Aluminum Billets Research Articles

On the large strain inelastic analysis in natural formulation part I: Quasistatic problems

Abstract The paper first establishes for the large strain domain the transformation of the homogeneous, natural presentation of the strain and stress states to the standard formulation and vice versa. Possible definitions of natural strains appertaining to deformations composed of elastic and inelastic parts are discussed. Furthermore, the natural stress-strain relations are given based on total elastic and incremental plastic deformations. The results apply immediately to the description of simple finite elements which may serve, moreover, as subelements for the derivation of higher order finite elements. A solution algorithm is developed unifying the Newton technique with respect to the geometric nonlinearity and the normal iteration technique with respect to the material nonlinear behaviour. A number of numerical examples is presented such as the necking of a simple tension specimen, the extrusion of an aluminium billet and the heading of a steel bolt.

Mathematical model for studies of metallurgical structures in aluminium DC castings

Detailed studies have been carried out of the heat transfer within the mould in the direct-chill casting of aluminium blocks and billets, together with studies of the conditions within the region of secondary flood or spray cooling below the mould. These measured parameters have been applied to mathematical simulations of the casting process, which have enabled the temperature fields within the mould and the casting to be computed, and these in turn allow the cell size distribution within the casting to be predicted. Casting systems which have been investigated include:(i) 97 x 30 cm blocks cast through conventional open-head moulds(ii) 15 cm dia. billets cast through a closed-head system (iii) 97 x 30 cm blocks cast with reduced secondary cooling.The cell size distributions as predicted by the mathematical model are shown to be in good agreement with measurements from cell counts on alloys cast through these three systems. In conventional open-head block casting the peripheral zone structure can determine the depth of surface metal which has to be scalped off prior to rolling, and the model indicated that this is primarily dependent on the metal depth in the mould during casting. The model also showed that average cell size in any casting is dependent on casting speed, particularly in billet casting, where a wide range of speeds can be employed. In conventionally cast billets, increased speed reduces the average cell size,. on the other hand, in spray-cooled castings, where the reduced secondary cooling produces much larger cells, an increase in casting speedgives rise to an increase in average cell size. A successful system for producing spray-cooled blocks is described in which the model played a key role in aiding the design.

Microstructural misorientations in extruded aluminium

Aluminium billets of two purities (99.999 and 99.7%) were extruded at 250°C using commercial equipment to produce 10 mm rod (extrusion ratio, 25:1). On air cooling, the resulting microstructures were investigated using optical and transmission electron microscopy, including Kikuchi line analysis. Thefine microstructure of the lower purity extrusion consisted of subgrains of about 2μm dia., formed by dynamic recovery. Although the microstructure of the higher purity extrusion appeared to be similar both in morphology and size, the misorientation measurements revealed that this extrusion was composed of small high-angle grains. These recrystallized grains were found to be stable and resulted in an associatedflow strength of50-62 MN/m2

Hydrodynamic Lubrication of Hydrostatic Extrusion

An analytical model for the hydrodynamic lubrication of hydrostatic extrusion is developed. This includes the effect of viscous heating on the film formation process and the effect of viscous and plastic heating on the friction and film thickness variation in the work zone. Theoretical predictions of film thickness and extrusion pressure show good agreement with experimental measurements for aluminum billets lubricated with castor oil.

９９．９％Ａｌ ＤＣ鋳造ビレットにおける発汗帯の生成

This study was made to investigate the formation of bleed bands in D. C. cast billets. the 99.9% aluminium billets, 13cm in diameter, were D. C. cast. By controlling casting conditions, billets with and without bleed bands were produced. Using thermocouples inserted in the mold wall, the temperature was recorded during D. C. casting. At the end of casting, a small amount of 198Au was added to the molten metal and then sump contours were observed by means of macro-and micro-autoradiography. Distribution of impurities such as iron and silicon was determined by X-ray microanalysis.The results obtained are summarized as follows:(1) In the billets with bleed bands, the base of ingot shell was remelted and in an extreme case, molten metal exuded on to the ingot surface, as proposed by Siebel et al1).(2) Remelting proceeded preferentially along grain boundaries where melting point was low due to segregation of iron.(3) Bleed bands likely to be formed by the Collins' mechanism2). were not observed.(4) By the remelting mechanism, the effects of the casting speed and the mold taper on bleed bands could be qualitatively explained.

