Warm Working Research Articles

Springback reduction of aluminum sheet in V-bending dies

The springback is one of the major defects associated with sheet metal–forming industry. The objective of this study is to minimize the springback and the process variability in V-bending operation. In all, 11 process parameters, the bending angle, sheet thickness, material type, material texture, punch speed, punch holding time, sheet width, punch radius, lubrication, warm working, and repeat bending, have been considered, and their effect on springback has been studied. Based on Taguchi L12211 orthogonal array design, bending tests were conducted on two types of aluminum sheets (Al 1100 and Al 6061), and investigation was focused mainly on the effect of process variables on the springback. As springback is a process defect, the smaller the better signal-to-noise ratio is utilized in the optimization process. Based on the analysis of variance results, the percentage contribution of each factor to springback was calculated and optimum levels of entire factors were ascertained. The punch holding time, material type, and lubrication were found to be the most significant factors affecting springback. The combined effect of these parameters on springback was about 70%. From the confirmation tests, there has been significant improvement in the standard deviation of the mean value of springback.

Informational Ontology: The Meaning of Gilbert Simondon's Concept of Individuation

Abstract The French philosopher Gilbert Simondon (1924-1989) was the first true philosopher of information, yet heremains relatively unknown outside of his native France. This situation is curious, given the warm receptionhis work has received from a small group of internationally renowned thinkers. Simondon’s lifelong projectwas to expound the appearance of what I call an “informational ontology,” a subject that deserves to beaddresses at length. This article limits itself by focusing on three aspects of Simondon’s philosophy ofinformation. First, it situates Simondon within the French intellectual scene in post-World War II Europe toget sense of his cultural milieu. Second, it positions Simondon’s work in the context of the Americancybernetic tradition from which it emerged. Finally, it offers an exegesis of Simondon’s informationalontology, a radically new materialism that stands to change contemporary debates surrounding issues relatedto information, communication, and technology.

Non-uniform multiresolution analysis for surfaces and applications

Haar wavelet can exactly represent any piecewise constant function. Beam and Warming proved later that the supercompact wavelets can exactly represent any piecewise polynomial function in one variable, attaining higher level of accuracy by increasing the polynomial order of the supercompact wavelets. The approach of Beam and Warming, which is based on multiwavelets (family of wavelets) constructed in a one dimensional context, uses orthogonal basis defined over sequences of uniform partitions of [0,1]. The work of Beam and Warming has been recently extended by Fortes and Moncayo to the case of surfaces by using orthogonal basis defined over sequences of uniform triangulations of [0,1]2. In that work the authors propose applications to data compression and to discontinuities detection, but both applications have the constraint that it is necessary to know information (at least) at the vertex of the triangulation, and so the data must be uniformly distributed. In the present work we overcome this constraint by considering a multiresolution scheme based on non-uniform triangulations. We develop the multiresolution algorithms and present two examples of the application of the algorithms to compress data and to detect discontinuities of data sets which need not to be uniformly distributed.

Regularities of Grain Refinement in an Austenitic Stainless Steel during Multiple Warm Working

The structural changes that are related to the new fine grain development in a chromium-nickel austenitic stainless steel subjected to warm working by means of multiple forging and multiple rolling were studied. The multiple warm working to a total strain of 2 at temperatures of 500-900C resulted in the development of submicrocrystalline structures with mean grain sizes of 300-850 nm, depending on processing conditions. The new fine grains resulted mainly from a kind of continuous reactions, which can be referred to as continuous dynamic recrystallization. Namely, the new grains resulted from a progressive evolution of strain-induced grain boundaries, the number and misorientation of which gradually increased during deformation. In contrast to hot working accompanied by discontinuous dynamic recrystallization, when the dynamic grain size can be expressed by a power law function of temperature compensated strain rate as D ~ Z-0.4, much weaker temperature/strain rate dependence of D ~ Z-0.1 was obtained for the warm working.

Inhomogeneity Through Warm Equal Channel Angular Pressing

In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 °C may provide the most homogeneous microstructure after multi-pressing as long as the total number of pressing passes is four. This indicates that a lower temperature (in the range of warm working) is favorable for achieving an ultrafine-grained/nanomaterial with a more homogenous microstructure. In order to quantify the inhomogeneity in the cross section of the as-pressed sample, an inhomogeneity index has been defined. The results show an increase in the hardness in the first pass with significant inhomogeneous deformation and a transition toward a more homogeneous structure with subsequent passes.

