不锈钢薄板的激光弯曲成形试验研究

以不锈钢薄板的激光弯曲成形为研究对象，通过实验研究其成形过程及影响因素。首先介绍了激光成形的工艺过程及影响因素；然后通过试验研究了激光能量、扫描速度、激光光斑大小和扫描次数等因素对弯曲成形角度的影响。     

工艺参数对管材激光弯曲成形影响规律的研究

管材激光弯曲成形是一种柔性金属塑性成形方法。将连续的激光光斑简化为一间歇跳跃的方形匀强面热源,并考虑材料性能参数与温度的相关性,建立了管材激光弯曲成形的热-机耦合有限元工艺仿真模型,对成形过程进行了数值模拟。有限元模拟结果表明:在其他条件不变的情况下,激光弯曲角度随激光功率的增大而增大,两者基本上成线性关系;弯曲角度随扫描速度的升高而减小,随光斑直径的减小而增大,但当光斑直径减小到一定程度后,弯曲角度开始减小;弯曲角度随扫描包角的增大而增大,当扫描包角为180°时,弯曲角度达到最大,弯曲角度随扫描包角的继续增大而减小;扫描次数与弯曲角度间成近似的线性关系,且第一次扫描管材产生的弯曲角度最大。     

金属薄板开槽弯曲成形技术与设备

V形弯曲成形前，对金属薄板折弯处进行一定深度的V形开槽，然后在V形开槽处进行弯制成形，此种加工方法称之为V形开槽弯曲成形技术。用V形开槽弯曲成形技术弯制的工件弯曲圆角半径小，色泽变化不明显，弯制成形力小，且减少了窄长工件弯曲棱边直线度误差。并在普通折弯机上用通用模具就能弯制断面形状复杂的工件。V形开槽弯曲成形技术的关键设备是薄板开槽机，有多种结构形式和控制方式供选择。     

薄板弧形零件的弯曲成形

图1是双塔牌4L系列谷物联合收割机的弧形板,材料为Q235A,加工后弯曲表面应光滑无裂纹,无明显翘曲,平面度达2mm。为此,我们经过技术攻关,找到了加工这类零件较经济的方法。 1.材料弯曲变形及加工方法分析 对如图2所示的弯曲成形板材,一般认为其相对宽度b<3t时为窄板(其中,b是板材的宽度,t是厚度,在t方向上进行弯曲)。窄板在弯曲时,在宽度b方向     

板料激光三维弯曲成形的工艺研究

激光成形是1种利用激光作为热源的热应力无模成形新技术.介绍了激光成形的工艺过程及加工设备,分析了激光成形机理,研究了板料激光三维弯曲成形的工艺以及典型工件的成形方案.最后综述了该工艺技术的发展前景.     

金属微弯曲成形方法的研究

介绍微弯曲成形方法——激光微弯曲成形以及塑性微成形方法。并提出了激光辅助加热微弯曲成形方法。即激光辅助加热待加工件使其达到合适的温度范围后进行微弯曲成形的方法，提高难成形材料的微塑性成形能力和质量。     

板料激光弯曲成形技术的研究现状及展望

综述了近年来国内外对激光弯曲成形技术的研究现状，概述了激光工艺参数、板料几何参数及材料性能等因素对弯曲成形的影响，分析了扫描轨迹对成形结果的影响以及激光成形闭环控制系统的应用，并对板料激光弯曲成形的应用和发展前景作了展望。     

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。     

板材激光弯曲成形技术的研究进展及其应用前景

板材激光弯曲成形是一种新型金属板材柔性成形技术，与传统成形工艺相比具有显著优势。综述了国内外此项技术的数值模拟和试验研究现状，并对其应用范围和发展前景作了展望。     

管材激光成形的工艺参数优化

建立了管材激光弯曲成形工艺优化模型,采用优化软件iSIGHT与有限元模拟软件MSC.Marc相结合,对管材激光弯曲成形工艺参数进行优化,得到成形一定角度并高效成形的最佳工艺参数组合。     

A general forming limit criterion for sheet metal forming

The forming limit of sheet metal is defined to be the state at which a localized thinning of the sheet initiates during forming, ultimately leading to a split in the sheet. The forming limit is conventionally described as a curve in a plot of major strain vs. minor strain. This curve was originally proposed to characterize the general forming limit of sheet metal, but it has been subsequently observed that this criterion is valid only for the case of proportional loading. Nevertheless, due to the convenience of measuring strain and the lack of a better criterion, the strain- based forming limit curve continues to play a primary role in judging forming severity. In this paper it is shown that the forming limit for both proportional loading and non-proportional loading can be explained from a single criterion which is based on the state of stress rather than the state of strain. This proposed criteria is validated using data from several non-proportional loading paths previously reported in the literature for both aluminum and steel alloys. In addition to significantly improving the gauging of forming severity, the new stress-based criterion is as easy to use as the strain-based criterion in the validation of die designs by the finite element method. However, it presents a challenge to the experimentalist and the stamping plant because the state of stress cannot be directly measured. This paper will also discuss several methods to deal with this challenge so that the more general measure of forming severity, as determined by the state of stress, can be determined in the stamping plant.     

Lubricant test methods for sheet metal forming

Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has proven successful and has in a number of examples assisted the substitution of environmentally hazardous lubricants by more friendly ones in industrial production.     

