Wyniki wyszukiwania - Biblioteka Nauki

1

Experimental investigations and numerical models of tool steel during semisolid forming

100%

Macioł P. , Zalecki W. , Kuziak R. , Jakubowicz A.

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2011

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tom Vol. 11, No. 1

141-147

EN

The main aims of the work were to determine material characteristics of cold work tool steel, grade 21 OCR 12 in semisolid forming conditions, as well as developing of numerical model of this steel. Moreover, possibilities of application of Computational Fluid Dynamic methods and solid mechanics modelling techniques were tested. Methodology and results of experimental investigation is described. The results of experiments were then utilized for developing series of numerical simulations. Two sets of simulations are presented, based on the Computational Fluid Dynamics or solid mechanic modelling methods. Comparison of experimental and numerical results is presented, as well as comparison of CFD and structural mechanics based numerical models.

PL

Zasadniczym celem pracy było wyznaczenie charakterystyk stali narzędziowej 21 OCR 12, formowanej w warunkach stałociekłych, a także opracowanie modeli numerycznych dla tej stali. Ponadto, zweryfikowane zostały możliwości stosowania metod dynamiki płynów (Computational Fluid Dynamics, CFD) oraz metod modelowania odkształcania ciał stałych do modelowania procesów formowania w stanie stałociekłym. Opisane zostały metodologia oraz wyniki prac doświadczalnych. Wyniki te zostały wykorzystane do opracowania symulacji numerycznych. Przedstawiono symulacje oparte na metodach CFD oraz oparte na modelach ciał stałych. W pracy porównano wyniki osiągnięte za pomocą metod doświadczalnych i symulacyjnych, jak również porównano wyniki uzyskane z metod CFD i strukturalnych.

2

Modelling of thixoforming using CFD methods

100%

Macioł P. , Pietrzyk M.

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2009

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tom Vol. 76, nr 8

617-619

EN

Main advantages and disadvantages of thixoforming are presented in the paper. Materials, which are presently used for thixoforming are described, as well. A short review of numerical methods dedicated recently to thixoforming modelling, is also included, dividing them into two groups – structural and Computational Fluid Dynamic methods. Internal Variable Convection method, which combines main advantages of both groups, is introduced IVC. Numerical models of two tests, as well as results of computations are shown. The first it the test designed to determine a semi-solid metal viscosity with a rotational viscometer. The second one is a filling of a T-shape mould. Main disadvantages, as well as expected improvements of the presented software are described in the paper.

PL

W artykule opisano wady i zalety technologii tiksoformingu, a także materiały stosowane w tej technologii. Omówiono obecnie stosowane techniki modelowania komputerowego procesów tiksoformingu, uwzględniając ich podział na metody wywodzące się z modelowania odkształcenia ciał stałych i z dynamiki płynów. Zaproponowano metodę Konwekcji Zmiennej Wewnętrznej, łączącą zalety obu tych metodologii. Przedstawiono wyniki numerycznych symulacji doświadczeń wykonywanych w celu wyznaczenia lepkości metalu w stanie stało-ciekłym oraz symulacji wypełniania formy T-kształtnej. Omówiono najistotniejsze wady obecnego rozwiązania oraz możliwości ich wyeliminowania.

3

Tiksoforming produktów spożywczych

100%

Bakier S.

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2002

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tom Nr 4

14-15

PL

Wprowadzono termin „tiksoforming" w odniesieniu do produktów spożywczych. Oznacza on modyfikację struktury dwufazowego układu typu „semi—solid" przez oddziaływanie mechaniczne. W pracy badano wpływ ścinania i mieszania na skrystalizowany miód pszczeli. Strukturę oceniano z wykorzystaniem techniki mi-krointerferometrii. Wyniki doświadczeń ukazują możliwość modyfikacji struktury miodu przez zastosowanie procesu mieszania.

4

Influence of thixoforming on structure development of the tool steel

75%

Stankova H. , Klauberova D. , Ronesovs A. , Masek B.

