Size effects in micro blanking of metal foil with miniaturization

Miniaturization of micro blanking process caused changes in the relative contribution of relevant process parameters and the grain size of metal foil reaches the same order with the blanking clearance. As a result, the size effects occur, which is different from the other micro forming processes, such as micro upsetting, micro tensile, and micro bending. In the paper, the size effects of micro blanking of metal foil with miniaturization were investigated. Similar to the traditional blanking process, the micro blanking process is still composed of three stages of elastic deformation, plastic shearing deformation, and fracture separation. However, the maximum blanking force appeared at punch stroke of foil thickness, which is much larger than the transitional blanking process of 1/3 of work material thickness. The cross section of micro-hole is also composed of rollover, smoothly shearing zone, fraction zone, and burr. But the distribution of the fraction zone and burr is uneven, which is caused by the influence of the material anisotropy with the decreasing of the foil thickness. The results show that the ultimate shear strength of micro blanking is decreasing with the increasing of the length scale ??, not only for the brass foil, but also for the stainless steel foil. The fracture mechanism of micro blanking of brass foil is significantly changed from shear dimple to slip separation with the decreasing of length scale ??, but the fracture mechanism of micro blanking of stainless steel is not changed and kept ductile fracture with equiaxed dimples     

薄板件台阶孔冲压冷锻组合工艺的数值模拟

针对构想的一种薄板件台阶孔冲压冷锻组合工艺,应用金属塑性加工有限元模拟的关键技术,包括几何模型、材料断裂破坏、网格划分等,用DEFORM-3D软件对此种薄板件台阶孔的冲压冷锻组合变形进行数值模拟。得到了工件材料的等效应力、应变分布,速度场和力—行程曲线。提出细观变形过程可分为冲头小直径处冲孔、冲头大直径处压凹和闭式模锻三个阶段的认识,分析组合工艺特点和材料成形性能。用料厚为2.35 mm的AL-1100铝板材料进行工艺试验,获得了清晰的台阶孔形状,验证了数值模拟的认识。     

滑台式液压冲剪机高速精密同步控制系统

目前国内型材辊压生产线的冲剪设备一般采用定尺停剪方式。该方式生产效率低,精度不易控制,常出现拉(压)痕等缺陷。所设计的系统将液压冲剪设备置于滑动平台上,平台速度由伺服电机驱动滚珠丝杆控制,将圆光栅传感器测得的工件进料速度送入微处理器,通过伺服控制器控制伺服电机,实现滑动平台与工件的同步运动。工程应用表明,所设计的系统同步控制精度±0.05mm,剪切速度大于50根(300mm/根)/min,冲压频率1Hz以上,工作效率提高1倍。     

薄板微小齿轮落料模的试制与探讨

在薄板微小齿轮落料模的试制过程中 ,分析了凸、凹模的加工方法及其间隙确定、研配等工艺方案的可实施性。采用上、下冲裁法 ,提高变形区静水压力 ,解决了冲裁中出现的齿尖塌陷、毛刺等缺陷。指出适当提高相对变形速度、提高静水压力 ,可有利于改善微小型制件的冲裁质量。     

基于Johnson-Cook模型的不锈钢管剪切数值模拟

剪切是乏燃料后处理工艺流程关键环节,因受强辐照制约,对该剪切工艺研究很少,剪切工艺参数需通过大量试验进行设计优化,成本高、周期长且无法掌握剪切机理。以乏燃料组件主要支承结构不锈钢管为研究对象,采用基于Johnson-Cook模型的有限元数值模拟方法来分析剪切过程。设计剪切试验验证上述模型的正确性,并研究剪切间隙、刀具角度、刀具棱边宽度等工艺参数对剪切的影响。结果表明：剪切试验与模型结果拟合性很好,证明了该模型的正确性;最大剪切力、断裂时剪切力随剪切间隙、棱边宽的增大而增大,随刀具角度增大而减小;剪切间隙对压紧段断口形貌影响较大,刀具角度和棱边宽对分离段开口高度影响较大。     

冲裁模具间隙及凹模圆角对凸模应力应变影响的有限元分析

冲裁模具的间隙和凹模圆角,对凸模的应力、应变有重要的影响。运用有限元分析了冲裁模具在不同间隙与圆角下凸模的应力、应变特性。分析结果表明,应力、应变随着间隙和凹模圆角的增加而减小。模拟分析的结果为模具间隙和圆角半径的选择提供了依据。     

Optimization of processing parameters for double-ridged rectangular tube rotary draw bending based on grey relational analysis

