基于弧形顶板模具结构的拼焊板回弹控制研究

运用弧形顶板模具结构回弹控制的原理对无凸缘U形件激光拼焊板弯曲回弹控制进行研究。考察补偿角、顶板力、凸模圆角半径及凸凹模间隙对激光拼焊板弯曲回弹的影响规律,与光板进行对比。试验表明,弧形顶板模具结构能有效控制激光拼焊板的回弹。     

高强钢拼焊板V形模压弯曲回弹数值预测

基于ABAQUS有限元软件的UMAT和VUMAT接口,利用径向回退映射算法开发变模量的各向同性强化、线性随动强化和非线性随动强化的本构模型,耦合Aitken算法提高了非线性随动强化模型的收敛速度。利用耦合变模量的三种强化准则的模型,基于显式计算成形隐式计算回弹算法,在不同模压力和不同凸模圆角半径下对高强钢拼焊板V形模具弯曲的回弹进行预测,通过试验验证耦合应力相关变模量的非线性随动强化模型的回弹预测精度较高,最大预测误差为2.2%。应用此模型在不同凸模圆角半径和不同模压力下对高强钢拼焊板V形模具弯曲回弹后模量场和卸载后弯曲角进行预测与分析,拼焊板厚侧母板模量变化区较薄侧母板变化区域大,并在凸模圆角与直边过渡段上方出现反弯区。卸载后弯曲角随凸模圆角半径增大而增大,随着模压力的增大而减小。验证通过施加不同模压力可提高高强钢拼焊板V形模具弯曲工艺柔性的正确性,为进一步研究高强钢拼焊板V形模具弯曲自适应成形奠定基础。     

基于试验设计和灰色关联度的橡皮囊成形回弹影响因素显著性分析

橡皮囊成形是飞机钣金零件的一种重要成形工艺方法,回弹问题是橡皮囊成形的难点,对其影响因素进行显著性分析可有效控制回弹。基于橡皮囊成形有限元数值模拟,将正交试验设计方法与灰色关联度相结合用于分析橡皮囊成形回弹影响因素的显著性,以某实际长直U形件为例分析压力、最大充液速率、最大节点速度、保压时间、弯曲半径、板料厚度以及轧制方向等因素对回弹的影响程度,结果表明,模具圆角半径、压力、板料厚度、保压时间是橡皮囊成形回弹的主要影响因素,而最大充液速度、最大节点速度、轧制方向对回弹的影响较小。分析结果与工艺试验结果相吻合,从而验证了该方法的有效性。     

TRIP600高强度钢板成形U型件回弹控制研究

针对高强度钢板冲压成形过程中普遍存在的精度问题,以U型件为研究对象,在分析TRIP600高强度钢板材料性能的基础上,分别研究了U型件成形时压边力和拉深筋的工作圆角半径对回弹的影响。结果表明,TRIP600高强度钢板在成形U型件时,回弹随着压边力的增加而发生有限减小;拉深筋工作圆角半径越大,回弹值越大。     

纵向拼焊板V形自由弯曲及回弹模拟研究

运用有限元软件ANSYS/LS-DYNA和ETA-DYNAFORM对纵向拼焊板的V形自由弯曲及其回弹过程进行了模拟分析.重点就纵向拼焊板V形自由弯曲的成形特点和影响回弹的主要因素进行了研究,通过分析可知,对纵向拼焊板V形件自由弯曲回弹影响较大的参数为拼焊板的凹模跨度、材料性能和厚度比,而模具的圆角半径、摩擦系数的影响较小.     

