Rod Extrusion Research Articles

Friction measurement and modelling in forward rod extrusion tests

Forward extrusion is one of the important processes in bulk metal forming. Friction stress can be estimated from the slope of the load-displacement curve at the steady state after the maximum load in a forward extrusion test. In this paper, forward rod extrusion tests are carried out to determine experimentally friction stress at various normal pressures, reductions in area, billet heights and lubrications. Tested materials include aluminium alloy, low carbon steel and stainless steel. Two lubrication methods are applied, conversion coating followed by either alkaline soap or molybdenum disulphide as the lubricant. Friction stresses are obtained from measurements of slopes of extrusion pressure-punch travel curves at the steady state stage. Normal pressures are evaluated by using Mohr's circle, in which shear flow stresses are estimated at the maximum elastic deformation points from the same extrusion pressure-punch travel curves. It is found that the relationship between normal pressure and friction stress appears linear, and therefore Coulomb's friction model fits the experimental data very well. Extrusion pressure-punch travel curves before the steady state can be divided into four stages: elastic deformation, filling container deformation, filling die aperture deformation and exiting inhomogeneous deformation.

Finite element simulation of die design for hot extrusion process of Al/Cu clad composite and its experimental investigation

A clad composite material is a variant of the typical composites which is composed of two or more materials joined at their interface surface. The advantage of clad material is that the combination of different properties of materials can satisfy both the need of good mechanical properties and the demand of user such as electrical properties simultaneously. This paper is concerned with the direct and indirect extrusion process of copper-clad aluminum rod. Extrusion of copper-clad aluminum rod was simulated using a commercially available finite element package, DEFORM which can be used to simulate metal forming and heat transfer, welding and machining processes. The simulations were performed for copper-clad aluminum rod to predict the distributions of temperature, effective stress, effective strain rate and mean stress for various sheath thickness, die exit diameters and die temperatures. From the simulations, it was found that the larger the die outlet diameter and the thickness of the sheath material are, the better results can be acquired. It was found that the experimental result for lubricant material with carbon oil has good agreement with extrusion force from finite element analysis.

Axisymmetric Rod Extrusion Through Smooth andPartially Rough Conical, Cosine, and Flat-Faced Circular Dies: Slip-Line Field Solutions Using Numerical Methods and Some Experiments

The numerical method of construction of axisymmetric slip-line fields is followed to obtain indirect type slip-line field solutions to axisymmetric rod extrusion using some smooth and partially rough conical, cosine, and flat-faced dies. A detailed computer program was written that calculates and plots both the slip-line field and the velocity field and carries out the entire procedure of estimating stresses and velocities in an iterative manner to reach either the desired or a reasonably valid solution, to each of these extrusion problems. The resultant values of the mean extrusion pressures are compared with those given by other authors and with some of the authors own experimental work in rod extrusion (tellurium lead) through conical dies of cone semi-angles, a varying from 11° to 26.5° and at reductions of 36-75%.

Extrusion of three-layer composite hexagonal clad rods

Composite clad rods consisting of three different materials are applied extensively as conductors, electrodes and chemical devices. Commercial applications involving low temperature niobium–tin alloy (Nb 3Sn) superconductor rods, which have a pure niobium (Nb) core, a copper–tin (Cu–Sn) alloy outer sleeve and a Nb 3Sn diffusion layer in between, stipulate these conductors as, electrodes that are intended for processing as rods of various shapes. During the extrusion process, non-homogeneous deformation tends to occur because the billet consists of materials with different mechanical properties. In this study, the authors present a numerical simulation model based on the upper-bound theorem to analyze three-layer composite clad rods with a hexagonal cross-section under extrusion. A velocity field is also generated with the assistance of a product’s cross-section profile functions. The velocity component in the extrusion axis is expressed as a convex distribution. Analytical results indicate that various process variables such as the semi-die angle, reduction of area, friction condition of the die and combinations of the three constituent materials, prominently influence the extrusion process. Moreover, the extrusion pressure, product dimension-change and the probability of sound extrusion are related closely to the process variables.

An investigation into the plastic deformation behavior within a conical die during composite rod extrusion

This paper proposes a set of stream functions to investigate the plastic deformation behavior of the rods during the axisymmetric extrusion of composite rods through a conical die. The velocity field and the rigid–plastic boundaries can be obtained immediately from the proposed stream functions. Relative slip at the interface of the rods is allowed. The friction factor between the rod and the die is determined by a ring compression test. By using the upper-bound approach, the radius ratio of the core layer at the exit of the die and the plastic region within the die are determined by the minimization of the total power. Experiments on the extrusion of composite rods composed of aluminum (the core layer) and copper (the sleeve layer) are also carried out. The predicted force, final radius ratio and flow pattern of the rods within the die are compared with the experimental results.

