Marginal-restraint mandrel-free spinning process for thin-walled ellipsoidal heads

Metal sheet spinning is an advanced near-net forming technology for the manufacture of thin-walled ellipsoidal heads. The exact control of dimensional accuracy, however, is a considerable problem for spinning thinwalled parts with large diameter-to-thickness ratios. In this work, a marginal-restraint mandrel-free spinning process with two passes is proposed for the fabrication of thinwalled ellipsoidal heads without wrinkling. A finite element model is established and verified to study the influences of spinning parameters on the dimensional precision of thin-walled ellipsoidal heads. It is found that the spinning parameters considerably influence the deviations of wall thickness and contour characteristics. A small forming angle or small roller fillet radius during the first pass spinning, as well as the small angle between passes or high feed ratio during the second pass spinning, can improve the wall thickness precision. Meanwhile, as the forming angle or feed ratio is increased during the first pass spinning, the contour precision initially increases and then decreases. During the second pass spinning, the contour precision can be improved at a small angle between passes, whereas it deteriorates at a larger roller installation angle. The optimized spinning parameters are obtained and verified by experiments.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00296-0     

A novel spinning process for simultaneously producing two cone parts with big angle

ABSTRACT

A new spinning forming method for simultaneously producing two cone parts with big angle was developed. The novel process with three passes was generated. The 3D finite element (FE) model of cone parts was established using ABAQUS software. Based on the metal plastic forming principle and the characteristic of spinning, technical parameters including the angle of forming surface and the radial feed speed of the roller, the spindle speed and the friction coefficient were determined. Based on the secondary development of above FE model, the fittability of cone parts was obtained, which is of great significance for improving the performance of cone parts.     

Residual-stress relaxation mechanism and model description of 5052H32 Al alloy spun ellipsoidal heads during annealing treatment

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. Nevertheless, the spinning-induced residual stress, which greatly influences the in-service performance of spun heads, should be removed. In this study, the effects of annealing on the residual-stress relaxation behavior of 5052H32 aluminum alloy spun heads were investigated. It is found that the residual stress first rapidly decreases and then remains steady with the increase in annealing time at the tested annealing temperatures. The relaxation of the residual stress becomes increasingly obvious with the increase in annealing temperature. When the annealing temperature is less than 220℃, there are no obvious changes in grain size. Moreover, the spinning-induced dislocations are consumed by the static recovery behavior, which decreases the residual stress during annealing. When the annealing temperature is approximately 300℃, the broken grains transform into equiaxed grains. In addition, static recrystallization and recovery behaviors occur simultaneously to promote the relaxation of the residual stress. Considering the different stress relaxation mechanisms, a model based on the Zener-Wert-Avrami equation was established to predict the residual-stress relaxation behavior. Finally, the optimized annealing temperature and time were approximately 300℃ and 30 min, respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00367-w     

Investigation of material deformation in multi-pass conventional metal spinning

This paper reports a study on material deformation during a multi-pass conventional spinning. A Finite Element (FE) analysis model has been developed based on a 5-pass conventional spinning experiment. The explicit Finite Element solution method has been used to model this multi-pass spinning process. Effects of mass scaling and reduced integration linear element used in the FE simulation have been evaluated by using various energy histories obtained from the FE analysis. The numerical results suggest that among three tool force components the axial force is the highest while the tangential force is the lowest. Certain correlations have been found between the FE analysis results and measured dimensions of the spun part. The blank thickness decreases after each forward pass and there are almost no thickness changes during the backward pass. Stress distributions of the local forming zone of the workpiece in both forward and backward passes have also been analysed, which gives an insight into the material deformation during the spinning process.     

