The application of Taguchi’s method in the experimental investigation of the laser sintering process

The selective laser sintering (SLS) of iron powder has been investigated through a number of experiments statistically planned as per Taguchi L8 design. Seven input parameters, namely, laser peak power density, laser pulse on-time, laser scan speed, stepping distance (distance traveled between pulses), interval–spot ratio (ratio of laser scan line interval and laser spot diameter), size range of iron powder particles, and powder layer thickness, were selected for the investigation. Density, porosity, and hardness were considered for the characterization of the sintered samples. Analysis of the results show that these properties are significantly affected by these factors. A discussion on the probable physical phenomena contributing to such dependence and an attempt towards the optimization of the process have also been included.     

LPE growth of InGaAsP:InP high purity layers using rare earth elements

Use of rare earth (RE) elements has allowed the growth of high purity InGaAsP:InP layers in liquid phase epitaxial (LPE) systems. Experiments show that purification of material takes place on account of interaction between the RE and mainly group VI donor impurities.     

Data integrity in an IGES description of turned part geometry

There is a growing interest in converting manually drawn engineering drawings into computer databases in a Computer Aided Design (CAD) format such as Initial Graphics Exchange Specification (IGES). This conversion is done by a high resolution scanning device. CAD drawings resulting from the scan-conversion process often contain discontinuities. A draftman using manual drafting equipment may adjust and reposition the ink pen for ease of drawing. This could cause breaks in the drawing, which, though unnoticeable to the human eye, are identified as discontinuities in the electronic scanning process. The subsequent CAD representation may then have broken geometries in place of continuous ones.

The work presented here is aimed at verifying the IGES file representing a scan-converted drawing. If any discontinuities are detected in the lines and arcs in the drawing, the breaks are mended. Algorithms are developed to identify and correct errors in the IGES files.

The algorithms are coded in Common LISP. The program runs on a VAX VMS system and can handle drawings of turned parts. This research is part of a larger project dealing with feature recognition of turned parts. Extension of the procedure to other geometries is straightforward. The program has been tested on some test drawings obtained from a scanning company. The results are very promising.     

Medium Access Control for ATM-to-CDMA Interface

An integrated medium access control framework for a direct sequence code-division multiple access (CDMA) radio access to an asynchronous transfer mode (ATM) network is considered. The system accommodates multimedia services such as voice and data. The inherently high error rate associated with the multipath fading channel is partly overcome by the introduction of a data link control layer employing one- and two-dimensional CRC codes for error detection/correction in voice and data packets, respectively. Analysis and simulations show promising average delay and error probability performance, as well as low coding redundancy. Two-dimensional CRC, particularly in conjunction with automatic repeat request (ARQ), outperforms convolutional coding with much less overhead and processing requirement at the ATM-CDMA interface.     

Krill herd and piecewise-linear initialization algorithms for designing Takagi–Sugeno systems

A method for designing Takagi–Sugeno fuzzy systems is proposed which uses a piecewiselinear initialization algorithm for structure generation and a metaheuristic krill herd algorithm for parameter optimization. The obtained systems are tested against real data sets. The influence of some parameters of this algorithm on the approximation accuracy is analyzed. Estimates of the approximation accuracy and the number of fuzzy rules are compared with four known methods of design.     

Performance analysis of charge plasma based dual electrode tunnel FET

This paper proposes the charge plasma based dual electrode doping-less tunnel FET (DEDLTFET). The paper compares the device performance of the conventional doping-less TFET (DLTFET) and doped TFET (DGTFET). DEDLTEFT gives the superior results with high ON state current (I_ON ～ 0.56 mA/μm), I_ON/I_OFF ratio ～ 9.12 × 10¹³ and an average subthreshold swing (AV-SS ～ 48 mV/dec). The variation of different device parameters such as channel length, gate oxide material, gate oxide thickness, silicon thickness, gate work function and temperature variation are done and compared with DLTFET and DGTFET. Through the extensive analysis it is found that DEDLTFET shows the better performance than the other two devices, which gives the indication for an excellent future in low power applications.     

TiN coating on an electrical discharge machined WC-Co hardmetal: surface integrity effects on indentation adhesion response

Electrical discharge machining (EDM) is an alternative-shaping route for manufacturing complex component shapes of hard and brittle materials such as hardmetals (WC-Co cemented carbides). It is well established that in these materials EDM typically induces a heat affected surface layer with poor integrity. This degradation effect may be compensated through specific post-EDM surface treatments either by thermomechanical means or material surface deposition. In the latter case, a key property for optimal performance is the level of coating to substrate adhesion and how this is affected by the EDM-induced surface. The main objective of this investigation was to evaluate the adhesion strength of TiN coatings on EDMed hardmetals. A series of hardmetal samples that had been subjected to different multi-pass sequential EDM levels were coated with TiN. Adhesion behavior was assessed using the indentation adhesion test and comparing the critical load for crack extension (P _c) and the interfacial fracture toughness (K _Ic,interface) to those exhibited by the TiN coating deposited on a ground and polished substrate (used as baseline control). Experimental results indicated that indentation adhesion increased with finer-executed EDM, almost reaching baseline level values. The results are discussed on the basis of the compromising EDM influence on both surface integrity of the substrate and tortuousness at the interface, the latter resulting in mechanical anchoring of the TiN coating to the hardmetal substrate.     

Effect of blends of Palm-Jatropha-Pongamia biodiesels on cloud point and pour point

To minimize use of biodiesels synthesized from edible oils like Palm due to raising food versus fuel issue, Palm biodiesel (PBD) was blended with biodiesels derived from tree borne non-edible oil seeds Jatropha, and Pongamia to examine the effect on cloud point (CP) and pour point (PP) of PBD. Dependence of CP and PP on esters of fatty acid composition was also examined. Good correlations between CP and palmitic acid methyl ester (PAME) and between PP and PAME were obtained. A correlation between CP and total unsaturated fatty acid methyl ester (X) was also obtained and correlation between PP and X was also determined. Using these four correlations, cloud and pour points of different biodiesel blends can be determined.     

Structure and high-temperature stability of compositionally graded CVD mullite coatings

Dense, uniform and crack-free mullite (3Al₂O₃·2SiO₂) coatings were deposited on SiC by chemical vapor deposition. The coatings were compositionally graded, with the Al/Si ratio increasing towards the outer surface of the coatings for improved corrosion resistance. The coatings were found to start out as a nanocrystalline layer, which is an intimate mixture of γ-Al₂O₃ nanocrystallites imbedded in a vitreous silica-rich matrix at the substrate/coating interface. Mullite grains nucleated when the surface composition of the growing coating was in a narrow range close to that of stoichiometric mullite. The phase transformations occurring in these coatings during high-temperature anneals in the range 1100–1400 °C were studied. These phase transformations, which include a tetragonal-to-orthorhombic transformation, mullitization and devitrification of silica in the nanocrystalline layer, and -alumina precipitation and twinning of the alumina-rich mullite, are discussed in light of the adhesion and corrosion resistance of the coatings.