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2007

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tom Vol. 28, nr 1-4

149-154

EN

Forming in the thixotropic state is one of the alternative forming methods, which allows producing semi-products with relatively complicated shape. The process is based on semi-product forming in the region between solid and liquid, where the material exhibits the thixotropic behaviour. This technology applies especially to higheralloyed steels, which are otherwise processed by pressure casting. Thixoforming runs in the die cavity. Among the advantages of this technology belongs the possibility to produce components with complicated shape in one step and to utilize lower forming forces. On the other hand, high forming temperatures and the narrow forming temperature interval can be considered as disadvantages. To reach the thixotropic behaviour necessary for obtaining the required component shape, the parameters of semi-solid state play an important role. These include, for example, the fraction of the liquid phase, the shape of solid particles and the location of the liquid phase in the structure. The tool steel was used for the development of an alternative forming process. The structures were observed using light and laser confocal microscopy. The fraction of liquid phase and the size of solid particles were evaluated via image analysis.

5

Analysis of the thixoability of ASTM A536 ductile iron

75%

Robert M. H. , Cristofolini R.

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2008

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tom Vol. 28, nr 2

115-122

EN

Purpose: Thixoability of the ASTM A536 nodular cast iron is analyzed, it meaning its ability to hold a thixotropic semi-solid state and to be formed as such. Thixoability can be characterized by the solidification range, fraction of primary phase and sensitiveness of liquid fraction with temperature (df1/dT) within the solidification range. It is also investigated the effect of thixocasting in the microstructure of the considered alloy. Design/methodology/approach: Differential thermal analysis, differential scanning calorimetry and thermodynamic calculation package THERMOCALC were used to predict transformations temperatures involving liquid formation and df1/dT within the solidification range. Microstructures of thixotropic slurries produced by partial melting were observed. Findings: Thixoforming of ASTM A536 nodular iron can be considered in a narrow window of about 28° C, were some dissolution of graphite nodules can still be afforded; this window meaning the range of temperatures of co-existence of austenite + graphite + liquid were the eutectic transformation is taking place. At higher temperatures the dissolution of graphite nodules in liquid can be significant. Research limitations/implications: Thixoability prediction models rely on sensitive experiments as thermoanalysis, with results strongly dependent on experimental conditions; and on thermodynamic data, sometimes not available or reliable for a specific alloy composition. Practical implications: The prediction of the thixoability of a certain alloy can make it more effective its thixoprocessing, allows better control of processing parameters and quality of final product; can also subsidize modifications in the alloy to make it more suitable to semi-solid processing. Originality/value: The study of the thixoability of a nodular hypereutectic cast iron is an original subject, not available in the specialized literature, however absolutely necessary if thixoprocessing of this family of alloys is to be considered.

6

Fizyczne i numeryczne modelowanie procesów formowania tiksotropowego

63%

Sołek K. P. , Kuziak R. , Białobrzeski A.

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2009

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tom z. 226

123-128

PL

W pracy zostały przedstawione, w formie opisowej, podstawowe rezultaty modelowania numerycznego oraz fizycznego procesów formowania tiksotropowego stopu aluminium A356 oraz stopu stali SW7M. Celem pracy jest identyfikacja podstawowych cech charakteryzujących płynięcie materiału w procesach kształtowania w stanie stałociekłym. Wiedza o zachowaniu materiału implikuje wytyczne jakie determinują opracowanie technologii w zakresie projektowania narzędzi oraz warunków procesów jakie się na tą technologię składają. Modelowanie numeryczne zostało wykonane z wykorzystaniem opracowanego w pracy modelu procesu w ramach oprogramowania komercyjnego FORGE3®. W modelu tym własności mechaniczne materiału, dla warunków występujących w procesie, zostały opisane z wykorzystaniem jednofazowego modelu występującego w prawie Nortona-Hoffa. Wartości parametrów tego modelu zostały wyznaczone z wykorzystaniem danych eksperymentalnych. Użyte modele materiałowe zostały opracowane przy pomocy testów materiałowych opartych na procesach wyciskania i spęczania wykonanych na symulatorze GLEEBLE. W oparciu o model numeryczny przeanalizowano szczegółowo powstawanie wad w postaci niekompletnych, przedwcześnie zakrzepniętych odlewów aluminium, jakie otrzymano w procesie wysokociśnieniowego odlewania. Odtworzenie zjawiska tych wad w oparciu o model numeryczny umożliwia zrozumienie zachowania materiału w rzeczywistych procesach tiksotropowych.

