Die design for axisymmetric hot extrusion

A comprehensive finite element model is presented to obtain the temperature distribution in the workpiece as well as in the tooling in hot and warm extrusion processes. Thermo-mechanical analysis of hot extrusion process is carried out by combining the comprehensive finite element thermal model with the deformation models [upper bound and rigid-plastic finite element models presented earlier (N. Venkata Reddy, P. M. Dixit and G. K. Lal, J. Mater. Process. Technol. 55, 331 (1995); N. Venkata Reddy, P. M. Dixit and G. K. Lal, ASME J. Engng Ind. 118 (1996)) [1, 2]. The predictions of the combined thermo-mechanical finite element method (TMFEM) are first compared with experimental results to validate the method. Then it is shown that the temperature distribution and the extrusion power obtained by the combined upper bound/finite element method (UBFEM) are in good agreement with those of TMFEM. Since UBFEM takes significantly less computational time than TMFEM, it is used to obtain the optimal die profile at various process conditions by minimizing the extrusion power.A simple fracture criterion proposed by Venkata Reddy et al. [ASME J. Engng Ind. 118 (1996)] [2] based on the concept of the hydrostatic stress component in the deformation zone falling to zero is used along with TMFEM to predict the die lengths at which the initiation of internal defects takes place. Finally, it is shown that the optimal die profiles satisfy the conditions for prevention of internal defects.     

固定针挤压铝合金无缝管材穿孔阶段挤压针分析

通过UG建立了固定针挤压铝合金无缝管材模具的几何实体模型。在此基础上,建立了铝合金无缝管材挤压过程有限元分析三维模型,得到了热机械耦合结果。获得了挤压针轴向压力、温度场和应力场的变化规律。预测了挤压针可能产生失效的部位,为挤压针的设计及修复提供参考。     

Analysis of the central cavity of axisymmetric forward extrusion by the upper bound approach

In this paper, the use of a kinematically admissible velocity field to predict the presence of a central cavity in the final stage of axisymmetric forward extrusion is advanced, in accordance with the results of Moire experiments. On the basis of the velocity field, the critical condition for central cavity formation is obtained by the upper bound approach. Furthermore, the quantitative relationships between central cavity formation and process parameters (reduction in area, frictional factors on the ram and chamber wall, relative residual thickness of the of the billet) are studied. The results show that (1) the critical relative residual thickness of the billet used for the central cavity formation is affected primarily by the reduction in area and the frictional factors on the ram, and slightly by the frictional factor on the chamber wall; (2) the relative dimensions of the central cavity increase with a decrease in the relative residual thickness of the billet; (3) the growth rate of the central cavity decreases with an increase in the frictional factors on the ram, but is affected by the frictional factors on the chamber wall only slightly. Good correlation is found between the analytical and experimental results.     

可压缩材料轴对称和平面应变单位挤压力之间的关系

在轴对称子午面和平面应变变形平面几何尺寸相同、外摩擦一致的前提下，利用有限元法、滑移线法和实验方法探讨了可压缩材料轴对称正挤和平面应变正挤间单位挤压力的关系。结果表明，轴对称单位挤压力与平面应变单位挤压力间的比值是一个数值范围，Px＝(1．2—2．1)Pp；该比值与相对密度、挤压比、摩擦条件以及材料状态有关。     

A deformation model for tube extrusion

Plastic forming processes, the origins of which go back to ancient times, have become more popular in the last five decades, amongst other material-shaping processes. As the needs of the modern world and competition between the processes increase, knowledge of the deformation pattern of the material during a process is being recognized as primary information in the related field. Today, this kind of information is made use of in all areas associated with the process, from the planning of the plant to the ensuring of the quality of the final product.

In this study a deformation model for axisymmetric tube extrusion is proposed, in which the flow lines in the deformation zone are chosen as straight lines passing through a fixed point on the axis of symmetry and the exit surface of the deformation zone which is the plane at the die exit perpendicular to the axis of symmetry. A kinematically admissible velocity field is obtained from this deformation model and the parameter contained in the model is found by introducing this velocity field into the Upper-Bound Theorem. Since there is not a model for tube extrusion in the literature it was not possible to carry out a comparative study, which is why only the results obtained in the study are given, along with the indication of some further research directions.     