Microstructure evolution during warm working of Ti–5Al–5Mo–5V–1Cr–1Fe at 600 and 800 °C

Microstructure evolution during compression to the true height strain 0.29, 0.69, or 1.2 at 600 and 800°C of the β-rich titanium alloy Ti–5Al–5Mo–5V–1Cr–1Fe (VT22) with an initial lamellar microstructure was established using scanning and transmission electron microscopy. It was found that microstructure evolution at both temperatures was controlled primarily by substructure evolution within the β phase. At 800°C, extensive recovery within the β phase resulted in the formation of a stable structure comprising subgrains ∼1.5μm in diameter. During deformation at this temperature, lamellae of the α phase fragmented via a boundary-grooving mechanism. Due to the sluggish diffusion kinetics, however, spheroidization at 800°C was incomplete. At the lower processing temperature, recovery processes within the β phase were much slower, leading to greater refinement of the β matrix. The decomposition of the metastable β phase during warm working, gave rise to very fine α-lath precipitates, which resulted in the formation of an ultrafine microstructure with a grain size of 0.5μm.

Effects of Warm Deformation on Mechanical Properties of TRIP Aided Fe-C-Mn-Si Multiphase Steel

Warm deformation tests were performed using a kind of tubby heater. The microstructures and mechanical properties of an Fe-C-Mn-Si multiphase steel resulting from different warm deformation temperatures were investigated by using LOM (light optical microscopy), SEM and XRD. The results indicated that the microstructure containing polygonal ferrite, granular bainite and a significant amount of the stable retained austenite can be obtained through hot deformation and subsequent austempering. Warm deformation temperature affects the mechanical properties of the hot rolled TRIP steels. Ultimate tensile strength balance reached maximum (881 MPa) when the specimen was deformed at 250°C, and the total elongation and strength-ductility reached maximum (38% and 28614 MPa · %, respectively) at deforming temperature of 100°C. Martensite could nucleate when austenite was deformed above M3, because mechanical driving force compensates the decrease of chemical driving force. The TRIP effect occurs in the Fe-C-Mn-Si multiphase steel at deforming temperature ranging from 15 to 350°C. The results of the effects of warm deformation on the mechanical properties of the Fe-C-Mn-Si multiphase steel can provide theoretical basis for the applications and the warm working of the hot rolled TRIP sheet steels in industrial manufacturing.

Grain boundary assembles developed in an austenitic stainless steel during large strain warm working

Abstract The evolution of strain-induced grain boundaries in a 304-type austenitic stainless steel during multiple warm forging was studied. The developed grain boundary distributions significantly depended on the processing temperature. The misorientation distribution of deformation boundaries that evolved after total strain of 4 at 500 °C is characterised by a sharp maximum against small angles below 10° and a flat‐type distribution with almost the same fractions for different misorientations for high-angle boundaries. On the other hand, two sharp peaks on the boundary misorientation distribution are developed after processing at 800 °C. One of them corresponds to low-angle subboundaries and the other results from twin boundaries with misorientations of 60°. The difference in the characters of strain-induced grain boundaries is associated with different mechanisms of dynamic recrystallization operating at 500 and 800 °C.

An analysis of the deformation characteristics of a dual phase twinning-induced plasticity steel in warm working temperature regime

The deformation behavior of a dual phase twinning induced plasticity (TWIP) steel has been studied by means of continuous heating compression (CHC) testing technique. This has been performed in the range of room temperature to 300°C (warm working regime) and the related experimental flow behavior has been compared with the theoretical ones. The derived deviations at 45±5°C, 100±5°C and 165±5°C have been properly addressed considering the related microstructural evolutions. The optical and scanning electron microscopy along with feritscope measurements have been carried out to explore the basis of any deviation. The results demonstrate the formation of ferrite at the austenite grain boundaries through deformation induced ferrite transformation mechanism. This effectively makes the structure softer at the initial stage of deformation (deviation i, 45±5°C). The initiation of twins within the austenite grains results in strengthening the structure and a small bump appears in the θ–ε curve (deviation ii, 100±5°C). In addition the responsible deformation mechanism of the steel is believed to change from mechanical twinning to dislocation slip at about 160°C thereby a local decrease in the rate of work hardening occurs (deviation iii, 165±5°C).

Dynamic Recrystallization Mechanisms Operating under Different Processing Conditions

Dynamic recrystallization (DRX) is one of the most important mechanisms for microstructure evolution during deformation of various metals and alloys. So-called discontinuous DRX usually develops in structural materials with low to medium stacking fault energy during hot working. The local migration, i.e. bulging, of grain boundaries leads to the formation of recrystallization nuclei, which then grow out consuming work-hardened surroundings. The cyclic character of nucleation and growth of new grains during deformation results in a dynamically constant average grain size. The dynamic grain size is sensitively dependent on temperature and strain rate and can be expressed by a power law function of flow stress with a grain size exponent of about-0.7 under conditions of hot working. Recent studies on DRX phenomenon suggest that a decrease in deformation temperature changes the structural mechanism for new grain formation. As a result, the grain size exponent in the relationship between the dynamic grain size and flow stress approaches about-0.25 under warm working conditions.

