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Recent 25

Vol. 10 (2009), No. 1 (25) March 2009

The 25th issue of RECENT journal was edited and multiplied with support of:

  • Romanian Association for Nonconventional Technologies

  • Transilvania University of Brasov, Romania

  • Brasov County Council (by Scientific Activities, Education, Culture, Cults Committee)


CONTENTS


  • Tibor BEDO, Ioan CIOBANU, Vlad MONESCU, Aurel CRIŞAN, Sorin Ioan MUNTEANU

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RESEARCH ON THE EFFICIENCY OF THERMALLY INSULATED FEEDERS

» Abstract. The paper discusses the influence of thermal insulation of feeders on the solidification of cast parts. The employed method was computer simulation of alloy solidification. Several casting variants were analyzed involving cores including thermally insulated materials at the superior part of the feeders. The solidification time was determined, as well as the position of the hot spot in the part - feeder system. Further an estimated analysis was conducted on the economic effect of feeder thermal insulation.

» Keywords: casting, solidification, feeder, hot spot, cast iron


  • Romeo CIOARĂ

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SIMPLIFYING THE KINEMATIC STRUCTURE OF MACHINE-TOOLS – A REQUIREMENT OF SUSTAINABLE DEVELOPMENT

» Abstract. Although to date no sufficiently accurate methods are available to quantify the environmental impact of material consumption, the positive effect of its reduction on the global costs of industrial goods production is evident. Consequently the minimization of material consumption is one of the main directions of ecological design. In current research this orientation is known as “dematerialization actions”. Numerous industrial goods are manufactured on machine-tools. Machines are made to a large extent from metal, including material, energy and –to an insufficient extent yet – information. Their functions are achieved mostly by material bearers of specific information, typically over-dimensioned, obtained by means of environment-aggressive technologies. In the case of machine-tools dematerialization needs to be achieved by reducing their total mass and implicitly by reducing resource consumption. This path is beneficial from both the manufacturing and, particularly, the environmental aspects. In addition, the paper shows that machine-tool dematerialization can be accompanied by a significant increase of their performance and applicability. The discussed example is that of a complex cylindrical gear shaping machine-tool with disk cutters. In order to achieve an additional function – gear cutting also along a non-circular contour – by itself a complex one, the traditional approach would be increasing the kinematic complexity of the machine, materialized by a in increased number of components (parts), thus an increased material consumption. A modern solution is based on a different materialization of information in machines manufacturing; thus most information are not materially included in machine parts, but are transferred by an adequate electronic system. The number of components of such a new machine is even smaller than that of the initial machine, used as a reference.

» Keywords: machine-tools, sustainable development, gear cutting, dematerialization, kinematics


  • Aurel FRATU, Jean-François BRETHÉ, Mariana FRATU

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INDUSTRIAL ROBOTS IN A FLEXIBLE ASSEMBLY SYSTEM

» Abstract. This paper describes the virtual assembly automation systems, as decision support systems, for the better knowledge of assembly operation. The study of this procedure is described as well as the necessity for assembly systems design. The work draws on research into product and manufacturing knowledge models, and uses a case study based on a simplified assembly line realized in Delphi programming medium.  The use of the virtual prototype suggests itself as the starting point to develop the real system. Based on this model, the authors developed a systematic procedure by means of Delphi language. The authors describe results obtained in their investigation concerning the virtual prototype of the flexible assembly system.
The paper describes with enough detail the adopted solutions used to perform those tasks, giving special attention to the software designed to supervise the system. To support robot work simulation, a simulator environment is developed. In this paper, the authors have proposed a virtual prototype model for assembly system architecture of robotic assembly automation and propose to extend this virtual model to prepare drive automation systems.

» Keywords: flexible assembly systems, virtual robotic assembly systems, assembly automation


  • Ivelin V. IVANOV, Svetlana PASKALEVA

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BLANK-HOLDER FORCE OPTIMIZATION FOR IMPROVING THE STABILITY OF DEEP DRAWING

» Abstract. The explicit finite element method is utilized to simulate the sheet-metal deep drawing process of a flanged cup. The problem is time scaled for more computational efficiency of the simulation. The results of the simulation are compared with experimental results as well as with the results of another implicit finite element simulation for validation. A lot of explicit finite element simulations are used to determine the technological window for the blank holder force and the blank thickness. Investigating the range of blank thickness deviation, it appears to be good choice for objective function corresponding to the process stability. An optimization problem is formulated for searching a stable and reliable forming process with constraints for wrinkling and fracture. The optimal solution is found with high efficiency by an automated computer procedure.

