Experimental Design Matrix Research Articles

Genetic algorithm for optimization of welding variables for height to width ratio and application of ANN for prediction of bead geometry for TIG welding process

This paper explains an integrated method with a new approach using experimental design matrix of experimental designs technique on the experimental data available from conventional experimentation, application of neural network for predicting the weld bead geometric descriptors and use of genetic algorithm for optimization of process parameters. The properties of the welded joints are affected by a large number of welding parameters. Modeling of weld bead shape is important for predicting the quality of welds. In an attempt to model the welding process for predicting the bead shape parameters (also known as bead geometry parameters) of welded joints, modeling and optimization of bead shape parameters in tungsten inert gas (TIG) welding process has been tried in the present work. Multiple linear regression technique has been used to develop mathematical models for weld bead shape parameters of TIG welding process, considering the effects of main variables as well as two factor interactions. Also by using the same experimental data, an attempt has been made to predict the bead shape parameters using back-propagation neural network. To optimize the process parameters for the desired front height to front width ratio and back height to back width ratio, genetic algorithmic approach has been applied.

The effects of superchilled storage at −2 °C on the microbiological and organoleptic properties of cold-smoked salmon before retail display

The aim of this study was to investigate the impact of superchilling (−2 °C) on the evolution of Listeria monocytogenes and organoleptic characteristics of cold-smoked salmon samples. An Hadamard matrix experimental design was carried out on artificially inoculated samples stored at +4 °C for 10 d and at +8 °C for 18 d to know the influence of four factors: salt content, strain, cold stiffening and superchilling time, on the level of L. monocytogenes in cold-smoked salmon. The growth of L. monocytogenes in naturally contaminated cold-smoked salmon and the organoleptic properties were investigated under superchilling conditions. Superchilling (−2 °C for 28 d) had a limited impact on some of the organoleptic properties but the level of L. monocytogenes at the end of the shelf-life (4 °C for 10 d and 8 °C for 18 d) could exceed the microbiological criterion set by the European legislation.

An Experimental Design Matrix that Prevents Narrow Minds in Design Education

An Experimental Design Matrix that Prevents Narrow Minds in Design Education

Performance Optimization Control of ECH using Fuzzy Inference Application

Electro-chemical honing (ECH) is a hybrid electrolytic precision micro-finishing technology that, by combining physico-chemical actions of electro-chemical machining and conventional honing processes, provides the controlled functional surfaces-generation and fast material removal capabilities in a single operation. Process multi-performance optimization has become vital for utilizing full potential of manufacturing processes to meet the challenging requirements being placed on the surface quality, size, tolerances and production rate of engineering components in this globally competitive scenario. This paper presents an strategy that integrates the Taguchi matrix experimental design, analysis of variances and fuzzy inference system (FIS) to formulate a robust practical multi-performance optimization methodology for complex manufacturing processes like ECH, which involve several control variables. Two methodologies one using a genetic algorithm tuning of FIS (GA-tuned FIS) and another using an adaptive network based fuzzy inference system (ANFIS) have been evaluated for a multi-performance optimization case study of ECH. The actual experimental results confirm their potential for a wide range of machining conditions employed in ECH.

RSM-based optimisation for the processing of nanoparticulate SOFC anode material

The relationship between porosity and electronic conductivity of a Nickel-Yttria Stabilised Zirconia (Ni/YSZ) material was investigated using the Response Surface Methodology (RSM) technique. This advanced material is intended for use as the anode of a Solid Oxide Fuel Cell (SOFC). Tests were structured around a central composite design of experiments matrix. Ni/YSZ specimens were fabricated via a powder processing route, using precursor powders of nickel oxide (NiO) and YSZ, mixed with graphite that acts as a pore former. Porosity and conductivity measurements were performed on the material in the as-sintered stage as well as after the reduction process. Statistical analysis was performed using selected process parameters (sintering temperature and amount of graphite pore former) as input variables and porosity and conductivity as outputs. The contour plots obtained from the RSM technique were used to study the trend of porosity and conductivity. The results indicate that the porosity values decrease significantly beyond a certain sintering temperature, while the electronic conductivity increases significantly. A super-imposed porosity-conductivity contour plot was used to determine the optimal region for the desired porosity volume and conductivity value.

