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Vol. 17 (2016), No. 4 (50), November 2016

 

This issue of the RECENT® journal was edited with the support of:

CONTENTS



  • Bogdan BARABAȘ, Tudor DEACONESCU

Hydroabrasive Machining Process Optimization through Statistical Analysis and Robust Design

» Abstract

Hydroabrasive jet cutting process has demonstrated its application need, thanks to the flexibility and simplicity. The objective of this research is optimization of the processing with hydroabrasive jet through the use of robust design of manufacturing processes. Implementing the method in parameterization of abrasive jet cutting, like statistical analysis performed, demonstrates the applicability of the proposed solution, namely, increasing of hydroabrasive processing efficiency by using robust design. Parameters proposed to be enhanced are dimensional accuracy and surface roughness, resulting from the processing with hydroabrasive jet. Parameters of process influence is changed in order to optimize, revealed the importance of their values correct elections and interdependence between them. The obtained results have confirmed the importance of exactly configuration of these input parameters, based on statistical analysis and robust design.

» Keywords

abrasive water jet cutting, robust design, hydro abrasive process optimization

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  • Sorin BARABAȘ, Adriana FLORESCU

Analysis of Contact Stresses Occurred Between Rolling Elements of Large Bearings with Hollow Rollers Provided with Automatic Lubrication System

» Abstract

Bearings lubrication in wind power assemblies, which have permanent operation in difficult conditions with high variability of both, the load and speed, is a problem widely studied because of difficulties arising. Lubrication process is influenced by geometry of raceway, temperature, rotation speed, static and dynamic loads, type and quantity of lubricant. All these factors determine the quality of process with consequences on wear, lifetime and efficiency of energetic assembly. A correct lubrication film lubrication between moving parts, reduce direct contact. Also it is studied an innovative model of lubrication system mounts in the hollow cylindrical rollers, controlled by an automated system. Comparison of tensions occurred in cylindrical rollers with hollowness and rollers provided with covers allow favorable conclusions. Finite element analysis was performed with Nastran software.

» Keywords

hollow roller, automatic lubrication, finite element analysis

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  • Nicolae BOIAN

Small Business Financial Management Optimization Model

» Abstract

The scientific financial management is one of the main important leverage that small companies can successfully used in competition with the large ones. Starting from a strategic financial management model specific to SME, this paper presents a method to optimize it with the final goal of improving business sustainability. Optimization method is developed in four directions: cost, stocks & receivables, investments and risk aiming at increasing profitability and financial balance of business. Cost optimization method requires both scientific determinations, which mean establishing consumption and cost calculations, and cost analysis, which involves the calculation of efficiency indicators on different cost categories. Stocks and receivables optimization method require a balance within current resources allowing continuity of production and financial flows that means to minimize working capital requirements (NFR) and ensuring rotational speeds of receivables under the current level of debt in terms of minimum liquidity values. Financial management of investments optimization method aimed to achieve a balance of permanent resources allowing performing investments without affecting the financial current cycle that means a level of working capital (FR) over at the investment. Business risk management optimization method aimed diminishing share of fixed and financial costs in operational result formation. Finally, an example of applying the method is presented and draws conclusions.

» Keywords

optimization, financial management, cost

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  • Imed BOUFEDJ, Azzedine BOUZAOUIT, Rachid CHAIB

Architecture Optimization of a Neural Network Model to Identify Defects of Rotating Machines

» Abstract

The objective of our work is to propose an approach for the development of a surveillance system against vibration faults of rotating machinery. This approach is based on the choice of a neural network architecture optimized, taking into account the activation functions used to know; the log type sigmoid function ‘logsig’ and the hyperbolic tangent sigmoid function type ‘tansig’ on one side, and another side, the type of learning algorithm. We considered eight '8' vibratory defects, the indicators chosen as variables of neural network inputs are: the spectral power density 'PSD' and the spectral energy density 'DSE'. The error function used to compare the output of neural networks optimized architecture compared to the expected output is the mean square error 'MSE'. Also by adopting a compromise between performance and the execution time. The number of inputs (independent variables) of the optimization process was optimized by Taguchi method. The adapted neural model and the proposed architecture have increased the probability of network convergence in significant time. The results show the feasibility and efficiency of the neural model used to approximate the cutting process.

