Modelling and multi-response optimization of hole sinking electrical discharge micromachining of titanium alloy thin sheet

Thin sheets of titanium alloys are widely used in aerospace and automotive industries for specific applications. The creation of micro holes with requisite hole quality in thin sheets of these alloys using energy of electric discharge is a challenging task for manufacturing engineers. Hole sinking electrical discharge micromachining (HS-EDMM) is one of the most promising micromachining processes to create symmetrical and non-symmetrical micro holes. The present paper is related to selection of optimum parameter settings for obtaining maximum material removal, minimum tool wear and minimum hole taper in HS-EDMM. In this paper an attempt has been made to develop an integrated model (ANN-GRA-PCA) of single hidden layer back propagation neural network (BPNN) for prediction and grey relational analysis (GRA) coupled with principal component analysis (PCA) hybrid optimization strategy with multiple responses of HSEDMM of Ti-6Al-4V. Experiments have been conducted to generate dataset for training and testing of the network where input parameters consist of gap voltage, capacitance of capacitor and the resulting performance parameters are represented by material removal rate (MRR), tool wear rate (TWR), and hole taper (T_a). The results indicate that the integrated model is capable to predict and optimize process performance with reasonable accuracy under varied operating conditions of HS-EDMM. The proposed approach would be extendable to other configurations of EDMM processes for different materials.     

Efficacy of indirect haemolysis test in the diagnosis of human brucellosis

The authors report one operated case of traumatic sternal segmental dislocation in a child, and propose a mechanism for this uncommon lesion. A fourteen year old boy was admitted in emergency for anterior chest pain, occurring during an exercise in parallel bars without any fall. X ray showed traumatic dislocation of the upper sternal segment. After 12 hours, because of bad clinical tolerance (pain, dyspnea with sweats and disphagia) reduction and plate stabilization (Senegas plate) was performed with immediate pain relief. The boy returned to school after 10 days. Plate was removed two months later after healing, with good clinical and radiological results. According to rare published cases, conservative treatment can be proposed in very young children because of dislocation remodeling. By others, in case of bad tolerance, surgical treatment is suggested despite the inconvenient of device's removal. The originality of this case is the indirect lesion mechanism. Hypothesis is given by authors. Treatment by plate is easy and gives immediate pain relief with good clinical and radiological results in teen-agers.     

Reduction of Mutual Coupling in Metamaterial Based Microstrip Antennas: The Progress in Last Decade

Compact multiple antennas are attracting much attention because of the rapid growth of the wireless multiple input multiple output communication systems. An important challenge in multiple antenna system is mutual coupling effects. A brief review of reduction of mutual coupling in antenna arrays by using metamaterial is presented. Different types of metamaterial structures like electromagnetic band gap substrate, defected ground structure, split ring resonator, complimentary split ring resonator, soft surfaces/high impedance surface and mender line structure are described along with their operational principles. Whereas the problems associated along with the comparison and comments on their scope of applications are analyzed.     

Finite element analysis of temperature distribution in single metallic powder layer during metal laser sintering

The metal laser sintering (MLS) is used to make strong or hard metallic models for tools and dies directly from metallic powders. Thermal distortion is the serious problem after cooling of the solidified part rapidly. Uncontrolled temperature distribution in the metallic powder layer leads to thermal distortion of the solidified part. The study of temperature distribution within the metallic layer during MLS is important from the quality of the layer point of view.The high temperature generated in the powder layer leads to thermal distortion of the part and causes thermal as well as residual stresses in the part. In this paper the powder layer is assumed to be subjected to plane stress type of temperature variation and a transient finite element method-based thermal model has been developed to calculate the temperature distribution within a single metallic layer during MLS. A finite element code has been developed and validated with the known results from the literature.The obtained results of temperature distribution show the temperature and temperature gradient variation along X- and Y-axis. The effect of process parameters such as laser power, beam diameter, laser on-time, laser off-time and hatch spacing on temperature distribution within a model made of titanium during MLS is studied. The results computed by the present model agree with experimental results. Temperature increases with increase in laser power and laser on-time but temperature decreases with increase in laser off-time and hatch spacing.     

Condition monitoring studies on spindle bearing of a lathe

In modern industry, machinery must become increasingly flexible and automatic. In order to increase productivity, enhance quality and reduce cost, machine tools have to work free of any failure. When a failure occurs in a machine tool, it is necessary to identify the causes as early as possible. Machine tool condition monitoring is very important to achieve this goal. Condition monitoring is generally used on the critical subsystem of any machine tool. This paper endeavors to focus on the condition monitoring aspects on the machine tool element. In the present study, a critical subsystem has been identified based on the failure data analysis. Condition monitoring techniques like vibration monitoring, acoustic emission, Shock Pulse Method (SPM) and surface roughness have been successfully used for fault identification.     