Roller path design by tool compensation in multi-pass conventional spinning

In conventional spinning, multiple roller passes are required to prevent material failures and to minimize thinning of wall thickness of spun parts. In the present industrial practice, the process design still relies on the trial-and-error approach to determine roller path and passes. In this paper, a tool compensation technique has been proposed and employed in multiple roller passes design, to ensure the workpiece fully conforming onto the profile of a mandrel. The Taguchi method is applied to design experimental tests and analyze the effects of material type, feed ratio and spindle speed on the dimensional variations of the spun parts. Finite element simulation is conducted to investigate the variations of tool forces, wall thickness and strains in this multi-pass conventional spinning process. The results show that the tool compensation technique can effectively prevent material wrinkling failures in the process. The type of material has the most significant effects on the variations of thickness and depth of the spun parts, followed by the spindle speed and the feed ratio. High feed ratios can help to maintain the original wall thickness unchanged but cracking failures may occur if a larger feed ratio is applied.     

Numerical simulation of single and dual pass conventional spinning processes

Due to the complex nature of sheet metal spinning processes, recent trends in analysis of the process are moving toward numerical techniques. These numerical methods, for instance finite element modelling, enable the study of parameters that can not easily be measured directly such as transient strains and stresses. Additionally, it allows a prediction of dynamic instabilities that may be used to control and achieve better product quality. In this investigation, a finite element dynamic explicit model has been used to simulate single and dual pass conventional spinning processes. The initial models are validated against published experimental data and show very good correlation. A variety of roller feed rates, roller passes and roller configurations are then simulated. Effects of roller feed rate on the axial force, radial force and thickness strain are established. The effect of roller pass and roller configuration on the axial force and thickness strain are also assessed.     

Investigation of effective parameters on surface roughness in thermomechanical tube spinning process

Tube spinning process is recognized as an effective process for fabricating of thin wall cylindrical parts, with precision tolerances, high surface quality and desired mechanical property. In this research, the influences of major parameters of thermomechanical tube spinning process such as preform thickness, percentage of thickness reduction, mandrel rotational speed, feed rate of rollers, solution treatment time and aging treatment time on surface roughness for fabricating of 2024 aluminum spun tubes using design of experiments are studied. Experimental data are analyzed by analysis of variance (Anova) and empirical models of surface roughnesses are developed. It is found that deeper percentage of thickness reduction with thicker preform thickness, slower feed rate of rollers and mandrel rotational speed and higher solution treatment time and aging treatment time are advantageous for obtaining smoother surface.     

A356铝合金车轮轮辋旋压成形工艺优化

目的 解决A356铸旋铝合金车轮内轮缘部位性能不足,满足客户的试验标准。方法 以某款车轮为研究对象,分析了现有成形工艺下导致内轮缘性能低的主要原因,提出了其性能提升的关键。在此基础上,更改旋轮形状、旋压成形轨迹和旋压参数,以获得内轮缘处更大的塑性变形量,并对该新的成形工艺进行了热旋压试验验证。结果 新的旋压工艺能增加旋压轮辋内轮缘处的变形量,变形组织更加均匀。结论 该旋压工艺的优化,大大提高了内轮缘的性能,力学性能提高10%以上,满足了主机厂的标准,已经应用于批量生产中。     

工业纯钛室温ECAP变形的组织和性能

采用BC方式等径弯曲通道变形(Equal Channel Angular Pressing,简称ECAP)对工业纯钛进行了8道次室温变形,研究了变形道次对显微组织和力学性能的影响。结果表明,铁素体组织随变形道次的增加逐渐演变为等轴状大角度晶界的超细晶组织;试验材料的硬度和强度随变形道次的增加而增加,伸长率曲线以第3道次为临界点,第3道次前材料伸长率曲线随挤压道次的增加而下降,而3道次后,曲线开始上升,材料伸长率增大。     

ECAP变形对20MnSi钢组织与性能的影响

采用C方式等径弯曲通道变形(Equal Channel Angular Pressing,简称ECAP)对20MnSi钢进行了4道次室温变形,研究了变形道次对显微组织和力学性能的影响.结果表明,铁素体组织随变形道次的增加逐渐演变为等轴状大角度晶界的亚微晶组织;试验用钢的硬度和强度随变形道次的增加而增加,4道次后强度有所降低;在本试验条件下,珠光体组织中的片状渗碳体表现出很强的塑性变形能力.     