EN

Numerical simulations and experiments of aluminium and steel alloy thixoforming processes are discussed. The aim of the work is to detect the major features of the flow behaviour in semi-solid processing in order to improve in the future designing dies and selecting manufacture conditions. Commercial software FORGE3® is employed to carry out numerical simulations. A one-phase Norton-Hoff model is used to describe mechanical properties of the material during processing. Rheological parameters required for this model are determined using experimental data. The constitutive equations used are developed with the help of compression and extrusion tests executed on a machine GLEEBLE. Manufacturing of low-temperature incomplete casts using a pressure die casting machine is analysed in detail. It is shown that by comparing low temperature simulated casts with experimental casts one may learn important information on actual behaviour of the material during thixoforming.

7

Thixoinfiltration: a new approach to produce cellular and other low density metallic materials

63%

Robert M. H. , Jorge A. F. , Gatamorta F. , Silva R. R.

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2010

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tom Vol. 40, nr 2

180-187

EN

Purpose: the work presents an innovative approach for the production of cellular metallic materials as well as low density metal matrix composites, by using thixoforming techniques; thixotropic semisolid metal is infiltrated into removable and non-removable space holder preforms. Different kinds of preforms are tested to obtain open cell material (sponges), syntactic foams and low density composites. Products are evaluated concerning relative density and mechanical behavior under compressive stresses. Design/methodology/approach: Al alloy AA2011 was infiltrated in the semisolid state into preforms of sintered NaCl particles, sintered glass spheres, vermicular ceramic particles and porous ceramic granulates. After solidification, preforms were either removed by leaching (NaCl) resulting in open cell cellular product, or not (all others), resulting in composites of low density. Tomography tests were used to observe internal quality, and semi-static and dynamic compression tests were performed to evaluate the deformation ability of the material. Findings: results show that thixoinfiltration is a simple and low cost technique to produce different types of low density, porous material. Open cell material as well as syntactic foams and low density composites can be produced with reliable internal quality and dispersion of cells and reinforcement. Composites containing porous reinforcements can present some mechanical characteristics of the conventional cellular metals. Research limitations/implications: as all new developments, the complete understanding of the influence of processing variables upon the final quality of the product, as well as its consistency, must be provided before the technology can be widely used commercially. Practical implications: the technique can represent an alternative, low cost processing route for the fabrication of sponges, foams and low density composites, which can avoid restrictions and operational difficulties of presently available manufacturing processes based in liquid manipulation or powder sintering methods. Originality/value: infiltration of appropriate preforms by thixotropic metallic alloys to produce low density composites and cellular material is a new technique under development by the proposing group at FEM/UNICAMP.

8

Producing thixotropic semi-solid A356 alloy: microstructure formation x forming behaviour

63%

Robert M. H. , Zoqui E. J. , Tanabe F. , Motegi T.

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2007

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tom Vol. 20, nr 1-2

19-26

EN

Purpose: The work discuss the phenomena involved in the formation of the microstructure of semi-solid thixotropic alloy A356 produced by different techniques and the relation between microstructure and forming behaviour of the material. Design/methodology/approach: Thixotropic slurries of A356 alloy were produced from liquid and from solid conditions; in the first case either by stimulating nucleation rate or crystal multiplication during solid growth; in the second case by recrystallization and partial melting of deformed structures. Flow behaviour was analysed by viscosity measurements or by flow ability in forging operations. Findings: Results show that different production techniques activate different mechanisms, leading to distinct structure features in the semi-solid slurry, and, as consequence, in its forming characteristics. Techniques which promote formation of isolate globules of primary phase, like those involving nucleation stimulation and recrystallization, result in a semi-solid with better flowing behaviour. On the other hand, techniques based on crystal multiplication during growth lead to more interconnected globules in the slurry and poorer forming behaviour. Research limitations/implications: Semi-solid processing is suitable only for alloys with appropriate liquid fraction x temperature relation. Practical implications: the konowledge of the phenomena involved in the formation of thixotropic metallic slurries produced by different techniques, and their consequences in the material structure and flow behaviour, allow the decision of the adequate slurry production method for a specific application, in order to take the best advantage of the semi-solid technology. Originality/value: The analysis of the relation between production process x flow behaviour of semi-solid thixotropic A 356 is original.

