Die Aperture Research Articles

Room-temperature plastic behavior and formability of a commercially pure titanium: Mechanical characterization, modeling, and validation

Data on the room temperature behavior of titanium is limited. To assess the anisotropy of the plastic behavior of a commercially pure grade 2 hcp–titanium T40 for different strain paths, in this study both uniaxial tests in various orientations with respect to the rolling direction as well as bulging tests using different die apertures were conducted. Under uniaxial tension, the plastic anisotropy in yielding is moderate, while the anisotropy in plastic strains is very strong. The material also displays tension–compression asymmetry, irrespective of the orientation the flow stress in compression being higher than in tension. The bulging tests data, namely the evolution of the thickness with the fluid pressure complemented with post-test DIC measurements reveal that T40 has unusual deformation and failure characteristics as compared to common materials with cubic crystal structure. Irrespective of the die aperture, instabilities occur suddenly, the reduction in thickness being drastic (snap failure). However, the evolution of strains depends on the die aperture aspect ratio (hemispherical vs. elliptical). The anisotropy of the titanium T40 also leads to a different response depending on the orientation of the material axes with respect to the die axes. To explain these specific characteristics of the behavior of titanium T40 under bulging, two orthotropic criteria were used, one that neglects the tension–compression asymmetry of the material (Hill, 1948) and another that accounts for the combined effects of anisotropy and tension–compression asymmetry (Cazacu et al. (2006) yield criterion). Determination of the parameters involved in both criteria was done using only uniaxial test data. The F.E. results presented show that neglecting the tension–compression asymmetry of T40 leads to less accurate predictions of the fluid pressure and strains at which fracture occurs, and in some cases an incorrect orientation of the zone of localized deformation. Using the Cazacu et al. (2006) criterion, it is possible to accurately predict the sudden occurrence of instabilities, the distribution of plastic strains, and the correct orientation of the zone of localized deformation in both the hemispherical and elliptical bulge tests.

Production of Helical Finned Tubes with Various Curvatures Using Extrusion Process through Inclined Die Aperture

Production of Helical Finned Tubes with Various Curvatures Using Extrusion Process through Inclined Die Aperture

Optimisation design of aluminium radiator extrusion die using response surface method

The most important way to improve the quality of aluminium extrudates and enhance the life‐time of extrusion dies is to ensure that the material flows through the die land exit with the same velocity. In this paper, an optimisation strategy was developed for an aluminium radiator extrusion die design. A computer aided optimisation model was built based on the Box‐Behnken experimental design, response surface method and particle swarm algorithm. The parameters, such as depth, location of the die aperture, etc. were selected as the design variables. Through a series of simulations and optimisations, an optimal aluminium radiator extrusion die with uniform velocity distribution was obtained. Compared to the original die, the velocity difference across the cross‐section of the extrudate was reduced from 16·5 to 4·4 mm s−1. The extrudate was not bent and met the practical requirements.

Effect of die aperture offset on flow behaviour in an extrusion process with aluminium alloy

In order to reveal the mechanism of die aperture offset on metal flow behaviour, numerical simulation was conducted to analyse the different processes. The stress field characteristics were used to create the deformation division. The results show that the shunt section at the bottom of the container moves towards the axis as the die aperture offset increases, and the complexity of metal deformation flow increases significantly. The distribution of the plastic zone gradually becomes non-symmetrical, and the dead zone at the bottom of the die cavity enlarges significantly, while the other side disappears completely. It can be observed that the velocity uniformity of metal flow towards the die pocket can be changed by using different die aperture offsets, and thus can effectively control the degree of bending of the extruded products. The simulation results are consistent with the experiment.

Prediction of curvatures of parts extruded through rotary die using fuzzy inference

Abstract A fuzzy model for predicting the shapes of rectangular bars with variable curvatures along their lengths in the extrusion system with rotary dies, whose mechanism has been developed by the authors, is proposed. In the fuzzy model, the height of the die aperture, the inclination angle of the die, the angular velocity of the rotary die and the distance between the predicted and the experimental central lines of the extruded bars, namely the error of the prediction, are used as the antecedent parameters, and furthermore a linear relation is assumed among the parameters and the curvature of the extruded bar. The shapes of the bars predicted by the proposed fuzzy model are compared with those obtained in the extrusion tests in order to evaluate the accuracy of the prediction. The distance between the predicted and the experimental central lines is confirmed to be less than 4.0% of the height of the extruded bar for all of the experimental conditions.

An investigation of the curvature of bars and tubes extruded through inclined dies

The extrusion process through a die aperture inclined at a fixed angle, previously proposed by the authors, is applied to forming of rectangular bars and tubes with various cross-sectional shapes, and the fundamental properties of the process are investigated. The curvature of the extruded bar is found to decrease as the height and width of the die aperture increase. The curvatures of the extruded tubes agree fairly well with those of the solid bars, and further, close correlations are found between the curvatures of the rectangular and H-type bars, and between those of the rectangular and H-type tubes. The curvatures of the rectangular bars and tubes with flanges can be predicted by combining the fundamental bending properties of the process obtained in extrusion of the rectangular bars with the shape effect of the bars and tubes.