Methodology for Assessing Safety-Critical Systems

A simple methodology to evaluate a variety of architecture designs for safety-critical systems is presented. The approach involves including all the appropriate components in a representative fault tree. Evaluating the fault tree results in the cutsets, the system availability, and the system reliability. Next, a Monte Carlo simulation that includes parameters such as mean time to repair and repair time distributions is applied to the fault tree. The parameters included affect the total downtime of the system and impact the system usability. Design of experiments (DOE) is used to track the parameters and the associated levels. The inputs for the Monte Carlo simulation can be adjusted from the elements in the DOE matrix and the results for those variables can be evaluated. Using the DOE methodology allows ranking the results according to their impact on the responses (number of failures, downtime, relative costs, and so on). Using these responses, a figure of merit is assigned to each design. The figure of merit is used to compare the alternative designs and determine the optimal one to implement. This paper uses an example of a simple sensor–controller–actuator system designed with multiple levels of redundancy to illustrate the methodology and the application of the figure of merit to compare the considered architectures.

PT and INR Interference by the Antibiotic Daptomycin in Commercial Thromboplastin Reagents: Dependence on Phospholipid Composition.

The antibiotic, daptomycin (brand name Cubicin, Cubist Pharmaceuticals) is approved in the US for treatment of complicated skin and skin structure infections caused by gram-positive pathogens (e.g., MRSA, methicillin-resistant Staphylococcus aureus). Recently, this antibiotic has been shown to interfere with prothrombin time (PT) assays, resulting in a prolongation of clotting times and artificial increases in the INR (International Normalized Ratio). The level of interference varies with Daptomycin concentration in the plasma, the brand of prothrombin time reagent as well as the type (normal or abnormal) of patient sample being analyzed. The bactericidal action of the antibiotic is known and is through a depolarization of bacterial membranes in the presence of physiologic calcium (Silverman, et al, Antimicrobial Agents and Chemotherapy, Aug 2003); therefore, daptomycin interference with the PT clotting assay is likely mediated through the phospholipid component of the thromboplastin formulations. To examine the dependence of daptomycin interference for a number of commercial PT formulations, testing was performed with daptomycin spiked samples of normal pooled plasma as well as abnormal samples from oral anticoagulant therapy (OAT) patients. For spiked normal samples, a small degree of prolongation in clotting times was observed with most PT reagents, with one reagent showing a significant prolongation. In OAT samples spiked with Daptomycin, the PT prolongation was greater for all formulations, with the one reagent again showing greater prolongation as for the normals. Ultimately, this variation in response was attributed to differences in phospholipid composition among the reagents, supported by previous studies of daptomycin with neutral and acidic phospholipids in the presence of calcium (D. Jung, et al., Chemistry and Biology, Jul 2004). A four-dimensional experimental design matrix was constructed using a mixture of four synthetic phospholipids (DOPC, DOPS, DOPE and DOPG), and the relationship of daptomycin-PT interference to percent composition of the phospholipids was examined. In both normal and OAT plasmas spiked with daptomycin, the major contributor to PT prolongation was the concentration of DOPG (phosphatidylglycerol) in the lipid mixture, with additional contributions correlated with DOPC (phosphatidylcholine). Because of the ubiquitous use of these phospholipids in commercial PT formulations, this work suggests that daptomycin interference should be assessed for each combination of PT reagent and INR range used.

A novel fabrication method for the mold insert of microlens arrays by hot embossing molding

AbstractThis paper reports a simple and novel procedure for fabricating the mold insert of microlens arrays. In this paper, an L9 experimental matrix design based on the Taguchi method is constructed to optimize the replication quality of molded microlens arrays. The results of the statistical analysis indicate that the processing temperature is the principal parameter affecting the sag height of the molded microlens array. The 200 × 200 arrays of molded microlens, with a diameter of 150 μm, a pitch of 200 μm and a sag height of 31.51 μm have been successfully fabricated. The average surface roughness of the Ni mold insert is 6.916 nm. The average surface roughness of the molded microlens array is 4.608 nm. The processing temperature is the most important factor for the radius of curvature of molded microlens. POLYM. ENG. SCI. 46:1797–1803, 2006. © 2006 Society of Plastics Engineers.

