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As interest in aluminum nitride (AlN), a high-performance ceramic, has been rapidly increasing, many researchers studied the possibilities of machining it. Since AlN is classified as a difficult-to-cut material, the electrical discharge machining (EDM) process using an assisting electrode is emerging as an effective machining method. Kerosene, as a dielectric fluid, plays an important role in forming a successive conductive carbon layer on the surface of the workpiece to induce and maintain discharge. Most previous methods used tubular electrodes to stably feed the dielectric fluids through their center hole. However, in the case of micro-EDM, the extremely small electrode diameter makes it difficult to fabricate a through-hole in the electrode, and a very narrow gap prevents the flow of dielectric fluid. In order to overcome dielectric fluid flow problems in micro-EDM, in this study, two kinds of flow-promoting methods are introduced: one is to use a D-shaped solid electrode to obtain a wider asymmetric flow channel, and the other is to use an O-shaped solid electrode with graphite-powder-mixed kerosene (GPMK) under a relatively wider discharge gap. Flow simulation results show that both methods promote kerosene flow, and the experimental results show similar results as well. When using the D-shaped section, the material removal rate increased, but increased tool wear was observed. In the case of GPMK, the metal removal rate increased 64%, and relative wear ratio decreased 73% compared to conventional methods. Through voltage scheduling, the problem of precision degradation that occurs during deep-hole drilling with the O-shaped solid electrode GPMK configuration was solved without sacrificing machinability.

Demands for micro-machining on glass have been increasing in various industries due to the unique properties of glass, such as transparency or biocompatibility. However, micro-channel fabrication on glass with high precision has been challenging due to its brittle characteristics. This research presents the CO2 laser-assisted micro-milling process and investigates the machining characteristics experimentally. Micro-channels without cracks were fabricated using micro-end mill and CO2 laser irradiation as an assisting heat source. Compared to the process without laser heating in the same matching conditions, the average surface roughness was reduced by 96%, and cutting force was reduced by 28% and 66% for the feed and thrust direction, respectively. Continuous and sheared chips were observed with laser heating, indicating the process is in ductile-regime machining. Through the investigation of machining parameters, it was found that micro-channels with low average surface roughness can be achieved at the proper laser power when the workpiece is heated up to the strain point at tool position, at low feed rate, and at high axial depth of cut, as long as the tool withstands the cutting forces. Consequently, it can be concluded that it is possible to increase the material removal rate in micro-milling of borosilicate glass with high quality by using the CO2 laser, which was found to be an effective and suitable heating method.

We present a novel method of realizing instant hydrophobic and long-lasting superhydrophilic states on stainless steel (SS) surfaces by micropatterning and thermally-induced surface layers (TISL). Heat treatment of SS surfaces in the air for 6 h yields hydrophobic TISLs at 140 °C and hydrophilic TISLs at 300 °C. The result of X-ray photoelectron spectroscopy reveals the correlation of chromium depletion with the hydrophilic TISLs, as well as surface oxidation with the hydrophobic TISLs. We fabricated superhydrophilic SS surfaces holding the wettability over 40 days, and hydrophobic SS surfaces realized in an hour-scale period via the fabrication process comprised of laser beam machining, electrochemical etching, and heat treatment in serial.

In the machining of silicon compound ceramic materials via laser beam, processing in water has been found to enhance machining quality, while processing in air has limitations such as the generation of a recast layer, heat affected zone, and thermal crack. However, few studies have investigated the effects of water on the ablation rate of silicon compound ceramics. In this research, the ablation behavior and machining principles of the laser beam machining of silicon compound ceramics in water are investigated. The research concluded that the increase in temperature induced by laser irradiation promotes hydrothermal reaction between the silicon compound ceramics and water. The hydrothermal reaction assists in the removal of the oxide layer at the machined area and enhances the efficiency of the process in water. The effects of water on ablation are confirmed for various machining parameters such as the flow rate of sprayed water on the workpiece and laser conditions. Finally, the various micro-structures were fabricated on the silicon compound ceramics to evaluate the processability.

Sustainable manufacturing has become of great importance in various fields include manufacturing, mechanical engineering, materials science, environmental science, and energy science. In this paper, we analyzed and reviewed the research trends of sustainable manufacturing technologies and suggested future perspective. Specifically, the state-of-the-art and historical trajectory of sustainable manufacturing are analyzed using data obtained from the Web of Science library and the Journal Citation Reports (JCR). Selected journals and research categories are evaluated by the number of publications, the number of citations, impact factor (IF), and H-indices. To suggest future perspectives on sustainable manufacturing research, growth rate of each research objects are evaluated and historically followed. Sustainable manufacturing is likely to be change in its nature in the era of digital transformation. It is expected to provide the status and future of research trends of sustainable manufacturing to the both manufacturing researchers and journal publishers.

