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.     

Positional deviation of bending point in asymmetric V-die bending process of HSS sheet: an experimental study

In this study, a series of experiments are performed to characterize the asymmetric V-die bending process for a High-strength steel (HSS) sheet. The main challenge in asymmetric V-die bending is positional deviation of the bending point during bending, given by a magnitude and a direction of deviation of the bending point. The effects of process parameters, such as radii of the punch head and the die shoulder, on the positional deviation of the bending point were experimentally examined to identify those that govern the deviation of the bending point in an asymmetric bending process. This work improves our understanding of deviations of the bending point, and can be used for developing process design guidelines for asymmetric bending of high-strength steel sheets to produce precise, asymmetrically bent parts.     

导管数控弯曲工艺知识管理技术研究

为实现导管数字化集成制造模式,分析了导管数控弯曲过程中工艺知识的内容、特征及其存在形式,采用基于重用的方法将工艺知识分为两类:重用型工艺知识和决策型工艺知识;针对其内容结构特点,研究了工艺知识的表示与存储方法,建立了它们的关系数据库存储模型,进而构建了导管工艺知识管理系统的结构模型;研究了知识推理技术,建立了基于关系数据库技术的正向和反向推理方法,实现了导管工艺设计过程中的可加工性分析和制造资源选择;针对导管工艺的特点实现了基于实例的工艺参数设计(CBR),提高了导管数控弯曲工艺设计的效率。     

Application of an analytical hierarchy process method and fuzzy compositional evaluation in the expert system of sheet bending design

This article is mainly targeted at establishing a set of Chinese and English expert systems for sheet bending design by using an analytical hierarchy process (AHP) method and fuzzy compositional evaluation using a personal computer. The fuzzy compositional evaluation in conjunction with the analytical hierarchy process method was used to solve the problem of the uncertainty faced by the users during the selection of the processing method. This system combines an AutoCAD graphic mechanism to form a complete system for items ranging from input of the shape and size of the component to the output of the inferred results of the system. At the same time, the fuzzy compositional evaluation and the analytical hierarchy process were employed to make the system more practical.     

Modelling of inelastic bending of a metal sheet with thermal coupling

The modelling and numerical analysis of inelastic bending of a metal sheet are presented. The distribution strains and stresses are found for slow and fast bending while taking into account the geometrical and material non-linearities. The constitutive relation of Klepaczko, (Int. J. Plast. 17 (2001) 87, Comput. Methods Appl. Mech. Eng. 175 (1999) 19) was used which includes strain hardening, strain rate sensitivity and temperature effect in material behaviour. The large strains are assumed under plane strain conditions. The results with complete thermal coupling are compared with solutions obtained in the isothermal conditions of bending.     

基于知识的计算机辅助导管加工工艺设计

为了满足导管加工质量和成形精度的要求,提出了一个基于知识的导管加工工艺设计系统。该系统采用面向对象的技术定义了导管加工通用约束、企业生产条件约束和用户导管质量需求约束,给出了导管弯曲加工工艺知识的面向对象表达。由于采用了以用户导管质量需求为目标的驱动的推理机制,实现了导管弯曲加工工艺的自动生成。     

Finite element analysis on the V-die coining bend process of steel metal

An elasto-plastic incremental finite element computer code based on an updated Lagrangian formulation was developed to simulate the V-die coining bend process of sheet metal under the plane-strain condition. A modified Coulomb’s friction law was introduced to treat the alternation of the sliding–sticking state of friction at the contact interface. The r-minimum method was used to treat the elastic–plastic stress state and to solve contact problems at the tool–metal interface. V-bends of sheet metals are classified according to the number of contact points of the sheet with the bending die, and include air bends, bottoming bends, and coining bends. The former has three contact points with the bending die at the punch top and die shoulders, and there have been many experimental and analytical research works reported on it. The latter two are in contact at a greater number of points. To clarify the bending characteristics, it is necessary to fully understand the process and stress state in the bent part. The experiment was performed to validate the theoretical formulation and to support the development of the computer code. Simulation was performed on the punch load of the coining bend and the bend angle of the bent part after unloading. Calculated sheet geometries and the forming force agree well with the experimental data. The simulation clearly demonstrates the efficiency of the code to simulate V-die coining bend processes that proceed under contact history.     