Temperature changes in dental pulp associated with use of power grinding equipment on equine teeth

To quantify the temperature changes in the dental pulp associated with equine dental procedures using power grinding equipment. A matrix experimental design with replication on the same sample was followed to allow the following independent variables to be assessed: horse age (young or old), tooth type (premolar or molar), powered grinding instrument (rotating disc or die grinder), grinding time (15 or 20 seconds) and the presence or absence of water coolant. Sound premolar and molar teeth from a 6-year-old horse and a 15-year-old horse, which had been removed postmortem, were sectioned parallel to the occlusal plane to allow placement of a miniature thermocouple at the level of the dental pulp. The maximum temperature increase, the time taken to reach this maximum and the cooling time were measured (n=10 in each study). The teeth were placed in a vice and the instrument used on the tooth as per clinical situation. Significant differences were recorded for horse age (P < 0.001), instrument type (P < 0.001), grinding time (P < 0.001) and presence or absence of coolant (P < 0.001). There was no significant difference for tooth type. Thermal insult to the dental pulp from the use of power instruments poses a significant risk to the tooth. This risk can be reduced or eliminated by appropriate selection of treatment time and by the use of water irrigation as a coolant. The increased dentine thickness in older horses appears to mitigate against thermal injury from frictional heat.

Application of Statistic Estimation to Weldline Strength of Injectionmolded Thermoplastic Composites

The injection molding of thermoplastic composite materials has become an important process in industry, due to the possibility of producing near shape article having exceptional physical and mechanical properties. However there are still some problems that confound the overall success of this technology. The forming of weldlines wherever polymer flow fronts meet is one of them. In this report, an L’18 experimental matrix design based on the Taguchi method was conducted to study the effect of different processing parameters on the weldline strength of injection-molded thermoplastic composites. Experiments were carried out on a 4.1 oz reciprocating injection molding machine. The materials used were acrylonitrile–butadiene–styrene, and 20 and 30% glass-fiber-filled ABS composites. A plate cavity with an obstacle in the center was used to create a weldline. After molding, the weldline strength of the composites was determined by a tensile tester. Various processing variables were studied in terms of their influence on the weldline strength of injectionmolded composites: melt temperature, mold temperature, melt filling speed, melt filling pressure, packing pressure, and size of the obstacle. For the factors selected in the experiments, size of obstacle and melt temperature were found to be the important parameters affecting the weldline strengths of injection-molded composites. The weldline strength of virgin material increased with the distance from the obstacle, while the weldline strength of composites decreased with the distance.

The Influence of Processing Parameters on Thin-Wall Gas Assisted Injection Molding of Thermoplastic Materials

Thin-wall gas assisted injection molding of thermoplastics has become an important process in industry because of its light weight, relatively lower resin cost per part, and faster cycle time. This report is devoted to investigate the effects of different processing parameters on the length of gas penetration in thin-wall gas assisted injection molded parts. The first part of this report is to find ways to optimize the gas penetration of molded parts. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the processing parameters that affect the length of gas penetration in thin-wall gas assisted injection molded parts. The second part of this report is to identify the relative significance of each processing parameter on the gas penetration of molded products. Two materials were used in the study: an amorphous acrylonitrile-butadiene-styrene (ABS), and a semi-crystalline polypropylene (PP). Experiments were carried out on an 80-ton reciprocating injection molding machine equipped with a high pressure gas injection unit. A plate cavity of various thicknesses (0.6, 1.2 and 2.0 mm) with a gas channel across the center was used for the experiments. After molding, the length of gas penetration in the molded parts was determined. For ABS materials, melt temperature and gas pressure were found to be the principal parameters affecting the thin-wall gas assisted injection molded parts, while for PP materials, the gas pressure and gas injection delay time were found to be the key processing parameters. In addition, warpage of molded parts was found to decrease with the length of gas penetration.

Learned dynamics of reaching movements generalize from dominant to nondominant arm.