This study proposes a new wear life model, focusing on the adhesive wear phenomena that occur in tripod type CVJs. For the development of the wear life model, kinematic analysis was performed to derive the relative coordinates of components and contact points. Then, the normal pressure at the contact points were calculated. In order to investigate the wear amount of each contact point, an Accelerated Life Testing (ALT) based on a reliability analysis theory was employed. In this study, a new experimental system was built to experiment the wear of CVJ components, which enables to measure the wear amount under much harsher conditions than actual driving conditions. The experimental results from the ALT were analyzed and organized for the wear life model. Finally, the developed model was verified by comparing the estimated results with the experimental results under an actual driving condition.

A real-time wear measurement system for tripod type Constant Velocity (CV) joints is proposed in this study. Adhesive wear on tripod type CV joints is very crucial to the life time of CV joints but it is very difficult to measure the wear depth of a tripod type CV joint separate from the drive shaft assembly. The wear measurement system developed in this study can measure the wear depth of a tripod type CV joint in real-time as it applies kinematics and forces to the CV joint. In order to apply the same motions as the motions of an actual CV joint, kinematics of the CV joint has been analyzed. As a result, reciprocating stroke and yaw motions have been completely implemented in the system. The wear measurement system comprises four parts. The first part is for applying normal forces to a set of spherical roller and housing track. One servo motor, spur gear and ball screw sets were employed to generate and augment the normal forces. The second and third parts are for applying reciprocating stroke and yaw motions, respectively. These parts synchronize with each other to make the same motion profiles as the actual CV joint. The fourth part is for measurement. This part consists of load cell and rotary encoder to measure the surge normal forces caused by the flaking phenomena and the wear depth caused by the adhesive wear. In the case of the encoder, the wear depth is augmented by the ball screw and spur gear sets so 0.18°/μm of measurement resolution can be achieved. For the validation of the system, a tripod type CV joint was selected, and its wear depth was measured by the system and the results were compared with the wear depth measured by a profilometer.

This study describes a TR-iso-pulse generator which has better machining performance than an RC-pulse generator in micro-electrical discharge drilling (micro ED-drilling). Although machining with a TR-pulse generator is more efficient compared to when using a RC-pulse generator in macro-scale EDM, an RC-pulse generator is often used in micro EDM because it can generate the short discharge pulse necessary to minimize the discharge energy. However, to increase the machining efficiency, it is necessary to develop a TR-iso-pulse generator capable of generating a small amount of uniform discharge energy. In this research, a TR-iso-pulse generator was constructed for micro ED-drilling. For an accurate performance comparison between an RC-pulse generator and a TR-iso-pulse generator, each pulse generator was set up to generate the same discharge energy for a single discharge. Through micro ED-drilling, material removal rate (MRR) and relative wear ratio (RWR) were measured with respect to feed rate, and then the periphery of the machined hole, longitudinal section, lateral overcut, and surface roughness were compared for machining accuracy analyses. As a result, MRR was increased by 121% and RWR was decreased by 39% in the TR-iso-pulse generator compared with the RC-pulse generator. In addition, while lateral overcut was increased by 4.63%, less amounts of re-solidified material were deposited at the periphery of the machined hole and surface roughness was also reduced by 22% in the TR-iso-pulse generator.

Glass is a well-known non-conductive material that has many useful properties, and considerable research has been conducted into making circuits on glass. Many deposition techniques have been studied, and laser-induced chemical liquid phase deposition (LCLD) is a well-known and cost-effective method for rapid prototyping of copper deposition on glass. However, the deposition results from the LCLD method on the surface of glass, which shows an issue in its detachment from the substrates because of the relatively low adhesion between deposited copper and the nontreated glass surface. This problem undermines the usability of deposited glass in industrial applications. In this study, the laser-induced backside wet etching (LIBWE) method was performed as a preceding process to fabricate microchannels, which were filled with copper by LCLD. Additional durable copper wire was produced as a result of the enhanced adhesion between the glass and the deposited copper. The adhesion was enhanced by a rough surface and metal layer, which are characteristics of LIBWE machining. Furthermore, the proposed method is expected to broaden the use of deposited glass in industrial applications, such as in stacked or covered multilayer structures with built-in copper wires, because the inserted copper can be physically protected by the microstructures.

An RC-type pulse generator is useful in micro-electrical discharge milling due to its small discharge energy. However, when using this kind of generator, the current between the tool and the workpiece oscillates because of the stray inductance of the circuit. This causes current to flow from the tool to the workpiece in reverse direction to the main discharge current. When the reverse current flows, tool polarity is changed which intensifies tool wear. In this research, the reverse current is eliminated by connecting a MOSFET to a normal RC-type pulse generator. As a result, tool wear was reduced and geometrical accuracy was increased during machining of stainless steel using cemented carbide tool. Tool wear was further reduced through the use of deionized water with low resistivity. However, the use of low resistivity water decreases tool wear but can also reduce geometrical accuracy. The combination of using a MOSFET with low resistivity water therefore reduces tool wear while maintaining geometrical accuracy. The addition of the MOSFET to the RC circuit reduced the relative wear ratio by up to 67%. Thus, removing the reverse current is effective in reducing tool wear in various machining conditions.

