Position deviation in V-die bending process with asymmetric bend length

Novel finite element analyses and a series of experiments are performed to clarify basic characteristics of high-strength steel sheet metal during fabrication by asymmetric V-die bending processes. The proposed strategy for elastic–plastic FE simulation is used to simulate asymmetric V-die bending process to test its viability for friction contact processes. Accordingly, a series of experiments is performed to verify the numerical simulation. The calculation agrees well with the experiment. The effects of process parameters such as lubrication (contact friction), material properties, and process geometries on position deviation in bending point were experimentally tested to determine the dominant parameters for minimizing position deviation in sheet metal bending processes. Moreover, springback phenomenon is also discussed to minimize bending defects and to obtain a precise asymmetric bent component. This study could be used as a process design guideline for asymmetric bending of high-strength steel sheets.     

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.     

Influence of blank profile on the V-die bending camber process of sheet metal

The finite element simulation is now widely used in the design of stamping tools. A trial and error procedure has been replaced by a simulation in which defects associated with sheet forming processes are predicted and evaluated. This paper aims to clarify the process conditions of the V-die bending of a sheet metal. It provides a model that predicts not only the correct punch load for bending, but also the precise final shape of the products after unloading. An incremental elastic-plastic finite element computer code, based on an updated Lagrangian formulation, was developed to simulate the V-die bending of sheet metal. In particular, the assumed strain field (ASF) element was used to formulate the stiffness matrix. The r-minimum technique was used to deal with the elastic-plastic state and solve contact problems at the tool-metal interface. A series of experiments were performed to validate the formulation in the theory, leading to the development of the computer codes. The predicted punch load in the finite element model agrees closely with the experimental results. The whole history of deformation and the distribution of stress and strain during the forming process were obtained by carefully considering the moving boundary condition in the finite element method .A unique feature of this V-die bending process is the camber after unloading. The computer code successfully simulates this camber. The simulation was performed to evaluate the effects of the size of the blank on the camber process. The results in this study clearly demonstrate that the computer code efficiently simulated the camber process .     

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。     

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.     

Double-action bending for eliminating springback in hat-shaped bending of advanced high-strength steel sheet

The International Journal of Advanced Manufacturing Technology - This paper presents a novel technology called ‘double-action bending (DAB)’ to eliminate springback in hat-shape forming...     

Numerical simulation of the failure process for an experimental sample with a concentrator under plane bending conditions

The results of the numerical simulation of elastic-plastic deformation, crack nucleation, and propagation in a sample are presented. The simulation is performed using the laws of mechanics of a damaged medium by considering different variants of the accumulation of faults. The obtained results are in good agreement with the experimental data for the case when during the simulation both plastic and brittle failures are taken into account.     

不锈钢钢板热应力成形试验研究及其工艺参数评价

以不锈钢钢板为研究对象,通过改变激光光束能量、光斑直径、机床扫描速度、扫描次数以及扫描路径对不锈钢钢板进行弯曲试验,研究了厚度一定的不锈钢钢板弯曲成形时的工艺参数对弯曲角度的影响,并对热应力弯曲成形的工艺参数进行评估。     

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.     

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     

Strain distribution characteristics of welded tube in NC bending process using experimental grid method

To understand the reason of defects and the basic mechanics involved in the welded tube numerical control bending process, it is important to study the effects of the weld and processing parameters on the strain distributions of the tube. The grid method that combines with vision-based surface strain measurement system GMASystem is used to research the strain distributions of the bent tube experimentally. The results show that the weld has a limited effect on the strain evolution as the weld is not located in the region of locally highest strains. As the weld line locates on the outside, the maximum tangent and thickness strain decrease by 0.94 and 8.78 %, while the maximum hoop strain increases by 22.15 % as compared with that the weld line locates on the middle. As the weld line locates on the outside and inside, the thickness strain decreases obviously in the weld region. The variation of thickness strain is little with smaller mandrel extension length, and the maximum thickness strain increases by 21.38 % as the extension length changes from 6 to 10 mm. The thickness strain decreases with larger push assistant level. The maximum thickness strain increases with larger bending angle.     

A CFD-aided experimental study on bending of micro glass pipettes

This paper presents a study on the temperature profile in the bending process of glass pipettes. To prevent undesirable deformation of the pipette at its bending section, such as kink and constriction, several factors influencing the bending quality are investigated, including the width and temperature of the heating element, heating and bending time. Taguchi method is used to study the key factors and to identify an optimal parameter combination. ANSYS is also employed to study the heat transfer and temperature distribution in the heating zone. It is concluded that the temperature distribution in the bending area is critical to the bending quality, and the width of the heating element decisively determines the temperature distribution.     

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.     

An experimental study of the in-plane stretching of sheet metal

Experimental results are presented of the limit strains for the in-plane stretching of steel, aluminium and brass sheets. The development of surface strains is studied in incremental tests and attention is drawn to “crazing” of the surface of sheet specimens and to “banding” in aluminium specimens. Despite the wide difference in the mechanical properties of the three materials the values for the limit strain are remarkably similar. For steel and aluminium the limit strains are greater than the predicted instability strains, but for brass the limit strains are considerably less than the predicted instability strains. The wide scatter in the experimental limit strains perhaps indicates that failure is largely influenced by random effects.     

Numerical and experimental analysis of wall thickness variation of a hemispherical PMMA sheet in thermoforming process

In thermoforming, a heated plastic sheet is stretched into a mold cavity by applying pressure, eventually assisted by direct mechanical loading. Since upon its contact with the cold surface of the mold the sheet is prevented from undertaking any further deformation, the forming sequence induces a thickness variation in the final part. This fundamental inherent defect of thermoforming technology highly affects the optical characteristics of optical products. Therefore, the more uniform the wall thickness, the less chance optical defects will occur. In this research, the production process of a hemispherical transparent PMMA sheet as an optical product was numerically simulated. The simulated process is a two-step process comprising a combination of free forming and plug-assisted forming. In the simulation, the acrylic sheet is assumed to undergo a nonlinear and large elastic deformation which merits application of hyperelastic models. Mooney–Rivlin hyperelastic model is used as the constitutive equation. The obtained numerical results are validated with those achieved from the experiments. Different combinations of free forming and plug-assisted forming methods are studied based on what percentage of total height of the final part is produced by each method. Finally, an optimum combination of the two-step forming process is proposed. With this optimum combination, satisfactorily uniform wall thickness and minimal mold marks on the product surface will be achieved.