» Keywords

optimization, vibration monitoring, neural networks, correlation coefficients, Levenberg-Marquardt, error gradient

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  • Romeo CIOARĂ

Kinematic Structures for Processing of Surfaces with a Circle Directrix and a Straight-Line Generatrix (Part V)

» Abstract

In modern industrial society, maximum importance comes to machines manufacturing with machine tools manufacturing as one of its main pillars. The machine tools are used for producing the majority of components of various industrial equipment and consumer goods, including the components for building new machine tools. Each part is characterised by one or more surfaces, simple or complicated, as the case may be. A well-known theory of surface generation asserts that any surface is characterised by a directrix and a generatrix, as well as by at least one modality of their physical achievement by means of the tools and machines deployed for processing. The evolution of industrial knowledge and practice over the last decades calls for the further development of this theory, such as to eliminate certain inadvertencies or limitations bound to create confusion, as well as to include an essential part that addresses the kinematics of machine-tools in a systematic and explicit manner. At present this latter part is not found either as integrated into the theory of surface generation, or as a distinctive theory, what determines but a weak connection to the theory of linkages and in general to the theory and practice of machine-tools. The present paper, as well as previous ones on similar topics, proves the kinematic synthesis of machine tools to be a necessary development and a natural part of the theory of surface generation. The paper exemplifies a set of particular cases, characterised by a programmed circle directrix and a straight-line generatrix obtained by any known modality of generation.

» Keywords

directrix, generatrix, kinematic structure, linkages, machine-tool, kinematic synthesis

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  • Tudor DEACONESCU, Andrea DEACONESCU

Applications of Pneumatic Muscles Developed within the Festo National Fluid Actuation and Automation Training Centre in Brasov

» Abstract

Pneumatic muscles are increasingly used for the actuation of robot or general industrial systems due to their benefits compared to pneumatic cylinders. The deployment of pneumatic muscles in rehabilitation equipment developed for the upper and lower limbs has been a concern of the Festo National Fluid Actuation and Automation Training Centre at Transilvania University of Braşov. The paper presents and discusses a number of constructive solutions devised for such rehabilitation equipment designed to ensure a swift and cost efficient social and workplace reintegration of the patients. The rehabilitation equipment discussed in this paper achieve the mobilisation of the lower limb bearing joints, as well as of the wrist, knuckles and elbow by continuous passive motion. The diagrams of principle and of actuation of such equipment are presented, the developed prototypes and their performance. The absolute novelty brought by such equipment consists in the utilisation of the pneumatic muscle as actuator, what ensures a light and highly compliant structure that satisfies the safety requirements related to interaction with humans.

» Keywords

Pneumatic muscles, rehabilitation equipment, continuous passive motion

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  • Raluca DAICU, Valentin DIŢU

Innovative Method to Reveal the Roughness of Land Surfaces at Sharpening Twist Drills

» Abstract

The specialty literature highlights the fact that the land surface roughness at regrinding cutting tools influences the life of the cutting edge. In order to reveal the roughness of land surfaces it is used, innovatively, the electrical current at cutting. It is known the fact that at cutting metals with metallic edges it appears an electrical current caused, mainly, by the temperature in the cutting zone. Because the temperature in the cutting zone shows how the cutting process develops and the resulted electrical current appreciates with accuracy the temperature, results that the analysis of the electrical current at cutting is a diagnosing method due to the ability to be measured with precision. The paper shows the influence of land surfaces roughness at twist drills on the electrical current at cutting, fact that leads to an easily reveal of roughness.

» Keywords

cutting, drilling, electric current (thermocurrent), roughness

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  • Uppalapati GAYATRI, Gunji SRINIVASARAO, Malkapuram RAMAKRISHNA

Fabrication and Testing of Composite Material made of Prawn’s Shell Powder

» Abstract

Prawn’s are an extremely good source of protein, yet are very low in fat and calories, making them a very healthy choice of food. In this article, we have discussed about the use of the bio-degradable wastes as a composite material. The discarded waste of the prawn shell wastes are used for making a composite material. Composite material consists of matrix and reinforcement. In this article, the particulate reinforcement used is prawn shell powder and the matrix used is lapatoxy - SP 100 resin along with hardener (MYK LATICRETE). The reinforcement used is prawn shell powder is mixed to the matrix taken in the fixed ratios. In this article, the composite material is fabricated and is tested for hardness. It is a discarded waste that can be easily available in the environment. Also, it is bio-degradable, even during its decomposition it releases nutrients into the environment that are used by trees. These composites cause no harm to nature and are eco-friendly. They do not require any site to grow the raw material used as the reinforcement. They possess high strength, toughness, can withstand loads, hardness etc. Composite materials are a substitute for conventional plastics and possess higher mechanical properties than those materials.

