A thermal hydrodynamic model for the lubrication breakdown in upsetting between overhanging dies

A thermal hydrodynamic model of the lubricant transport process in plane strain upsetting between overhanging dies is developed. It is shown that at the start of the process the lubricant is transported at half the workpiece surface speed. As the process proceeds the workpiece heats up and the rate of lubricant transport is reduced. Since the lubricant cannot keep up with the outward motion of the workpiece an unlubricated zone is formed near the workpiece edges. The width of this zone predicted by the model is in good agreement with experimental measurements made on aluminum workpieces lubricated with silicone oils.     

Measurement of equivalent residual stresses generated by milling and corresponding deformation prediction

We introduce a method to measure the equivalent residual stresses and depths of the affected layers, which are generated in the workpiece during the milling process. These layers lie immediately under the milled surface. After machining, two material layers on the opposite side from the machined surface were chemically removed, and strain changes on the machined surface were measured after each layer removal. Based on the strain changes and the thickness of each removed layer, the equivalent residual stresses and depths of the affected layers in different directions were obtained. Based on the measured results, the corresponding deformations caused by the milling induced residual stresses can be predicted in workpieces with different rigidities. The predicted deformations were validated by the experimental results. We found that our measuring method can be successfully used in practice to evaluate the machined surface properties and predict the deformations caused by milling induced surface residual stresses accurately.     

Matrix-presentation linear least square error method of inverse elastic-plastic large deformation finite element model for upsetting

The main purpose of this paper is to develop the matrix presentation linear least square error method of inverse elastic-plastic large deformation finite element model for upsetting to obtain the friction coefficients during the upsetting process. This inverse model assumed the linear material and based on the modified experimental loading increments using the linear modified experimental upsetting loading standard proposed in this paper. Then the friction coefficients of contact boundary between the workpiece and the die at specific finite element analysis stages can be derived. Finally, using the cubic spline fitting, the history of friction coefficient during the upsetting process can be obtained. It is demonstrated that the workpiece profile of upsetting experiment is quite identical to the workpiece profile of simulation using the result obtained in this paper as the history of friction coefficient of contact boundary, and furthermore the distribution of stress and strain of the workpiece during upsetting process can be understood.     

Benefits of Cold Plane Finishing

For cylindrical and annular workpieces, a method is proposed for increasing the precision obtained in cold deformation on the basis of plane finishing. Modeling results are presented. The stress–strain state of the workpiece in upsetting is determined.     

Workpiece temperature rise during the cutting of AISI 4340 steel

Temperature rises in workpieces were measured during the cutting of various hardnesses of steel by a ceramic tool. Thermocouples were embedded in a specially designed workpiece for the temperature measurement. This workpiece provided practical and accurate positioning of the thermocouples and it allowed the acquisition of reliable data from the cutting experiments. The effects of the workpiece hardness and cutting speed were examined and analyzed. The relationships between the workpiece temperature rise and residual stresses or structural change in a machined surface layer were discussed.It is concluded that the temperature rise in a steel workpiece during cutting by a ceramic tool is so low that it is less likely to cause any surface damage under normal conditions.     

MODELING AND SIMULATION OF WORKPIECE TEMPERATURE IN GRINDING BY FINITE ELEMENT ANALYSIS

The quality of ground workpieces is largely determined by the accuracy of dimensions and geometry, and by the surface finish. The thermal stress to which workpieces are subjected during the grinding process, characterized by the temperatures that develop, plays a major role as far as the economical fulfillment of high-quality requirements is concerned. Too high thermal stresses have a deleterious effect on the workpiece, leading to changes in specific service characteristics. This paper predominantly concerns experiments to determine the temperature when grinding cemented carbides. In this context, the temperature fields developing in the workpiece were examined for different grinding conditions, both on the basis of experiments and calculations by means of finite element analysis (FEA). The simulations show a rise in surface temperatures in the workpiece from the run-in to the run-out phase of the grinding process. The analysis indicates that the-grinding process gives rise to an inho-mogeneous distribution of the material properties of the workpiece, along the grinding direction.     

Finite element analysis and experimental investigation on deformation mechanism of non-axisymmetric tube spinning

This paper developed 3D elastoplastic finite element analysis (FEA) models to investigate non-axisymmetric tubes neck spinning. The three-roller mandreless neck spinning process was simulated by commercial FEA software, MSC. Marc. The distribution of the transient von Mises stresses in the contact zone between the roller and the blank, and the equivalent plastic strains after spinning were obtained. The locations and causes of fractures were analyzed. The thickness distribution of the spun workpiece was investigated numerically and experimentally. It shows that during 3D non-axisymmetric tubes spinning, diametral elongation and fractures mostly occur at the opening end of workpiece, which considered as the primary location of defects. Fractures may also occur easily at the initial spinning area, which may be considered a secondary location of defects. The distributions of equivalent stresses and strains are non-uniform during both offset and oblique 3D non-axisymmetric tubes spinning. The maximum stress and strain values occur at the location where the biggest offset or inclination is induced, while the minimum values occur at the opposite location of 180° away from the maximum values. For the oblique tube, however, the strain distribution changes gradually along the axial direction, which is different from that of the offset tube. Thinning occurs during forward path spinning and thickening occurs during backward path spinning. Therefore, for multipath neck spinning processes, forward and backward paths should be applied alternately to avoid excessive thinning or thickening of workpiece.     