The rotary draw bending of double-ridged rectangular tube is a complex nonlinear physical process with multifactors coupling effects. Processing parameters, especially clearances and friction coefficients between tube and various dies, have a significant effect on the forming quality of the double-ridged rectangular tube in rotary draw bending. If the values of these processing parameters are inappropriate, some defects including cross-sectional deformation, wall thinning, and wall thickening easily occur in the bending process of double-ridged rectangular tube. So optimization of these processing parameters is of great importance to control these defects. Based on the grey relational analysis method combined with the orthogonal experimental design and finite element simulation, a grey relational analysis model was established for the rotary draw bending process of double-ridged rectangular H96 brass tube. With the model, optimization of clearances and friction coefficients between tube and various dies was implemented with consideration of interactive effects of the above defects. The results show that (1) the main factors influencing cross-sectional deformation, wall thickening, and wall thinning are tube–mandrel clearance Δc _m, tube-bending die clearance Δc _b, and tube–mandrel clearance Δc _m, respectively. (2) The optimal values of clearances Δc _m, Δc _p, Δc _w, and Δc _b and friction coefficients μ_m, μ_p, μ_w, and μ_b of tube–mandrel, tube–pressure die, tube–wiper die, and tube-bending die are 0.15, 0.2, 0.2, 0.2, 0.02, 0.3, 0.06 and 0.17 mm, respectively. Furthermore, the verification for the optimal values of these processing parameters was carried out, and the double-ridged rectangular H96 bent tube obtained by using the optimal values of these processing parameters has the minimum values of cross-sectional deformation, wall thinning, and wall thickening and can satisfy the national aviation industry standards.     

A comparative evaluation of the turning of reinforced and unreinforced polyamide

This work presents an experimental study on the cutting process for polyamides PA 6 and PA 66-GF30 (reinforced with 30% glass fiber). The experiments were carried out on extruded workpieces using cemented carbide (K15) tools in turning. The objective of this study is to evaluate the influence of the glass fiber reinforcement on the chip compression ratio R _c, chip deformation å, friction angle ρ, shear angle Φ, normal stress σ, and shear stress τ under prefixed cutting parameters (cutting velocity and feed rate). The experimental physical model was compared with the Merchant equation.     

A photoelastic investigation of contact stresses in the backward extrusion process

Photoelasticity is used for investigating the normal and shear stress distribution at the billet-container interface in the process of backward extrusion in cylindrical and flat containers.Photoelastic gauges made from birefringent material were embedded in the side walls of special experimental dies. Cylindrical and flat lead specimens were extruded in experimental dies in a laboratory testing machine. As a result of the experiments it has been established that the contact stress distribution in backward extrusion has a complex character. The curves for the normal stresses at the container walls have a peak located ahead of the punch and this drops abruptly after the metal has penetrated into the clearance between the container wall and the punch. The shear stress changes its sign along the contact zone. The normal and shearing stresses at the cylindrical container walls are considerably higher than at the flat container walls at the same value of reduction ratio.     

Application of response surface methodology for predicting bend force during air bending process in interstitial free steel sheet

In this work, bend force has been modeled using response surface methodology for air bending operation of interstitial free steel sheet. The process parameters considered in this investigation are punch travel (d), strain hardening exponent (n), punch radius (r), punch velocity (v), and width of the sheet (w). The experimental plan was based on the central composite design. The model results are in satisfactory agreement with the experimental results. In addition, an analysis for the effect of the individual input bending parameters on the response has been carried out and presented in this study. This study shows that the punch travel is the dominant factor determining the bend force followed by punch velocity and punch radius. The interaction effects of punch travel and punch radius are considerably significant.     

叠层金属薄板材料的冲裁特性研究

在冲裁分离过程中,单层与叠层金属板材存在很大的差异。通过对比2者的不同特点,选取并分析微元体的应力应变状态,发现在叠层冲裁过程中,变形区内中间层的材料处在3向压应力状态,表现出很强的可塑性。分析冲裁中各因素对应力状态的影响发现,合理地减小凸模与凹模的间隙可以提高变形区的静水压,抑制裂纹的产生,使冲裁过程控制在塑剪变形阶段。以叠层母线冲孔为例来验证理论分析,试验结果与分析一致,叠层冲裁比同厚度单层冲裁所要求的模具间隙更小,其值取在普通冲裁间隙经验公式的基础上乘以0．4左右的修正系数为宜。     

Deformation characteristics and grain size effect of thin silicon steel sheet during shearing

Abstract

The characteristics of shearing force and shearing surface, working hardening at the shearing edge, and structural evolution of microstructures during the transverse shearing of thin silicon steel sheet (SSS) were explored. On this basis, the influences of the thickness and grain size of the thin SSS and lateral clearance of the tool on shearing deformation processes were further analyzed. The results showed that on the condition that the grain size of the thin SSS increased, the compatibility of deformation was worsened and thus the orientation of grains influenced the deformation process more, consequently leading to the expansion of the plastically deformed zone and therefore increased shearing force. On the condition of having the same lateral clearance of the tool, with the growth of grain size, the rollover zone of shearing surface increased, the burnish zone reduced, burr increased, the plastically deformed zone size increased, the range and degree of work hardening increased, and the quality of shearing surface was impaired. The shearing of the thin SSS with a large grain size was more sensitive to lateral clearance of the tool: various defects were more likely to occur in the shearing fracture surface.     

