Fabrication of micro-electrodes by multi-EDM grinding process

In this study, a multi-EDM grinding process is adapted to fabricate micro-electrodes. Equipments such as a wire EDM machine and a traditional CNC-EDM machine are used for machining micro-electrodes. Rod electrodes of copper with diameter 3.0 mm were cut to be 0.15 mm on wire-EDM machine at first step. EDM grinding process was used to grind micro-electrodes to fine diameter bellow 20 μm on a CNC-EDM machine at second step. For EDM grinding, rotating mechanisms are mounted on both the WEDM machine and the CNC-EDM machine. A CCD camera is provided for viewing and for on-line dimensional controlling, when micro-electrodes were cutting. Fine electrodes could be processed to a smaller size using proposed two-steps EDM grinding process. Higher L/D ratio could be also achieved by this method. The processed fine electrodes can be used for drilling micro-holes, micro-deep holes, micro-milling, micro-punching, and manufacturing of micro-nozzles.     

Micro-hole fabrication by mechanical punching process

In the present investigation, micro-hole punching was studied, and the standard punching condition was scaled down to produce 25 μm size holes. For this, a micro punching press was designed and assembled, meeting requirements of process accuracy for 25 μm size holes. Tungsten carbide tooling sets were designed and fabricated by micro machining techniques. Three different size holes of 100, 50, and 25 μm in diameter were punched successfully on thin metallic foils such as brass and stainless steel of 100, 50, and 25 μm in thickness, respectively. Punched holes were examined in terms of surface qualities and results were analyzed in connection with shear fracture behavior. The results in this paper show that the mechanical punching process is promising to produce high quality holes even in the micro scale application.     

Development of a micro-punching machine and study on the influence of vibration machining in micro-EDM

This paper describes the development of a novel micro-punching machine that is capable of producing precision micro-holes. A significant feature of this machine is to fabricate the micro-punch and then the micro-die in the same machine, totally eliminating the eccentricity between the punch and the die when punching is proceeded. By applying vibration machining technique, we can decrease the possibility of electric short-circuiting during the micro-EDM process. The utilization of a proportional solenoid as the power unit of the micro-punching machine and as the source of vibration is found to be a successful attempt. Experiments to punch micro-holes with diameters of 0.1 and 0.2 mm on an SUS 304 stainless steel strip with 0.1 mm in thickness were carried out. The results show that the performance of this machine and the geometry of punched micro-holes are satisfactory.     

Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining

Because of its excellent anodic bonding property and surface integrity, borosilicate glass is usually used as the substrate for micro-electro mechanical systems (MEMS). For building the communication interface, micro-holes need to be drilled on this substrate. However, a micro-hole with diameter below 200 μm is difficult to manufacture using traditional machining processes. To solve this problem, a machining method that combines micro electrical-discharge machining (MEDM) and micro ultrasonic vibration machining (MUSM) is proposed herein for producing precise micro-holes with high aspect ratios in borosilicate glass. In the investigations described in this paper, a circular micro-tool was produced using the MEDM process. This tool was then used to drill a hole in glass using the MUSM process. The experiments showed that using appropriate machining parameters; the diameter variations between the entrances and exits (DVEE) could reach a value of about 2 μm in micro-holes with diameters of about 150 μm and depths of 500 μm. DVEE could be improved if an appropriate slurry concentration; ultrasonic amplitude or rotational speed was utilized. In the roundness investigations, the machining tool rotation speed had a close relationship to the degree of micro-hole roundness. Micro-holes with a roundness value of about 2 μm (the max. radius minus the min. radius) could be obtained if the appropriate rotational speed was employed.     

High-strength superelastic Ti–Ni microtubes fabricated by sputter deposition

Ti–Ni microtubes are attractive materials for biomedical devices, such as micro-catheters and micro-stents, but it is difficult to fabricate them with dimensions of less than 100 μm by conventional tube-drawing. In this study, Ti–Ni microtubes with 50 μm inner diameter and a tube wall thickness of 6 μm was successfully fabricated using a novel method in which Ti–Ni was sputter-deposited on a Cu wire with a diameter of 50 μm. All the microtubes exhibited shape memory behavior after crystallization at 873 K for 3.6 ks. Microtubes fabricated without rotating the Cu wire during deposition have low fracture strength due to the columnar grains and non-uniform tube wall thickness. Microtubes fabricated by depositing Ti–Ni on a rotating wire have a uniform wall thickness and the fracture strength increased with increasing rotation speed. Microtubes made by the rotating-wire method exhibited superelasticity of 3% strain at room temperature with high fracture stress of 950 MPa, suggesting that they are suitable for practical applications.     