Some Results of Investigations into High-Rate Hot Extrusion of Malleable Cast Iron

Based on the results of our investigations, an optimal temperature and strain-rate regime of high-rate extrusion is established (with strain rates V0 = 10–100 m/s, temperatures T0 = 800–1000°C, and elongations λ = 1.94–4.0) in which a deformable material (KC 37-12 malleable cast iron) manifests a high ductility. In addition, the mechanical properties – the compression strength σcs and the Brinell hardness – increase 2–3 times compared to those of cast specimens. Based on the data obtained, a novel method of rod extrusion from malleable cast iron has been developed.

Research on the “shear-extrusion” process to form large-scale cut-off valve bodies

Focused on the metal plastic forming of large-scale cut-off valve bodies used by power plant boilers, and based upon a deep study of combined backward cup–forward rod extrusion, this paper presents a new forming process named “shear-extrusion”, of which the main characteristic is that it is labor saving. The new shear-extrusion process was studied by the methods of numerical analysis and simulating experiment, and the optimal process variables to be applied in the forming of valve bodies were obtained. Finally, large-scale cut-off valve bodies were formed successfully using a 10,000 kN screw press. The new process can be applied to produce not only cut-off valve bodies but also components with branches such as sluice valve bodies, tee-junctions and so on.

Extrusion behavior of metal–ceramic composite pipes in multi-billet extrusion process

Two-layer composite pipes consisting of zirconia and stainless steel were fabricated by a multi-billet extrusion (MBE) technique. The MBE process is characterized by coextruding different kinds of particulate pastes containing a water-based binder, joining them in chambers and finally obtaining a desired extrudate by means of dies. It is shown that sound extrudates can be obtained no matter what mixing ratios of zirconia and stainless steel powders in both inner and outer layers are used. The MBE requires a larger amount of binder compared to conventional rod extrusion. Furthermore, a better flowability is necessary for the outer layer than for the inner one in the extrusion process of a two-layer pipe, as a result of the characteristic structures of the extrusion dies. The amount of binder can be minimized by using mixed powder with a wider particle size distribution and a die with a longer land. It is effective to add a small amount of glycerol or use partially stabilized zirconia powder in restraining the crack formation in extrudates during drying period.

The Direct Extrusion of Copper Clad Aluminum Composite Materials by Using the Conical Dies

This paper describes experimental investigations in the direct extrusion of copper clad aluminum rods through conical dies. Composite materials consist of two or more different material layers. Copper clad aluminum composite materials are being used fur economic and structural purposes and the development of an efficient production method of copper clad aluminum composite material rods by extrusion is very important, It is necessary to know the conditions in which successful uniform extrusion ,and sound cladding may be carried out without any defects in the direct extrusion. There are several variables that have an influence on determining a sound clad extrusion. In order to investigate the influence of these parameters on the hot direct extrudability of the copper clad aluminum composite material rods, the experimental study have been performed with various extrusion temperatures, extrusion ratios and semi-cone angles of die. Subsequently, the microscopic inspection of interface bonding is carried out for extruded products. By measuring hardness, along extrusion way of products, a variation of hardness has been discussed. Proportional flow state has been considered by measuring radius ratio of Cu sleeve and Al core before and after extrusion.

A study of surface topography, friction and lubricants in metalforming

In this paper are presented the results of investigations concerning the relation between friction behaviour and surface topography using various lubricants and initial workpiece surface conditions in ring upsetting and rod extrusion processes. The tests were carried out using either a liquid lubricant or under clean dry conditions. Two types of workpiece surfaces, random and directional, were prepared by either shotblasting, or EDM or turning to different levels of surface finish. Not only has the friction effect of lubricant and initial surface been studied, but also the surface topography of the finished products has been examined in detail, to obtain a better understanding of the mechanism of lubrication and surface interaction. It was found that, for random surfaces, smoother ones could retain more lubricant and decrease friction resistance. The experimentation also demonstrated that turned surfaces were effective in reducing friction, but the final surface finish of the workpiece was not as good as that from random surfaces.