Design of horn for rotary ultrasonic machining using the finite element method

The cutting performance of an ultrasonic machining machine (USM) depends primarily on the ability of the design of the acoustic horn (also known as concentrator or tool holder). A horn is a waveguide-focusing device with a cross-sectional area that decreases from the transducer end to the toe end. It amplifies the input amplitude of vibrations so that at the output end the amplitude is sufficiently large for machining. In the present work, a finite element method (FEM) design procedure has been developed for the design of a horn for rotary ultrasonic machining (RUM). The double conical horn shape has taken as a domain with a hole at the tip for the cooling purpose. The analysis of the various stress components in the horn domain has been studied. The stresses at the middle of the horn are found to be maximum but it is within the allowable stress of the horn material due to the sudden change in the area of the horn. The stresses on the horn for various frequencies are also studied and concluded that at resonance condition the stress is minimum.     

Finite element prediction of material removal rate due to traveling wire electrochemical spark machining

Manufacturing engineers are facing new challenges during machining of electrically nonconducting or partially conducting materials such as glass, quartz, ceramics, and composites. Traveling wire electrochemical spark machining (TW-ECSM), a largely unknown technology, has been applied successfully for cutting these types of materials. However, hardly any theoretical work has been reported related to machining performance of TW-ECSM process. The present work is an attempt in this direction. In the present work, a 3-D finite element transient thermal model has been developed to estimate the temperature field and material removal rate (MRR) due to Gaussian distributed input heat flux of a spark during TW-ECSM. First, the developed code calculates the temperature field in the workpiece and then MRR is calculated using this temperature field. The calculated MRR has been compared with the experimental MRR for verifying the approach. Computational experiments have been performed for the determination of energy partition and spark radius of a single spark. The effects of various process parameters such as energy partition, duty factor, spark radius, and ejection efficiency on MRR have been reported. It has been found that MRR increases with increase in energy partition, duty factor, and ejection efficiency but decreases with increase in spark radius.     

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa₂SnO_5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa₂SnO_5·5 has a complex cubic perovskite (A₂BB’O₆) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa₂SnO_5·5 are in a range suitable for its use as substrate for microwave applications. YBa₂SnO_5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa₂SnO_5·5 substrate gave aT _c(0) of 92 K and a critical current density (J _c) of 4 × 10⁴ A/cm² at 77 K. A screen printed BiSCCO thick film on YBa₂SnO_5·5 substrate gaveT _c(0) = 110 K and current density 3 × 10³ A/cm² at 77 K.     

Fracture of a tin-lead eutectic alloy in Region III of superplastic flow

With the aid of scanning electron microscopy, cavitation and fracture behaviour in the Sn-Pb eutectic alloy, whose reduction in area of cross-section before failure is close to 100%, has been investigated in Region III of superplastic flow (where both the elongationto-fracture and the strain-rate sensitivity index decrease with increasing strain rate). It has been demonstrated that, although it decreases, grain-boundary sliding persists in this range as the strain rate is increased. At all strain rates the final failure was due to tearing by plastic flow of the inter-cavity ligaments, but the interlinkage of cavities along the graininterphase boundaries decreased with increasing strain rate. The features of cavitation and fracture did not differ much from an earlier study on a pseudo-single phase copper alloy, although copper alloys usually fail non-ideally, i.e., a large area of cross-section is present at fracture.     

Modeling and Simulation of Cylindrical Electrochemical Magnetic Abrasive Machining Process

Cylindrical Electrochemical Magnetic Abrasive Machining (C-EMAM) is an advanced abrasion-based hybrid machining process that constitutes magnetic abrasive machining and electrochemical dissolution. During the C-EMAM process, a large amount of material is removed from the peaks of the surface irregularities under the simultaneous effect of electrochemical dissolution, abrasion and abrasion-passivation synergism. This article presents the mathematical modeling for material removal and surface roughness during the C-EMAM process. Magnetic potential distribution between the two magnetic poles in which a cylindrical workpiece was placed was calculated using the finite element method. It was further used to find the forces acting on the ferromagnetic particles at contact surfaces. An empirical relation has been also developed considering the effect of electrochemical dissolution and abrasion-passivation synergism based on experiments conducted on a self-developed C-EMAM setup. Finally, a surface roughness model was developed by considering the total volume of material removed with the assumption of a triangular surface profile. The simulated results for material removal and surface roughness were validated using self-conducted experimental results. The computed results were found to be in good agreement with experimental observations.