Forward extrusion through steadily rotating conical dies. Part II: theoretical analysis

Forward extrusion of a cylindrical rod from a round billet was carried out through steadily rotating conical dies. Die rotation was shown to decrease the extrusion load and impose a twist shear strain into the partially extruded billet. The material twisting occurred both inside the container and inside the convergent die. However, not all the rotary work was transferred into shearing the bulk of the material, and this led to circumferential slippage at the rotating tool/material interface. The twisting degree on the outer surface of the material is quantified by a simple measurement technique. The influences of various process parameters on the extrusion load are also studied, including die semi-cone angle, die rotating speed and lubrication condition.     

An analysis for extrusion of helical shapes from round billets

A method of analysis is proposed for three-dimensional extrusion of a helical shape from a round billet. It is reported that a helical shape can be made by hot extrusion through a square die. In this paper, it is suggested that a helical shape be effectively cold extruded through a continuous die with appropriate lubrication. The extrusion of helical shapes can find practical application in some useful products. However, the analytical method regarding this kind of extrusion has not been attempted so far.A kinematically admissible velocity field is derived for the extrusion model where a round billet is extruded into a twisted helical section with a long elliptic cross section. The axis of the cross section is rotating during extrusion. By assuming proper stream surfaces, the velocity field is obtained by deriving the equation of a stream line. Then, an upperbound solution is formulated for the rigid-perfectly plastic material. Computation for the upperbound pressure is carried out for various process variables such as reduction of area, friction, rotation of axis, aspect ratio of a product, die length and overall die profiles.     

Evaluation of a pyramid die extrusion for a hollow aluminum profile using FE simulation

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For this purpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusion process was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state, transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load, material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzed and compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were well concluded, which should be important information for die designers and makers.

     

Numerical and experimental study on the three-dimensional extrusion of square section from square billet through a polynomial shaped curved die

The geometry of die profile plays a major role in reducing the extrusion pressure and ensuring the smooth flow of material. In general, the extrusion process is mostly affected by billet geometry, die geometry, and interface frictional force at the die billet geometry. In the present investigation, an analysis using three-dimensional upper bound method using fifth-order die profile function has been carried out for extrusion of square sections from square billet. The extrusion pressure and optimum die length have been computed by multivariable optimization technique. The present die shape profile is found to be superior to many other profiles. The results obtained will help in design of optimum die profile and investigation of its performance.     

温度和摩擦条件对不锈钢管材挤压过程的影响

以316LN不锈钢管材挤压件为例,采用3种温度状态和4种摩擦因子的不同组合共进行12组挤压过程的数值模拟,得到了不同参数下坯料温变、模具载荷及材料流动情况,掌握了温度和摩擦条件对挤压力和材料流动的影响规律,为管材挤压工艺优化提供了理论依据。     

Round-to-channel section extrusion through linearly converging die: a three-dimensional analysis

Metal flow in the extrusion process is an important factor in controlling the mechanical properties of the extruded products. It is, however, difficult to predict the metal flow in three-dimensional extrusion of sections due to the involvement of re-entrant corners. The present work is an attempt to find an upper bound solution for the extrusion of channel section from round billet through the taper die. The rigid-perfectly plastic model of the material is assumed, and the spatial elementary rigid region (SERR) technique is presented for which the kinematically admissible velocity field is found out by minimizing the plastic dissipation of power. The presented analysis allows for specification of process control parameters and their relation to extrusion load, equivalent die angle, reduction ratios and friction factor.     

An investigation of the tribological interaction between die damage and billet deformation during MMC extrusion

This study deals with material flow behaviour during the extrusion process of a metal-matrix composite (MMC), and the effects of this behaviour on the damage to die flat surfaces. AA 6063 aluminium matrix composite billets reinforced with SiC particles (167 μm) were prepared using the stir-casting method for extrusion. Extrusion of the MMC billets were conducted at 500 °C with a ram speed of 2 mm s⁻¹ and an extrusion ratio of 25:1 under laboratory conditions. The extrusion die with two different channel profiles was manufactured from AISI H13 steel that was hardened, tempered and grounded. The flow patterns of the deformed billet during the MMC extrusion determine the positions of the SiC particles in the deformation zone. While some of the SiC particles flow within the deformed material, some flow at the deformed billet surface; these SiC particles play the most important role in the damage mechanism of the die-bearing surface and the geometry of the dead metal zone (DMZ). The possible damage to the die-bearing surfaces is severe at the entrance of the die bearing. On the other hand, some SiC particles are broken in this zone due to the severe deformation stress of the MMC billet.     