中炭素鋼の温間変形抵抗と加工材強度

The purpose of this study is to clarify the optimum approach to obtain high tensile strength after warm working, without increasing warm deformation resistance during warm working of medium carbon steel. Increase in warm deformation resistance during warm working by addition of Cr is small. On the other hand, Cr has the effect of suppressing the annihilation of dislocations in the air cooling process after warm working. Thus, by adding Cr, the tensile strength after warm working is effectively improved, without increasing warm deformation resistance during warm working. Increasing of Si is effective as a method to obtain high tensile strength after warm working, without increasing warm deformation resistance during warm working, too. Si has an effect of the solid solution hardening. This effect by increasing Si is due to the large temperature dependence of solid solution hardening effect. The control of microstructural factors, that are pearlite fraction and cementite spacing, is not effective as a method to obtain high tensile strength after warm working, without increasing warm deformation resistance during warm working.

Investigation on Formability of AISI 304 Circular Cups by Warm Deep Drawing

Deep drawing is one of the sheet metal forming processes used widely in industries like automobile, aerospace etc. In drawing operation, the limiting draw ratio (LDR) is used as an index of drawability of a material. In this investigation, stainless steel AISI 304 grade blanks of 1.0 mm thickness with different diameters are drawn into a circular cups in single stage. The experiments were conducted at room temperature as well as at temperatures 100oC, 200oC, and 300oC. The LDR values obtained in each condition were analyzed. The experimental results show that there is a significant improvement in LDR values by warm working.

Grain Refinement through Warm Rolling of Wedge-Shaped Low Carbon Steel

Study of grain refinement has developed to improving the mechanical properties of low carbon steel. Wedge shaped slab of low carbon steel were deformed through warm rolling methods of 500, 550, and 600oC to produce a finer ferrite grains. The thickness reduction of deformation is 80, 75, 67 and 50% .Dynamic recrystallizations were confirmed at warm working temperature in this study. Grains size which obtained through this process could improve the hardness and its mechanical properties and also its performance in corrosive environment. The smallest grain size was obtain from 80% deformation is 5.2 µm and the tensile strength is 817.65 MPa. Its gives the evidence that warm rolling can use to produce the fine grain at warm temperature of 600oC.

ADAPTATION AND SELECTION OF CULTIVARS OF GRAPEVINE FOR QUALITY WINES IN WARM CLIMATE

Currently, there is a general tendency to produce quality wines using international cultivars. These cultivars are considered malleable and universal because they adapted very well in different climatic and soil conditions. Nevertheless, this is causing a loss of originality and typicality on wines. To bet on autochthonous minority and local cultivars to produce quality wines lead to produce wines with terroir distinctive characteristic. These autochthonous cultivars need to prospect and collect over vine zones and study their behaviour. In Spain, prospecting research has been realized, as well as collection and study of autochthonous cultivars and so the vine sector have sufficient vegetable material to can cultivate them. In this paper the adaptation of several cultivars in a warm climate work has been studied. We present the results of agronomic and oenologic behaviour of six international cultivars (Cabernet sauvignon, Chardonnay, Gewurztraminer, Merlot, Sauvignon blanc and Syrah) and six autochthonous cultivars (Melonera, Moscatel de Malaga, Palomino fino, Tempranillo, Tintilla de Rota y Vijiriega), all of them cultivated in the Center of Research IFAPA Centro Rancho de la Merced (Jerez de la Frontera, Andalucia, Spain). This study has been realized from 2003-04 to 2007-08.

Deformation and temperature aided sintering during hooker extrusion of sintered PM preforms of steel

Warm hooker extrusions of sintered powder metallurgical preforms of steel were investigated at different temperatures ranging from room temperature to 773 K in steps of 100 K for strains of 0·87, 1·0, 1·14 and 1·3. The resident densities for extrusion were chosen from the formability limit diagrams generated at different temperatures, which demarcates the safe zone from fail zone. Microstructure characterisations vide pore closure revealed the possibility of deformation and warm working assisted sintering of preforms extruded at warm working temperatures. The rate of force/stroke (dF/dS) and ratio of actual force to theoretical force called correction factor φ for different temperatures were evaluated to substantiate the deformation and warm working assisted sintering. Hardness data of the extruded samples were measured to determine the densification. The extruded samples were analysed for the surface roughness along their length and the optimum temperature for extruding steel preforms for better properties were identified.