Delamination effects in grinding

Delamination of the surface layers of brass workpieces was observed during single-grit grinding. In most instances, complete delamination did not occur and the delaminated material was still attached to the workpiece. Transmission electron microscope examination of the ground surface layers showed that they had a fine subgrain structure; no evidence of a dislocation-free surface layer was obtained. Delamination was found to occur in the fine-grained surface layers, and it is suggested that this occurs by a process of shear separation within the fine subgrain structure. The manner in which the delaminated sheets were observed to lift away from the workpiece surface seems to indicate the presence of both residual tensile and compressive stresses within the surface layers.     

Die design optimization for axisymmetric hot extrusion of metal matrix composites

Strain rate sensitive materials such as Ti alloys, superplastic materials and metal matrix composites (MMCs) can be deformed only in very narrow range of strain rate. In this work, a new process design method for controlling strain rate in workpiece during hot extrusion process is proposed. In this approach, a coupled numerical approach of finite element analysis and optimization technique to optimal profiled die which yields more uniform strain rate distribution in the deforming region is applied to the hot extrusion process of MMCs. Extrusion die profiles are defined by Bezier curves, and FPS (flexible polyhedron search) method is used as optimization technique. The change of relative deviation of strain rate, the progressive development of die profiles with increase of iteration for optimization and the corresponding strain rate distributions are investigated. In addition, the die profiles by optimization scheme for different extrusion ratios are compared with those by analytical solution.     

薄壁弧形件装夹布局有限元优化

关于航空结构件加工变形控制的研究是高效数控加工研究的一部分。薄壁弧形零件加工中的弹性变形对加工质量影响很大,而装夹布局影响切削变形的大小和分布。以减少加工中工件最大弹性变形为目标,建立了弧形件铣削加工装夹布局的优化模型,采用商业有限元软件的设计优化模块进行计算。在对计算结果进一步分析的基础上,提出了最终的装夹布局方案,采用该方案可以得到整个加工过程中更低的变形量,变形分布更均匀,为采取相应数控补偿措施提供条件。优化方案和实际加工方案结果基本一致。所提出方法可推广至其他类型工件夹具布局优化设计。     

H13淬硬模具钢精车过程的数值模拟

采用热力学耦合有限元方法研究了淬硬钢精车过程中切屑形成规律。运用H13 淬硬模具钢流动应力模型进行数值模拟,考查了H13淬硬模具钢精车过程中工艺参数对工件性能和刀具的影响。结果表明:切削速度愈高,进给量愈小,刀具刀尖半径愈大,则工件加工层上的静水拉应力愈小,表面质量愈好; 淬硬钢精车时径向力起主要作用,大于切削力;切削速度愈大,切削力和径向力则愈小,愈有助于改善工件加工层上的表面质量;切削速度、进给量和刀具刀尖圆角半径愈大,工件和刀具温度愈高,愈易导致刀具前刀面扩散磨损和刀具后刀面磨损。研究结论有助于优化H13淬硬模具钢精车过程中工艺参数选择和改进刀具镶片设计。     

Inverse calculation of the friction coefficient during the warm upsetting of molybdenum

This study focused on the variation of the friction coefficient during the upsetting process and the concept of treating the solution of unknown parameters as an inverse problem. Based on the experimental measurement data, the Levenberg–Marquardt method, a numerical optimization approach was used in conjunction with the constrained function, convergence criterion and the axial symmetry thermo-elastic-plastic finite element method to solve, inversely, the variation of friction coefficient during the upsetting process.The inverse calculation steps of the warm upsetting of the molybdenum proposed in this paper was based on the load values measured in the upsetting experiment. The inverse calculation procedures were taken to solve the variation of the friction coefficient during the warm upsetting process. The results related to stress distribution, strain distribution, temperature distribution and shape variation were then compared with those reported in other studies. The comparison further confirmed the justification of using the load to solve the friction coefficient inversely. By means of the inverse algorithm presented in this paper, physical phenomena that better approximated the reality could be obtained, and the entire upsetting forming simulation could be more complete.     

倾斜管件多道次缩径旋压成形的数值模拟及试验

以6061T1(退火态)铝合金为研究对象,以MSC.MARC软件为分析手段,采取有限元法对三维非轴对称倾斜管件多道次缩径旋压过程进行数值模拟,并利用网格圆及显微组织的变化从试验的角度验证模拟所得到的应变分布规律。结果表明,倾斜使得工件的应力应变呈不均匀分布规律;等效应力沿轴向呈分层分布的特点,在口部达到最大值;等效应变沿周向0°～180°域逐渐减小,在0°域存在最大值,180°域存在最小值;沿轴向从起旋处到口部,等效应变在0°域具有逐渐增大和在180°域具有逐渐减小的特征。由于返程旋压的明显增厚效应,多道次旋压时,工件变形中间部位壁厚增加。多道次缩径旋压时工件变形中间部位壁厚变化规律的试验结果与模拟结果的相对误差不大于10%,说明所建立的有限元模型是合理可靠的。在理论分析及试验研究的基础上,成功研制出倾斜类汽车排气歧管样件。     