This study proposes a new generated axial force (GAF) estimation model of tripod-type constant velocity (CV) joints. For development of the model, kinematic analysis was performed to derive the rel...

This study proposes a new explanation of how tool wear is reduced during powder-mixed micro electrical discharge machining. Owing to its lower discharge energy than a transistor discharge circuit, an RC discharge circuit outperforms in micro EDM. Given that the energy distribution of a cathode is lower than that of an anode during discharge, a tool is negatively charged to reduce tool wear and increase the material removal rate. However, due to the stray inductance of an RC discharge circuit, the tool polarity and direction of the current fluctuate before the discharge plasma channel is extinguished, which increases the tool wear. In this study, it was found that graphite powder in a dielectric fluid disperses the charged energy into several small discharge plasma channels. These small channels were extinguished quickly before the tool polarity and direction of the current fluctuate; which decreases the amount of tool wear. The machining time and tool wear length in powder-mixed micro ED-drilling were evaluated with various particle diameters and concentrations of powder-mixed dielectric fluid. With the optimal tool feeding conditions, the machining time and tool wear length of graphite-powder-mixed kerosene were reduced by 30.9% and 28.3%, respectively, as compared to those in non-powder-mixed EDM.

In this paper, a novel selective copper metallization technique that can be used on various materials, such as glass, plastic and ceramic, is proposed. The process consists of three steps: seed layer development, pattern fabrication using jet-circulating electrodeposition, and seed layer removal. A copper seed layer for electrodeposition was formed on various materials by electron beam evaporation. Jet-circulating electrodeposition was implemented to fabricate micro-metal patterns. Localizing the circulation of a jetted electrolyte through two concentric nozzles enables rapid selective electrodeposition. The geometry of the copper pattern was investigated by means of scanning electron microscopy (SEM) and a surface profiler. As a result, copper pattern in various shapes was fabricated. The usage of an outer diameter of 290 μm electrode nozzle, results in a copper pattern with a width of 430 μm and a height of 28 μm. Parameter study of the jet-circulating electrodeposition condition to investigate the electrodeposition mode, electrolyte jetting pressure, and average current was performed to control the width, height and surface roughness of the deposited pattern.

An RC-type generator circuit is suitable for micro-electrical discharge machining (micro EDM) owing to its low single discharge energy. In micro EDM, negative tool polarity has the advantage of reducing the tool wear rate and the relative ratio. However, when using an RC-type generator circuit in micro EDM, the direction of the current fluctuates at the plasma channel between the tool and the workpiece due to stray inductance. Because the current flowing from the tool to the workpiece can intensify the tool wear rate, it is preferable to prevent the fluctuation of the current direction. In this study, we propose the RC-type generator circuit using an n-channel MOSFET to prevent the fluctuation of the current direction and to increase duty ratio to enhance the material removal rate. Using a micro ED drilling process, the material removal rate, relative ratio, and surface roughness were measured with respect to the feeding control conditions and electrical conditions. As a result, by using the RC-type generator circuit with a MOSFET, the relative ratio is reduced by up to 40%, with the same material removal rate and surface roughness, compared with the results without a MOSFET.

Laser induced backside wet etching (LIBWE), a simple-setup process capable of processing transparent materials, has been studied to overcome difficulties in glass micromachining. However, LIBWE still show practical difficulty in machining various glass applications due to the crack occurrence and unprecise final geometry. This study proposes the error-compensating scan path generation method for the precise fabrication of glass microstructures without additional devices. In conventional scan paths, the overlap of scan path’s initial and final points, constant scan path patterns and uneven distributions of laser irradiation were the leading causes of geometric errors. The scan path generation method was developed to minimize or eliminate the causes of geometric errors in conventional scan path methods. Machined results, with error-compensating scan path, showed the removal of significant error from conventional paths with proper material removal rates. The effects of scan path generation parameters on the machining characteristics were also investigated. By adjusting the scan duty ratio and laser irradiation distribution of the entire scan path, micropockets with an average surface roughness of 0.26 μm could be processed at a material removal rate of 29,700 μm3/s. Based on machining characteristics of the error-compensating scan path, various glass microstructures were fabricated and the feasibility of the proposed method was verified.