» Keywords

composite material, prawn shell powder, MYK Laticrete - latapoxy resin and hardener, strength of composite materials

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  • Ionuț IONESCU, Ioan CIOBANU, Sorin Ion MUNTEANU, Tibor BEDO, Aurel CRIȘAN, Mihai Alin POP, Maria STOICĂNESCU

Calculation of Desired Coefficients for the Characteristic Equation of Closed Automatic Control System

» Abstract

At the solidification of rotationally symmetrical parts, which require small casting cores (diameter of core comparable with the part wall thickness) the hot spots are positioned at the interface casting - core. Due to casting geometry, most often, they do not use lateral feeder. Using direct feeders create problems caused by the cores fixture in the mold and the appearance of micro shrinkage areas into part, under the feeder. A study on the possibility of shrinkage elimination in such parts is presented. The study is conducted by computer solidification simulation. Seven versions of casting were studied. There were examined the possibility to direct the solidification of the alloy inside the part - feeder system by thermal insulated core, by coolers or by technological additions. There are analyzed the shrinkage position, the amount of liquid alloy in feeder, available to feed the casting during solidification, and the yield of liquid alloy used at casting.

» Keywords

alloy solidification, solidification simulation, casting, shrinkage, feeder

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  • Ion NEAGOE

Combined Blank Holding Deep Drawing Die Adaptable on Single Action Presses

» Abstract

Deep drawing is one of the extensively used sheet metal processes in the industries for mass production of cup components. One direction of research in this area is to obtain higher drawing ratio in order to reduce the number of drawing operations necessary to obtain a product. One way to increase the drawing ratio is the use combined blank holding deep drawing dies. However, these dies have a complex construction and require double-action presses. The paper presents the design of combined blank holding deep drawing die, adaptable on single action presses, which eliminates the above disadvantages.

» Keywords

deep drawing, combined blank holding, simple action press

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  • Gabriela PASCA PASCARIU, Vladimir MĂRĂSCU-KLEIN

Specific Consumption Efficiency in Tourism Industry

» Abstract

The algorithm for calculating the specific consumptions (SC) is an innovative application for the tourism industry, restaurants and similar units (bars, pizzerias, fast-food units, snack-bars and other public food service units). The determination of the consumptions is obtained through the production recipes, named „New/modified product chart”. These contain all the raw materials of the product on sale in the restaurant, in the established quantities for each material, including the loss coefficients. According to the loss coefficients of raw materials, one can estimate the weight of the final product of the prepared food without actually weighing it. According to the acquisition price of the raw materials and the quantities used in the recipes, the F&B systems (Food&Beverage) automatically calculate the price of the final product. A declared trade margin is added to the price from the system, thus obtaining the sale price of the product, or, according to the imposed sale price, a new quota is calculated.

» Keywords

bettering, specific expenditures, algorithm, food products

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  • Cristian PISARCIUC

Application of Production Management Methods for Improving Manufacturing Processes

» Abstract

The paper presents several stages developed in order to improve the production quality of an impeller by using Six-Sigma-DMAIC methodology. The paper highlights the importance of implementing, in the area of production, of management activities seen from Lean Six-Sigma point of view, as instruments for activities improvement. It involves a number of techniques, which lead, in case of correct implementation, to stable processes based on eliminating defects and reducing variation. Combining Lean instruments with the ones for reducing variations (Six Sigma) determines, in the end, not only elimination of errors but also preventions further of errors. In the case analysed, the large number of scraps is leading to delays in product delivery to customers. As documented not only process identification but also practical changes in manufacturing process is the key to delays and scraps reducing.

» Keywords

DMAIC, impeller, balancing, scraps, delays

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