基于微细电火花加工机床的微孔冲裁加工装置

为实现微孔冲裁高效、高质量加工,避免微冲头、冲模孔离线加工而引起的二次装夹问题,在实验室自行研制的微细电火花加工机床上进行微冲裁加工装置的设计。利用该装置进行微冲头、冲模孔的在线制备和冲裁加工试验,成功制备出了直径100μm的微冲头与直径110μm的冲模孔。并在厚度20μm的黄铜箔上冲裁出直径105μm的微孔。验证了该装置的可行性。     

Production of submicrocrystalline structure in large-scale Ti–6Al–4V billet by warm severe deformation processing

The “abc” deformation method for production of large-scale billets with submicrocrystalline structure was developed. A large billet of Ti–6Al–4V alloy (150-mm diameter × 200-mm length) with a homogeneous submicrocrystalline structure was produced. The refined structure with a grain/subgrain size of about 0.4 μm leads to a substantial mechanical properties improvement.     

Giant magnetoimpedance effect in electroplated CoNiFe/Cu wires with varying Ni, Fe and Co content

Giant magnetoimpedance (GMI) behaviour has been studied for wires consisting of an 8.82–13.75 μm thick magnetic layer containing either Co_20.77Ni_61.74Fe_17.49, Co_18.21Ni_41.20Fe_40.59, Co_18.97Ni_49.60Fe_31.43, Co_46.01Ni_39.87Fe_14.12 or Co_33.67Ni_51.44Fe_14.89. These magnetic layers were electroplated onto a 50 μm diameter Cu non-magnetic wire. A large and sensitive GMI effect (about a 257% magnetoimpedance ratio) with nearly no hysteresis has been found in Co_18.97Ni_49.60Fe_31.43 wire at a 90 kHz ac driving current. Scanning electron microscopy (SEM) images showed that samples have globular and crack-free deposits with a grain size that varies between 3.06 and 9.17 μm.     

Development of a micro-forming system for micro-punching process of micro-hole arrays in brass foil

Micro-forming technology poses much higher demands on positioning accuracy, velocity and mass production, and the common forming machines cannot satisfy these requirements using traditional drive methods. Micro-forming equipment using novel drive methods with high speed and high precision has become an important research field for industrial application. In the paper, a novel drive mechanism was designed with a symmetric distributed double linear motors and a micro-forming system was developed with micro-punching tools and automatic feeding apparatus for metal foil. The servo control system of this micro-forming system was designed using SIMOTION D445, and a parallel control model was adopted with a single motor module to solve the synchronous control problems of double linear motors. Micro-punching process of brass foil was studied with the micro-forming system, and micro-holes of 600 μm, 300 μm and 150 μm in diameter were manufactured with high dimensional accuracy. An array of 50 × 4 micro-holes, each 600 μm in diameter, was manufactured using an automatic feeding apparatus guided by a microscopic visualization system for assisted localization. The results indicate that the micro-forming system with high-accuracy and high-speed is suitable for the mass production of micro-scale parts.     

Application of micro-EDM combined with high-frequency dither grinding to micro-hole machining

This research presents a novel process using micro electro-discharge machining (micro-EDM) combined with high-frequency dither grinding (HFDG) to improve the surface roughness of micro-holes. Micro-EDM is a well-established machining option for manufacturing geometrically complex small parts (diameter under 100 μm) of hard or super-tough materials. However, micro-EDM causes the recast layer formed on the machined surface to become covered with discharge craters and micro-cracks, resulting in poor surface quality. This affects the diameter of the micro-hole machined and undermines seriously the precision of the geometric shape. The proposed method that combines micro-EDM process with HFDG is applied to machining high-nickel alloy. As observed in SEM photographs and surface roughness measurement, HFDG method can reduce surface roughness from 2.12 to 0.85 μm Rmax with micro-cracks eliminated. Our results demonstrated that micro-holes fabricated by micro-EDM at peak current 500 mA followed by HFDG at 40 V can achieve precise shape and good surface quality after 6–8 min of lapping.     