This paper describes a state of the art in micro-structuring high strength metallic materials. Tungsten micro pin arrays in a variety of shapes are fabricated using a micro carving technology, which combines laser beam machining and electrochemical etching processes. First, micro pin arrays were rough-shaped by laser beam machining along a pre-defined scanning path to control their structural shape. The micro pin array in this stage had near-conical shape of structures due to a recast layer. Next, the genuine shape of micro pin arrays came to the surface via electrochemical etching process to elute the recast layer into electrolyte. Quantitative elemental analysis with energy-dispersive spectroscopy (EDS) was implemented to characterize the formation of recast layer on a micro pin structure after the laser beam machining process. The atomic percentage EDS maps indicated that higher percentage of tungsten was detected on the core micro pin structure, whereas relatively large percentage of oxygen was found on the recast layer (O 9%, W 91% in the center area, and O 53%, W 47% in the outer area).

This research investigated the microdrilling characteristics of metal foils depending on the materials of the cover plates and metal foils in the cover plate-laser beam machining (c-LBM) process, which is a method to achieve better quality in metal foil machining with a given piece of equipment. Laser beam drilling using a nanosecond pulsed laser was carried out on 10-µm-thick stainless steel 304 (STS304), nickel, and copper foils with 100-µm-thick cover plates of each material. Consequently, STS304 was found to be an effective cover plate material for reducing the hole diameter and spatter deposition on metal foils. Compared to the results without using a cover plate, the average hole diameter and the area of spatter deposition decreased by up to 77% and 96%, respectively, by using the STS304 cover plate. Meanwhile, the thermal deformation of the STS304 and nickel foils was prevented by using a cover plate, while the copper foil was barely deformed even without a cover plate. Lastly, it was remar...

This study proposed a new model to estimate the manual steering torque of steer-by-wire systems. The current steer-by-wire system uses the steering-actuator torque at the end of the rack-and-pinion gear to obtain the manual steering torque. However, there is a need for a new method to obtain the manual steering torque because a steer-by-wire system is expected to develop as it eliminates or at least simplifies more mechanical parts in order to enable them to be combined with other technologies such as an in-wheel motor. In order to propose a new estimation model, this study employs vehicle dynamics modeling and steering-system modeling. Vehicle dynamics modeling is used to estimate the self-aligning moment that arises between the tires and the ground. The slip angle and the normal force, as well as the tire properties of the vehicle, were considered to obtain the self-aligning moment. In addition, the steering system was also considered in this study because the calculated self-aligning moment is transferred through the steering system. The universal joint, the rack-and-pinion gear, and the lower-body linkages were modeled to calculate the manual steering torque delivered to the driver’s hands. For validation of the new model, there are two sets of simulation and verification processes in this study. First, the steering-system model was verified through experiments. A steering system was set as the target system, and its mechanical characteristics such as the inertial coefficient, the damping coefficient, and the stiffness were adopted for modeling and verification. Second, the manual steering torque estimation model was verified using field tests. A vehicle was set as the target vehicle, and its specifications such as the dimensions, the steering system, and the lower-body linkages were adopted for modeling and verification. The verification results were presented and show accurate estimation results. The new model proposed in this study does not need mechanical parts to estimate the manual steering torque apart from the steering actuator and the steering feedback actuator and, therefore, it can contribute to the development of a steer-by-wire system.

Manufacturing paradigms have historically been shaped by social, economic, and technological aspect, including limitations and needs. Design for manufacturing (DFM) has been the main paradigm for last three decades since design is defined by the limitations of available manufacturing processes. Since reducing the time required for the development of new products has been one of the key issues for businesses, removing the gap between designers and manufacturers has been one of today’s main goals. Many methods were developed to reduce this gap including information and communication technologies (ICT). However, current issues have been shifting towards design-related issues such that researchers have been trying to make products desired by the customers rather than that which is cheaper to manufacture. In this article, hybrid manufacturing (HM) and the concept of smart factory are introduced as key technologies for the future paradigm of manufacturing: Manufacturing for Design (MFD). Issues related to the development of HM process and examples of HM process are explained, and the importance of smart factories for the implementation of MFD is shown. Finally, future trends of HM and smart factory are predicted at the end of this article.

Laser-induced backside wet etching (LIBWE) is one of the most promising manufacturing processes for fabricating high aspect ratio microfeatures of glass. However, cracks inside the glass during the LIBWE process due to high thermal stress limits the manufacturable shape. In this study, we propose a new technique to prevent the crack generation in the near-infrared (NIR) LIBWE process by adding phosphoric acid to the absorbent. It was possible to increase the maximum fabricable depth by approximately five times compared to the absorbent without phosphoric acid. The nature of the crack suppression mechanism in the absorbent with added phosphoric acid was investigated by in situ observation of the process and chemical analysis. To investigate the effects of phosphoric acid on LIBWE with added phosphoric acid, the influences of phosphoric acid concentration on maximum fabricable depth, fabrication speed and sidewall roughness were studied. Based on the investigated principle and process characteristics, we found that high aspect ratio microchannels of different shapes could be produced.