9

Modelling of semi-liquid aluminium flow in extrusion

63%

Skorulski G. , Piwnik J.

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2007

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tom Vol. 7, iss. 2

31-36

EN

Experimental modeling using substitute materials is usually a simply way to obtain satisfacted results. This kind of experiment is characterizing by low cost. The significant results may be quickly applying using theory of probability. The way of modelling the deformation mechanisms during extrusion of aluminium alloys in semi - liquid phase, the way of preparing samples and experimental technique has been analysed in the following work. On the ground of received results (i.e. registrations of consecutive process steps) the grid of the flow velocity vectors on a flat sample surface was done. It allowed to draw conclusions which one of the basic deformation mechanisms is dominant in particular stage of the process. The technique of measurement has been shown as well. Experiments are made using plasticine and rape oil as a substiute materials. Some kind of different variants have been investigated. To ensure that such model experiments provide useful information it is essential to select model materials and prepare samples that would exhibit (preferably at room temperature) similar behaviour and similar deformation mechanisms as those present during the actual deformation process of aluminium alloys in a semi-liquid state. In particular the FLS, SS and PDS mechanisms should be adequately reproduced.

10

Modelling of semi-liquid aluminium flow in extrusion with temperature effect

63%

Skorulski G. , Piwnik J.

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2007

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tom Vol. 7, iss. 2

25-30

EN

During thixoforming, when the material is in the semi-liquid state, it exhibits thixotropic properties, i.e. the unsupported material remains stiff and holds its shape so it can be readily handled, but rapidly thins and flows like a liquid when sheared. It is this behaviour that is the key to the thixoforming process where material flows as a semi-liquid slurry into a die, as in conventional die-casting. Modelling the influence of the temperature distribution heterogeneity on deformation mechanisms during extrusion of the aluminium alloys in semi-liquid phase, the way of preparing samples and experimental technique has been analysed in the following work. There were made an analysis on the influence of the possible temperature distribution in recipient obtained during heating it on the extrusion process proceedings. The conclusions concerning stability of the process and appearing during it deformation mechanisms had been drawn on the ground of the received results. The plasticine and rape oil have been choosen as a substitute materials. Some kind of different variants have been investigated used a special experimental stand. The results of the tests presented below prove that the proposed technique can provide valuable insight into the material flow during deformation of aluminium alloys in the semi-liquid state and thus can give some guidance concerning the desirable temperature distribution within the workpiece.

11

Analiza właściwości reologicznych stali w stanie stało-ciekłym

63%

Korolczuk-Hejnek M. , Karbowniczek M. , Sołek K.

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2010

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tom Vol. 77, nr 9

464-467

PL

Głównym celem pracy była analiza właściwości reologicznych stali w stanie stało-ciekłym. Otrzymane wyniki zostały wykorzystane do opracowania modelu atematycznego lepkości pozornej. Znajomość własności reologicznych jest konieczna do przeprowadzenia numerycznego modelowania procesów technologicznych. Procesy kształtowania w stanie stało-ciekłym, nazywane również formowaniem tiksotropowym, są nowatorską metodą przetwórstwa stopów metali, posiadającą szereg zalet w porównaniu do klasycznych metod stosowanych w plastycznej przeróbce oraz odlewnictwie. W chwili obecnej prowadzi się szereg badań, których celem jest wdrożenie tej metody w przetwórstwie stopów stali [1, 2]. Zasadniczym osiągnięciem tej pracy jest wykorzystanie do pomiaru lepkości stali wiskozymetru specjalnie zaprojektowanego do badań materiałów w skrajnie wysokich temperaturach. W pracy przedstawione zostały wyniki analizy reologicznej stali narzędziowej z gatunku NC11 (EN X210Cr12). Analiza została przeprowadzona przy wykorzystaniu wiskozymetru rotacyjnego z nieruchomym cylindrem zewnętrznym.