厚壁管件无芯棒开式冷挤压塑性变形的分析

给出了厚壁管件开式冷挤压的流函数方程 ,由该方程建立了运动学许可的速度场及相应的运动学许可的速度间断线边界方程。分析了三种间断线 ,确定了适于厚壁管件开式冷挤压的简化可行的速度间断线型式 ;以及由此求得内边界的方法。     

行波管零件挤压成形质量影响因素分析

以电子行业中铣床加工的行波管零件作为研究对象,其加工形状复杂、尺寸小、形位公差要求高、加工难度较大,生产成本较高。针对这些要求和问题,设计了两种冷挤压成形方案,并利用Deform软件对成形过程进行了数值模拟,依据仿真结果采用了有四周约束的凹模,同时分析了上模加载速度、摩擦系数和保压时间对最终产品质量的影响。最终以尺寸相对偏差为评价指标,通过正交实验得到了行波管零件挤压成形最佳工艺参数组合:上模加载速度为60 mm·s^-1、摩擦系数为0.08、保压时间为3 min。并据此参数进行实验验证,得到了成形效果良好的行波管零件。研究结果对类似产品在生产中的工艺改进具有一定的指导意义。     

A feature based analysis of tube extrusion

The paper presents a feature based upper-bound model to analyze three dimensional complex geometry tube extrusion process having generalized die and mandrel profiles. The analysis is based on kinematically admissible velocity field to obtain the optimal extrusion pressure by optimizing the die length using Variable Interval Golden Section Method. Various parameters such as product profile, shape complexity factor, die and mandrel profiles, reduction, friction, ram velocity and die length, etc., have been chosen for the process and parametric study on extrusion. The experimental and the proposed analytical results have been compared with experimental work by authors and analytical works of other researchers to validate the model that shows good agreement.     

微型微通道管的连续挤压成形工艺

微型微通道管产品具有孔道数量多、孔道尺寸小、壁厚薄、尺寸精度要求高等特点,制备加工难度很大。采用连续挤压制备方法,通过采取双槽挤压方式、增加金属导流板等措施,对模具结构与加工方法、挤压工艺进行优化设计,明显改善了微型微通道管产品挤压成形时金属在产品宽度方向的流动均匀性、孔道部位的有效填充及焊合质量,解决了挤压过程中模具模芯强度不足导致的尺寸超差与失效问题和溢料过多导致产品无法挤出等问题。最终成功试制了厚度为2.2 mm、宽度为45 mm的52孔微型微通道管产品,产品外形尺寸和组织结构均满足设计要求。     

杆-杆型轴对称复合挤压过程的数值模拟及流动规律

采用刚塑性有限元法对杆－杆型轴对称复合挤压过程进行了数值模拟,其结果表明影响上下两端金属流出量大小的主要因素是变形程度的大小,摩擦条件在上、下变形程度相同且较小的情况下,对两端金属流出量的影响比较明显。变形力和金属流出长度的计算结果与实验结果较为吻合。     

扁管类铝型材挤压模分流孔设计方案的比较分析

通过实际例子介绍了扁管类铝型材挤压模结构特点,提出了成形扁管类铝型材的5种挤压模分流孔结构,分析了每种分流孔结构的特点和适用性,提出了得到最佳优化设计的方法,可为成形扁管类铝型材挤压模设计提供参考。     

An upper-bound solution for axisymmetric extrusion of composite rods through curved dies

The study is concerned with an analysis of forward extrusion of composite rods through curved dies. A kinematically admissible velocity field is derived by assuming proper streamlines and applying the flow function concept to each material region of plastic deformation. Two kinds of flow functions are chosen in order to compare the effect of the choice of the flow functions. The effect of work-hardening is incorporated approximately by calculating the strains at the exit of both materials. The upper-bound method is then employed to determine the extrusion pressure for various process variables. The experiments are carried out with commercially pure aluminum and copper billets for various reductions of area and cone angles at room temperature. The experimental results are then compared with the theoretical calculations. The comparison shows that the second-order flow function is in better agreement with the experimental observation both in extrusion loads and in deforming regions.     

An advanced model of designing controlled strain rate dies for axisymmetric extrusion

This paper presents an advanced model for the design of stream-lined axisymmetric extrusion dies based on a prescribed strain rate variation. This is vital to the preparation of the workpieces with mechanical properties that are very sensitive to the strain rate distribution during a manufacturing process. The proposed model, which incorporates Tresca’s yield criterion and velocity field with the die angularity, can give an accurate prediction of the die shape. Influences of the interfacial friction and the ram velocity on the die geometry are also studied. As a verification of the proposed model, an updated Lagrangian formulated, elasto-plastic finite element program was developed to analyze the axisymmetric extrusion process. A clear derivation of the load-correction matrix, which is in dispensable for the surface traction rate equilibrium in the updated Lagrangian formulation, is described for the application of the finite element simulation. A friction-correction matrix based on a constant shear law is used to solve the interfacial friction. From the comparison of the resultant strain rate distribution, it verifies that the advanced model can determine the surface angularity and friction force in the extrusion process.     