In this study, a novel process for fabricating micro Al2O3 patterns using local anodization is proposed. On the basis of double layer theory, the anodizing region was localized on an aluminum surface near a micro tool electrode with a small inter-electrode gap. The localized oxide formation process was observed by field emission scanning electron microscope (FE-SEM) including energy dispersive spectroscopy (EDS). It was confirmed that micro-scale localized aluminum oxide was fabricated on the aluminum surface. Features of the anodized oxide line were investigated using different ratios of sulfuric and oxalic acid mixtures at various pulse durations and voltage conditions. The experimental results show that an insulating aluminum oxide line pattern was fabricated on 10 µm aluminum foil. Subsequently, a coplanar waveguide (CPW) micro patch antenna was fabricated and characterized by a PNA network analyzer. The local anodization can be used for fabricating micro-electric circuits without masks and substrate; which will promise the next generation of micro electronic devices.

Strip EDM is similar to wire EDM, except that the electrode is a roll of brass strip. In this study, investigated is the effect of machining area on material removal rate (MRR) in strip EDM, The MRR was measured according to different machining areas and different electrical discharge conditions. For a given discharge condition, optimal machining area for maximum MRR was identified. The optimal machining area was larger under higher discharge energy condition. It is shown that strip EDM is much more efficient than wire EDM because material removal rate is much higher and the electrode consumption is much less.

We present a straightforward method to realize a wettability-controlled stainless steel surface via wire electrical discharge machining. Samples of AISI 304 stainless steel were prepared, having various depth of groove, while width and pitch of groove were set to be 500 μm and 600 μm. Wetting properties of the fabricated samples were quantified by measuring static contact angle of deionized water and silicone oil, and sliding angle of water droplets. Mechanical robustness test was conducted by comparing static contact angle of water and silicone oil before and after 1000 cycles of abrasion. In order to propose potential applications, we demonstrate oil–water separation and polymer molding for fabricating superhydrophobic surfaces.

The fabrication process of metallic hydrophobic surfaces was investigated using copper electrodeposition and oxidation. Hierarchical structures have well known advantages for producing super-hydrophobic surfaces. A micro-pillar array with a hierarchical structure of copper was fabricated through a sequential process of laser ablation followed by electrodeposition. Heat oxidation enhanced the hydrophobicity of both flat and micro-structured copper surfaces. Electrodeposition at higher current density gave a hierarchical structure with low surface energy, resulting from the presence of copper oxide. Fabricated surfaces with a depth of more than 100 micrometers display super-hydrophobicity. The effects of copper oxide and hierarchical structure were confirmed by an oxidation test of the fabricated structures, because the thickness of copper oxide was undetectable by XRD and XPS.

Commercial metals have recently been reconsidered as useful materials for functionalized surfaces with controlled wettability, yet the intrinsic wettability of various metal surfaces remain uncertain. In this study, we report that the wettability of a stainless steel (Type 304) surface exhibits a time-dependent transition, initially from a hydrophilic state to a relatively hydrophobic state. The static contact angle of a water droplet was monitored on polished stainless steel surfaces every 24 h, and a rapid increase in the contact angle, from 44° to 81°, was found during the first three days. The contact angle reached 98° in 40 days. To clarify the main factor causing the phenomenon, we compared the contact angles of water stored in four different environments for five days, where the oxygen and moisture levels were controlled. From the difference in contact angles depending on the amount of oxygen, we reached the conclusion that oxygen is likely the main cause of the aforementioned phenomenon. Finally, we demonstrated time-dependent wettability on a micro-grooved stainless steel surface whose initial superhydrophilicity became superhydrophobic after 30 days.

This study proposes hardware-in-the-loop simulations to develop the motor speed map of electrohydraulic power steering systems for heavy commercial vehicles. The current method that relies on the test driver’s hands and feet to obtain electrohydraulic power steering motor speed maps causes a number of problems, such as inaccurate steering rates and vehicle speeds and the risk of rollover during tests. In order to overcome these weaknesses, this study employs a hardware-in-the-loop simulation system, a vehicle model, and an experimental development method. A hardware-in-the-loop simulation system was set up to simulate a steering system on the road. The system includes a system drive, data acquisition, system controller sets, and an electrohydraulic power steering system. This hardware-in-the-loop simulation system is controlled in real time because the amount of the torque from the resistant torque motor, which applies the self-aligning moments generated between the ground and the tires to the steering system, is affected by the steering angle of the steering-wheel motor. For calculation of the resistant torque with respect to various driving conditions, a vehicle model was employed in this study. It includes calculation of the self-aligning moments with the tire property data, the moments due to the kingpin inclination, the vehicle dynamics, and the steering-system modeling. The resultant values were input into the resistant torque motor. In addition to the hardware-in-the-loop simulation system and the vehicle model, the concept of a desirable steering torque which parameterizes the steering feel was introduced in this study. Using the desirable steering torque, the steering feel could be quantified, and desirable steering feels were established. In this study, in order to validate the hardware-in-the-loop simulations, a heavy commercial vehicle was designated as the target vehicle. The target vehicle’s tire and specifications such as the dimensions, the weight, the steering system, and the mechanical links were adopted, and a desirable steering-torque map was established by a professional test driver. The development results were presented.

