润滑条件下铝合金板成形模拟中摩擦模型的研究

对润滑条件下铝合金薄板筒形件拉深成形过程进行了工艺分析，在作出一些简化和假设的基础上，建立了基于流体润滑的筒形件拉深成形过程摩擦模型；将该模型运用到板料成形过程有限元分析中，计算出筒形件成形时摩擦系数动态变化的数值；开发出基于探针测试的铝合金板温成形动态过程摩擦测试系统，并对筒形件成形时的摩擦系数进行了测试实验。计算结果与实验数据表明，板料成形过程中的摩擦系数不是一个常数，随着凸模行程的增加，摩擦系数具有增加的趋势。     

应用数值模拟技术研究摩擦对板料拉深成形的影响

本文论述了摩擦对板料成形的特点和重要性,应用数值模拟技术研究摩擦对板料拉深成形的影响。结果表明：模拟某复杂零件成形性能与摩擦系数关系密切;当摩擦系数为μ3时,冲压方向最大应力最小。研究结果表明采用数值模拟技术便于研究摩擦与板料冲压成形之间的相互关系。     

摩擦圆辊直径与摩擦包角对板成形摩擦系数测量的影响

基于Duncan方法设计了一种板料成形摩擦系数测试装置,用以考察摩擦圆辊的直径和摩擦包角对摩擦系数计算的影响。正交试验分析表明:随着摩擦圆辊直径和摩擦包角的增大,由板料弯曲和包角边界造成的摩擦系数计算干扰效应将逐级减小,进而计算摩擦系数也逐步减小,并且最终趋向真实摩擦系数。基于最终试验分析结果,得出包角在90°,圆辊直径在30 mm左右时,测得的摩擦系数可以忽略弯曲效应和包角边界效应,能反映真实摩擦状态,可以用于后续的金属板料成形有限元模拟。     

板料拉深成形摩擦系数测量系统

建立了一套基于自主开发的探针式组合传感器的摩擦系数测量系统，并将此传感器耦合到拉深凹模结构中，以此来实时测量板料法兰平面测量点处所受到的垂向正向压力和径向切向拉力，并根据计算公式μ（摩探系数）=P（切向拉力）／F（正向压力）直接计算出该测量点处的实时摩擦系数大小，进而通过选择几个特征点来推导出整个板料法兰平面的摩擦分布情况及其变化规律。最后实际试验数据证明，该系统能够真实地反映板料拉深成形过程中法兰平面亡的实际摩擦分布情况。     

基于正交试验的车身覆盖件冲压成形回弹分析

以车身覆盖件为研究对象,根据板料成形特点及回弹规律,利用dynaform软件对前围板冲压成形进行了回弹仿真试验.依据回弹仿真试验结果,用正交试验法对冲压参数(压边力、摩擦系数、板料厚度)与前围板冲压回弹之间的关系进行了分析.结果显示,压边力、摩擦系数对前围板的冲压回弹有显著影响,随着压边力的增大,前围板的回弹量相应地减小.在摩擦润滑条件较差即摩擦系数较大的情况下,前围板的回弹量较小.而板料厚度对回弹仅有一定的影响,但影响关系较复杂.     

基于PSO-RBF代理模型的板料成形本构参数反求优化研究

为了准确获取材料在复杂应力应变状态下的板料成形本构参数,提高板料成形有限元数值模拟的精度,提出了基于改进径向基函数代理模型的板料成形参数反求优化方法。将径向修正系数引入径向基函数（RBF）核函数中,利用粒子群算法（PSO）对径向修正系数进行优化,提高模型的预测精度。将PSO-RBF模型应用到一个非线性测试函数中,结果表明,PSO-RBF模型比RBF模型的预测精度提高很多;同时将PSO-RBF模型应用到板料成形本构参数反求中,代替有限元模型进行正问题计算,可节省计算成本和提高效率。结果表明,基于PSO-RBF模型反求优化得到的材料参数,能够更加准确地反映材料的流动趋势以及应变分布。     

