser sintering formed a gold film with a diameter of 0.3-0.8 mm and a thickness of 0.3-0.5 μm on the nickel-electroplated phosphor-bronze substrate; a laser with a wavelength of 915 nm enabled instantaneous sintering within 1 s in air; the laser-sintered gold nanoparticle film had such a high adhesion to the substrate that no separation occurred after 90° -0.5R bend-peel tests; the high adhesion was attributed to interdiffusion of gold and nickel in the course of sintering; optical properties of the gold nanoparticle paste depend on preheat conditions. A relatively high-preheat temperature around 523 K for 60 s produced a paste surface with a suitable absorbance of the infrared laser; a primary sintering of the preheated gold nanoparticles with a small amount of solvents followed by an auxiliary sintering from the substrate side made possible an efficient sintering of the nanoparticles as well as high adhesion to the substrate with a high thermal conductivity; and the film possesses such a good electrical property as that of the electroplated one in reciprocating abrasion tests.

Laser-based conductive film forming with gold nanoparticles for electrical contacts

The present study discusses the formation of a conductive film from noble metal nanoparticles as an alternative to conventional electroplating for electrical components, such as connectors, switches, and memory cards. The proposed method consists of inkjet printing with nanoparticle paste followed by laser sintering. The aims are fourfold: to establish sintering technology for gold nanoparticles placed on a nickel-electroplated-phosphor bronze substrate, to characterize the laser-sintered film, to discuss the laser sintering mechanism, and to examine applicability to industry. The major results obtained are as follows: the laser sintering formed a gold film with a diameter of 0.3-0.8 mm and a thickness of 0.3-0.5 μm on the nickel-electroplated phosphor-bronze substrate; a laser with a wavelength of 915 nm enabled instantaneous sintering within one second in an atmosphere; the laser-sintered gold nanoparticle film had such a high adhesion to the substrate that no separation occurred after 90°-0.5R bend-peel tests; the high adhesion was attributed to interdiffusion of gold and nickel in the course of sintering; optical properties of the gold nanoparticle paste depend on preheat conditions. A relatively high-preheat temperature around 523 K produced a paste surface with a suitable absorbance of the infrared laser; and a primary sintering of the preheated gold nanoparticles with a small amount of solvents, followed by an auxiliary sintering from the substrate side made possible an efficient sintering of the nanoparticles as well as high adhesion to the substrate with a high thermal conductivity.

Property and Recyclability Change of Corrosion-Inhibition-Improved Amine-Free Water-Soluble Cutting Fluid with Repeated Recycling

Cutting fluid is commonly used during metal cutting process for cooling and lubrication. Fluid types are generally classified into mineral or fatty oils and water miscible oils. In Japan, the former is called water-insoluble coolants, and the latter is called water-soluble coolants. Water-insoluble coolants are specified as dangerous material by the Japanese law due to its flammability. Therefore, the water-insoluble coolants are not appropriate for unmanned operation of machine tools. Therefore, the usage rate of water-soluble coolants is increasing. Water soluble coolants are diluted with a water by several ten times. The waste management of the water-soluble coolant become important for environment-conscious green manufacturing. We have been developing a recycling system for water-soluble coolants. In the recycle system, water is extracted from the waste coolant and the water is then reutilized as a diluent of a new coolant. We have developed various types of chemical or bio-chemical water recovery methods for recycling systems. We found a commercially available amine-free water-soluble coolant is suitable for the recycling system. The processing time, processing cost, and the biochemical and chemical oxygen demand of the extracted water are improved by the amine-free water soluble coolant compared with a conventional amine-containing coolant. However, its corrosion inhibition performance was poor in general machining applications. Our cooperative company developed a prototype of a corrosion-inhibition-improved amine-free water-soluble cutting coolant. The prototype coolant showed a good stability and cooling and lubricating performances, and its recyclability was as good as that of conventional amine-free coolants. In this study, we focused on repeated recycling of the prototype coolant. We repeatedly applied the water recycling process to the recycled coolant. The recyclability of the prototype coolant was not affected by repeated recycling; however, process residues increased with the number of recycles, and a deterioration was noticed in the corrosion-inhibition performance of the coolant diluted with recycled water.