We report on the design, optimization, and performance evaluation of a new wheel-leg hybrid robot. This robot utilizes a novel transformable wheel that combines the advantages of both circular and legged wheels. To minimize the complexity of the design, the transformation process of the wheel is passive, which eliminates the need for additional actuators. A new triggering mechanism is also employed to increase the transformation success rate. To maximize the climbing ability in legged-wheel mode, the design parameters for the transformable wheel and robot are tuned based on behavioral analyses. The performance of our new development is evaluated in terms of stability, energy efficiency, and the maximum height of an obstacle that the robot can climb over. With the new transformable wheel, the robot can climb over an obstacle 3.25 times as tall as its wheel radius, without compromising its driving ability at a speed of 2.4 body lengths/s with a specific resistance of 0.7 on a flat surface.

Fine surface finish of micro features processed by micro EDM is difficult due to small feature size. In this work, we investigated electrochemical finishing process after micro EDM. The product shape was machined by micro EDM, and the surface was finished by electrochemical process. For both processes, deionized water was only used as dielectric fluid for EDM and electrolyte for finishing. Surface formation characteristics during finishing and side gap increase were analyzed according to machining conditions. In addition, surface roughness and hardness were measured to compare three cases of surface processed by micro EDM in deionized water, by micro EDM in kerosene, and by finishing in deionized water after micro EDM, respectively. Micro grooves and pockets were fabricated by micro EDM milling and electrochemical finish. In the case of drilling, electrochemical finish in deionized water not only finished inner surface of the holes but also expanded entrance and exit hole size. Using this phenomenon, micro drawing die was fabricated by controlling finishing conditions.

This paper proposes a method of selective electrochemical dissolution on the cylindrical surfaces of stainless steel shafts. Selective electrochemical dissolution was achieved via electrochemical etching using laser masking. A micropatterned recast layer was formed on the surface via ytterbium-doped pulsed fiber laser irradiation. The micropatterned recast layer could be used as a mask layer during the electrochemical etching process. Laser masking condition to form adequate mask layer on the planar surface for etching cannot be used directly on the non-planar surface. Laser masking condition changes depending on the morphological surface. The laser masking characteristics were investigated in order to form a uniform mask layer on the cylindrical surface. To minimize factors causing non-uniformity in the mask layer on the cylindrical surface, synchronized laser line scanning with a rotary system was applied during the laser masking process. Electrochemical etching characteristics were also investigated to achieve deeper etched depth, without collapsing the recast layer. Consequently, through a series process of laser masking and electrochemical etching, various micropatternings were successfully performed on the cylindrical surfaces.

In this research, the fabrication process of a super-hydrophobic metallic surface using laser ablation and electrodeposition was investigated. Re-entrant structure and surface roughness play an important role in forming a super-hydrophobic surface on intrinsically hydrophilic material. A micro pillar array with a re-entrant structure of copper on stainless steel was fabricated through a sequential process of laser ablation, insulating, mechanical polishing and electrodeposition. Spacing of the micro pillars in the array played a major role in the structure hydrophobicity that was confirmed by measuring the water contact angle. Surface morphology changed relative to the parameters of the laser ablation process and electrodeposition process. Under a gradual increase in current density during the electrodeposition process, surface morphology roughness was maximized for fabricating a super-hydrophobic surface. Finally, the super-hydrophobic surface was successfully fabricated on metal.

This study suggested use of strip electrical discharge machining (strip EDM) for fabricating V-grooves. Traditional methods, such as cutting or grinding, make it difficult to deal with hard-to-cut metals and burr formation on machined portions is a concern. Although EDM does not cause these problems, this machining method has the disadvantage of electrode wear. The wear causes shape error and low productivity. To overcome these problems, an experiment using strip EDM was conducted to produce V-grooves. A thin conductive strip used as an electrode was bent around an electrode guide and its corner was shaped into a right-angle triangle. This shaped electrode was used to fabricate a V-groove. Since the suggested process was not concerned with electrode wear, new electrodes for finish cuts and tool path compensation were not required during the machining process. It was also possible to complete high precision machining because no burr or deformation was caused by the cutting force when compared with traditional machining methods. In the practical machining of this research, the patterns of V-grooves, prisms and pyramids were fabricated on a stainless steel workpiece.