C5210磷青铜薄板微弯曲回弹的尺寸效应

采用RG-2000型微机控制电子万能试验机,通过微弯曲试验,研究了C5210磷青铜薄板的厚度、晶粒尺寸以及弯曲半径等相关尺寸对其微弯曲回弹的影响。结果表明:C5210磷青铜薄板的厚度、晶粒尺寸和弯曲半径等对其回弹均有显著的影响,具有明显的尺寸效应;薄板的厚度越大,回弹量越小,厚度对回弹量的影响非常显著;薄板的晶粒尺寸越大,回弹量越小,当晶粒尺寸大于40μm时,回弹量呈缓慢减小趋势;回弹量随着弯曲半径的增大而增大,而且薄板的厚度越小,增大的趋势越明显。     

激光冲击软模大面积微弯曲成形方法

为了实现金属箔板大面积微弯曲成形,本文结合激光冲击微弯曲成形技术与软模成形技术的优点,提出了激光冲击软模大面积微弯曲成形方法。 该方法是在脉冲激光冲击波压力下,将软模作为柔性冲头作用于金属箔板来实现工件成形的。实验中使用了Innolas Gmbit公司生产的Spitlight 2000 THG脉冲激光器,将250 μm厚的聚氨酯橡胶薄膜作为软模,采用德国LPKF-ProtoMat-C60型雕刻机在印刷电路板上加工出深度为120 μm的U型多槽模具,实现了在厚度为30 μm的铜箔板上一次性对3个U型凹槽冲击成形。用KEYENCE VHX-1000C超景深三维显微系统进行工件观测,结果显示工件上的微成形槽具有良好的轮廓质量。以ANSYS/LS-DYNA为平台,使用有限元建模（FEM）方法对微弯曲过程进行了数值模拟。实验和模拟结果均表明,加载软模的工件与模具的U型凹槽特征在形状上更加接近,成形工件更加均匀,而且具有较好的表面质量,其最大平均成形深度可达110 μm,大于激光直接冲击成形的最大深度（88 μm）,说明使用软模提高了充型能力。     

拼焊板方盒件成形参数优化

通过数值模拟与正交优化的有效结合,对影响拼焊板方盒件成形因素:板料厚度比、凹模圆角半径以及坯料形状和尺寸等进行了研究.最终提高了拼焊板方盒件冲压成形深度并减小了焊缝移动.由实际冲压试验也表明:此正交设计优化方法对拼焊板方盒件冲压成形参数优化是有效可行的.     

小型浪形保持架成形模的设计计算

根据浪形保持架成形过程和模具使用机理,采用数学分析方法,从几何关系上推导了浪形保持架成形模冲头和接头板中主要尺寸的计算公式。这种设计方法,由于成形冲头直径减小,冲头中心径增大,从而提高了成形模冲头接头板和卸料板的强度,改善了模具加工工艺性。这种采用解析计算的设计还便于计算机辅助模具设计。附图3幅。     

U形弯曲模结构浅析

在弯曲成形方式中,U形弯曲是最常见的一种。在U形弯曲中最难解决的工艺问题是弯曲件的回弹。在弯曲工艺设计时,人们一般根据经验(经验公式计算或查表),粗略计算其回弹值(回弹角、回弹半径),在设计模具结构时考虑弥补。下面就以消除回弹为重点,对几种常用U形弯曲模结构进行分析,     

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     

激光诱导空化微孔冲裁试验研究

针对微尺度下金属箔模具冲孔存在模具挤压磨损、对中困难,激光打孔存在烧蚀、吸收层无法补偿等问题,提出通过激光诱导空泡对金属箔进行加载来实现冲裁小孔的方法。研究了不同激光焦点位置(H=0~4 mm)、激光能量(E=10.3~50.8 mJ)和铜箔厚度(T=20~70μm)对铜箔冲孔的影响,发现激光焦点位置影响明显,当铜箔变形平均深度达到147.0μm后,铜箔发生剪切断裂,可实现冲裁,并且制备的小孔边缘正表面无烧蚀、毛边、裂纹和卷边等缺陷。同时,利用高速摄影仪对激光诱导空化微孔冲裁过程进行研究,结果表明激光诱导空化微孔冲裁过程是激光等离子体冲击波、空泡溃灭冲击波和微射流共同加载的过程。     

Influence of size effect on burr formation in micro cutting

Burr is an important character of the surface quality for machined parts, and it is even more severe in micro cutting. Due to the uncut chip thickness and the cutting edge radius at the same range in micro cutting process, the tool extrudes the workpiece with negative rake angle. The workpiece flows along the direction of minimum resistance, and Poisson burr is formed. Based on the deformation analysis and experiment observations of micro cutting process, the factor for Poisson burr formation is analyzed. It is demonstrated that the ratio of the uncut chip thickness to the cutting edge radius plays an important role on the height of Poisson burr. Increasing the uncut chip thickness or decreasing the cutting edge radius makes the height of exit burr reduce. A new model of micro exit burr is established in this paper. Due to the size effect of specific cutting energy, the exit burr height increases. The minimum exit burr height will be obtained when the ratio of uncut the chip thickness to the cutting edge radius reaches 1. It is found that the curled radius of the exit burr plays an important role on the burr height.     

