1060铝材双点渐进成形几何精度的研究

针对单点渐进成形几何精度差的问题,提出了一种双点渐进成形加工技术。以1060铝为研究对象,确定目标零件,从成形轨迹和进给量两个方面编制双点渐进成形工艺和单点渐进成形工艺。然后根据编制的工艺在渐进成形设备上编制数控程序,制作了单点与双点渐进成形样品。再使用FARO便携式三坐标测量仪,测量了双点渐进成形与单点渐进成形样品的几何精度。最后,提出了一种对比分析数据的方法,对单点渐进成形和双点渐进成形的几何精度进行了定量的对比分析。实验结果表明,在工艺参数相同的前提下,双点渐进成形的几何精度远高于单点渐进成形的几何精度。     

Electric hot incremental forming of low carbon steel sheet: accuracy improvement

Currently, incremental forming (IF) is known as a novel technology, which promises to a higher flexibility in process, lower production price and lead time, in addition to improved formability of material compared to conventional forming processes. However, relatively low dimensional accuracy of finish part has been frequently considered as the major drawback of IF in the literature. This research, extending the application of electric hot incremental forming to low carbon steel DC04, aimed to enhance the dimensional accuracy of formed part. In order to avoid discharge phenomenon during the forming process, a new method of helical tool path optimization without interference was proposed. The details regarding the appropriate parameters for forming pyramid frustums of acceptable geometrical accuracy are provided as well.     

Force-based failure criterion in incremental sheet forming

In incremental sheet forming, a hemispherical tool deforms a sheet moving along a predefined path. The process, useful for making prototypes or small series, is characterized by high flexibility and development times and costs reduction. The part feasibility is strongly influenced by the adopted tool path and, in particular, tool path corrections are requested to obtain the final geometry and to prevent the sheet rupture. To save time and costs, sheet failure criteria are therefore essential. In this paper, a real time force-based sheet rupture criterion is presented and tested on steel, aluminum, and titanium alloys. In particular, it will be shown that the sheet rupture can be related with the tangential forming force, the geometry of the component to be realized, and the sheet material characteristics.     

Improvement of formability for the incremental sheet metal forming process

In order to obtain competitiveness in the field of industrial manufacture, a reduction in the development period for the small batch manufacture of products is required. In order to meet these requirements, an incremental sheet metal forming process has been developed. In this process, a small local region of a sheet blank deforms incrementally by moving a hemispherical head tool over an arbitrary surface. In this work, an incremental sheet metal forming process controlled three dimensionally by a computer has been accomplished. It has been shown by the experiments that a sheet blank is mainly subject to shear-dominant deformation. Therefore, the final thickness strain can be predicted. The uniformity of thickness throughout the deformed region is one of the key factors to improve the formability in the sheet metal forming processes. Using the predicted thickness strain distribution, the intermediate geometry is decided in the manner that a shear deformation is restrained in the highly shear-deformed region and vice versa. This double-pass forming method is found to be very effective so that the thickness strain distribution of a final shape can be made more uniform.     

Improving industrial suitability of incremental sheet forming process

Although in the last years a large amount of research work has been spent on incremental sheet forming process, industrial applications are not spreading accordingly. This is due to process characteristics such as slowness and limited accuracy. In the paper, the authors investigated the suitability of incremental sheet forming at very high feed rates to strongly reduce processing time. What is more, a simple strategy to reduce the part inaccuracy was implemented. The investigation concerned a simple conical shape but the obtained results are quite general.     

Efficient force prediction for incremental sheet forming and experimental validation

Incremental sheet forming (ISF) has been attractive during the last decades because of its greater flexibility, increased formability and reduced forming forces. However, traditional finite element simulation used for force prediction is significantly time consuming. This study aims to provide an efficient analytical model for tangential force prediction. In the present work, forces during the cone-forming process with different wall angles and step-down sizes are recorded experimentally. Different force trends are identified and discussed with reference to different deformation mechanisms. An efficient model is proposed based on the energy method to study the deformation zone in a cone-forming process. The effects of deformation modes from shear, bending and stretching are taken into account separately by two sub-models. The final predicted tangential forces are compared with the experimental results which show an average error of 6 and 11 % in respect to the variation of step-down size and wall angle in the explored limits, respectively. The proposed model would greatly improve the prediction efficiency of forming force and benefit both the design and forming process.     

Tool path correction algorithm for single-point incremental forming of sheet metal

There exists some error between the manufactured part shape and the designed target shape due to springback of this part after forming. To reduce the error, an iterative algorithm of closed-loop control for correcting tool path of the single-point incremental forming, based on Fast Fourier and wavelet transforms, has been developed. Moreover, the data of the springback shapes, after unloading, of the sheet metal parts formed with the trial and corrected tool paths, used for iterative correction of tool path in the algorithm, are obtained with finite element model (FEM) simulation. Then, a truncated pyramid-shaped workpiece, whose average errors are +0.183/?0.175 mm, was made with the corrected tool path after three iterations solved by the above algorithm and simulation data. The results show that the tool path correction algorithm with Fourier and wavelet transforms is reasonable and the means with FEM simulation are effective. It can be taken as a new approach for single-point incremental forming of sheet metal and tool path design.     

Modeling and simulation for multiple-step incremental air-bending forming of sheet metal

Based on Hill’s yielding criterion and plane strain condition, the explicit expressions of elastoplastic constitutive model are derived in this paper which takes into account the effects of transverse stress, neutral surface shifting, and sheet thickness thinning on the sheet springback of air-bending. Then, this model is embedded into ABAQUS software platform by means of programming. Finally, 3D ABAQUS finite-element models (FEM), used to form the semiellipse-shaped workpiece with super length and large opening of sheet metal, are established, and the multiple-step incremental air-bending forming and springback processes are simulated. The simulation and experiment results show that the data predicted with the new constructed constitutive model under the plane strain condition are in much better agreement with experimental data than those predicted with the constitutive model built-in ABAQUS. It can be taken as a valuable mathematical tool used for multiple-step incremental air-bending forming simulation of large area sheet metal.     