A method to model the column-type electric power steering system considering viscous friction is proposed. In general column-type electric power steering systems, viscous friction occurs in the reducer. However, it is very difficult to predict with respect to modelling because it varies with the conditions, and accordingly many parameters should be considered. In this study, in order to estimate the dynamic behaviour of a column-type electric power steering system which uses a worm gear as a reducer, the viscous friction generated in the worm gear was derived through theoretical approaches, and the results were applied to modelling the steering system. In the theoretical approaches, the gear geometry and Hertz’s law were employed to derive parameters such as the normal load and the sliding velocity from the worm gear’s driving conditions. Then, the derived parameters were applied to a tribometer to measure the friction coefficients between the worm and the worm wheel. Finally, the friction coefficients were converted to the viscous friction torque of the steering system. By applying the converted viscous friction torque to the modelling, the entire steering system was modelled and the results were verified by comparative simulations and experiments. To model the entire steering system, the individual subparts of the steering system such as the steering column, the universal joint and the rack-and-pinion gear were modelled with MATLAB/Simulink. Then, for verification of the steering-system model, the dynamic behaviour of the steering system was measured experimentally and compared with the simulation results. Taking into account viscous friction and all the mechanical characteristics of the steering system, the established steering-system model which considers viscous friction was employed to estimate very accurately the dynamic behaviour of the steering system, whereas use of the steering-system model which does not consider viscous friction did not achieve accurate estimations.

Turning by electrical discharge machining (EDM turning) is an effective method to machine hard-to-cut materials. Generally, a wire-EDM is utilized in EDM turning because it is not concerned with electrode wear. However, wire-EDM turning has a slow machining speed due to its small machining area, and the wire may break due to overheating electrodes. For these reasons, its machining speed must be limited. In this study, a strip-EDM was created in an effort to overcome the problems in the EDM-turning process. This machining method used a conductive strip as an electrode. The strip was fed continuously, like a wire-EDM; therefore electrode wear was not a concern. One advantage of the strip-EDM was that it increased the material removal rate because of its large machining area and non-breaking electrode. In the experiments, machining characteristics were investigated according to machining conditions, and practical machining was carried out via fabrication of complex shapes on a shaft workpiece.

One of the most significant problems of electrical discharge machining (EDM) is electrode wear, which results in shape errors and low productivity. In this study, a new EDM method using a strip electrode (strip EDM) was developed in order to overcome the wear problem. The strip EDM uses a continuously applied strip electrode that is similar to the wire electrode used in wire EDM. The strip electrode apparatus can be used as a simple shape tool, which is similar to electrical discharge milling (ED-milling). In the suggested strip electrode method, a conductive strip moves on the electrode guide. The worn strip is removed, and the new strip is supplied continuously. Therefore, the tool electrode can be regarded as having no wear during the machining process. The strip EDM promises precise machining without tool wear and can be substituted for a general ED-milling. This method uses a conductive strip made of copper or brass. To estimate the machining performance of the strip EDM, the material removal rate (MRR) and surface quality were investigated according to the machining parameters, such as depth of cut, peak current, and tool materials. The machining results were compared with the results from general ED-milling. In the practical machining study, precise molds with 3D shapes were machined using the strip EDM method.

This paper proposes a novel selective metal deposition process that uses a combination of laser irradiation and electrodeposition. Via the selective electrodeposition using laser irradiation (SELI) process, metal can be deposited selectively on a metal surface without a special mask, which is in contrast to conventional deposition processes that routinely require a metal mask or a photo-resist. The SELI process consists of three steps: laser irradiation, electrodeposition, and ultrasonic vibration cleaning. In the course of experimentation, a recast layer was formed via the laser irradiation process, which acts as the sacrificial layer in the SELI process. The sacrificial layer was removed after the cleaning step. The separation of the sacrificial layer was due to the hydrogen evolution effects of the hydrogen embrittlement via the hydrogen bubbles and the hydrogen absorption. The results were observed via focused ion beam (FIB) analysis of the cross-sectional images. Electron probe X-ray micro-analyzer (EPMA) analysis was used to detect the surface components. Through the SELI process, selective copper deposition was successfully performed with various micro-patterns of the approximately 4 μm thick deposited copper.

This paper proposes a systematic method to develop electrohydraulic power steering (EHPS) motor speed maps. To overcome the weaknesses of the existing method, which depends on the test driver's steering feel at a proving ground, this paper utilized theoretical approaches and experimental developments to develop an optimal EHPS motor speed map. Steering torque of the target vehicle according to steering angle and vehicle speed was estimated through theoretical calculations. For the theoretical estimation of steering torque, tire properties of the target vehicle were measured, vehicle dynamics were employed to estimate slip angles, and the steering system was modeled. These estimation results were verified through field tests and then applied to the resistant motor of the EHPS Hardware-In-the-Loop Simulation (HILS) system, which represents the moments generated between the ground and tires. As the experimental development of EHPS motor speed map, an EHPS HILS system was set up, and the concept of desirable steering torque was established to quantify steering feel and catch-up effect. By means of the desirable steering torque, steering feel that was subject to the test driver's hands had criteria at various driving conditions. As the final procedure of this paper, the developed motor speed map was numerically compared with the existing map developed by the existing method, and then, it was verified through field tests with the target vehicle. The developed motor speed map provided sufficient steering assist to the driver and prevented the catch-up effect under all driving conditions. In addition, the steering torque from both maps had the same profiles at all driving conditions, even if the developed map demands lower motor speeds up to 1950 r/min than the existing map at almost all driving conditions.