面向CIMS的板类零件下料工艺系统

介绍了一个以优化排样为核心，为企业板类零件下料生产提供有效整体解决方案的集成工艺设计系统。提出了基于企业局域网、面向GIMS的总体集成设计方案，开发了以优化排样为核心的下料工艺设计流程，设计并实现面向多种下料工艺的优化排样算法。最后以广西某集团为对象介绍了上述思路的具体实施方案及实施效果。     

金属线材折弯虚拟仿真系统的设计与实现

针对金属线材产品种类多、结构复杂度高、加工过程动作多且易发生碰撞干涉等特点,研究金属线材产品建模和仿真加工技术,实现线材产品的加工仿真,以检查产品设计和机床加工动作的合理性,优化加工工艺。分析了折弯机械的运动控制和折弯工艺,推导出产品建模参数与样机运动参数的数学关系式。基于OpenGL API,使用分段建模的方法实现线材产品参数化三维建模;使用“嵌套矩阵法”和运动控制函数实现线材的加工仿真。虚拟仿真系统由产品建模模块和仿真加工模块组成,前者用于产品建模和三维模型显示,后者用于加工轨迹规划和加工动画演示。实验表明,仿真系统可以实现金属线材产品在线设计和加工工艺优化,能够加快产品设计和试加工过程。     

硅片激光弯曲成形的数值模拟与实验

介绍了一种利用脉冲激光塑性化弯曲单晶硅片的新方法。在分析和描述光脉冲时空特性的基础上,运用有限元分析软件ANSYS对硅片弯曲过程进行建模仿真,得到了脉冲激光弯曲过程中温度场与应力应变的仿真结果。对脉冲激光作用过程中温度场与应力应变的周期性瞬间变化特征进行了描述,指出了脆性材料硅片的脉冲激光弯曲机理不属于简单意义上的温度梯度机理或屈曲机理,而是二种机理共同作用的结果。通过6次扫描试验实现了对硅片的有效弯曲,弯曲角度达6.5º,仿真结果与验证性试验相符。     

Fracture limits of sheet metals under stretch bending

Fracture limits in sheet stretch bending were theoretically obtained on the assumption that the fracture occurs when the stretching force reaches its maximum value. From the calculated results, a fracture criterion has been presented where limit wall stretch, L_max/L₀ (L_max: limit wall length of a sheet, L₀: initial wall length), is explicitly given as a function of the non-dimensional bending curvature, t₀/R (t₀: sheet thickness, R: bending radius) and the material's work hardening exponent (n-value). To verify this criterion, three-point stretch bending tests with various punch-radii were performed on three types of aluminum sheets (A5182-O, JIS6061-T4 and JIS6N01-T5). The predicted limit wall stretch, as well as limit forming height, were in good agreement with the experimental results.     

Parameter prediction in laser bending of aluminum alloy sheet

Based on the basic platform of BP neural networks, a BP network model is established to predict the bending angle in the laser bending process of an aluminum alloy sheet (1–2 mm in thickness) and to optimize laser bending parameters for bending control. The sample experimental data is used to train the BP network. The nonlinear regularities of sample data are fitted through the trained BP network; the predicted results include laser bending angles and parameters. Experimental results indicate that the prediction allowance is controlled less than 5%–8% and can provide a theoretical and experimental basis for industry purpose. __________ Translated from Optics and Precision Engineering, 2007, 15(6): 915–921 [译自: 光学精密工程     

板材大圆弧冷弯辊型设计与应用

对客车顶棚的金属板材成型机实行改进 ,进行成型方案的确定、辊型圆弧半径及成型次数等的计算 ,并在实验的基础上设计出辊型 ,经安装调试后达到了设计要求     

An investigation on multistage bending of blank sheet into cylindrical tube by experiment and numerical simulation