Axisymmetric extrusion through adaptable dies—Part 2: Comparison of velocity fields

In Part 1 of this series of papers, six kinematically admissible velocity fields, along with the power terms, were developed for use in upper bound models for arbitrarily shaped dies for axisymmetric extrusion. The three base velocity fields in the deformation zone were derived:

(1) assuming proportional angles in the deformation zone,

(2) assuming proportional areas in the deformation zone, or

(3) assuming proportional distances from the centerline in the deformation zone.

In each case the base velocity was modified by an additional term comprised of two functions, each function containing pseudo-independent parameters. One function allows extra flexibility in the radial direction, and the second function allows extra flexibility in the angular direction. In Part 2, the results obtained in upper bound models for the six velocity fields for extrusion through a spherical die are compared to one another. The velocity fields are compared based upon: (a) the base velocity field, (b) the number and distribution of pseudo-independent parameters in the flexible functions, and (c) the form of the angular flexible function. A spherical extrusion die shape is used to evaluate and compare the three velocity fields. The results demonstrate that the sine-based velocity field is the best. Furthermore, a natural boundary condition exists which allows the shear surface associated with the streamlined portion of a die to energetically disappear. Part 3 uses the best velocity field to determine an adaptable die shape, which minimizes the extrusion pressure and compares the shape to the arbitrarily curved and streamlined die shape of Yang and Han.     

通用可微调快换冲模设计

设计了一种可应用于组合冲模及柔性冲压系统的快换冲模机构。通过斜楔机构的设计，模具间隙可做微量调节，工作安全可靠。模具更换快捷、方便并带自锁功能。适合中小型冲压制品的多品种、中小批量生产及系列产品的开发。     

Investigation of sheet metal forming by bending—Part IV: Bending and wrinkling of circular sheets pressed by a hemispherical punch

This paper reports on an investigation of the bending forming processes in circular sheets pressed by a hemispherical punch into a conical die. Both theoretical and experimental considerations are provided. It is pointed out that the deformation mechanism of such a circular plate is different from that of the workpiece in the conical die cup test studied previously in part III of this series [Int. J. Mech. Sci.31, 327–333 (1989)]. The theoretical analysis shows that a central gap appears between the plate and the hemispherical punch at small deflections and disappears when the punch force increases beyond a certain magnitude. It is then shown that the previous approximate analytical treatment of the distribution of punch force is no longer appropriate to the wrinkling of the plate. It is shown that, as in the case of the conical die cup test, the circumferential wave number for the wrinkling mode corresponding to the critical wrinkling load of the present workpiece is four. In addition, the paper reveals that a doubling of the wrinkling wave may occur in the first stage of the forming process.     

凸轮在数控剪板机刀片间隙调整机构中的应用

介绍了数控剪板机刀片间隙自动调整机构中两种不同电位器反馈刀片间隙值的方式。实践证明：凸轮和直线电位器并用的结构,能真实反馈刀片间隙,准确控制间隙精度,从而可靠地保证了剪板质量。     

剪切散斑干涉术中剪切量的测量

由于采用剪切散斑干涉术测量离面应变和面内应变都与剪切量有关,所以剪切量的测量精度决定了应变场分布测量的准确性.本文论述了公式法、成像法、莫尔条纹法和相关法等4种剪切量测量法的测量原理,定性分析了它们的测量范围.搭建了一套剪切量测量系统,利用成像法、莫尔条纹法、相关法测量剪切散斑系统的剪切量,并以公式法计算的结果为准,比较其他3种方法的测量结果.结果表明:剪切量＞3 mm时,利用相关法测量具有较高的测量精度;剪切量＜3 mm时,奠尔条纹法测量效果会更好.因此,实际应用中,应该先根据实际测量条件估算剪切量的大致范围,然后依据估算范围选择合适的测量方法.     

冲模热处理变形的预防措施

通过模具热处理变形的原因分析，提高有关预防措施，以提高冲模寿命。     

基于Dynaform的圆筒拉深件数值模拟

以Dynaform为模拟分析平台,对典型圆筒件拉深成形过程进行了模拟。用正交实验的方法评定了压边力、冲压速度、凸凹模间隙三个因素对零件成形质量的影响,并得到一组优化的参数值。圆筒件拉深成形相关参数的最优值压边力为20kN,冲压速度为2000mm/s,凸凹模间隙为1.1mm。     

A Study on the mechanics of shear spinning of cones

The shear spinning process, where the plastic deformation zone is localized in a very small portion of the workpiece, shows a promise for increasingly broader application to the production of axially symmetric parts. In this paper, the three components of working force are calculated by the newly proposed deformation model in which the spinning process is understood as shearing deformation after uniaxial yielding by bending, and shear stress, τ _rz becomesk, yield limit in pure shear, in the deformation zone. The tangential forces are first calculated and the feed forces and the normal forces are obtained by the assumption of uniform distribution of roller pressure on the contact surface. The optimum contact area is obtained by minimizing the bending energy required to get the assumed deformation of the blank. The calculated forces are compared with experimental results. A comparison shows that theoretical prediction is reasonably in good agreement with experimental results.