EN

The main objective of this work was an analysis of the rheological properties of steel in the semi-solid state. The results were used for development of the mathematical models of the apparent viscosity. A knowledge of the rheological properties is crucial for numerical modeling of technological processes. Shaping in the semi-solid state, also called thixoforming processes, is innovative method of processing of metal alloys, having a lot of advantages in comparison with the classical metal forming and foundry processes. Nowadays, some research are conducted which goal is the practical application of this method in steel processing [1,2]. The main result of this work is the application of the viscometer, which was specially designed for the material tests executed in extremely high temperatures, in the measurement of steel viscosity. This paper presents the results of the rheological analysis of X210Cr12 (PN NC11) tool steel. It was performed using a rotational viscometer with a stationary external cup.

12

Investigations on the suitability of some ferrous alloys for semi-solid processing

63%

Robert M. H. , Galdino A. G. S.

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2009

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tom Vol. 34, nr 2

188-195

EN

Purpose: the work analyses the thixoability of SAE 1070, SAE 1548 and SAE 4340 steels; the possibility of producing thixotropic semi-solid by partial melting of these alloys and the phase transformations taking place during the process. Design/methodology/approach: thixoability was characterized by differential scanning calorimetry (DSC) to determine transformation temperatures involving liquid formation and dfl/dT within the solidification range. Thixotropic slurries were produced by heat treatments at different temperatures above Ts, and distinct holding times. Microstructures were analysed by RX diffractometry, optical and electronic microscopy and EDS microanalysis. Findings: results show that the three alloys investigated present high thixoability, given by wide solidification ranges associated with affordable sensitivity of liquid fraction with temperature within these ranges. Higher thixoability is presented by SAE 1070, followed by SAE 1548 and SAE 4340. Results show also that is perfectly feasible the production of thixotropic slurries of all investigated alloys, by simply heating to temperatures where a liquid phase can be present. Spheroidisation of solid primary phase is fast and increasing holding time at the semi-solid temperature leads to excessive growth of the globules in the thixocast material. Research limitations/implications: thixoability prediction models rely on sensitive experiments as thermoanalysis, with results strongly dependent on experimental conditions; and on thermodynamic data, sometimes not available or reliable for a specific alloy composition. Practical implications: the prediction of the thixoability of a certain alloy can make it more effective its thixoprocessing, allows better control of processing parameters and of the quality of final product. The viability of producing thixotropic semi-solid of ferrous alloys by simple partial melting can definitively insert these families of metallic alloys in the semi-solid processing field. Originality/value: ferrous alloys have become part of the thixoforming scenario more recently, when compared to aluminium and magnesium alloys. Therefore, the study of the thixoability of three commercial steels can bring important information as far as their utilization in thixoforming processing is concerned.

13

The application of Thermodynamic calculations for the semi-solid processing design

51%

Sołek K. , Kuziak R. M. , Karbowniczek M.

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2007

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tom Vol. 52, iss. 1

25-32

EN

Semi-solid metal processing is now a commercially successful manufacturing route producing lots of near net-shape parts. One member of such processing technologies is thixoforming which is based on the special behaviour of alloys with non-dendritic microstructure in the partially liquid state. The semi-solid processing design requires the use of faithful values of thermodynamic material properties. Thermodynamic modelling is a potential tool for predicting alloy compositions suitable for thixoforming. Thixoformable alloys must have a wide melting range with some additional feature. Namely, the slope of the curve of the liquid fraction versus the temperature should be low at the liquid fraction value of 40%. The data from thermodynamic calculations might be also applied in the industrial thixoforming processes design. It is very helpful to find different thermal properties of alloys in order to simulate precisely the temperature distribution inside the formed materials. The thermodynamic calculations allow one to find the heat transfer coefficient, the specific heat value and the latent heat value. The purpose of the present paper is to provide examples of the numerical modelling of the thermodynamic properties for commercial, industrial Al alloys. All the calculations in the present work are performed using JMatPro software. The determination of the phase composition for multi-component alloys is originally based on the Gibbs energy minimisation. Furthermore, the conditions of the non-equilibrium solidification are determined using the Scheil-Gulliver equation. An additional advantage of the software used is the possibility of calculation of the formation conditions for metastable phases which have also an influence on the mechanical properties of the alloys.