Optimal design of an extrusion process for a hinge bracket

This study considers process design in forming a hinge bracket. A thin hinge bracket is typically produced by bending a sheet panel or welding a hollow bar into a sheet panel. However, the hinge bracket made by bending or welding does not have sufficient durability in severe operating conditions because of the stress concentration in the bended region or the low corrosion resistance of the welded region. Therefore, this study uses forming to produce the hinge bracket part of a foldable container and to ensure durability in difficult operating conditions. An extrusion process for a T-shaped hinge bracket is studied using finite element analysis. Preliminary analysis shows that a very high forging load is required to form the bracket by forging. Therefore, extrusion is considered as a candidate process. Producing the part through the extrusion process enables many brackets to be made in a single extrusion and through successive cutting of the extruded part, thereby reducing the manufacturing cost. The design focuses on reducing the extrusion load and on ensuring shape accuracy. An initial billet is designed to reduce the extrusion load and to obtain a geometrically accurate part. The extruded part is bent frequently because of uneven material flow. Thus, extrusion die geometries are designed to obtain straight parts.

     

Applying ANN to predict the forming load and mechanical property of magnesium alloy under hot extrusion

This study establishes the database concerning magnesium alloy hot extrusion, and uses it to conduct various investigations. Firstly, artificial neural networks (ANN) analysis is used to determine the die shapes of various extrusion ratios. Secondly, the process parameters for the hot extrusion of magnesium alloy are determined, and thirdly, the tensile strength and maximum extrusion load of the finished product are predicted. The database includes 11 parameters, associated with 108 sets of experiment, determined by material type (AZ31 and AZ61), extrusion ratio (14.41, 35.9 and 55.85), product shape (tubular and sheet), semicone angle of the die (90° and 30°), extrusion speed, temperature to which the billet is heated, temperature to which the container is heated, lubricant, hold-time at a specified temperature, extrusion load and tensile strength. ANN is applied to learn from this database, and backward propagation analysis is conducted to find the mechanical properties of the products under various extrusion ratios. This study adopts the orthogonal array of the Taguchi method to hot extrusion experiments that involve dies with different extrusion ratios, and sets the tensile strength and extrusion load of the finished product as the quality characteristics, to acquire the optimal parameter condition. Then, based on the results obtained from the additive model, confirmatory experiments are performed. An Analysis of Variance (ANOVA) analysis is then performed to investigate and analyze the influence of factors on the hot extrusion process. The weight of important factors in the database is increased, and subsequently, the forming load and mechanical properties of magnesium alloy under extrusion are accurately predicted.     

The effect of billets extruded by a curved and flat-face die on the semisolid characteristics and tensile properties of thixoformed products

In this study, A356 aluminum billets in different extruded states are used as feedstock for the thixoforming. The extrusion billets were fabricated by a hot extrusion process through a flat-face and a curved die. After the induction reheating of the extrusion billets into a semisolid state, the microstructural evolution was thoroughly investigated. For the extrusion alloy by the flat-face die, there was a large variation in the average grain size (20 %) and the mean roundness (17 %) of equiaxed α-Al grains. This, together with evidence of elongated grains in the interior regions of the billet, indicated that a noticeably nonuniform globular microstructure had been obtained. In contrast, for the extrusion alloy through the curved die, the obtained globular microstructure was more uniform. There were slight variations of 5 % and 7 % in the average grain size and the mean roundness, respectively. By using the extrusion billets, some parts fabricated via the thixoforming process those underwent T6 heat treatment. The tensile test results for the fabricated parts showed that when the extrusion billet through the conventional flat-face die was used as the feedstock, there was a large scattering in the tensile properties throughout the part. In contrast, when the extruded billet through the curved die was used as the feedstock, limited variation was observed in the tensile properties.     