Strengthening of Zn–22Al–2Cu alloy wire by artificial ageing

Changes in hardness, measured at room temperature, were detected after continuous artificial ageing at 250°C, for different periods, in a Zn–22Al–2Cu (wt.%) alloy wire. The presence of the ternary stable τ′ phase precipitate (Al 4Cu 3Zn) and the decomposition of the Zn-rich hcp metastable η T′ phase as a consequence of the ageing, are shown in this work. Then, X-ray diffraction showed that after 1 h of ageing the hcp η phase is present in the microstructure of the wire, this phase remaining stable along the heat treatment. The wire was prepared by rapid solidification by using the semicontinuous casting technique, followed by extrusion of the semicontinuous casting rods and, finally, wiredrawing of the extruded material.

Theoretical analysis of extrusion of rectangular, hexagonal and octagonal composite clad rods

Composite clad rods with non-axisymmetric cross-sectional areas are commercially important owing to their extensive industrial applications such as in electrodes, conductors and chemical devices. For instance, in the processing of superconductor wire, increasing the packing density involves closely packing superconductor rods which have a hexagonal cross-section next to each other inside the high purity copper tube. During extrusion process, non-uniform deformation tends to occur because the core and sleeve of a composite clad rod is usually composed of materials with different mechanical properties. The first recognized paper on round-to-square drawing/extrusion with variable corner radius was presented by Boer et al. in 1979. In this study, we present a model based on upper-bound theorem to analyze the extrusion of composite clad rods with non-axisymmetric cross-section. Velocity fields for both core and sleeve are generated with the assistance of a product's cross-sectional profile functions. Products with rectangular, hexagonal and octagonal sections are chosen as the study objects. Also discussed herein are numerical results for various process variables such as semi-die angle, reduction of area, frictional condition of die, and product shape complexity. According to these results, the extrusion pressure and product dimensional change are closely related to the process variables.

A universal velocity field for the extrusion of non-axisymmetric rods with non-uniform velocity distribution in the extrusion direction

This study formulates a universal velocity field that is kinematically admissible for application in the extrusion of non-axisymmetric rods. Then upper bound theorem dictates that a better upper bound solution heavily depends on the precise conformity of the velocity field postulated. However, a compromise must frequently be made, since the formulation is in general rather complicated. The kinematically admissible velocity field proposed herein has the following features: (a) it is three-dimensional, (b) it is non-uniformally distributed in the axial direction, and (c) the formulation is straight-forward once the boundary of the deformation zone is specified. In addition, the velocity field is applied to the extrusion of rectangular, hexagonal, and octagonal rods from round billets. Moreover, the extrusion loads are calculated against process variables such as the semi-die angle, the percentage reduction of area, and the friction factor. Furthermore, the velocity field is compared with results from the literature, indicating that the present results render a better upper bound solution for application in extrusion than do previous results.

Finite-element modelling of cold forward extrusion

Simulating metal forming processes using an updated Lagrangian finite-element formulation is not ideal when steady-state material flow conditions prevail. Firstly, repeated calculations of large non-linear finite element systems are needed for continuously updating the mesh, and secondly, remeshing operations must be undertaken to avoid excessive mesh distortion and to introduce localised refinements in regions where large gradients are likely to occur. The combined Eulerian–Lagrangian formulation overcomes these difficulties by using a temporary incremental mesh to calculate the strain and stress fields, coupled with a mathematical scheme to interpolate the updated mechanical state into a spatially fixed mesh. In this paper the cold forward extrusion of rods is analysed using both the updated Lagrangian and the combined Eulerian–Lagrangian finite-element formulations. The theoretical background for both formulations is reviewed, and the numerical results obtained with the two formulations are compared with experimental extrusion data. Excellent agreement is found for the flow pattern and for the distribution of strain within the plastically deformed region. In what concerns the extrusion load curve, the results demonstrate that the latter can be predicted more accurately using a combined Eulerian–Lagrangian finite-element formulation.