» Keywords: deep drawing, explicit finite element method, optimization, stability of manufacturing processes


  • Aurel LUNGULEASA

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QUICKLY DETERMINING OF WATER SORPTION AND SWELLING FOR SPRUCE

» Abstract. The paper presents two main aspects of spruce wood behavior in moist environment, namely the water sorption and the thickness swelling. It presents the working method and results of fulfilling researches. Finally on the base of obtained results it is drawn a cumulative diagram which makes possible the quick determination of two features of spruce wood.

» Keywords: spruce, water sorption, thickness swelling, wood samples


  • George NICOLAE

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MEASUREMENT METHOD FOR DETERMINING ELECTROMAGNETIC FIELD ATTENUATION IN NANOMATERIALS USING THE TEM CELL (1st Part)

» Abstract. This paper presents the results of experimental determinations concerning electromagnetic field attenuation in materials containing micro-particles of iron, graphite or carbon black in their structure. In order to determine the shielding effectiveness of electromagnetic absorbents to electromagnetic field, a measuring system based on the TEM cell was proposed and tested. This measurement system was used to determine the electromagnetic shielding properties of materials at frequencies ranging between 1MHz and 1000 MHz. The paper presents both the measuring method and the methodology adopted in order to obtain maximum measurement accuracy. The experimental investigations were conducted in the frame of the CNCSIS project No 429/2006 ”Study of shielding properties of materials obtained by nano-technologies and nano-processing with application in electrical and electronic equipments in order to improve the quality of the environment”.

» Keywords: shielding effectiveness, attenuation measurement system, shielding materials, nano-materials


  • Rumen NIKOLOV, Todor TODOROV

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DYNAMICAL SYNTHESIS OF OSCILLATING SYSTEM MASS-SPRING-MAGNET

» Abstract. On the basis of a qualitative analysis of nonlinear differential equation, which describes the behavior of the oscillating system mass-spring-magnet, a dynamical synthesis is performed. The magnetic force is obtained using the finite element method and approximated by an analytical expression. The parameters of the system which ensure periodical oscillations with given properties are determined.

» Keywords: nonlinear dynamics, qualitative analysis, phase portrait, separatrix, magnetic force, FEM


  • Tudor PĂUNESCU

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STATISTICAL PREDICTION OF THE TWO-HOLE TWO-PIN LOCATING ACCURACY

» Abstract. The mechanical assembly method of two pieces having: one two parallel holes, the other two pins, is often used when have to achieve a high position and orientation accuracy. The prediction of the assembly accuracy is a one of the indispensable stages in design process. In this paper the geometrical tolerances are involved, the RFS tolerancing (the geometry tolerance is applied regardless of its feature size), a mathematical model of the geometric errors and the associate algorithm are proposed, the results of the Monte Carlo simulations are presented and analysed. The weights of the errors factors are analysed and based on its several design recommendations are indicated.

» Keywords: CAD, Monte Carlo simulation, statistical geometrical design, tolerance analysis


  • Ciprian SZABO, Ioan CIOBANU, Daniel FERARU, Aurel CRIŞAN

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OPTIMIZATION OF FEEDER DESIGN FOR THE CASTING OF A “SUPPORT”

» Abstract. Optimized design of feeders in the casting of parts is based on the comparison of several technological variants. The optimized variant is established by taking into consideration part quality and manufacturing cost. Priority needs to be assigned to qualitative aspects. The paper exemplifies the compared analysis of three variants of feeder design for the casting of a given part. The method of the real solidification modulus was applied for the analysis of technologies from the viewpoint of part solidification. The efficiency (index) of liquid alloy utilization in casting was calculated in view of economic analysis.

» Keywords: casting, solidification, simulation, feeder


  • Dragomir VRAZHILSKI

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DYNAMIC MODELING OF A VIBRATING SEPARATOR WITH INERTIAL EXCITATION CONSIDERING GYROSCOPIC EFFECTS

» Abstract. Subject of this work is examination of vibrating separator dynamical behaviour under directed inertial force excitation provided from synchronous spinning of two unbalanced shafts. For that purpose a dynamical model representing the separator as system of three rigid bodies and seven degrees of freedom is created, gyroscopic couples resultant from unbalanced shafts spinning are accounted. With this model are performed numerical experiments for area of small forced displacements around the static equilibrium position. Time and frequency domain characteristics are obtained.

» Keywords: spatial oscillations, dynamical modeling, vibrating separator, FFT, gyroscopic effects


 

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