Accurate performance of reaching movements depends on adaptable neural circuitry that learns to predict forces and compensate for limb dynamics. In earlier experiments, we quantified generalization from training at one arm position to another position. The generalization patterns suggested that neural elements learning to predict forces coded a limb's state in an intrinsic, muscle-like coordinate system. Here, we test the sensitivity of these elements to the other arm by quantifying inter-arm generalization. We considered two possible coordinate systems: an intrinsic (joint) representation should generalize with mirror symmetry reflecting the joint's symmetry and an extrinsic representation should preserve the task's structure in extrinsic coordinates. Both coordinate systems of generalization were compared with a naïve control group. We tested transfer in right-handed subjects both from dominant to nondominant arm (D-->ND) and vice versa (ND-->D). This led to a 2 x 3 experimental design matrix: transfer direction (D-->ND/ND-->D) by coordinate system (extrinsic, intrinsic, control). Generalization occurred only from dominant to nondominant arm and only in extrinsic coordinates. To assess the dependence of generalization on callosal inter-hemispheric communication, we tested commissurotomy patient JW. JW showed generalization from dominant to nondominant arm in extrinsic coordinates. The results suggest that when the dominant right arm is used in learning dynamics, the information could be represented in the left hemisphere with neural elements tuned to both the right arm and the left arm. In contrast, learning with the nondominant arm seems to rely on the elements in the nondominant hemisphere tuned only to movements of that arm.

Correlations between operating conditions, microstructure and mechanical properties of twin wire arc sprayed steel coatings

An experimental design matrix was set up in which carbon steel coatings were deposited with a twin wire arc spray gun (TAFA 9000™), using either compressed air or nitrogen as spraying gas. The coating's mechanical properties were studied. Some correlations were made between these properties, spraying conditions and the microstructure of the deposits. Young's modulus was estimated by the single beam method using finite element modeling. Results show that direct relationships do exist between spray conditions, oxide content in the coating and microhardness. Young's modulus of the coatings depends on the lamella thickness and the oxide content. When increasing the compressed air flow rate, Young's modulus increases at first because smaller particles and finer lamellae were made and it decreases later because of a higher oxide content. The increase of nitrogen flow rate lowers the oxide content and increases Young's modulus.

An empirical study of gas penetration in full-shot gas-assisted injection moulded parts

Full-shot gas-assisted injection moulding has increasingly become one of the most important methods used to produce plastic components. It has the advantage of eliminating the switchover mark, which usually occurs on the surface of short-shot gas-assisted injection moulded parts. This paper is devoted to an investigation of the effects of different processing parameters on the length of gas penetration in full-shot gas-assisted injection moulded parts. The first part of this report shows how the gas penetration of moulded parts is optimized. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the processing factors that affect the length of gas penetration in full-shot moulded parts. The second part of this paper identifies the relative significance of each processing parameter on the gas penetration of moulded products. The materials used were general-purpose polystyrene and polypropylene. Experiments were carried out on an 80 ton injection-moulding machine equipped with a high-pressure nitrogen gas injection unit. For the factors selected in the main experiments, melt temperature, gas injection delay time and gas hold time were found to be the key processing parameters affecting the length of gas penetration in full-shot gas-assisted injection moulded parts. In addition, the sink mark of full-shot moulded parts decreases with the length of gas penetration. Bending strength of full-shot gas-assisted injection moulded parts is higher than that of short-shot moulded parts.

Reliability studies and design improvement of mirror image CSP assembly

In this paper, both simulation and testing techniques were used to address the reliability issue of mirror chip scale package (CSP) assembly. First, finite element modeling was employed to study the stress and strain of a mirror image CSP with comparison to a single-sided CSP. The study clearly illustrates that the strain distribution is not equally distributed across both sides of the CSP. The highest strain on one side of the mirror image CSP is often larger than the other one, which reduced the reliability of the package as a whole. In order to study the effects on the reliability of the mirror image CSP assembly, several parameters, such as PCB board materials selection, board thickness and warpage, PCB via design and routing, were investigated. Moreover, a design of experiment matrix was constructed to identify significant factors to minimize the highest strain in solder joints of mirror image. The test vehicle was then designed and assembled. Thermal cycling (0 to 100 °C) and thermal shock tests were thereafter performed to the mirror image CSPs and single-sided CSPs to compare with the simulation results.