金属表面改性的预应力磨削机理研究

本文提出了利用预张应力磨削来提高磨削加工的表面质量问题。建立了预应力磨削的理论分析模型,较透彻地阐述了预应力磨削对表面残余应力的影响。还就各种磨削条件和装恶化条件对磨削加工中表面残余应力的存在与分布,以及对工件几何精度的影响进行了试验研究。并探讨了这种对金属表面改性有利的新磨削工艺的可行性与实用性。     

减小电镦下沉深度与混晶改善的增材调控研究

在电镦成型时,尤其是大型件的成型时,为了获得所要求的“蒜头”直径,往往会造成坯料前端的下沉缺陷。下沉缺陷的存在,一方面,大的下沉深度会使坯料端面晶粒分布极其不均匀,出现混晶;另一方面使坯料在后续的模锻成型时出现闭气问题。通过增材调控的方法,不仅能使下沉深度减小,而且可以使电镦端面的混晶区域的晶粒趋于均匀化,大大提升了电镦件的质量。     

mini轧机轧制AISI1015钢轧件温升和应变的有限元模拟

利用Deform软件建立mini轧机轧制模型,研究了轧制过程中不同规格(?8 mm,?10 mm,?13 mm)和不同初始温度(800,850,900,950℃)AISI1015钢轧件的温升和应变,分析了轧制温升差异的原因.结果表明:mini轧机轧制模型模拟得到出轧机时轧件的表面温度与实测结果的相对误差在13％以内;轧...     

Analysis of the dissimilar interface frictional constraints during the upsetting process

A thermo-elastic-plastic coupling model combined with frictional functions is proposed to analyse the plastic upsetting of a cylinder, accounting for dissimilar interface frictional constraints. The flow stress of the deforming workpiece is considered as a function of strain, strain rate and temperature, and the properties of the interface frictional constraints are approached through the use of two continuously varying functions which are presented in terms of the amount of the workpiece deformation.The effects of various combinations of dissimilar interface frictional constraints at the top and bottom die surfaces on the temperature, strain and strain rate distributions are investigated. The asymmetrical flow inducing uneven billet profiles, together with the variations in top and bottom die surface loads, are predicted. The results obtained are consistent with the observations of upsetting experiments.     

麻花钻加工20Cr的断屑仿真分析

利用有限元软件DEFORM-3D,对麻花钻钻削20Cr的断屑过程进行了仿真分析。根据塑性材料断裂强度理论,以切屑卷曲变形为断屑判据。通过模拟分析,得出了工件的等效应力、应变及其分布,以及工件上P点最大等效应变的变化规律,阐释了该点最大等效应变与切屑卷曲变形的正相关性。提出并验证了P点最大等效应变的峰值可作为麻花钻加工20Cr的断屑判据。     

In situ 3D measurement of lubrication behavior at interface between tool and workpiece by direct fluorescence observation technique

A new direct observation method, which is based on an optical microscopy and a conventional fluorescence method, is developed in order to measure the oil film thickness at the interface between the tool and the workpiece in lubricated upsetting. The oil film thickness is measured using this method. The oil film thickness and the distribution at the interface during lubricated upsetting can be measured three dimensionally. The calculated central thicknesses at the instant of entrapment are in good agreement with the measured ones for lubricants with higher viscosity at higher compression speed. The 3D surface topography of workpiece at the end surface can be clearly visualized.     

Design and fabrication of a novel polishing tool for finishing freeform surfaces in magnetic field assisted finishing (MFAF) process

Surface finish is a critical requirement for different applications in industries and research areas. Freeform surfaces are widely used in medical, aerospace, and automobile sectors. Magnetic field assisted finishing process can be used very efficiently to finish freeform surfaces. In this process, magnetorheological fluid is used as the polishing medium and permanent magnet is used to control its rheological properties to generate finishing force during polishing. To avail sufficient magnetic field in the finishing zone, it is necessary to design an optimum polishing tool. In the present study, a specially designed polishing tool is designed using a finite element based software package (Ansys Maxwell^®) based on Maxwell equations. At first, dimension of the permanent magnet is determined for designing optimum tool geometry. After that, dimension and configuration of the magnet fixture are optimized. A special type of metal named mu-metal which is a nickel-iron based alloy is selected for magnet fixture due to its magnetic-field shielding property. Mu-metal directs the magnetic flux lines in such a way that in the finishing zone the magnetic flux can be concentrated on the workpiece surface required for finishing. Also, the Mu-metal magnet fixture shields the magnetic field from outside environment so that MR fluid as well as any surrounding magnetic materials do not stick to the polishing tool. Experiments are carried out to validate the Maxwell simulation results to compare the magnetic flux distribution on the workpiece surface which shows good agreement between them. Also, finishing of flat titanium workpieces are carried out and it is found that the novel polishing tool has the capability to finish the workpieces in the nanometer range.