Assessment of ZK60A magnesium billets for forging depending on casting methods by upsetting and tomography

The workability of ZK60A billets fabricated by semi-continuous casting, subsequent extrusion, and die casting were evaluated. To determine the deformation capability of the three different billets, upsetting tests were conducted at elevated temperatures and two different strain rates. The differences in critical height reduction depending on the casting methods were investigated based on inherent defects inside the billets, and variation in the mechanical property with the location within the semi-continuously casted billet was investigated by X-ray tomography and electron backscatter diffraction. Uniformity of density substantially affected the mechanical properties of the billet. The drastic decrease in the workability of the die-casted billet at temperatures higher than 320°C was also discussed.     

Effects of extrusion variables on temperature distribution in axisymmetric extrusion process

A numerical method was developed to simulate the non-steady-state temperature distributions during forward extrusion process. The velocity, strain rates, and strain fields within the deformation zones during extrusion were obtained, using upper bound method of analysis to obtain internal heat generations coupled to the necessary heat transfer conduction equations. The computer program written in C++ language essentially simulates the extrusion process and takes into account extrusion variables such as material properties, friction conditions, extrusion velocity, extrusion ratio, die preheat temperature, billet height, percentage reduction in area, and die land length. The effects of billet height and percentage reduction in area on the temperature distributions within the dead metal zone give good agreements with experimental results. It is found that the higher the billet's heights and higher the percentages reduction in areas, the higher the temperature rises during the extrusion process. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no effect on the dead zone temperature. Also, increasing speed of deformation shows an increasing dead zone temperature rise than a more gradual die land temperature rise. It can be stated that the extrusion temperature increases proportionally to the increase of the container temperature.     

On the equivalent friction factor in hydrofilm extrusion

Hydrofilm extrusion is a kind of hydrostatic extrusion which uses a minimum amount of oil as lubricant and pressure-transmitting medium. In hydrofilm extrusion energy dissipation in the fluid lubricant between the die and working material corresponds to sliding friction in ordinary lubricated extrusion using solid lubricants. Utilizing the upper-bound theorm, an “equivalent” friction factor is defined so that the overall frictional effect between the die and working material can be conveniently investigated in terms of geometrical parameters and press velocity. On the basis of this definition, the effects of various process parameters on the frictional characteristics in hydrofilm extrusion are discussed. It is consequently found that the dominant contribution to frictional energy dissipation is made by reduction of area and press velocity. Die length is found to have very little influence on the equivalent friction factor in so far as it is longer than billet diameter.     

A Study on the Extrusion by a two-step process for manufacturing helical gear

Much research has been carried out in the manufacturing of helical gears by cold forging or by extrusion. Although cold forging is applied to some bevel, spur, and helical gears, problems in connection with the reduction forming load and tool life still make it difficult for these methods to be commercialized. In this study, focusing on reducing a load in forming helical gears, the extrusion of helical gears by two-step process is proposed. This process is composed primarily of extruding a billet to a spur gear and then twisting the previous spur gear extruded to a helical gear. Cylindrical billets of Cr-Mo steel(SCM 415) and aluminium alloy(Al60 series) were used as specimen materials for the experiments. The maximum loads obtained by upper-bound analysis and FEM are compared with the results of experiments. The loads of the analysis have good agreements with those of the experiment. The newly proposed method can be used as an advanced technique that remarkably reduces the forming load and replaces the conventional forming.     

Extrusion of axi-symmetric tubes from hollow and solid circular billets: : a generalised slab method of analysis and some experiments

To analyse the mechanics of extrusion of an axi-symmetric tube starting from either a hollow or a solid circular billet, a generalised analytical approach based on the slab method of analysis is developed for a somewhat general case of tube extrusion through a general profile-shaped die and over a general profile-shaped mandrel. The results of mean extrusion pressures obtained from the theoretical analysis for the various die–mandrel combinations are compared with the experimental investigation carried out on a model material and with the work of other authors. These show reasonably good agreements.     

Portholes-equal channel angular pressing: novel technique for extrusion of 6061 aluminum alloy tube by subsize billet

Wrought 6061 Al alloy exhibits the prospective applications in the form of tube extrusions. In this study, billets of 6061 Al alloy were extruded under optimized conditions by a novel technique namely portholes-equal channel angular pressing (P-ECAP) extrusion. This technique is different from the conventional extrusion as the dimension of the product is greater than that of the billet. The extruded tube produced by the method was characterized for their microstructure as well as for their physical and mechanical properties. The tube that was fabricated using P-ECAP die showed significant refinement in microstructure with improved mechanical properties outside the seam joint portion. However, the extrusion loads using porthole die were less compared to that in the conventional method by using columniform billet because of the decrease in billet dimension or extrusion ratio. Furthermore, microstructure at seam joints of 6061 Al alloy extrusion was discussed in detail in this study. Thus, the P-ECAP technique has significant potential for substantial energy saving.     