Experimental and numerical analysis of hydrodynamic deep drawing assisted by radial pressure at elevated temperatures

Nowadays, due to the demand for lightweight construction and fuel consumption reduction, especially in automotive and aerospace industries, the use of aluminum alloys has drawn much attention. Nevertheless, poor formability at room temperature is the main drawback of using these alloys. To overcome the problem, the work material is formed at elevated temperatures. In the present paper, Hydrodynamic Deep Drawing assisted by Radial Pressure (HDDRP) process has been selected over other forming methods. The aim of the study is to investigate the applicability of this process in conjunction with warm forming. For this purpose, experimental and numerical attempts have been made on warm forming of flat-bottom cylindrical cups in isothermal condition. At first, a series of warm hydroforming experiments were performed to determine the effect of tool temperature and forming speed on the thickness distribution of the final part and on the required forming load. Then, a set of finite element analyses (FEA) were performed using ABAQUS explicit to extend the findings. The Response Surface Method (RSM) was then used to build the relationship between the input parameters such as temperature and forming speed, and output responses including minimum part thickness and maximum punch force. It is demonstrated that the required forming force was decreased with increase in punch speed and tool temperature. Additionally, minimum thickness of the part is increased with increasing temperature and decreasing punch speed. Studying the Limiting Drawing Ratio (LDR) revealed that elevating the forming temperature causes reduction in LDR, while rising the punch speed leads to a slight enhancement in it. For the evaluation of part dimensional changes after forming, springback analysis was done via studying the through-thickness hoop stress distribution. It is found that using warm isothermal HDDRP in high forming rate results in more uniform stress distribution and lower level of stress and so a better springback behavior.     

Prediction of bend force and bend angle in air bending of electrogalvanized steel using response surface methodology

This paper presents the development of predictive models for bend force and final bend angle (after springback) in air bending of electrogalvanized steel sheet employing response surface methodology. The models are developed based on five-level half factorial central composite design of experiments with strain hardening exponent, coating thickness, die opening, die radius, punch radius, punch travel, punch velocity as input parameters and bend force and final bend angle as responses. The results obtained from the models are in good accord with the experimental results. The effects of individual parameters and their interactions on the responses have also been analyzed in this study.     

Springback prediction of the vee bending process for high-strength steel sheets

The precise prediction of springback is a key to assessing the accuracy of part geometry in sheet bending. A simplified approach is developed by considering the thickness ratio, normal anisotropy, and the strain-hardening exponent to estimate the springback of vee bending based on elementary bending theory. Accordingly, a series of experiments is performed to verify the numerical simulation. The calculation of the springback angle agrees well with the experiment, which reflects the reliability of the proposed model. The effects of process parameters such as punch radius, material strength, and sheet thickness on the springback angle are experimentally tested to determine the dominant parameters for reducing the springback angle in the sheet bending process for high-strength steel sheets. Moreover, the effects of the thickness ratio, normal anisotropy, and the strain-hardening exponent on the springback angle in the vee bending process for high-strength steel sheets are theoretically studied. Therefore, improving understanding on and control of the springback reduction of the vee bending process in practical applications is possible.     