On-demand gold laser-plating onto stainless steel for electrical contacts

The present study discusses the formation of a conductive film from noble metal nanoparticles onto stainless steel substrate for electrical components, such as connectors, where conventional electroplating is not applicable. The proposed “laser plating” method consists in on-demand dispensing with nanoparticle paste followed by a short-time preheating and laser sintering. The aims are fourfold: to establish sintering technology for gold nanoparticles placed on an 18%Cr-8%Ni stainless steel substrate covered with a passivation film, to characterize the laser-sintered film, to discuss the laser sintering mechanism, and to examine applicability to industry. The major results obtained are as follows: the laser sintering formed a gold film with a diameter of 0.8 mm and a thickness of 0.3-1.0 μm on the stainless steel substrate without any surface pretreatment; a laser with a wavelength of 915 nm enabled instantaneous sintering within one second in air; the laser-sintered gold nanoparticle film had such a high adhesion to the substrate that no separation occurred after 90°-0.5R bend-peel tests; the high adhesion was attributed to interdiffusion of gold, iron, chromium and nickel in the course of sintering; a relatively high-preheat temperature around 523 K for 60 s produced a paste surface with a suitable absorbance of the infrared laser; a primary sintering of the preheated gold nanoparticles with a small amount of solvents, followed by an auxiliary sintering from the substrate side made possible an efficient sintering of the nanoparticles as well as high adhesion to the stainless steel substrate with a high thermal conductivity; the laser-sintered gold film possesses such a good electrical property.

A Utilization Method of Big Sensor Data to Detect Tool Anomaly in Machining Process

The essential features and scale of sensor data was discussed to monitor the tool anomaly in the machining process from the pattern variation of large scale sensor data such as vibration and effective power. The cycle data, the time series sensor data collected with an acceleration or power sensor in one periodical machining of the given groove shape, had been measured periodically. In this study, the graphic pattern formed by overwriting the time series cycle data on a specific coordinate system was treated as the “big sensor data”. The big data from the effective power sensor can stably respond to the cutting power changes and showed a strong possibility as a detecting device for tool anomaly such as abrasive wear and chipping. While the big data from the acceleration sensor only responded to a big event like the chattering vibration. The number of cycle data needed to generate the big sensor data also affected on the detection sensitivity for tool anomaly. It had been required a family of time series sensor data enough to represent the cutting power change as a visual graphic pattern.

Evaluation of the Thermal Shock Fatigue Resistance of Cutting Tools Using a CO2 Pulse Laser Beam

It is well-known that a series of cracks sometimes gets initiated perpendicular to the cutting edges on the rake faces of brittle cutting tools made of materials such as cemented carbide, ceramics, and cermet under high-speed intermittent cutting. The tools used in intermittent cutting processes are exposed to elevated temperatures during cutting and then cool quickly during the noncutting time. Previous studies have suggested that such repeated thermal shocks generate thermal stress in the tool and that the thermal cracks are then propagated by thermal fatigue. Recently, high-speed machining techniques have attracted the attention of researchers. To apply new cutting tool materials to this machining process, it is important to evaluate their thermal shock fatigue resistances. During high-speed intermittent cutting, the frequency of thermal shocks becomes high and the action area of the thermal shocks is limited to the rake face of the tool. Therefore, conventional thermal shock resistance evaluation methods are unsuitable for this case. Consequently, the authors have developed a new experimental evaluation method using a CO2 laser beam. In this study, we irradiated cemented carbide and TiN cermet cutting tools with the CO2 pulse laser beam and gauged the effectiveness of the proposed thermal shock fatigue resistance evaluation method. The results show a correlation between the thermal shock due to the CO2 pulse laser beam and those due to the intermittent cutting experiments.

Influence of the Brittle Behavior of Work Materials on Microgrooving

An electroplated diamond wire tool is frequently used for the machining of hard and brittle materials such as silicon ingots, magnetic materials, ceramics, and sapphires. This study aims to examine the influence of brittle behavior of work materials on machinability (including tool wear); therefore, we conduct dynamic ultramicro hardness measurements and microgrooving experiments for three types of ceramics. The results indicate that the groove depth of a work material tends to increase with the processing time. Moreover, material properties of a work material, such as hardness and toughness, have a significant impact on the fluctuations in its groove depth. However, kerf width of a work material does not depend on the processing conditions and material properties. In addition, a faster relative velocity improves processing efficiency but also increases tool wear.