In this paper, one pair of punch and die was employed to experimentally investigate the pure bending of blank sheet into cylindrical tube by multistage process. The investigated material was hot-rolled HSLA370 with the thickness of 2?mm. Numerical simulation was conducted on bending and springback with LS-DYNA solver. Results showed that multistage bending technique was an alternative way to produce cylindrical tubes. The sequence is described as $ {\text{Blank}}\,{\text{sheet}}\xrightarrow{{{\text{Multistage}}\,{\text{bending}}}}{\text{C - tube}}\xrightarrow[{{\text{Welding}}}]{{{\text{Squeezing}}}}{\text{O - tube}} $ . Gap width and roundness of C-tube (configuration like letter ??C??) were two dominant parameters to evaluate the bending performance. The effects of blank positioning on both of them were investigated by means of numerical simulation. Laser-welded tubes meeting roundness and the tolerance limit of diameter were produced. Simulation revealed that effective plastic strain along circumferential direction was much low, mostly ranging between 0.03 and 0.05. Severe thinning and shape defects were not observed in the finished tubes. A numerical model was developed and its effectiveness was verified by a comparison between the predicted results and the corresponding experiments.     

Optimum blank design in sheet metal forming by the deformation path iteration method

Optimum blank design methods have been introduced by many researchers to reduce development cost and time in the sheet metal-forming process. Direct inverse design method such as Ideal Forming (Chang and Richmond, Int J Mech Sci 1992; 34(7) and (8): 575–91 and 617–33) [7, 8] for optimum blank shape could play an important role to give a basic idea to designer at the initial die design stage of the sheet metal-forming process. However, it is difficult to predict an exact optimum blank without fracture and wrinkling using only the design code because of the insufficient accuracy. Therefore, the combination of a design code and an analysis code enables the accurate blank design. In this paper, a new blank design method has been suggested as an effective tool combining the ideal forming theory with a deformation path iteration method based on FE analysis. The method consists of two stages: the initial blank design stage and the optimization stage of blank design. The first stage generated a trial blank from the ideal forming theory. Then, an optimum blank of the target shape is obtained with the aid of the deformation path iteration method which has been newly proposed to minimize the shape errors at the optimization stage. In order to verify the proposed method, a square cup example was investigated.     

弯曲成形数值模拟与数控系统研究

弯曲在工业生产中是一种重要成形工艺。研究弯曲过程以减小回弹,有着十分重要的意义。本文简单介绍了弯曲成形工艺过程,建立了系统控制模型,并开发了弯曲成形过程计算机模拟与数控软件系统,实现了弯曲成形过程的计算机模拟和控制,提高了成形精度。     

Spring-back characteristics of fiber metal laminate (GLARE) in brake forming process

The brake forming process has been considered as a feasible method for producing fiber metal laminate (GLARE) stringer. However, the spring-back developed during brake forming leads to serious problems in the final dimensional tolerance of the stringer. A series of experiments were performed to examine the effect of tool design and process parameters on the spring-back of GLARE. The parameters studied include punch radius, punch speed, forming load, and forming temperature. This paper shows that both design and process parameters can significantly affect the amount of spring-back. Scanning electron microscopy (SEM) was also carried out for the observation of delamination or cracking in the bent zone.     

基于人工神经网络的板料弯曲成形工艺优化及回弹分析

结合人工神经网络所表现出来的良好特性,利用正交试验获得的数据作为神经网络的训练样本,建立输入为弯曲工艺参数、输出为回弹量的神经网络模型,并通过样本检验了ANN模型的准确性,从而缩短设定工艺参数的时间,在工艺参数取值范围内,采用ANN模型代替CAE软件模拟试验,结合正交试验法,对工艺参数进一步优化.结果表明:将神经网络与正交试验、数值模拟三者结合用于板料弯曲成形参数优化,可以缩短优化工艺参数的时间.提高工艺设计效率,并能获得比单纯使用正交试验和数值模拟方法更为优化的结果.