Forgeability of ultra-fine grained aluminum alloy for bolt forming

In the present investigation, an equal channel angular extrusion (ECAE) was used to make bulk nanostructure of the commercially available aluminum alloy AA1050 at room temperature. In order to investigate the effect of the ECAE routes on formability, three different routes A, Bc, and C were applied up to three passes by employing a split die set-up, which required less extrusion load compared with the conventional dies. Formability of the conventional and ultra-fine grained specimens was measured by applying a compression test. Considering the formability obtained from the compression test, bolt forming sequences were developed into three stages and applied to manufacture a high strength bolt using a cylindrical ultra-fine grained specimen at room temperature. The effects of processing routes and number of passes in the ECAE on strength increase and its homogeneity in the manufactured bolts were investigated by the tension and microhardness test, respectively. According to this investigation, a novel approach to utilize the ECAE to manufacture high strength bolt using the conventional material is demonstrated. This approach can be extended to other manufacturing parts that require high strength and lesser weight at a competitive manufacturing cost.     

镁合金等径角挤压的研究与进展

对等径角挤压工艺的基本原理及其工艺参数在挤压过程中对镁合金显微组织、力学性能的影响,等径角挤压过程中镁合金的晶粒细化机理、变形机理及其微观结构、力学性能等的演变规律作了综述,并对等径角挤压镁合金超塑性研究现状和镁合金等径角挤压发展趋势作了介绍.     

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。     

Rate-dependent transient extrusion

Plane strain slip line field solutions are developed for deformation at the edge of a cylindrical billet when this is backward extruded to form a thin-walled cup. The extrusion pressure for a perfectly plastic material is then derived assuming homogeneous compression in the centre of the billet. A geometric factor, derived from the slip line field, is identified which permits the extrusion pressure to be determined for a nonlinear viscous material.Theoretical results agree well with recent experimental data on back extrusion of highly rate-sensitive superplastic alloys. It is shown that an apparent steady state exists in the process and that extrusion pressure increases with ram speed with a rate index approximately equal to that of the material. The punch profile shape has a greater effect on extrusion pressure for viscous materials than for perfectly plastic ones. The method of analysis appears to have a generality beyond the particular process considered and may be used to optimize extrusion equipment designs.     

An analytical solution of the ECAE process of bi-layer strip using a Bezier type streamline

Co-extrusion of strips of different strength and ductility is a process in the production of bimetal rods of desirable physical and mechanical properties. Equal channel angular extrusion (ECAE) is an innovative process for applying severe plastic deformation to materials. The present study is concerned with the ECAE of different bi-layer strips. Developing a kinematically admissible velocity field using a Bezier-type streamline is the aim of present research. In this analysis, using the mentioned velocity field and the upper bound theorem, the extrusion force as well as the strain distribution in the deformation zone of the ECAE process are predicted. The solution takes into account the die profile, friction conditions, strength, arrangement and thickness ratio of the layer materials. Experimental results of ECAE of aluminum/copper and aluminum/mild steel bi-layer strips showed a good agreement with the predicted results.

     

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.     

Forward extrusion through steadily rotating conical dies. Part I: experiments

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.     

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.     

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.     

铝合金轴固定件热挤压成形的有限体积法模拟研究

由于变形剧烈，复杂铝型材挤压成形有限元模拟会因网格不断重划分而精度欠佳。文中基于可以有效避免网格重划分难题的有限体积法，对铝合金门轴固定产品的热挤压过程进行数值模拟，详细分析挤压成形中各个阶段金属流动情况以及应力、应变、温度、速度等场量的分布变化情况。棒料进人模口至完全流出工作带这段时间是型材挤压最为困难的阶段，材料在工作带处的应力、应变最大，温度最高，因而对模具工作带处造成的磨损也最为严重。进人到最终稳定挤压阶段时挤压方向金属流速计算值与理论挤出速度吻合很好。模拟结果表明所用有限体积法是有效的，可以为铝型材挤压的模具设计与工艺参数的选择提供理论指导。     

Microstructure Evolutions during the Hot Extrusion Process of AZ 31B Magnesium Alloy

The hot bulk deformation processes (such as extrusion, forging and rolling) are efficient ways to produce fine microstmcture. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm·s-1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase (β-Mg17A112) are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure-In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed free reerystallized grains.     