A generalized method for analysis of three-dimensional extrusion of arbitrarily-shaped sections

Despite increasing demand for and application of three-dimensional extrusion of various sections through continuous dies, so far very little work has been done by systematic and general analysis to predict the plastic flow properly. For effective die design, efficient design method and the related method of theoretical analysis are required for extrusion of complicated sections. In generalized three-dimensional extrusion of sections through continuous dies, a new method of die surface representation, using blending function and Fourier series expansion, is proposed by which smooth transitions of die contour from the die entrance to the die exit are obtained. The flow patterns as well as the upper-bound extrusion pressures are obtained on the basis of the derived velocity field. The effects of area reduction, product shape complexity, die length and frictional condition are discussed in relation to extrusion pressure, the distorted grid pattern and distribution of the final effective strain on the cross-section of the extruded billet. As computational examples for arbitrarily-shaped products rounded rectangles and ellipses are chosen for the extruded sections. Experiments are carried out for aluminum alloys at room temperature for a rounded square section and an elliptic section. In order to visualize the plastic flow, the grid-marking technique is employed. The theoretical predictions both in extrusion load and deformed pattern are in good agreement with the experimental results.     

温度和背压方式对等通道转角挤压过程的影响

建立了用于分析等通道转角挤压过程的热力耦合有限元模型。通过对纯钛等通道转角挤压过程的数值模拟,获得了模具及试件内部的应力、应变和温度分布。研究结果表明,等通道挤压过程中试件温度分布不均匀,在模具转角剪切部位温度最高且存在明显的温度梯度。在较高的温度条件下进行挤压,有利于降低成形压力和获得较大的变形量;接触摩擦的存在导致模具受力状况恶化及试件变形的不均匀;而带背压的挤压方式可以在有效地增加试件变形量和变形均匀性的同时降低材料产生破坏的可能性。     

Analysis of lateral extrusion of gear-like form parts

The analysis of lateral extrusion process was carried out. A three dimensional FE model was developed to analyze the effects of some important geometrical parameters such as initial billet dimensions, gap height and frictional condition on the required forging load, the material flow pattern and effective plastic strain distribution. The FE code of DEFORM-3D was employed. A series of experimental tests on commercial lead billets were carried out to verify the FE results. The simulation work has been performed by the rigid-plastic FE method. The results obtained using the numerical solutions have been compared with the experimental data for each case study in terms of required forming load and material flow pattern in different regions. Comparison between FE and experiment results showed good agreement. Both the simulation and experimental results highlight the major role of above mentioned parameters on the required forming load and material flow pattern. The results showed that the gap height has the greatest effect on the forming load and material flow. The results presented in this paper could be used as basic data in the design of the lateral extrusion process.     

An analytical formulation as an alternative to FEM software giving strain and stress distributions for the three-dimensional solution of extrusion problems

A new improved analytical method based on the upper bound theorem is presented for the solution of extrusion problems. This method has been formulated in such a way as to eliminate the deficiencies in the previous works in order to enable it as a powerful analytical tool as an alternative to finite element software. The proposed formulation is a general method of solution, which could be used for the analysis of many bulk forming processes. However, in this paper, the forward extrusion of a square section from a round billet has been presented as an example. Kinematically admissible velocity fields were computed which gave a more physically realistic material flow patterns as compared to previous works. The distribution of strain and stress as well as the results for the effect of process parameters on the extrusion load and die geometry was also given. These results were compared with FEM data to observe the accuracy and effectiveness of the present method. For the extrusion of square sections from round billets, detailed analysis of strain distribution on the exit section was carried out using the components of the power due to internal deformation, interface friction, and velocity discontinuities at the entry and exit surfaces. Comparison with experimental data was made, and verification of the theoretical results was carried out. The improvement of the results computed using the present method was shown by comparison with the previous works.