Sectional finite element analysis of forming processes for aluminum-alloy sheet metals

The sectional finite element analysis of the forming processes for the aluminum-alloy sheet metal known to be planar anisotropic was performed. The two-dimensional rigid-viscoplastic FEM formulation based on the bending augmented membrane theory as well as the anisotropic yield criteria was introduced. For modeling the anomalous behavior of aluminum-alloy sheet metals, Barlat's strain rate potential and Hill's (Journal of the Mechanics and Physics of Solids 1990;38:405–17) non-quadratic yield theory with an isotropic hardening rule were employed. Furthermore, a new method to determine anisotropic coefficients of Barlat's strain rate potential was proposed. For evaluating bending effects in the forming process of aluminum-alloy sheet metals, the bending equivalent forces were calculated in terms of the changes in the interior angle at a node between two linear finite elements and were augmented to the membrane stretch forces. In order to verify the validity of sectional finite element formulation based on the bending augmented membrane theory, the plane strain stretch/draw forming processes of a square cup test were simulated and simulation results are compared with experimental measurements. Friction coefficient was obtained from drawbead friction test. The properties of selected material were obtained from uniaxial tensile tests. Simulation shows good agreement with measurements. For the application of the sectional finite element formulation introduced in this research, the drawing process of a rear seat back upper bracket of passenger cars is simulated assuming plane strain condition. The thinning distribution of the simulation agreed well with that of the measurement, so that the sectional analysis is acceptable in the design and analysis of aluminum-alloy sheet stamping dies.     

Wear of aluminium bronze in sliding contact with lubricated stainless steel sheet material

Aluminium bronze, well known for its good sliding properties, is frequently applied as tool material in sheet metal forming (SMF) of stainless steel, e.g. for the production of washing, refrigeration and cooking equipment. The limited hardness of the material makes it, however, sensitive to tool wear that is: volumetric wear of the tool due to sliding contact with the sheet material. Conventional wear tests like the rubber wheel abrasion test or the Taber abrader test cannot be used to simulate the interaction of the tooling with lubricated sheet material. Dedicated tribo tests are therefore conducted with the slider-on-sheet test. The aim of the research is to measure the specific wear rate of aluminium bronze at SMF-like conditions. Experimental results showed a pronounced influence of lubricant selection and sheet material selection. The measured specific wear rate varied from 10⁻⁸ mm³/N m for a smooth stainless steel sheet quality to 10⁻⁶ mm³/N m for a rough surface quality.     

同机分体异步薄板冲压工艺

提出一种新的薄板冲压成形工艺,根据薄板的成形特点进行模具板块分体离散并安装在同一台压力机上进行异步冲压板片。分析金属薄板成形零件的形状特点,并根据分析结果给出模具分体部件的几个原则。分析异步冲压中模具衔接区域的薄板变形状况以及提出的解决方案。     

On the prediction of the effect of process parameters upon forming limit strains in sheet metals

Plasticity analysis of sheet metal forming requires a detailed knowledge of the influence of process parameters on the stress–strain relationships from yielding up to localized necking, for accurate prediction of forming limits. Achievable strain and stress–strain relationships are sensitive to modulations in process parameters, chiefly temperature and strain rate. However, the effects of changes in strain rate and temperature are often complex as they also depend on the levels of strain, strain rate and the temperature employed. Such variations could be either triggered by the process dynamics of the forming operation or imposed for optimal exploitation of the material ductility. In this study, the influence of such process parameter modulations upon formability has been theoretically modelled, following the Sing–Rao prediction approach. The limit strains thus predicted compare favourably with experimental results for a drawing steel, thus validating the present formalism. This approach can also be adopted to accommodate non-linear straining conditions. Thus, theoretical modelling of strain-path-dependent forming limits, which has not been explored adequately so far, now becomes feasible.     

Finite element analysis of the effects of martensitic phase transformation in TRIP steel sheet forming

This paper aims at investigating the effects of the martensitic phase transformation on the formability of unstable austenitic steel sheets. To this end, the constitutive model developed by Iwamoto and Tsuta (International Journal of Plasticity 2002;18:1583–606) has been implemented in the user's material subroutine of the finite element code Abaqus/Explicit. The different contributions of the martensitic transformation to the overall plastic behaviour are analysed with the aim of assessing their influence in sheet-metal forming. The effects of transformation strains, and of the stress-state dependence of the kinetics of phase transformation are critically discussed in the case of the cup drawing test. The simulation results are also compared with experimental cup tests from the literature.     

等效拉延筋模型及其在板料成形数值模拟中的应用

讨论等效拉延筋的建模方法、常用模型及其在板料成形数值模拟中的应用情况,并指出研究中仍存在的问题及今后的发展方向。     

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.     

Determination of stretch-bendability of sheet metals

Today's sheet-metal forming industry relies mostly on experience-based methods for finding the forming limits which assure successful forming processes. Such methods are inefficient and there is an obvious need for cost-effective knowledge-based computer-aided techniques.In this paper, a mathematical model for the stretch-bending processes is introduced. The model is capable of performing all calculations necessary to determine the effect of material properties on the process parameters such as forming loads, product geometry, springback, and residual stresses. From this model, the significance of various material parameters from productivity, ease of fabrication, and tool design viewpoints can be evaluated. This should contribute to the development and optimum use of sheet materials with improved properties.Notation c,d distances on the cross-section of the beam, m - h depth of the cross-section of the beam, m - K,n material constants in the power law equation: =K ⁿ - M bending moment, Nm - M _e maximum elastic bending moment, Nm - m non-dimensional bending moment,M./M _e - N axial tensile force, N - N _e maximum elastic tensile force, N - n _r non-dimensional axial force,N/N _e - non-dimensional parameter,c/(h ₂) - non-dimensional parameter,d/(h ₂) - effective stress, MPa - effective strain