Process sequence design in cold extrusion to form an axisymmetric shell body

The multi-stage cold extrusion process to produce a steel axisymmetric shell body is investigated for process sequence design by using the finite element method. The main design goal is to obtain the optimum process sequence which can produce the required part most economically. The established process sequence is simulated and design criteria are examined. Based on the results of preliminary simulation, two strategies for improving the sequence are derived for the type of preform. Using the approach taken with a plate preform, the finished product of a shell body is produced in three operations and two annealing treatments while the conventional sequence consists of five forming operations and four annealing treatments. The final design of the improved sequence is achieved by controlling process parameters and through creative punch design based on the finite element simulations.     

中空消音螺旋管挤出模设计

以排水管的中空消音螺旋管为研究对象,制定了中空消音螺旋管成型工艺的优化方案,介绍了优化设计的要点,设计的中空消音螺旋管挤出模,结构简单,成本低,生产效率高,易于加工,不易损坏,使用寿命长。     

Rigid-plastic boundaries approach to the analysis of arbitrary profile dies in axisymmetric extrusion

A new theoretical model to analyze arbitrary profiles of extrusion dies is proposed in this paper. In this model, generalized rigid-plastic boundaries with optional variables are used to minimize the power by the upper-bound method. To satisfy the velocity boundary conditions at the entrance and exit, the streamline function is designed in the normal form of r(η, z), which satisfies the flow conditions and the rigid-plastic boundaries. Four sets of profile dies (cosine, elliptic, hyperbolic, and conic) are represented with different slopes at the entrance and exit in order to illustrate this method. Experiments were conducted in order to compare the results with those of the theoretical model. It was found that the predicted load and flow patterns were in agreement with the experimental observation and the results from the literature.     

管材挤压力能参数物理模型

采用主应力法确定了管材挤压力理论计算公式 ,分析了变形温度、凹模锥半角、润滑剂、挤压比等对管材挤压力的影响及规律 ,经实验验证 ,其理论计算结果与实验结果相吻合 ,相对误差小于 2 0 %。     

铝合金筒件侧向等温挤压成形的金属流动分析

尾翼筒体结构件为某飞行器重要零件,采用铝合金等温挤压成形代替传统的钢质工件机械加工能有效提高材料的利用率、降低生产成本。通过分析形状特征,本文提出反挤压带通筋的筒体和侧向挤压凸台两步成形的方法。侧向挤压是成形的关键,通过数值模拟分析了侧向挤压过程中金属质点的流动方向、速率及等效应变的变化。结果显示:成形时,金属质点流线清晰、完整;金属流动速度均匀,层次分明;筋部产生的等效应变可增强性能,筒壁处的应变小,对筒壁性能无影响。最后通过实验,印证了模拟结果,进一步论证了该工艺的可行性。     

亚毫米孔径微通道铝合金管挤压成形的数值模拟

基于DEFORM-3D有限元分析平台,采用网格分步重划分的方法,实现了对微通道管成形非稳态过程的三维数值模拟,获得了成形过程模具中的金属应力和流速分布,以及模具受力情况。利用数值模拟结果,结合压力-时间判据,对焊合质量进行评估,并利用热模拟试验机模拟了挤压成形中相应温度和接触压力下的焊合过程。该文研究可对实际生产微通道管时工艺参数优化和挤压模具设计等问题提供参考。     

大口径厚壁无缝钢管热挤压过程中挤压力的求解

分别采用了主应力法、功平衡法以及上限法推导了大口径厚壁无缝钢管在挤压过程中挤压力的3种计算公式,并且利用有限元模拟法对大口径厚壁无缝钢管挤压力进行了模拟计算。与有限元计算相比较,主应力法和上限法计算结果的平均相对误差分别仅为7.70%和7.61%,表明这两种公式具有一定的工程适用性;功平衡法计算结果的平均相对误差较大,但若取理论计算结果除以120%后的值,再与模拟结果作比较,则平均相对误差可降至3.18%,仍可精确预测大口径厚壁无缝钢管挤压力。