Laser generated acoustic emission in water

A Q-switched Nd-YAG laser light source (pulse duration of 8 ns with a maximum energy of 50 mJ at a wavelength of 1.064 μm) was launched through an optical fibre (core diameter 800 μm and a numerical aperture (NA) of 0.25) delivery system into a tank containing natural water. The resulting acoustic wave generated by thermoelastic process was picked up using a broadband AE transducer (frequency bandwidth of 0–1 MHz) placed along the optical axis of the optical fibre carrying the laser source. Results of the experiments show that, the mean square voltage of the photo-acoustic emission (PAE) generated decreases with increase in the source-to-transducer distance in the range of 10–50 mm. Also the measurements show a good degree of repeatability at different input laser power levels. The result of the experiment is compared with an analytical model that has been proposed for this configuration. Application for on-line monitoring of fluid based processes is envisaged.     

Cutting process of glass with inclined ball end mill

Cutting processes with ball end mills are discussed for machining microgrooves on glasses. A surface is finished in undeformed chip thickness less than 1 μm at the beginning and at the end of the cut during the cutter rotation. The milling process is applied to glass machining. A crack-free surface can be finished in a large axial depth of cut more than 10 μm. Because glass undergoes almost no elastic deformation, roughness on a cutting edge in glass machining has a larger influence on surface finish than that of metal machining. The rotational axis of the tool is inclined to improve the surface finish. The cutting processes are modeled to show the effect of the tool inclination on the machined surface with considering the edge roughness. The tool inclination compensates for deterioration of the surface finish induced by the edge roughness in the presented model. The improvement of the surface finish is verified in the cutting experiments with the tool inclination. The orthogonal grooves 15–20 μm deep and 150–175 μm wide, then, are machined with the crack-free surfaces to prove efficiency and surface quality in the milling process.     

Fe7S8 nanorods and nanosheets

Fe₇S₈ nanorods and nanosheets were synthesized in large scale by a novel flux method. The starting materials are Fe, S powder and KI flux. XRD patterns demonstrated the as-prepared products were Fe₇S₈. The morphology could be controlled by the synthetic temperature easily. Nanorods and nanosheets were synthesized at 750 and 850 °C, respectively. The thickness of synthesized nanosheets was smaller than 100 nm. The nanorod diameter was about 200 nm, its length was about 2 μm, and the growth direction of nanorod was [0 1 2]. The growth mechanism for Fe₇S₈ nanorods and nanosheets are discussed in detail.     

Freeform surface finish of plastic injection mold by using ball-burnishing process

The objective of this study is to introduce the possible ball-burnishing surface finish process of a freeform surface plastic injection mold on a machining center. The design and manufacture of a burnishing tool was first accomplished in this study. The optimal plane ball-burnishing parameters were determined by utilizing the Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. Four burnishing parameters, namely the ball material, burnishing speed, burnishing force, and feed, were selected as the experimental factors of Taguchi’s design of experiment to determine the optimal burnishing parameters, which have the dominant influence on surface roughness. The optimal burnishing parameters were found out after conducting the experiments of the Taguchi’s L18 orthogonal table, analysis of variation (ANOVA), and the full factorial experiment. The optimal plane burnishing parameters for the plastic injection mold steel PDS5 were the combination of the tungsten carbide ball, the burnishing speed of 200 mm/min, the burnishing force of 300 N, and the feed of 40 μm. The surface roughness R_a of the specimen could be improved from about 1 to 0.07 μm by using the optimal burnishing parameters for plane burnishing. Applying the optimal burnishing parameters for plane burnishing to freeform surface plastic injection mold, the surface roughness R_a of freeform surface region on the tested plastic injection part could be improved from about 0.842 to 0.187 μm, through a comparison between using the fine milled and using the ball-burnished mold cavity.     

Film synthesis of SrTiO3 by the spray-ICP technique

SrTiO₃ films were synthesized by spray pyrolysis in combination with a high-temperature inductively-coupled plasma (ICP) as the heat source (spray-ICP technique). Sapphire and fused quartz were used as substrates. Ten minutes of film formation yielded films of 0.5–1.0 μm in thickness. The structure of the films consisted of crystallites about 0.1 μm in size. With respect to the homogeneity of the size and shape of the crystallites, sapphire is superior over fused quartz. X-ray diffraction measurements of the films revealed preferred orientation peaks of (2 0 0), (1 1 1), and (1 1 0) depending on the substrates and their locations from the ICP source.     

Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing

Al/Cu metal joints applied for the electrical connector was joined by the friction welding method to limit the formation of intermetallic compound under optimum friction welding condition. To guarantee the reliability of the Al/Cu joints in service requirement, the effects of the intermetallic compound layer on the electrical and mechanical properties have been investigated under various annealing conditions. Two kinds of intermetallic compounds layer were formed in the joints interface and identified by AlCu and Al₂Cu. The growth kinetic of these intermetallics during the annealing can be followed by volume diffusion process. The activation energy of Al₂Cu, AlCu and total intermetallic compound (AlCu + Al₂Cu) represented 107.5, 98.42 and 110.22 kJ/mol, respectively. A thicker intermetallic compound layers could seriously degrade the electrical resistivity and tensile strength. The electrical resistivity with 21 μm thickness of intermetallic compound was 45 μΩ cm and increased to be 85 μΩ cm with 107 μm of intermetallic compound. Tensile strength remarkably decreased from 85 MPa to near zero at the annealing condition of 773 K and 129.6 ks and fracture occurred through the intermetallic compound layers.     

SEM and TEM characterization of magnesium hydride catalyzed with Ni nano-particle or Nb2O5

The microstructures of MgH₂ catalyzed with Ni nano-particle or Nb₂O₅ mesoporous powders are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. For MgH₂ catalyzed with Ni, the Ni particles with the diameter smaller than 1 μm were detected on the MgH₂ particles with the diameter smaller than 5 μm by the back scattering electron (BSE) microscopy. In details, the TEM micrograph indicates that the Ni particles distribute 20 nm in diameter on MgH₂ uniformly, which was the same size as the additive doped in MgH₂ before milling. On the other hand, for MgH₂ catalyzed with Nb₂O₅, the additive particles could not be found anywhere in the BSE image. Even in the TEM micrograph by much larger magnification than the SEM micrograph, the particles corresponding to the additive cannot be observed at all. Furthermore, an energy dispersive X-ray (EDX) analysis in spots with a diameter of 20 nm indicated that the existing ratio of Mg to Nb was evaluated to 98:2, being the same as the starting ratio before milling. Therefore, the metal oxide Nb₂O₅ becomes extremely small particle that could not be observed by the present work after milling compared to metal Ni^nano.     

Effects of growth rate and temperature gradient on the microstructure parameters in the directionally solidified succinonitrile–7.5 wt.% carbon tetrabromide alloy

Succinonitrile (SCN)–7.5 wt.% carbon tetrabromide (CTB) alloy was unidirectionally solidified with a constant growth rate (V = 33 μm/s) at five different temperature gradients (G = 4.1–7.6 K/mm) and with a constant temperature gradient (G = 7.6 K/mm) at five different growth rates (V = 7.2–116.7 μm/s). The primary dendrite arm spacings, secondary dendrite arm spacings, dendrite tip radius and mushy zone depths were measured. Theoretical models for the microstructure parameters have been compared with the experimental observations, and a comparison of our results with the current theoretical models and previous experimental results have also been made.     

Population of excited erbium levels in Er:Na0.4Y0.6F2.2 (Er:NYF) laser crystals

We have studied theoretically and experimentally the population dynamics of six radiative erbium levels in concentration series of Er³⁺:NYF crystals. The radiative transition probabilities were calculated by the Judd–Ofelt method; the nonradiative transition probabilities were estimated; energy transfer (ET) microparameters (for migration, selfquenching (SQ), and upconversion (UC) processes) in studied crystals were estimated theoretically using the method of quantum–mechanical model calculation. The rate equations for the six lowest energy levels of erbium in Er³⁺:NYF crystals, including the 3 μm laser transition levels, were numerically solved for the case of excitation by nanosecond pulse at λ_pump=1.53 μm. The theoretical and experimental results for Er³⁺:NYF crystals are in good agreement. Single mode CW laser action was achieved in Er:NYF crystal at 2.8 μm with InGaAs LD pumping of the ⁴I_11/2 level. Output power about 72 mW with slope efficiency 4% was achieved in longitudinal pump scheme.     

Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder

Porous t-ZrO₂ ceramic was fabricated by pressureless sintering, using commercial t-ZrO₂ and different volume percentages of poly methyl methacrylate (PMMA) powders (20–80%). The spherical pores ranged from about 120 to 170 μm in diameter. By increasing the PMMA content, the number of pores, material properties and pore morphology were changed dramatically. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at 1550 °C, were about 43%, 40 GPa, 170 MPa and 248 Hv, respectively.