Metastable states in a food extrusion cooker II: The effects of die resistance and minor ingredients with rice flour

Normally, in extrusion cooking, a reduction in the size of the die aperture causes an increase in die resistance and, therefore, an increase in die pressure. However, with some experimental recipes based on rice flour, following a reduction in the diameter of twin circular dies from 4 to 3 mm, the reverse was found to be true under certain conditions of screw speed, using a screw system comprised of separated kneading and die head pumping zones in an APV Baker twin-screw extruder. This behaviour was attributed to phenomena related to both the screw design, in which the screw has a high pumping capacity following the shearing zone, and to a relatively low biopolymer melt viscosity in the barrel.

On the behavior of viscoelastic free jets with elliptical cross section

In [1,2] we develop a comprehensive theory of one space dimensional closure models (closed systems of 1-D equations for the unknown, or modal, variables) for free viscoelastic jets. These closure models are derived via asymptotics from the full 3-D boundary value problem under the conditions of a Von Kármán-like flow geometry, a Maxwell-Jeffreys constitutive model, elliptical free surface cross section, and a slender jet scaling. The focus of the present paper is to determine the consequences and predictions of the lowest order system of equations in this asymptotic analysis. For the special cases of elliptical inviscid and Newtonian free jets, subject to the effects of surface tension and gravity, our model predicts oscillation of the major axis of the free surface elliptical cross section between perpendicular directions with distance down the jet, and draw-down of the cross section, in agreement with observed behavior. In the absence of surface tension the transformation from a cross section with major axis in one direction to a cross section with major axis in the perpendicular direction occurs only once, in agreement with the observation of Taylor [4]. In viscoelastic regimes, our model predicts swell of the elliptical extrudate and distortion of the elliptical extrudate cross section from the dimensions of the die aperture.

Production of thin fibers from powders

Analytical expressions have been derived relating the thickness of powder fibers to the parameters of the shaping and sintering processes. A coefficient of fiber thinning, equal to the ratio between the diameter of the die apertures and of the fibers after sintering, has been chosen as a criterion for assessing the practical feasibility of obtaining thin fibers from powders. It is shown that the key processing parameters influencing the fiber thickness are the die aperture diameter, the powder content of the mixture, the relative change in length experienced by the fibers during processing, and the powder particle size.

Formability Assessment by Bulge Test Employing Grooved Disks (Investigation into the Optimum Geometry of the Groove)

The optimum geometry of the groove is investigated in the bulge test employing concentrically grooved disks which was earlier proposed as a press-formability test by the authors. It is recommended that a groove is formed with the circular arc profile to 0.125 t0 in depth at the radial position of 0.4 r2 on the disk surface, where t0 is the initial thickness of a blank and r2 is the radius of the die aperture. It is concluded that both deep-drawability and pure-stretchability of sheet metals can be accurately assessed by a single blank test. The deformation behavior of grooved specimens is examined also by numerical analysis.

Cold Forming and Extrusion of Steel: Properties and Tooling

The dimensiians of the extruded ptfioduct may be less or greater than that of the die aperture, depending on the profile of the die entry. The diameter of rod extruded through square-entry dies (1.25 mm nominal radius) of 12.5 mm diameter at a punch impact speed of 63.5 mm/s is 0.25 mm,less than that of the die, while rods extruded thraugh 60, 50, and 40° conical-entry dies emerge with a diameter 0.04 mm greater than that of the die.

Flow behaviour of glass during extrusion

Within their working range the inorganic glasses can be regarded as Newtonian liquids. Their flow behaviour during the extrusion process is therefore generally in good agreement with the Hagen-Poiseuille law, if the boundary condition of a stagnant glass layer at the die wall is fullfilled. The extrusion velocity was found to increase proportionally with the applied pressure as long as the viscosity remains a constant. For pure boric oxide glass the pressure dependence of viscosity was confirmed. - If the shear stress at the die wall exceeds a critical value the emerging glass rod becomes irregular in shape. - The pressure demand increases proportionally with the extrusion ratio. By providing a non-wettable die material with good antifriction properties, slippage of the glass along the die wall occurs. This results in a considerable increase in the extrusion rate. Together with this, a more homogeneous distribution of pressure across the die aperture is obtained, leading to high accuracy of shape of the extruded products.

THE THEORY OF EXTRUSION

Extrusion is essentially a process in which a slug of material or a billet is forced through a suitably shaped die and converted into a continuous product of uniform cross-section. Specialized developments, such as the extrusion of taper sections and the manufacture of extrusion forgings, retain the essentials of the basic process. Two methods of extrusion are commonly employed, namely, direct and inverted. In direct extrusion, the die is locked in the end of the chamber and the billet is forced through the die aperture by the ram, relative motion occurring between the billet and the chamber wall. In the inverted process, the billet is placed in the chamber and the die is rammed into it, with no relative motion taking place at the chamber/billet interface (see Fig. 1). The choice of which press components are held stationary, is a matter of convenience of design.