Grain Refinement in Commercial Purity Titanium Sheets by Constrained Groove Pressing

Grain refinement studies in titanium have gained significant interest owing to its importance as a biomaterial. Severe plastic deformation techniques have been widely applied for grain refinement in metals and are capable of producing ultra fine and nano sized microstructures. In this study, repetitive shear deformations by constrained groove pressing have been applied to commercial purity titanium sheets of 2 mm thickness at a warm working temperature of 300oC. Microstructure studies reveal the formation of elongated grains with widths of the order of 0.5μm from an initial grain size of 40μm in the annealed condition. An increase in strength is also observed.

Spheroidization of the lamellar microstructure in Ti–6Al–4V alloy during warm deformation and annealing

The spheroidization behavior of an α colony microstructure in Ti–6Al–4V alloy during warm working and subsequent annealing at 600 and 800 °C was established. The principal features of microstructure evolution were found to be temperature dependent. At 800 °C transformation of the lamellar microstrucuture into a globular one was associated primarily with the classical boundary splitting mechanism followed by further spheroidization of α particles by means of termination migration. For thick α lamellae, however, new grains were formed due to continuous dynamic recrystallization during deformation, but spheroidization per se was limited. A decrease in temperature to 600 °C resulted in increased shear strains, lower diffusivity, and a decrease in the volume fraction of the β phase. Consequently, the thin β interlayers transformed relatively quickly into separate particles while α became the matrix phase. Evolution of the α phase during deformation/annealing at 600 °C was associated with continuous dynamic recrystallization with only limited dynamic or static spheroidization. Static spheroidization kinetics during annealing following warm working were explained in the context of approximate models of boundary splitting and termination migration.

Effect of deformation temperature on microstructure and mechanical behaviour of warm working vanadium microalloyed steels

Plane strain compression tests of two V microalloyed steels and one plain C–Mn steel have been done to analyse the influence of the deformation temperature, in the warm working range, on the final microstructure and subsequent mechanical behaviour. In the case of V microalloyed steels, the reheating temperature has an effect on the amount of vanadium in solution prior to deformation. This factor influences the austenite evolution during warm deformation and the transformation during cooling. As a consequence, in the microalloyed steels complex multiphase microstructures are obtained that lead to a wide range of strength–toughness combinations. In contrast, in the case of the plain C–Mn steel minor effects are observed in the deformation range from 800 to 870 °C.

Temperature dependence of haemoglobin–oxygen affinity in heterothermic vertebrates: mechanisms and biological significance

As demonstrated by August Krogh etal. a century ago, the oxygen-binding reaction of vertebrate haemoglobin is cooperative (described by sigmoid O(2) equilibrium curves) and modulated by CO(2) and protons (lowered pH) that - in conjunction with later discovered allosteric effectors (chloride, lactate and organic phosphate anions) - enhance O(2) unloading from blood in relatively acidic and oxygen-poor tissues. Based on the exothermic nature of the oxygenation of the haem groups, haemoglobin-O(2) affinity also decreases with rising temperature. This thermal sensitivity favours oxygen unloading in warm working muscles, but may become detrimental in regionally heterothermic animals, for example in cold-tolerant birds and mammals and warm-bodied fish, where it may perturb the balance between O(2) unloading and O(2) requirement in organs with substantially different temperatures than at the respiratory organs and thus commonly is reduced or obliterated. Given that the oxygenation of haemoglobin is linked with the endothermic release of allosteric effectors, increased effector interaction is an effective strategy that is widely exploited to achieve adaptive reductions in the temperature dependence of blood-O(2) affinity. The molecular mechanisms implicated in heterothermic vertebrates from different taxonomic groups reveal remarkable variability, both as regards the effectors implicated (protons in tunas, organic phosphates in sharks and billfish, chloride ions in ruminants and chloride and phosphate anions in the extinct woolly mammoth, etc.) and binding sites for the same effectors, indicating multiple evolutionary origins, but convergent physiological functionality (reductions in temperature dependence of O(2) -binding affinity that safeguard tissue O(2) supply).

Effect of Chemical Composition on Secondary Hardening of WD1 Steel Used for Warm Work Dies

A new kind of die steel, WD1 used for warm work dies, was developed. The secondary hardening behavior and its affecting factors were studied. The results show that the secondary hardness increases with the content of C, Mo and V elements and Si element can significantly improve the secondary hardening effect though it’s not one of secondary hardening elements. The hardness of WD1 steel tempered at 520°C is more than HRC60, which can meet the requirements of warm work dies.