基于正交试验的拉深旋压制杯工艺参数研究

对杯形毛坯的旋压成形工艺进行了研究,以期获得最佳的工艺参数。首先采用正交试验的方法,对旋压杯形毛坯的关键工艺参数进行分析;然后采用综合平衡分析法对工艺参数组合进行了优化,最后通过实际的旋压试验对所获得的优化工艺参数组合进行了验证。结果表明,采用综合平衡分析进行的工艺参数优化,可以制造出能够满足后续内齿轮旋压要求的杯形毛坯。     

带环形凸台薄盘形件旋压成形规律研究

目的 探明带环形凸台薄盘形件旋压成形工艺的可行性,揭示成形过程的特点、成形缺陷的类型和产生机制,以及工艺参数对成形极限的影响规律。方法 基于ABAQUS\Explicit有限元模型,分析成形过程中的材料流动、应力分布、缺陷的产生机制和工艺参数对成形极限的影响规律。结果 旋压成形过程分为内槽填充、轴向隆起和径向扩展3个阶段,应力场沿径向和周向呈梯度分布,坯料在径向扩展阶段由于受压失稳产生了凸台凹坑缺陷。成形极限随凸台增厚比、盘缘宽厚比和型槽倾角的增大而增大,随旋轮进给比f的增大,成形极限先增大后减小。结论 总结了增厚旋压工艺的成形特征、缺陷演化机制以及工艺参数对成形极限的影响规律,为带环形凸台薄盘形件旋压成形工艺的设计和优化提供指导。     

基于响应面法的无芯模成形精度研究

目的 提高无芯模旋压零件的尺寸精度.方法 利用双旋轮旋压机床,采用响应面实验优化设计方法,对铝合金零件分别从旋轮进给速度、芯模转速、锥形件的成形角度、坯料与成形件最大开口直径比等方面进行研究,建立其与尺寸精度的预测模型,采用Design-Expert软件对尺寸精度进行回归系数及方差分析,并对此工艺参数进行优化,得到最优...     

Pregelled gel spinning of polyacrylonitrile precursor fiber

A new spinning method - pregelled gel spinning method for polyacrylonitrile (PAN) precursor fiber was reported. The physical and structural properties of the pregelled gel spun PAN precursor fibers as well as dry-jet wet spun PAN precursor fibers were studied. Compared with the dry-jet wet spun fibers, the pregelled gel spun fibers had reduced core-shell difference, circular cross sections and fewer internal pores. The pregelled gel spun fibers were found to have higher crystallinity and larger crystallite size than the dry-jet wet spun fibers. The tensile stress relaxation tests suggested that the pregelled gel spun fibers had higher elasticity and better developed supermolecular structure.     

皮带轮筒壁铲旋成形工艺模拟及参数优化

针对皮带轮筒壁成形,提出一种新的旋压工艺——铲旋技术。利用CATIA软件进行造型,Deform软件建立有限元模拟模型,以旋轮转速、直径、进给速度、圆角半径为优化参数,成形载荷为优化目标,通过设计正交实验,对皮带轮的内筒成形进行有限元模拟,并提取成形载荷曲线进行分析。研究得出一组最佳工艺参数。     

Mesophase pitch-based carbon fiber spinning through a filter assembly and the microstructure evolution mechanism

A filter assembly in the upper stream of the spinneret was used to disturb the mesophase pitch (MP) melt flow during the spinning of precursor fibers. We studied the microstructure evolution mechanism of the MP-based carbon fibers during this process. Results showed that the use of filter assembly had a significant effect on the size of the split in the cross-section of carbon fibers. The split has been completely depressed in the carbon fibers spun with 50 layers of plain-weave. Selected area electron diffraction results showed that carbon fibers spun with 50 layers of plain-weave screens exhibited an apparent decrease of the orientational order of the (002) diffraction plane in both center and transition regions. The results of Raman spectroscopy indicated that, the size of graphitic microcrystalline domain in carbon fibers decreased with increasing the number of plain-weave screens in the filter assembly. Our studies confirmed the roles of the filter assembly in precursor fiber spinning to disrupt the mesophase domain formation in the MP melt and thus induce a reduced domain size.     