A new formulation for three-dimensional extrusion and its application to extrusion of clover sections

The metal flow in the extrusion process is an important factor in controlling the mechanical property of the extruded products. It is, however, difficult to predict the metal flow in three-dimensional extrusion of complicated sections due to the difficulty in representing the geometry of the die surface and in expressing the corresponding velocity field. In this study a new kinematically admissible velocity field for a generalized three-dimensional flow is derived, in which the flow is bounded by the die surface expressed by an analytic function. Then, by applying the upper-bound method to the derived velocity field, the flow pattern as well as the upper-bound extrusion pressure are obtained. As a computational example, extrusion of clover sections from round billets is chosen. A new method of die surface representation is proposed by which there is a smooth transition of die contour from the die entrance to the die exit. Computation is carried out for work-hardening materials such as aluminium and steel. The analysis takes into account the effect of product shape complexity, lubrication condition and reduction of area on extrusion pressure, average effective strain and distribution of effective strains on the cross-section of the extruded product.     

凹模型线对挤压过程的数值模拟和试验研究

本文用数值拟和试验研究相结合的方法分析凹模型线对挤压过程变形状态的影响。模拟计算采用刚塑性有限元法,试验研究用坐标网格法和密栅云纹技术。文章对文献中提出的圆锥凹模、余弦曲线凹模、等应变率曲线凹模、双曲线凹模、椭圆曲线凹模和最短流线凹模,以及另外新设计的正弦曲线凹模,进行数值模拟,得到了各种型线模挤压时的速度场、应力场和应变场,以及由于变形热效应引起的试件和模具温升。并用光刻网格法和密栅云纹法进行试验校核。计算结果与实验结果相互吻合良好,研究结果表明七种曲线凹模中,以新设计的正弦曲线凹模最佳,余弦曲线凹模次之,这两种型线凹模的挤压力低,而且内部应变分布均匀。     

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.     

Effect of ECAE on Microstructure and Tribological Properties of Cu–10%Al–4%Fe Alloy

Equal channel angular extrusion (ECAE) process was carried out for a commercial aluminum bronze alloy (Cu–10%Al–4%Fe) produced by hotrolling at high temperature. The effect of ECAE on microstructure, mechanical, and tribological properties of the alloy was investigated. Experimental results showed that the grain size of the alloy decreased with the increase of the pass number of ECAE. After applying ECAE with six passes, the hardness and yield strength of the alloy increased from 118 kgf/mm² and 356 MPa to 165 kgf/mm² and 588 MPa, respectively. The friction coefficient and wear rate of the aluminum bronze alloy were largely reduced due to the improvement of mechanical properties after ECAE. The adhesive wear was the primary wear mechanism for the specimen without ECAE, while abrasive wear was dominant for the specimen with ECAE after six passes.     

Factors influencing paste extrusion pressure and liquid content of extrudate in freeze-form extrusion fabrication

Freeze-form extrusion fabrication process extrudes an aqueous ceramic paste of high solids loading by ram extruder to fabricate 3-D ceramic green parts. An appropriate extrusion pressure is necessary to get the desired extrusion velocity, and the extrudate should be keep in the same composition during the extrusion process for fabricating uniform green parts. The ram velocity, die land geometry, and paste property are three main factors influencing paste extrusion process. In this paper, the experiments were carried out to determine the effect of the three factors on the extrusion pressure and liquid content of extrudate. The experimental results show that the ram velocity is a strong factor governing the extrusion pressure profiles and too low ram velocity can result in liquid phase migration. The die land diameter and paste viscosity have obvious impact on paste extrusion process, which is largely consistent to the Benbow–Bridgwater model but sometimes is influenced by liquid phase migration. A further analysis of paste extrusion process indicates that the varying of paste structure in different extrusion stage leads to the experimental phenomenon. The research can help to get better understanding of influence factors in paste extrusion and to give reference of controlling the process in freeze-form extrusion fabrication process.     

Three-dimensional analysis of round-to-angle section extrusion through straight converging die

The increasing interest in the modeling of metal-forming processes in recent years has brought the development of different analytical and/or numerical technique. However, due to the complexity nature of the problem, most of the attempts are made with plain strain assumptions. Among the different techniques used, the upper bound method is a convenient tool for evaluating the rate of work in processes involving predominantly plastic deformation of rigid/perfectly plastic material. The present study is an endeavor to remodel and apply the spatial elementary rigid region technique for analyzing extrusion of angle-section bars from round billets through the linearly converging die. Optimized values of the nondimensional average extrusion pressure at various area reductions have been computed and compared with experimental results. It is observed that the proposed technique can be used effectively with adequate accuracy to predict the optimal die geometry which requires a minimal forming stress at different reduction of areas and friction conditions.     