An Empirical Study of the Surface Blush in Gas-Assisted Injection Molded Parts

Abstract Gas-assisted injection molding of thermoplastic materials has become an important process in industry, because of its capability of producing parts that have thick and thin sections with a good structured rigidity. However, there are some unsolved problems that confound the overall success of this technique. Surface blush of the molded parts caused by glossy difference of the materials is one of them. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the surface blush of gas-assisted injection molded thermoplastics. The material used was black-pigmented polypropylene. Experiments were carried out on a 4.1 oz reciprocating injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. A plate cavity with gas channels of different geometry was used to mold the parts. After molding, the surface quality of the parts was characterized by a gloss-meter. For the factors selected in the main experiments, mold temperature and gas pressure were found to be the principal factors affecting the surface quality of gas-assisted injection molded parts. The surface glossy difference increases with the content of the pigment in the materials. In addition, a trapezoidal gas channel of small width was found to mold the parts with the least glossy difference. An aluminum mold helps reducing the surface blush in molded parts.

Optimization of the magnesium-solution phase catholyte semi-fuel cell for long duration testing

A magnesium semi-fuel cell (Mg-SFC) was investigated as an energetic electrochemical system for low rate, long endurance undersea vehicle applications. This electrochemical system uses a Mg anode, a sea water electrolyte, a Nafion membrane, a carbon paper cathode catalyzed with Pd and Ir, and a catholyte of hydrogen peroxide in a sea water/acid electrolyte. Unique to the approach described here is the use of a magnesium anode together with the introduction of the catholyte in solution with the sea water, thus operating as a semi-fuel cell as opposed to a battery. Five critical operating parameters were optimized using a Taguchi matrix experimental design. Using these optimized conditions, high voltage and high efficiencies were obtained during long duration tests.

Gastric evacuation in horse mackerel. I. The effects of meal size, temperature and predator weight

Gastric evacuation experiments were performed on horse mackerel Trachurus trachurus. A nearly full matrix experimental design with respect to the variables predator weight (&lt;10–400 g) meal size (up to 7·8% body weight) and temperature (10–20°) was covered with 0‐group smelt Osmerus eperlanus as prey. A general evacuation model without meal size as a variable was fitted to the data on wet weights as well as on dry weights by means of non‐linear regression technique. Two methods of data transformation, relative data and square root transformation, were applied to improve variance homogeneity. The most reliable model fit was achieved on dry weight data applying the square root transformation technique: image where St=stomach content (g wet weight) at time t after ingestion, S0=the initial meal size, W=predator (g wet weight), and T=temperature. The estimated coefficient of the exponential temperature function, δ=00·032, corresponds to a Q10 value of 1·4 which is outstandingly low in comparison with results on other species. However additional experiments to determine maximum daily food rations indicated that appetite in contrast to gastric evacuation is strongly temperature dependent.

Optimizing the Weldline Strength of Injection Molded Liquid Crystal Polymers

The injection molding of liquid crystalline polymers has become an important process in industry, due to its capability of producing near net-shape articles having exceptional physical and mechanical properties. There are still, however, some problems that confound the overall success of this technology. The forming of weldlines wherever polymer flow fronts meet is one of them, In this study, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of injection-molded liquid crystal polymers. Experiments were carried out on a 4.1 oz injection-molding machine. A plate cavity with an obstacle at the center was used to create a weldline. After molding, the weldline strength of the parts was determined by a tensile tester. Of the parameters selected in the main experiments, geometry of obstacle and polymer melt temperature were found to be the principal parameters affecting the weldline property of injection-molded thermotropics. The weldline strength of injection-molded parts decreased with the size of the obstacles. It is shown that by setting the optimum processing parameters, one will be able to mold LCP parts of the highest weldline strengths.

Application of the Taguchi Method to Optimize the Surface Quality of Gas Assist Injection Molded Composites

Gas assist injection molding of short glass fiber reinforced composites has become an important process in industry, because it enables the production of parts with thick and thin sections and with a good structural rigidity. However there are some unsolved problems that confound the overall success of this technique. Part roughness of the composites caused by inappropriate mold design and processing conditions is one of them. An L' 18 experimental matrix design based on the Taguchi method was conducted to optimize the surface quality of gas assist injection molded composites. The material used was a 35% glass fiber reinforced Nylon-6 composite. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. A float-shape mold cavity was used. After molding, the surface quality of the parts was characterized by a roughness meter. For the factors selected in the main experiments, melt temperature and gas injection delay time were found to be the principal factors affecting the surface quality of gas assist injection molded composites. Experimental investigation of a gas assist injection molding problem can help reveal the formation mechanisms of surface roughness, so that steps can be taken to improve the surface quality of molded parts.