形状沉积制造及其应用

文章在分析了常规的快速原型制造所存在的缺点后，详细地介绍了形状沉积制造区别于快速原型制造过程中单纯地添加材料的过程——添加／去除零件材料方法，正是由于这一差别使得该方法制造的零件精度不受分层厚度的影响，并且可以采用多种材料制造零件。介绍了形状沉积法的具体工艺过程、可采用的材料沉积工艺方法、沉积制造的设备构成、分层技术、特点及基于形状沉积制造的新方法——模具形状沉积制造，最后介绍了形状沉积制造在功能零件、模具及预装配机构快速制造中的应用实例。     

模具参数对轴向冷挤内花键挤压成形力的影响

通过对轴向冷挤内花键的数值模拟,研究了模具参数对挤压成形力的影响,发现模具的工作长度对挤压成形力的分布有明显影响,较短的模具会产生一定的残余挤压应力;模具的导向长度除了影响挤压成形力外还直接影响零件的质量,在挤压过程中刮出余料;以挤压过程中毛坯受到的平均载荷为参考,在选定范围内挤压角的大小与挤压成形力成正比。根据模拟试验的结果选定了各参数在预定范围内的最优参数值;针对初始设计的模具端面形状容易造成挤压成形力过大的问题,优化了模具端面形状,发现带有梯形模面形状的模具产生的挤压成形力比初始模具小30%,成形质量也更高。     

一种高形状精度U形件的弯曲模优化设计

介绍了一种高形状精度U形件的弯曲成型方法。分析了U形零件的工艺特点及检验要求,对零件的形状精度进行了合理评估。在充分考虑卸载后的弹复变形后,对模具结构进行了优化设计。与改进前的弯曲模相比,改进后的凸模为带有凸筋的结构,在成型过程中集成了弯曲与镦挤的复合变形,使U形件原本以凹模为成型基准变成了以带筋凸模为成型基准,改进后模具结构更加简单,零件的形状精度得到保证,外观轮廓清晰,满足了质量要求。     

盆形端盖零件的拉深模设计

介绍了一种机器零件——盒形端盖的冲压工艺分析、工艺方案确定以及合理冲压模具的设计。并具体介绍了盒形工艺方案确定的方法，合理选取凸、凹模间隙及最佳模具的设计方法和过程。此次模具设计的突出特点是尝试使用复杂的复合模具，解决常规冲压工艺模具套数多、工艺路线长、生产成本高、效率低等缺点，并为以后此类零件冲压工艺的编制及模具设计提供了可靠的依据。     

基于SolidWorks平台的挤压模具CAD系统

基于SolidWorks平台的挤压模CAD系统将大量的专家知识和设计经验存储于模具结构和零件模型中,通过选用不同模具组件的结构形状,达到挤压模具的优化设计,并利用模具零件间的装配形式和装配关系实现挤压模具的自动装配,生成模具零件工程图和装配体工程图,从而提高了挤压模具设计的智能度,减少了设计人     

铜合金压气缸的热挤压模具设计

分析了高度为340mm的压气缸的热挤压工艺及模具的设计过程。如果采用一次挤压成形，现有3150kW压力机无法解决脱模和挤压力问题。采用新的模具结构，分2次挤压成形，将一、二序挤压凹模通用并且把第2序挤压凸模设计成中空式，很好地解决了以上问题，同时给出了一种在小设备上成形大零件的方法。     

板材成形加工的润滑(上)

板材成形加工是冷冲压技术的重要组成部份。它是将各种不同规格金属板料在常温下对其施加压力(通过压力机、模具等)使之变形,以获得所需形状零件的方法。它广泛用于机械、电子、轻工等工业中,有60%以上的零件需用模具进行加工。因为板材成形加工是靠模具使板材压成各种形状的零件,所以模具与工件之间必然会产生摩擦,为减少挤压力、保症工艺条件,必须采取润滑。润滑条件的好坏直接影响成形工艺的发展。     

挤压参数及模具结构参数对某大长径比铝合金零件冷挤压流变成形载荷的影响

代号为SD-L的大长径比铝合金零件采用冷挤压成形工艺,其挤压载荷直接与挤压参数相关.采用DEFRORM-3D软件对该零件冷挤压成形过程进行仿真模拟,在不同挤压速度v、摩擦系数f以及凹模拐角处圆角半径R下对该零件冷挤压成形过程进行了数值模拟研究,获得了成形载荷随挤压参数及模具结构参数变化的规律.结果表明:成形载荷峰值随着挤压速度和凹模拐角处圆角半径的增加而减小,摩擦系数的增加则会导致成形载荷峰值增大.     