アルミニウム押出棒の不均一流れ

Most of extrusion defects are caused by inhomogeneous flow of materials during extrusion, and there are many singular phenomena resulted from inhomogeneous flow in the outer parts of the products. But few quantitative studies of the metal flow in extrusion, especially near the outer surface of the products with high reductions, have been made. The present work was carried out to study quantitatively the flow of aluminum extruded with high reductions. The redundant strain from center to surface of the products was evaluated and compared with the slip line field theory. The results are summarized as follows:1) By a unique method of extruding aluminum billets with high purity Au wires as flow line markers, redundant strain values in the outer parts of the extruded bars could be obtained quantitatively.2) It can be said, within the experimental errors, that the intervals between longitudinal markers of the billet are similarly reduced in the extruded rod. Consequently, the displacement in the direction of the diameter agrees with that in plane strain analysis by the slip line field theory.3) The flow lines of the products could be represented by a function, Y = a exp (bX), where X is the distance from the center line of the bar, Y is the hight of the marker from X-axis, and a and b are constants. On the other hand, the flow lines from the slip line field theory under equivalent conditions were represented as Y = mXn, where m and n are constants, irrespective of extrusion ratios and friction conditions.4) The redundant strain in the outer part of the product is almost ten times as much as that from the theory. This may give a clue to make clear the anomalous structure near the surface of the extruded metals.

Some crystallographic observations of growth-twinned dendrites in aluminium

Growth-twinned dendrites in semi-continuously cast aluminium billets were studied with the object of elucidating some of their crystallographic details. It is shown that there is no unique growth direction for twinned dendrites in aluminium and that under the conditions of D.C. semi-continuous casting, twinned dendrites can occur in competition with columnar dendrites when the twin plane deviates by as much as 30° from the normal to the solid-liquid interface. The growth advantage experienced by twins in competition with normal columnar dendrites is explained in terms of a growth mechanism which depends upon twin boundary energy, solute content, freezing rate and temperature gradient.

AN INVESTIGATION INTO THE KINETIC FORMING OF TUBULAR AND OTHER THIN-WALLED COMPONENTS FROM SOLID CYLINDRICAL ALUMINIUM AND COPPER BILLETS

SUMMARY Experiments are described in which cylindrical aluminium and copper billets were fired from an industrial stud-driving gun into closed die sets of a variety of cavity forms. Where the forming process commenced with a piercing operation, as in the production of conical or tubular components, the effect of piercer radius upon the flow of billet material was investigated. It is shown how a tendency to rupture during “hoop” expansion of the billet material may be suppressed by elimination of hoop tensile stresses, either by using slightly converging die walls, or by constraining the material to move along a curved path so that heavy inertia stresses are developed in the “thickness” direction. Line diagrams of equipment are provided and photographs and photomacrographs of typical formed components are presented and discussed.

An investigation into kinetic forming

Tests are described in which small cylindrical aluminium billets were fired from an industrial gun, at speeds of up to 1700 ft/sec, into closed die sets, so that the billet material would flow under the heavy inertia stresses developed upon impact, to produce close tolerance and good finish “castings”. The degree to which thin walls and flanges could be formed was investigated, along with an examination of the effects of supplementing the kinetic energy of the billet by the addition of a steel “driver”. Comparison is made with specimens formed statically, using a universal testing machine. Photographs and photomacrographs of formed specimens are included.

On the extrusion of aluminium

Aluminium billets (extrusion ingots) of 18mm in diameter and 20 to 80mm in length were "direct-extruded, " with an Amsler type universal testing machine, into rods of 2 to 5.8mm in diameter. From this experiment, the following were found out:(1) As the extrusion temperature increases, the extrusion pressure decreases. The extrusion pressure goes down as the ram goes, but, regardess of the length of billets the minimum pressure required for extrusion is kept almost constant under the certain temperature and extrusion speed.(2) The approximate values of the resistance to deformation and coefficient of friction are 4.2 to 10.7kg/mm2 and 0.06 to 0.11 respectively. Assuming that the mechanical work done by extrusion is entirely converted into heat which raises the billet temperature, that temperature is to rise by 40 to 110°C.(3) The increase in the extrusion temperature makes the recrystallized surface layer thicker and the grains coarser.(4) As the extrusion temperature goes up, the core part of the billet, where the fiber structure is remained, starts to recrystallize in parts.(5) The longitudinal strength of the front end of the extrusion is more than that of the back end, when extruded at the ram speed of 66 to 123mm/sec and under the temperature of 400 to 500°C. However, inverse is the case of being extruded at 570°C or at 30mm/sec under 500°C. This difference is considered to be resulting from the difference of the cooling rate of each postion of the billet in the container before extruded.