基于摩擦特性实验的齿面摩擦因数计算方法研究

从摩擦特性实验出发,对基于两种等效原理(啮合点曲率半径等效原理和功率损失与摩擦功耗等效原理)的齿面摩擦因数的计算方法在实验原理、实验条件及结论方面进行了比较分析;指出了齿面摩擦因数动测实验的优越性;在总结前人实验成果并结合自身研究的基础上,引入有限元单元法和反求技术,提出了基于摩擦多性态概念和"计算—试验综合模型"的摩擦因数反求方法;该方法为复杂润滑条件下齿面摩擦因数的求解提供了一种新的思路。对齿轮摩擦因数求解的深入研究,对探索齿轮摩擦机理和促进减振降噪技术的开发,均具有较重要的意义。     

一种模拟热成形工况的高温摩擦试验机的设计及探讨

销-盘摩擦试验机是摩擦学领域的标准摩擦实验设备，但是面对热成形过程中的摩擦过程，销-盘摩擦试验机中的往复摩擦引起磨屑在轨道内快速堆积，与热成形实际工况并不一致。提出一种新的高温滑移摩擦试验机设计方案，该方案控制模具钢销在板料滑条上单向长距离滑移，用以实现对连续热成形摩擦过程的模拟。通过分析销-盘摩擦试验机和高温滑移摩擦试验机的实验结果，发现后者的实验过程更接近热成形的实际工况，利于展开对摩擦磨损机制的定性定量分析。     

基于响应面方法的材料参数反求

板料在冲压过程中处于复杂的各向异性三维弹塑性变形状态,若采用基于传统的单向拉伸试验得到的材料参数进行计算,必然会引入较大的计算误差。提出一种直接从冲压成形过程反求材料参数的方法。该方法将参数反求的问题转换为求试验测量值与仿真计算值之差最小二乘最小的优化问题。试验测量值为冲头的力–位移曲线,而待求的参数包括材料的特性参数和本构参数。采用移动最小二乘响应面法作为优化方法以减少调用正问题计算的次数。由于对冲压成形过程的模拟耗时较多,减少优化迭代的次数意义重大。     

润滑对板料胀形和拉深性能的影响

胀形和拉深是板料成形中重要的工序,摩擦状况直接关系到成形效果.在胀形和拉深实验中其他条件不变的情况下,通过采用6种不同的润滑剂、液压成形和无润滑剂,对同样形状的板料进行胀形和拉深实验,比较润滑剂对钢和铝板料成形性能的影响.实验结果表明:在板料成形中,干润滑剂润滑效果好于湿润滑剂润滑效果;润滑剂对钢和铝板两组试件成形性能的影响基本一致,并对结果进行了分析.     

Determination of coefficient of friction under conditions of deep-drawing and stretch forming

Lubrication plays an important role in deep-drawing and stretch forming processes. It effects the boundary frictional (shear) stresses and modifies the strain distribution across the product quite considerably. The location of plastic instability and fracture, and the magnitude of the instability or fracture strains in stretch forming and deep-drawing depends largely on the lubrication conditions between sheet metal and the tools. The effectiveness of boundary lubricants can be determined by finding the operatuve coefficient of friction between sheet metal and the tool. For this purpose, two different methods for the determination of coefficient of friction were developed. The first method is applicable to the radial drawing region (between sheet metal and die) in deep-drawing. The second method is applicable by finding the operative coefficient of friction between sheet metal and the tool, experimentally measured quantities such as loads and strain distributions, the coefficients of friction can be calculated using analytical equations.The results indicated that the coefficient of friction varied as a function of the plastic deformation. Coefficients of friction in stretch forming were found to be much higher than those in radial drawing. Experimental results indicated that plastic films could be more effective in reducing friction than grease type lubricants. The methods developed can be used in the evaluation of the lubricants in such processes. They can also be used to provide the necessary coefficients of friction to be used in metal forming theories.     