铝合金曲面内腔筋件工艺分析及模具设计

通过对带内筋的铝合金桶形件的工艺分析,确定采用径向挤压工艺对该种类型零件进行制作,并介绍了挤压此类零件时所使用的模具结构设计.     

冲压模具精加工过程控制浅析

基于对模具精加工过程中工艺处理的经验方法的介绍,指导具体生产实践中零件的变形、内应力、形状公差及尺寸精度等许多技术参数的控制。良好的加工控制过程,能够有效减少零件的超差与报废,提高模具加工的一次成功率及使用寿命。     

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。     

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.     

Axisymmetric extrusion through adaptable dies—Part 3: Minimum pressure streamlined die shapes

In Part 1 of this series of papers, six kinematically admissible velocity fields, as well as the power terms, were developed for use in upper bound models for arbitrarily shaped dies for axisymmetric extrusion. Part 2 compared the results obtained in upper bound models for the six velocity fields through a spherical die shape and demonstrated that the sine-based velocity field was the best. In this final part, the application of the sine-1 field to extrusion through streamlined dies is developed. By fixing the values of two additional constants in the radial flow flexibility function, the two surfaces of velocity discontinuity, which separate the deformation zone from the incoming and outgoing material, will have no shear. In effect, the analysis for streamlined dies can be modeled without the surface of velocity discontinuity power terms. The results for an arbitrarily curved streamlined die, as proposed by Yang and Han, using the sine-1 velocity field and the cylindrical velocity field from the work by Yang and Han are compared. It is found that the upper bound model using the sine-1 velocity field predicts lower values for the extrusion pressure. A method to determine a streamlined die shape is proposed. The method allows flexibility between the entrance and exit by the use of a Legendre polynomial series for representation of the die surface. The method is termed an adaptable die design. The adaptable die design method is used to determine streamlined die shapes, which will minimize the pressure required for the extrusion process.     

套管叉热挤压成形凸模结构对锻件终成形的影响研究

采用三维有限元法对套管叉锻件热挤压成形过程进行了数值模拟仿真分析。针对其成形过程中出现的叉部顶端及底端充不满现象进行了深入分析，提出了防止这种缺陷形成的一种特殊的凸模结构。生产实践表明，采用这种特殊的凸模结构后，锻件所用的坯料高度减小，每件可节约材料0．08kg；顶部废料厚度的减小，使后续工序切边模具的实际使用寿命至少提高为原来的2倍；台阶约束避免了过多的废料产生，减少了材料的相对流动，延长了终成形模具的实际使用寿命；与传统的锻造工艺相比，采用热挤压方法能获得较高的形状精度和尺寸精度，较好的纤维流向和机械性能。     

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.

     

Analysis and porthole die design for a multi-hole extrusion process of a hollow,thin-walled aluminum profile

The appropriate die design for multi-hole extrusion is still a challenging task because of the complicated circumstances and large material deformation during extrusion process. In the present study, the material flow during multi-hole extrusion process for producing a hollow and thin-walled profile was revealed by means of numerical simulation based on the Arbitrary Lagrangian Eulerian (ALE) method. The effects of eccentricity ratio, shape of the second-step welding chamber, and uneven bearing length on the exit velocity distribution of extrudate were synthetically investigated, and a two-hole porthole die was designed accordingly. The exit velocity and temperature on the extrudate in this optimized die were analyzed and compared with the initial die, and it was found that both of them exhibit better uniformity, which is beneficial for the enhancement of product quality. Through performing the current work, a logical and effective route for designing multi-hole porthole die was proposed as the guidance for die designers.     