Springback evaluation in hot v-bending of Ti-6Al-4V alloy sheets

In this paper, v-bending of Ti-6Al-4V alloy sheet was conducted from room temperature to 850 °C at a fixed velocity of 0.1 mm/s. Punches with punch radii of 1, 2, 4, and 6 mm, as well as several holding times were used. V-bending and springback behaviors were numerically analyzed with an isotropic hardening model that considered rate-dependent effects. Using a punch radius of 1 mm always leads to negative springback in the temperature range of 550–750 °C. This behavior occurs because an arc formed in the transition side near the end of bending and flattened at the end of bending, leading to an internal bending moment which causes specimen to bow inward after unloading. At a punch radius of 2 mm, positive springback occurs at 300–650 °C, while negative springback occurs at 700–750 °C. At punch radii of 4 and 6 mm, positive springback occurs at 600–750 °C, and the angle decreases as temperature increases. At 850 °C, negative springback occurs at a punch radius of 4 mm due to the decrease in yield strength. At a punch radius of 1 mm, cracking occurs at room temperature and 500 °C, while at 2 mm, it occurs only at room temperature. This discrepancy is ascribed to the greater plastic deformation caused by the smaller punch. As holding time increases, the shape of the deformed specimen more closely matches the desired shape.     

Estimation of springback in double-curvature forming of plates: Experimental evaluation and process modeling

This paper presents the results obtained from a series of experiments on double-curvature forming of 300 mm square and 15 mm thick plates of type 316L(N) stainless steel to evaluate the inherent springback and also to validate finite element method (FEM) based process model developed for forming of multiple-curvature sectors of large size vessels. The experimental results show that twisting of the plate occurs during pressing, which is unavoidable in an actual forming setup on the shop floor. Twisting increases with increase in slope of the die cavity. Springback in the plate changes in an ascending order towards the centerline of the plate from the edges. The final radius of curvature (ROC) on the pressed plate after springback does not remain constant along a particular axis although the die and the punch had constant ROC along that axis because of varying constraint to opening up of the plate from centerlines to the edges. Springback also increases with reduction in the stiffness of the die and punch. The simulated plate profiles obtained from the FEM process model for multiple-curvature plate forming compared well with the experiments, the maximum error being within 6%. The process model used a sequential dynamic explicit formulation for the plate pressing phase and a static implicit formulation for the unloading (springback) phase in the Lagrangian framework. Reduced integration shell elements were used for the plate and the die and the punch were considered rigid. Dynamic explicit FEM for pressing and static implicit FEM for the unloading phase are adequate and economic for modeling of plate forming process by using FEM. The necessary material and frictional property data needed for the FEM process model were generated in-house. This model can be applied to design of dies and punches for forming the petals of large pressure vessels. The FEM process model predicts the final shape of the product and the residual cold work level for a given die, punch and plate configuration and this information can be used to correct the die and punch shapes for springback to manufacture the petals to the desired accuracy.     

Effects of process variables on V-die bending process of steel sheet

This investigation aims to clarify the process conditions of the V-die bending operation of steel sheet. It provides a model which predicts the correct punch load for bending and the precise final shape of products after unloading, in relation to the tensile properties of the material and the geometry of tools. The process variables are punch radius (R_p), die radius (R_d), punch width (W_p), punch speed (V_p), friction coefficient (μ), strain hardening exponent (n) and normal anisotropy (R).This investigation is carried out by performing some experiments and by finite-element simulation. Experiments determine the punch for bending for various process variables, such as punch radius, punch speed and lubrication, were carried out. As a result it was found that punch load increases as punch radius and punch speed increase or lubrication decreases.An elasto-plastic incremental finite-element computer code based on an updated Lagrangian formulation was developed to simulate the V-die bending process of sheet metal under the plane-strain condition. Isotropic and normal anisotropic material behavior was considered including nonlinear work hardening. A modified Coulomb’s friction law was introduced to treat the alternation of sliding–sticking state of friction at the contact interface. Simulation results, such as the punch load of bending and the bend angle of the bent part after unloading, are compared with experimental data; satisfactory agreement was observed. The simulation clearly demonstrates that the code to simulate V-die bending process was efficient.Simulations were made to evaluate the effects of die radius, punch width, strain hardening exponent and normal anisotropy on punch load of bending. The punch load for bending is smaller for materials with a larger strain hardening exponent. The effect of punch width on punch load is limited. The punch load decreases in the early stage and increases in the final stage of the bending process as the die radius increases. The influences of all of the process variables on the final bend angle of the bent parts of sheet after unloading were also evaluated. The effects of process variables except die radius on the bend angle after unloading are also limited. The angle of spring-back is greater for tools with larger die radius.