Micro electrochemical machining (ECM) of tungsten carbide with cobalt binder (WC–Co) was studied using ultrashort pulses. In ECM, the machining characteristics were investigated according to machining conditions such as electrolyte, workpiece potential, and applied voltage pulse. Using a mixture of sulfuric acid and nitric acid, microstructures with a sharp edge and good surface quality were machined on tungsten carbide alloy. The potentials of workpiece electrode and tool electrode were determined by considering the machining rate, machining stability, and surface quality of products. With the negative potential of the workpiece electrode, oxide formation was successfully prevented and shape with good surface quality in the range from Ra 0.069 μm to 0.075 μm were obtained by electrochemical machining. Moreover, the performance of ECM, which includes machining gap, tapering, surface roughness, and machining time, without tool wear was compared with that of electrical discharge machining (EDM). Microstructures of WC–Co with a sharp edge and good surface quality were obtained by electrochemical milling and electrochemical drilling. Micro electrochemical turning was also introduced to fabricate micro shafts.

Omni-directional robot is a typical holonomic constraint robot that has three degrees of freedom movement in 2D plane. In this study, a new omni-directional robot whose wheels are arranged in radial directions was proposed to improve driving performance of the robot. Unlike a general omni-directional robot whose wheels were arranged in a circumferential direction, moments do not arises in the proposed robot when the robot travels in a straight line. To analyze driving performance, dynamic modeling of the omni-directional robot, which considers friction and slip, was carried out. By friction measurement experiments, the relationship between dynamic friction coefficient and relative velocity was derived. Dynamic friction coefficient according to the angle difference between robot travel direction and wheel rotation direction was also obtained. By applying these results to the dynamic model, driving performance of the robot was calculated. As a result, the proposed robot was 1.5 times faster than the general robot.

`Multi-scale mass-deployable cooperative robots` is a next generation robotics paradigm where a large number of robots that vary in size cooperate in a hierarchical fashion to collect information in various environments. While this paradigm can exhibit the effective solution for exploration of the wide area consisting of various types of terrain, its technical maturity is still in its infant state and many technical hurdles should be resolved to realize this paradigm. In this paper, we propose to develop new design and manufacturing methodologies for the multi-scale mass-deployable cooperative robots. In doing so, we present various fundamental technologies in four different research fields. (1) Adaptable design methods consist of compliant mechanisms and hierarchical structures which provide robots with a unified way to overcome various and irregular terrains. (2) Soft composite materials realize the compliancy in these structures. (3) Multi-scale integrative manufacturing techniques are convergence of traditional methods for producing various sized robots assembled by such materials. Finally, (4) the control and communication techniques for the massive swarm robot systems enable multiple functionally simple robots to accomplish the complex job by effective job distribution.

Electrical discharge machining (EDM) is a widespread machining method for the die and mold industry. This method can machine all conductive materials, including hard-to-cut metals, because the machining process uses electro-thermal energy without a cutting force. During EDM, discharge sparks remove not only the material of a workpiece but also the material of an electrode. This machining mechanism thereby causes electrode wear, which creates serious problems, including make-shape errors and low productivity. In order to overcome such problems, a new EDM method using a strip electrode (strip EDM) was developed in this study. Strip EDM uses a continuously applied strip electrode similar to the wire electrode in wire EDM. In the suggested strip-electrode method, a conductive strip moves on the electrode guide. The worn strip is removed, and a new one is supplied continuously. Therefore, the tool electrode acquires no wear during the machining process. This method uses a conductive strip that is made of brass. In the practical machining process, the strip EDM method was applied to EDM milling and EDM turning and their machining characteristics were compared with general EDM methods.

Small mobile robots which use round wheels are suitable for driving on a flat surface, but it cannot climb the obstacle whose height is greater than the radius of wheels. As an alternative, legged-wheels have been proposed by many researchers due to its better climbing performance. However, driving and climbing performances have a trade-off relationship so that their driving performance should be sacrificed. In this study, in order to achieve both driving and climbing performances, a new transformable wheel was developed. The developed transformable wheel can have a round shape on a flat surface and change its shape into legged-wheel when it makes a contact with an obstacle. For design of the transformable wheel, the performance of legged-wheel was analyzed with respect to the number and curvature of the leg, and then the new transformable wheel was designed based on the analysis. Contrary to the existing transformable wheels that contain additional actuators for the transformation, the developed transformable wheel can be unfolded without any additional actuator. In this study, in order to validate the transformable wheel, a simple robot platform was fabricated. Consequently, it climbed the obstacle whose height is 2.6 times greater than the wheel radius.