TC4板料电辅助加热数控渐进成形时摩擦和润滑的研究

难成形板料局部自阻电辅助加热数控渐近成形是一种新技术,由于该技术涉及高温、电流和塑性变形等因素,摩擦机理复杂,因此选择正确的润滑方式对提高加工件的表面质量至关重要。笔者首先对渐近成形的摩擦机理进行了分析,提出摩擦分为3个区域,黏着摩擦、边界摩擦和流体润滑。然后又对电辅助加热渐近成形的摩擦机理进行分析,指出摩擦主要由黏着摩擦和边界摩擦组成,并提出了摩擦力计算公式。为了提高电辅助加热渐进成形加工件的表面质量,关键是增加润滑剂与板料之间的结合力。通过选用不同润滑剂进行实验,对比加工件表面质量,发现用电沉积制备的铜基二硫化钼复合材料具有良好的自润滑性能,加工的TC4钛合金钣金件表面质量良好。     

Analysis of the tribological behaviour of polymer composite tool materials for sheet metal forming

Today's automotive industry shifts its focus on customised production, facing an increasing demand for medium and small batch production, where cost-effective manufacturability of sheet metal forming dies comes into the foreground. Filled polymers offer possibilities to fulfil such requirements in the ambit of prototype tools manufacturing or in small batch production of sheet metal components. This paper presents investigations dealing with tribological and tool design aspects of using polymeric materials for sheet metal forming purposes. Friction and wear behaviour of two polymer composites on sheet metal counterface materials have been investigated. A new testing method for wear evaluation of polymeric materials for sheet metal forming using a Strip Drawing Test facility is presented and discussed. A method to predict lifetime of polymeric stamping dies using the linear wear–distance relation W_l/s measured with the new testing method is also proposed. Significant improvements in friction and wear performance of polymer composites have been observed using sheet materials with structured surfaces. A theoretical model for abrasive friction and wear of polymer composites on sheet metal counterface material pairs has been developed, based on the results obtained by measurement of friction and wear.     

Influence of Surface Topography on the Tribological Behaviour of Aluminium Alloy 5182 with EDT Surface

Friction is one of the most important parameters in sheet metal forming. Friction conditions are influenced by the texture of the sheet surface, by the surface or coating of the tools and by the lubrication. The aluminium alloy AA 5182 with EDT surface has been studied and tested at various angles between rolling and sliding direction. The friction behaviour observed in experiments at different normal pressures based on Coulomb’s friction law are shown and discussed in this article. Moreover, local surface topography and lubricant distribution in the contact area are described.     

Hydrodynamic effects of macroscopic deterministic surface structures in cold forging processes

The tribological conditions between tool and workpiece are crucial for process feasibility and tool durability especially in bulk metal forming processes. Therefore, friction as one main parameter in forming needs to be adjusted sensitively. While in sheet metal forming lubricant pockets are known as an appropriate way to minimize friction forces, these reservoirs for lubricants are not state of the art in bulk metal forming. This paper describes the tribological benefit of macroscopic deterministic structured semi-finished parts in cold forging.     

Analysis of deep drawing of sheet metal using the Marform process

This paper deals with the deep drawing of metal cups using the Marform process. Using this technique, higher limiting drawing ratios can be obtained compared with the conventional deep drawing process. The analytical model of the process is presented initially, followed by the finite element simulations using ABAQUS software. A new friction model based on local contact conditions is presented and used in the finite element (FE) simulations of the process. Compared with traditional Coulomb friction model, the results of the FE simulations with the new friction model showed good correlation with experimental results. The results showed that the maximum thinning occurs at the punch profile portion, and by increasing the forming pressure, thinning of the sheet metal propagates from the punch profile portion to the side wall. At low forming pressures, wrinkles appear in the flange, whilst at higher pressures, fracture is the main defect of the Marform process.     

Formability evaluation of a pure titanium sheet in the cold incremental forming process

Owing to its ability to deform a sheet metal locally, the single point incremental forming (SPIF) process produces larger deformations as compared to the conventional forming processes. In the present study, we investigated the effect of some process parameters – pitch, tool diameter, feed rate and friction at the interface between the tool and blank – on the formability of a commercially-pure titanium sheet. Trends between the process parameters and formability are presented in this paper.     

带凸缘高圆筒件一次拉深成形新工艺的数值分析

提高板料的成形性能始终是拉深工艺中的一个关键因素,本文分析了一种能大幅度提高板料成形性能的新工艺措施。这项新技术是通过减小压料接触面上的流动阻力,实现对板料成形性能的优化。文中采用这一新工艺措施对带凸缘的高圆筒件的一次拉深成形过程进行有限元数值模拟,得到很好的验证,同时分析了这项新技术的机理。