数值模拟方法在挤压工艺参数优化中的应用

以出口速度场相对标准速度场偏差(RSDV),平均挤压力P和最大von Mises等效应力σmax作为优化设计目标函数,通过正交设计试验方法和数值模拟手段,对一款双T形截面型材的挤压工艺参数进行优化设计,探讨了一种挤压行业工艺和模具尺寸标准化的方法,并且通过实验验证,证明了经过优化后的工艺合理,实验结果与数值模拟分析结果相吻合。分析发现,在保证模具强度和模具寿命的前提下,提高挤压的速度和模具工作带的高度,能够提高型材挤出的稳定性。     

聚合物双腔微管挤出成型工艺试验研究

针对尺寸小、壁厚不均匀、截面形状复杂的多腔微管挤出成型难度大的问题,以双腔异形微管为研究对象,在挤出过程中引入微量注气系统,采用非对称流动平衡设计方法和微细电火花成型加工技术,设计制造双腔异形微管直角挤出模具。以聚丙烯为试验材料,以双腔微管制品截面的轮廓椭圆度和壁厚均匀度为评价指标,研究微管挤出成型中主要工艺参数对制品形状精度的影响规律。试验结果表明,型腔注气量、螺杆转速、模具温度、水箱真空度和牵引速度对制品椭圆度的影响依次减弱;制品壁厚均匀度主要取决于挤出模具,基本不受工艺参数变化的影响。通过对试验规律的分析,揭示不同工艺参数对双腔微管制品截面变形的作用机理,并得出较优的工艺参数组合,获得满足设计要求的双腔微管制品。     

The use of generalised deformation boundaries for the analysis of axisymmetric extrusion through curved dies

A generalised kinematically admissible velocity field is derived for axisymmetric extrusion through curved dies by employing rigid-plastic boundaries expressed in terms of arbitrarily chosen continuous functions. The corresponding upper-bound extrusion pressure is related directly to boundary functions for the plastically deforming region when the die shape, lubrication condition and material characteristics of the billet are given. The proposed method of analysis makes it possible to predict the deformation pattern as well as extrusion pressure. In computation a third-order polynomial is chosen for the die boundary and the bounding function for the plastic region is chosen to be a fourth-order polynomial. The workhardening effect is considered in the formulation. The plastic boundaries as well as stream lines are affected by various process parameters. The theory predicts the relatively faster axial flow at the center than near the die boundary for greater friction factor even with the same die shape. The effects of area reduction and die length are also discussed in relation to extrusion pressure and deformation. Experiments are carried out for steel billets at room temperature. Deformation patterns are measured for several area reductions by the photoetching technique and the extrusion pressure is measured using a load-cell. The predicted extrusion pressure is in excellent agreement with the value computed by the finite element method. The deformation patterns agree well with the experimental observation.     

Optimal Shape Design of an Extrusion Die Using Polynomial Networks and Genetic Algorithms

Designing the optimal shape for an extrusion die to produce a high-quality extrusion product is often required by industry. Design from experience is unsatisfactory for achieving the flexibility and precision requirements in die design. In this paper, a design method has been developed for the optimum shape design of extrusion die. The extrusion process was modelled and analysed by using the finite-element method to obtain the extrusion force and effective strain for different die shapes. A polynomial network was applied to identify the force and strain models in terms of the geometric parameters of the extrusion die. An improved genetic algorithm was used to optimise the identified model for optimal shape with minimum force and strain. It has been verified that the modelling error is extremely small. The designer can quickly and accurately access the optimal shape of an extrusion die through this new approach. RID=" ID=" <E5>Correspondence and offprint requests to</E5>: Dr Y.-C. Hsu, Department of Mechanical Manufacturing Engineering, National Huwei Institute of Technology, 64 Wun-Hua Road, Huwei, Yunlin, Taiwan. E-mail: jasonych&commat;sunws.nhit.edt.tw