Off-centric extrusion of circular rods through streamlined dies, CAD/CAM applications, analysis and some experiments

The previously given analytical method [1], which was based on the upper-bound theory, was used to design the streamlined dies and to investigate the three dimensional off-centric extrusion of circular sections from initially circular billets through linearly converging (ruled-surface) and smooth curved (advancedsurface) dies. For a reasonably correct upper-bound to the load, a set of generalised kinematically admissible velocity fields were derived on the assumption of Bezier-type streamlines by incorporating a special velocity function that takes care of the non-uniform material flow. Based on the present method, for a given reduction in area, material property, friction condition and off-centric positioning of the exit cross-section, computations were carried out to predict the upper-bound to the extrusion pressures, the deforming grid patterns and curvature of the extruded product. Experiments were carried out for some off-centric circular sections with varying die lengths and reduction in areas. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the off-centric extrusion of circular rods. Both the solid and split-type specimens made of tellurium lead under both the lubricated and the dry conditions were used for experimental investigations in order to assess pressures, deformation modes and to visualise the deforming grid patterns. The theoretical predictions were observed to be in good agreement with the experimental.

Application of an upper bound method to off-centric extrusion of square sections, analysis and experiments

In the present study, previously developed analytical approach (Chitkara and Celik) which was based on the upper-bound theory, for the design of three dimensional off-centric extrusion of arbitrarily shaped dies was applied to the off-centric extrusion of square sections from initially round billets with experimental verifications. A computer program was written to obtain optimum die design which yield the lowest upper-bound for a given reduction in area, die length, off-centric positioning and frictional conditions. Computations were carried out both for the converging (ruled-surface) and smooth curved (advancedsurface) dies. Curvature of the extruded product and simulated deforming grid pattern were also predicted. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the off-centric extrusion of square section rods. The theoretical predictions were observed to be in good agreement with the experimental results.

Axi-symmetric tube extrusion through a smooth conical or cosine die and over a conical or ogival mandrel: numerical construction of axi-symmetric slip-line fields and associated velocity fields

The numerical method of construction of axi-symmetric slip-line fields and their associated velocity fields suggested earlier for rod extrusion (Chitkara NR, Butt MA. Axi-symmetric rod extrusion through smooth conical, cosine and lat-faced dies, International Journal of Mechanical Sciences, submitted) and tube extrusion (Chitkara NR, Butt MA. Axi-synnetric tube extrusion through a flat-faced circular die: International Journal of Mechanical Sciences, 1997;39(3);341–366) is employed to construct slip-line fields and their associated velocity fields for a few cases of forward tube extrusion through smooth, rigid conical and cosine dies and over a smooth rigid conical or ogival mandrel. The computographic plots of slip-line fields and associated velocity fields are given in the form of weighted and directed velocity vectors as are the normal pressure distribution on both the die and the mandrel surfaces. The values of the non-dimensionalised mean extrusion pressures, ρ ̄ /2k are compared in each case with a similar case of plane strin extrusion and the results commented upon.

Fabrication of bimetallic rods by explosive cladding and warm extrusion

Abstract The fabrication of bimetallic aluminium sheathed/copper axisymmetric rods by explosive cladding and subsequent warm extrusion is reported. The effect of the cladding and the extrusion parameters on the macro- and the microscopic features and the soundness of the product at the various stages of the fabrication are indicated using microhardness testing and optical metallography. By employing warm extrusion as a post-welding forming technique, instead of the cold extrusion, the soundness of the components is improved due to advantageous plastic flow of the extruded composite rod at elevated temperatures and the minimization of the characteristic extrusion defects. A theoretical analysis pertaining to the extrusion of axisymmetric bimetallic rods is proposed.

Finite element modelling of cold forward extrusion using updated Lagrangian and combined Eulerian–Lagrangian formulations

Abstract Finite element analysis of metal forming processes is predominantly treated by the updated Lagrangian formulation in which the mesh moves and deforms in space, in accordance with the deformation history of the material. However, the steady-state deformation characteristics of some metal forming processes such as extrusion, drawing and rolling, can be advantageously analysed using a combined Eulerian–Lagrangian formulation. In this paper cold forward extrusion of rods is analysed using both the updated Lagrangian and the combined Eulerian–Lagrangian finite element formulations. The numerical results obtained with the two formulations are discussed and compared with experimental data obtained from metal experiments carried out with steel rods. Excellent agreement is found for the flow pattern and for the distribution of strain within the plastically deformed region. In what concerns the extrusion load curve results demonstrate that it can be predicted more accurately using a combined Eulerian–Lagrangian finite element formulation.

New repetttive pellet injector with a screw extruder

Abstract A new repetitive injector providing an unlimited amount of pellets has been designed for plasma fuelling applications. A screw extruder was used for a continuous extrusion of a solid hydrogen rod for one hour of steady-state operation. Over one thousand of 2 mm pellets were produced continuously at the rates of 1 and 2 Hz and accelerated to 0.8 km/s.