PL

Procesy przetwórstwa metali w stanie stało-ciekłym są nową, sprawdzoną komercyjnie, metodą precyzyjnego kształtowania dużej ilości elementów. Przykładem takiej technologii jest formowanie tiksotropowe, właściwością którego jest specyficzne zachowanie formowanych stopów posiadających niedenndrytyczną mikrostrukturę w częściowo ciekłym stanie. Projektowanie procesów formowania w stanie stało-ciekłym wymaga użycia prawidłowych wartości własności termodynamicznych materiałów. Modelowanie termodynamiczne jest potencjalnym narzędziem opracowania składu chemicznego stopów odpowiednich dla formowania tiksotropowego. Tiksoformowalne stopy muszą posiadać szeroki zakres temperatur krzepnięcia. Ponadto, nachylenie krzywej ułamka fazy ciekłej w zależności od temperatury powinno być jak najmniejsze dla wartości 40% tego ułamka. Wyniki obliczeń termodynamicznych mogą mieć również zastosowanie w trakcie projektowania przemysłowych procesów formowania tiksotropowego. W szczególności symulacje rozkładu temperatury wewnątrz formowanego materiału wymagają znajomości wartości jego właściwości termo-fizycznych. Obliczenia termodynamiczne pozwalają, między innymi, wyznaczyć współczynnik wymiany ciepła, ciepło właściwe czy ciepło przemiany fazowej. Celem tej pracy jest przedstawienie przykładów zastosowania modelowania numerycznego własności termodynamicznych przemysłowych stopów aluminium. Wszystkie obliczenia zostały wykonane z wykorzystaniem oprogramowania JMatPro. Wyznaczenie składu fazowego dla wieloskładnikowych stopów zostało oparte na minimalizacji energii Gibbs’a. Ułamek fazy ciekłej w warunkach nierównowagowego krzepnięcia został wyznaczony w oparciu o równanie Scheil-Gulliver’a. Dodatkową zaletą wykorzystanego oprogramowania jest możliwość przewidywania warunków powstawania metastabilnych faz, które maja wpływ na właściwości mechaniczne stopów.

14

Manufacturing of cellular A2011 alloy from semi-solid state

51%

Robert M. H. , Delbin D.

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2007

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tom Vol. 24, nr 1

115-122

EN

Purpose: The work presents a new method to produce cellular metallic material by pressing the alloy in the thixotropic semi-solid state into a layer of space holder particles, which are removed from the product after the forming operation. Design/methodology/approach: It is investigated the influence of the thixoforming temperature and the size of space holder particles, in the ability of penetration of the slurry in the porous preform as well as the structure of the obtained porous material (general aspect, quantitative and qualitative characterization of porosity microstructure of cells walls and density of the product). Findings: Cylindrical samples presenting three different ranges of porosity were produced. The cellular material obtained contains open porosity, being characterized as sponge. Products were analyzed by tomography and metallographic techniques. Results show that the proposed process is able to produce acceptable porous material, in a simple and low cost technique. The quality of the product depends rather on the processing temperature than on the size of space holder particles. Low liquid fraction in the thixotropic slurry can lead to incomplete infiltration and deformation of the preform. In the analyzed conditions influence of the size of space holder particles could be observed neither in the processing ability nor in the quality of the product. Density of produced porous material increases as processing temperature increases, due to the increase of cells walls thickness. Research limitations/implications: The investigated process is suitable only for alloys with a significant solidification range. Practical implications: The new method to produce cellular metals can represent energy savings and is highly operational when compared to conventional methods based on liquid infiltration, since lower temperatures are involved and no need of liquid handling is required. Originality/value: the process proposed is a new one; no techniques based on thixoforming of the alloy into porous preforms are known so far.