The Wear Characteristics of a Wire Tool in the Microgrooving of Ceramics

A wire tool having electrodeposited diamond grains is frequently used for machining hard and brittle materials such as silicon ingots, magnetic materials, ceramics, and sapphires. This study aims to examine the wear characteristics of the tool during the microgrooving of ceramics. We conducted microgrooving experiments for alumina ceramics. The results indicate that the grooving time and the machining distance influence the groove depth. However, as the damage in a wire tool progresses, the groove depth does not depend on the machining distance. A fast relative velocity leads to serious damage in the wire tool even when the machining time is short. In the case of wet grooving, the damage to the wire tool was smaller than that in the case of dry grooving.

Wear resistance of laser-sintered gold-nickel composite film for electrical contacts

Materials for electrical contacts not only require good electrical properties but must also satisfy requirements for wear resistance, low-friction coefficient, and corrosion resistance. To improve wear resistance, composite plating with dispersed nanoparticles on a metal matrix has been developed. The noble metal processes of dispensing gold nanoparticle paste with dispersed nickel nanoparticles on a phosphor-bronze substrate followed by sintering with an infrared laser to form a laser-sintered gold-nickel composite film are described. Tests for adhesion, wear resistance, and electrical property of the laser-sintered film lead to the following conclusions: (1) an infrared laser enables the formation of a gold film containing dispersed nickel nanoparticles in an air atmosphere; (2) the laser-sintered film possesses an equally good adhesion to the substrate, wear resistance and electrical property as an electroplated one; (3) as nickel content increases, the distribution of nickel nanoparticles deposited on the gold composite film becomes uneven. The use of nickel nanoparticles with 0.5 mass% dispersion results in a relatively uniform distribution; (4) although contact resistance of the 0.5 mass% nickel-content film is slightly greater than that of a pure gold one, a low contact resistance of less than 100 mΩ is maintained, as shown by a reciprocated-sliding test consisting of 3000 repetitions; (5) the proposed on-demand method has considerable advantages as it takes just over 1 min to form a 0.3μm-thick film, and material consumption is reduced by a factor of ten in making a contact area with a diameter of 0.8 mm.

Effects of cooling conditions on thermal crack initiation of brittle cutting tools during intermittent cutting

It is well known that a series of cracks running perpendicular to the cutting edge are sometimes formed on the rake face of brittle cutting tools during intermittent cutting. The cutting tool is exposed to elevated temperatures during the periods of cutting and is cooled quickly during noncutting times. It has been suggested that repeated thermal shocks to the tool during intermittent cutting generate thermal fatigue and result in the observed thermal cracks. Recently, a high speed machining technique has attracted attention. The tool temperature during the period of cutting corresponds to the cutting speed. In addition, the cooling and lubricating conditions affect the tool temperature during noncutting times. The thermal shock applied to the tool increases with increasing cutting speed and cooling conditions. Therefore, to achieve high-speed cutting, the evaluation of the thermal shock and thermal crack resistance of the cutting tool is important. In this study, as a basis for improving the thermal shock resistance of brittle cutting tools during high-speed intermittent cutting from the viewpoint of cutting conditions, we focused on the cooling conditions of the cutting operation. An experimental study was conducted to examine the effects of noncutting time on thermal crack initiation. Thermal crack initiation was found to be restrained by reducing the noncutting time. In the turning experiments, when the noncutting time was less than 10 ms, thermal crack initiation was remarkably decreased even for a cutting speed of 500 m/min. In the milling operation, the number of cutting cycles before thermal crack initiation decreased with increasing cutting speed under conditions where the cutting speed was less than 500 m/min. However, when the cutting speed was greater than 600 m/min, thermal crack initiation was restrained. We applied the minimal quantity lubrication (MQL) coolant supply to the intermittent cutting operation. The experimental results showed that the MQL diminished tool wear compared with that under the dry cutting condition and inhibited thermal crack initiation compared with that under the wet cutting condition.