Some analytical and experimental studies of axi-symmetric cold forging and extrusion—II

The results obtained from several forging and extrusion tests at room temperature and low speed are compared with theoretical results, and the following conclusions emerge. 1. (1) The working pressures for the compression of soft aluminium cylinders between rough flat dies, for the compression of soft aluminium annuli in a container between lubricated or rough dies and for the steady-state lubricated extrusion and piercing of hard aluminium and copper cylindrical billets, are 10–20 per cent below the calculated upper bound. 2. (2) Calculated upper bounds agree qualitatively with the working pressures obtained during some non-steady extrusions and piercings of soft aluminium, hard aluminium, copper and soft brass. 3. (3) The steady pressures divided by the mean yield stress in combined bar and tube extrusions from cylindrical billets and in tube extrusions from hollow billets, together with those in ordinary extrusion and piercing, were found to be almost entirely a function of the total reduction in area, when the tools are lubricated. 4. (4) The working pressure in opposed extrusion-piercing-forging is considerably lower than that for a one-way extrusion-forging. The working pressures in opposed extrusion-forging with two dies and in opposed piercing-forging with two punches were lower than that in corresponding one-way working, using a die or punch of the larger orifice when the length of billet is moderate. In symmetrically opposed working, the pressure exceeds that in one-way working when the billet length becomes very small. When the material flow through one orifice is interrupted midway in an opposed forging, the working pressure thence follows that of the corresponding one-way working. 5. (5) The deformation of hard aluminium and copper annuli compressed between lubricated flat dies was as predicted from the most suitable velocity field. The speed of efflux of material through two separate orifices was affected by the frictional resistances acting on the material rather than by the difference in the areas of the orifices when the billet length was moderate. But, as the length was reduced, the speed from the wider orifice tended to increase. These results were in qualitative accordance with those derived from plane-strain analysis. 6. (6) The internal flow pattern observed on the meridian section of a lead billet as photographed through a glass plate was in qualitative agreement with the corresponding most suitable velocity field and was very similar to that of the comparable plane-strain working. 7. (7) The main types of defect found in the various extruded and extrusion-forged products were skin inclusion, cavity formation and internal cracking. They were predicted quantitatively and qualitatively from the velocity field of the least upper bound. The inclusion was prevented by using a rough die in contact with the material surface from which the skin was unfolded. Cavity formation and internal cracking was thought to be prevented by restraining the material flow through the orifices. The onset of the latter defects was retarded by intermediate annealing. 8. (8) The internal pressure acting on the container during extrusion-forging and coining was found to be lower than the mean working pressure within the range of conditions tested. The pressure acting on the projection of the coining die was in excess of the mean working pressure, the difference being larger for higher projections and for thinner slug thicknesses. The residual pressure between the material and the container after extrusion or closed-die coining was found to be nearly equal to the uniaxial yield stress of the material.

Comparison of Slip-Line Solutions With Experiment

Abstract Plane-strain and axially symmetric approximate solutions for a perfect plastic are compared with experimental results obtained from the extrusion of a billet of commercially pure aluminum. The extrusion process was carried out at room temperature under essentially negligible external wall friction with a reduction of area of 87.8 per cent. It is found that the plane-strain solution is in good agreement with the experimental results, if a constant k = σ̄/2 = 20,000 psi (maximum shear stress for Tresca’s criterion) is substituted in the plane-strain solution. The flow stress (σ̄ ≅ 40,000 psi) was determined from a property test for the aluminum billet, at a strain equivalent to the uniform deformation in the extrusion (i.e., same area reduction without shear deformation). It is found that the Haar and von Karman yield condition is not valid for the present case, and further that the axially symmetric solution demonstrates no real advantage over the simpler plane-strain solution in predicting the stress distribution in an axially symmetric extrusion problem.