Evolution of microstructure and texture in an ultrafine-grained Al6082 alloy during severe plastic deformation

The evolution of microstructure and texture in Al6082 precipitation-hardened alloy during equal-channel angular pressing (ECAP) was studied. It was found that although the dislocation density and the subgrain size saturated after 1 pass, the size of grains bounded by high angle boundaries reached its minimum value only after 4 passes. Furthermore, the grain orientation distribution changes between 4 and 8 passes, indicating the development of grain boundary structure even after the saturation of the parameters of the microstructure. As a result of this evolution, the initial texture of the commercial alloy was diminished after 8 passes and the grain orientation distribution became to be close to random case.     

Nano grained AZ31 alloy achieved by equal channel angular rolling process

Equal channel angular rolling (ECAR) is a severe plastic deformation process which is carried out on large, thin sheets. The grain size could be significantly decreased by this process. The main purpose of this study is to investigate the possibility of grain refinement of AZ31 magnesium alloy sheet by this process to nanometer. The effect of the number of ECAR passes on texture evolution of AZ31 magnesium alloy was investigated. ECAR temperature was controlled to maximize the grain refinement efficiency along with preventing cracking. The initial microstructure of as-received AZ31 sheet showed an average grain size of about 21 μm. The amount of grain refinement increased with increasing the pass number. After 10 passes of the process, significant grain refinement occurred and the field emission scanning electron microscopic (FESEM) micrographs showed that the size of grains were decreased significantly to about 14-70 nm. These grains were formed at the grain boundaries and inside some of the previous larger micrometer grains. Observation of optical microstructures and X-ray diffraction patterns (XRD) showed the formation of twins after ECAR process. Micro-hardness of material was studied at room temperature. There was a continuous enhancement of hardness by increasing the pass number of ECAR process. At the 8th pass, hardness values increased by 53%. At final passes hardness reduced slightly, which was attributed to saturation of strain in high number of passes.     

铬青铜厚板零件的旋压加工

利用加工实例论证了旋压加工空心厚壁回转体铬青铜零件的加工方案。结果表明,采用“普旋与强旋相结合辅以热旋”的复合方案旋压成形零件,可以避免零件内外表面出现疲劳裂纹,提高贴膜精度,缩短了生产周期,更为科学、快速有效。“普旋与强旋相结合辅以热旋”的复合方案旋压加工空心回转体厚板铬青铜零件的经验,可以推广到类似产品的旋压加工中去,具有一定的实用性。     

工艺参数对剪切旋压旋压力和壁厚差的影响

在锥形件剪切(变薄)旋压过程中,旋压力分析对于确定工艺参数及设备选型都具有重要意义,而壁厚差是衡量旋压件成形质量的关键指标之一.基于ABAQUS/Explicit平台建立了锥形件剪切旋压的三维有限元模型,进而获得了偏离率、旋轮圆角半径、旋轮进给量、芯模转速及旋轮直径对LY12M锥形件剪切旋压旋压力和壁厚差的影响规律.研究表明:旋压力随偏离率增加而减小,随旋轮圆角半径、旋轮进给量、芯模转速的增加均呈上升变化趋势;偏离正弦律的程度越大,壁厚差越大;旋轮圆角半径为毛坯厚度的1～2倍,壁厚差较小;较大的旋轮进给量和芯模转速有利于减小壁厚差.旋轮直径对旋压力和壁厚差的影响不显著.