Modeling and simulation of polymer melts flow in the extrusion process of plastic profile with metal insert

The extrusion technology of plastic profile with metal insert is recently an advanced plastic processing method whose products keeps rising today for their excellent performance. However, the related fundamental research on polymer forming mechanism in the extrusion process of plastic profile with metal insert is lagging behind. With the development of computational fluid dynamics (CFD) theory, numerical method becomes an effective way to investigate such complex material forming problems as in the polymer extrusion process. In the present study, the mathematical model for three-dimensional non-isothermal viscous flow of the polymer melts obeying a Carreau model is developed based on the CFD theory. The Williams–Landel–Ferry equation is employed to involve the temperature dependence of material parameters. A decoupled numerical algorithm based on the penalty finite element method is conducted to predict the rheological behaviors of polymer melts within the complex flow channel. The streamline upwind/Petrov–Galerkin scheme is employed to improve the computational stability for the calculation of temperature field. Based on the theoretical model, the essential flow characteristics of polymer melts in the extrusion process of plastic profile with metal insert is investigated. The distributions of principal field variables like flow velocity, melt temperature, flow stress and pressure drop are predicted. The effects of die structure parameters including the intake angle and the distribution section length upon the melts flow patterns are further discussed. The variations of melt rheological properties versus different processing conditions like the volume flow rate and the metal insert moving velocity are also investigated. Some advice on practical processing operations of the extrusion process of plastic profile with metal insert is accordingly put forward based on the numerical results.     

Evaluating the effects of process parameters on maximum extrusion pressure using a new artificial neural network-based (ANN-based) partial-modeling technique

Metal extrusion process accounts for the production of the majority of industrial and domestic aluminum sections. A major limitation to the success of any extrusion operation is the capability of the particular extrusion press to meet the maximum pressure requirements for that operation. In the present work, the effects of industrial extrusion process parameters and their interactions on the resulting maximum extrusion pressure, of an industrially extruded aluminum alloy, have been studied using a newly devised ANN-based partial modeling technique. Two operating parameters (initial billet temperature and ram speed) and three geometrical parameters (extrusion ratio, profile average thickness, and number of die cavities) were investigated. The main objective for developing this modeling technique is to overcome the limitations of presently available statistical modeling tools, as foreseen by the modeling needs for a complex thermo-mechanical process such as extrusion. The main present limitations are accounting for non-linearity in the process behavior, incorporating interaction effects and a meaningful determination of the highly significant process parameters and/or interactions. These three features have been, collectively, incorporated into the present model by means of combining statistical analysis of variance into ANN and by using a partial sum of squares analysis, which we propose to call the “present factor analysis.” Normal linear regression has been also employed for comparison purposes. According to the present model, maximum extrusion pressure has shown various degree of non-linearity in behavior with respect to the different process parameters and their significant interactions. It has been found that variations in the maximum extrusion pressure are mainly a function of initial billet temperature and its interactions with other process parameters, especially the ram speed. The present ANN-based model has shown superior prediction capabilities compared to the linear model with a marginal overall prediction error value of ±2.5 %.     

Analytical,numerical and experimental approach for design and development of optimal die profile for the cold extrusion of B4C DRMM Al 6061 composite billet into hexagonal section

Aluminium based matrix composites with boron carbide as particle reinforcement called Discontinuous reinforced metal matrix composites (DRMMs) possess high specific strength, high elastic modulus, good wear resistance, damping capacity and thermal stability. But during the development of DRMM composites, compression process like extrusion is an advisable secondary process for homogenous structure. This research work investigates the metal flow behavior of Al-B₄C based DRMM composite through six different die profiles namely third order polynomial, fourth order polynomial, cosine, elliptical, hyperbolic and conical geometry. Extrusion load, stress and strain distribution, and metal flow for above said die profiles are predicted by using analytical approach upper bound technique and compared with finite element method. Cosine and third order polynomial profiles are found to be most optimal in terms of homogenous and minimal extrusion load requirement. To validate the results, specially made Al-B₄C composite through stir casting route was extruded from round to hexagon through an exclusively fabricated cosine die. Results observed from the experiment have good agreement with both analytical and numerical.