Effects of forming parameters on temperature in frictional stir incremental sheet forming

Frictional stir Incremental sheet forming (ISF) is a new technology used to fabricate parts of hard-to-form materials without using heating equipment. Thus far, limited information is known about the effects of main forming parameters, except spindle speed of the tool, on the temperature of formed sheet in friction-stir ISF. The effects of six forming parameters, namely, sheet thickness, tool vertical step, tool diameter, spindle speed, feed rate, and wall angle of the formed part, were identified using the design of experiment of orthogonal array, analysis of response tables and graphs, and analysis of variance. Results show that spindle speed, feed rate, sheet thickness, and tool vertical step significantly affect the temperature of the sheet. In addition, the temperature of the sheet is significantly increased by increasing sheet thickness, tool vertical step, and spindle speed but significantly decreased with increasing tool feed rate.

     

金属板材数控渐进成形支撑CAD模型自动生成

为满足金属板材数控渐进成形中支撑制作的需要,提出一种从板材件的计算机辅助设计模型自动生成支撑计算机辅助设计模型的方法。采用STL数据模型,根据板材件曲面曲率的变化和成形过程中板材的减薄规律,计算出成形过程中板材厚度的变化量,通过对STL模型进行不等距偏置,生成了能够自适应板材厚度变化、并能保证挤压工具头与支撑之间合理间距的支撑计算机辅助设计模型。最后,给出了支撑计算机辅助设计模型生成实例。     

Numerical simulation and experimental investigation of multistage incremental sheet forming

Multistage forming is usually adopted to form those parts which have steep angles or even vertical walls during incremental sheet forming (ISF) process. In order to study the multistage incremental forming further, based on a finite element method model which was experimentally verified, different forming strategies were adopted to form a frustum of cone with a wall angle of 30° to research the influence of the number of forming stages (n) and the incremental wall angle between the two adjacent stages (?α) on the formability of ISF. The simulation results including the thickness distribution, the equivalent plastic strain, and the magnitude of springback were analyzed in detail. It was found that with the growth of n, the minimum thickness increases largely, and more uniform thickness distribution is achieved, but the quantity of springback becomes larger in contrast with a single-pass process because of the accumulation of springback during each forming stage. Furthermore, an expression to figure out the appropriate value of n was given. In addition, the maximum thickness reduction decreases initially and then increases as the value of ?α grows. Meanwhile, it indicates that there is no relation between ?α and the quantity of springback.     

Thickness distribution and design of a multi-stage process for sheet metal incremental forming

Sheet incremental forming (ISF) is a promising technology. It is inexpensive and does not require particular dies. Sheet thinning, however, has always been one of the forming defects which impede the process’s wide application. Although a multi-stage forming process is supposed to be effective to deal with this problem, it is still uncertain how the process can reduce thickness thinning and there is no applicable rule to determine the favorable number of forming stages. In this work, based on a truncated cone, a finite element method (FEM) model for a double-pass forming was established first. Unlike simplifications in previous studies, with the process of the three-dimensional coordinates in numerical controlled (NC) machining code, the tool trajectory in this simulation model is the same as that in real work. With this approach, it was expected to gain reliability of the simulation result, and then this simulation result and a single-pass forming result were analyzed. The results of the analysis indicate that more uniform thickness distribution in the double-forming process largely benefits from the increase of the total plastic deformation zone. Finally, under the condition of constant volume in deformation, an equation was proposed to work out the right number of necessary forming stages and the rule of this equation was verified with a relatively complex product.     

A multipass incremental sheet forming strategy of a car taillight bracket

In order to characterize quantificationally the wear topography of the brazed polycrystalline cBN (PcBN) grains during grinding, the reconstruction model of grain topography is established through the photographs grasped with three-dimensional (3D) optical video microscope. The relationship between 3D fractal dimension and the complicated topography change of the PcBN grains is investigated based on fractal theory. The results obtained show that it is reasonable to calculate 3D fractal dimension according to the protrusion height of the abrasive grain. The fractal dimension of the grain wear topography formed due to microfracture is higher than that formed due to large fracture and attritious wear. The fractal dimension range of the wear topography of the brazed PcBN grains is limited to 2.0325–2.0475 with a concentrated value of 2.04 under the present experimental condition.     

Investigation on the forming force and surface quality during ultrasonic-assisted incremental sheet forming process

The integration of ultrasonic vibration into the incremental sheet forming (ISF) process can significantly reduce the forming force and bring other benefit     

Numerical simulation of incremental sheet forming with considering yield surface distortion

The incremental sheet forming processes (ISF) are attracting lots of attentions due to their advantages on rapid prototyping, without special dies and short lead time. The numerical simulation can be a valid method to investigate the forming process and predict the defects. In this study, an extended fully coupled ductile damage model with mixed nonlinear hardening was used to simulate the ISF process. At the same time, the yield surface distortion was also considered in this model, which can enhance the capability of modeling metallic material behavior under complex loading paths. Afterwards, some simulations were conducted with the proposed model. Additionally, one tension-shear orthogonal loading test was assigned on the one representative element in order to investigate the loading path effect during ISF process. By comparing the equivalent plastic strain and ductile damage evolution of the blank, the influence of the yield surface distortion on the ISF process was proved.