Deformation pattern,forces and process limits in combined radial and backward can extrusion

As a new method for a combined process in cold extrusion a combination of radial extrusion and backward can extrusion is presented. The investigations show an important influence of the tool geometry on the material flow. Control of the material flow is possible by little variation of gap height or die radius. According to the described mechanism an equilibrium between can and flange forming exists for a suitable tool geometry. Measurements of the hardness showed a more homogenious distribution as for simple radially extruded workpieces. Low loads, as well as good geometric properties are giving this combined extrusion process a good chance to become an alternative to other cold forming processes.     

芯棒直径对楔横轧5Cr21Mn9Ni4 N空心气门壁厚均匀性的影响规律

楔横轧空心轴类件存在壁厚分布不均问题,特别是在小直径大长径比空心件楔横轧成形中更为突出.本文在Gleeble-1500D热模拟实验机上进行了5Cr21Mn9Ni4N耐热钢的热压缩实验,得到了5Cr21Mn9Ni4N的热变形本构方程.通过改变芯棒直径,采用有限元仿真和实验相结合的方法,研究了楔横轧轧制空心气门过程中的壁厚变化规律.研究结果表明,带芯棒轧制时,芯棒直径存在临界值,在该值下进行轧制,空心气门预制坯壁厚均匀性最优;楔横轧空心件时,金属轴向均匀流动是壁厚均匀的必要条件;轧件轴向拉应变减小,径向压应变变大,周向应变在0附近且为拉应变时,壁厚较为均匀.      

Peter Groche

Tube hydroforming (THF) is a relatively new but established technology among metal tube forming processes. It is the technology of forming closed sections, hollow parts with different cross‐sections by applying an internal hydraulic pressure and sometimes additional axial compressive loads to force a tubular blank to conform to the shape of a given die cavity. Material properties have a significant influence on the process stability. Often roll‐formed, non‐heat treated tubular materials made of steel with longitudinally oriented welding lines are used in tube hydroforming. Different production processes involve a change of the material properties from the initial flat sheet to the hydroformable tube. Testing methods such as tensile tests and conventional forming limit diagrams do not accurately reflect the state of stress and strain conditions seen in the tubular blank during the hydroforming process. Thus, inaccuracies in FEA predictions and design failures occur. Test methods were developed to characterize the relevant geometrical and mechanical properties of tubular semi‐finished products.     

Material Flow Control in High Pressure Sheet Metal Forming of Large Area Parts with Complex Geometry Details

Working media based forming processes show advantages compared to the conventional deep drawing in the range of sheet metal parts with complex geometry details. By High Pressure Sheet Metal Forming (HBU), complex parts can be formed with reduced tool costs, fewer process steps, and improved part properties, particularly by the use of high strength steels. In order to use these advantages to full capacity, the material flow into the area of the geometry details needs to be optimised. The key element for the material flow control is a multi‐point blank holder. In combination with flange draw‐in sensors, a closed loop flange draw‐in control can be built up which guarantees a reproducible material flow and, consequently, defined part properties. Furthermore, a favourable pre‐distribution of sheet metal material can be reached which leads to a widening of the process limits. Considering a large area sheet metal part with a complex door handle element as example, strategies for the material flow control will be discussed in this paper. The conclusions are based on FE‐simulations as well as experimental findings.     

New Technology for Producing Molybdenum Wire Billets

On the basis of systematic studies of intense methods for metal forming, a production scheme has been developed, substantiated by experiment and realized for manufacturing molybdenum wire. The main stages are helical rolling of small rounded bars, vibratory drawing with induction heating of wire billets, and cold wire drawing with hydrodynamic introduction of lubricant and application to the tool of vibration in the transitional stages of the process (start-up, speed-up, slow-down, and stopping the pulling tool drive).     

棒材挤压新工艺

采用空心挤压垫即挤压管材用的挤压垫和穿孔针复合使用的新工艺,解决了在只配备锯的管材挤压机上挤压棒材时压余难以分离的问题。     

钛-铜复合棒的主要生产方法及其基本特点

重点介绍了拉伸法、挤压或挤压 拉伸法、爆炸或爆炸 轧制法等钛铜复合棒材的生产方法及其基本特点。并分析了生产方法对产品质量的影响。     

钢管空拔增壁量数学模型的建立

根据重钢厂厂钢管车实测数据，阐述了钢管空拔时，拔前壁厚与直径之比值、减轻量、材质和加工硬化对增壁量的影响，并用数学回归法建立了各因素影响增壁量的子方程和总方程，在生产车间实际应用，数学模型的准确性在９０％以上。     

Neutron Stress Imaging of Drawn Copper Tube: Comparison with Finite-Element Model

Seamless tubes are used for various mechanical applications, often produced by several cold drawing steps to reach the required dimensions. The first process step, for example, extrusion or rolling, typically results in ovality and eccentricity of the tube caused by nonsymmetric material flow and being present during the cold drawing process, i.e., no homogeneous deformation. Because of this nonsymmetrical deformation, and deviations over the length of the tube caused by moving tools, this process step generates inhomogeneous residual stresses. To understand the interconnection between geometrical changes in the tubes and the resulting residual stresses, the residual strain distribution in a copper tube was measured by neutron diffraction. The aim of this study is to evaluate residual stresses generated during cold drawing of copper tubes. This research comprises experimental measurements and numerical analysis. An industrially produced copper tube was cold drawn, and the profile of residual strain over circumference and across wall thickness was measured by neutron diffraction. In parallel, a three-dimensional finite-element model (FEM) was developed to calculate the residual macrostress state generated by the forming process. Good agreement between experimental results and numerical computations was obtained. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.     

The effect of the strain path on the work hardening of austenitic and ferritic stainless steels in axisymmetric drawing

The work-hardening characteristics of metals deeply affect the analytical and numerical analyses of their forming processes and especially the end mechanical properties of the products manufactured. The effects of strain, strain rate, and temperature on work hardening have received wide attention in the literature, but the role of the strain path has been far less studied, except for sheet-metal forming. Strain-path effects seem to have never been analyzed for bulk-forming processes, such as axisymmetric drawing. In the present work, drawn bars were considered as composed of concentric layers strained along varying strain paths. The tensile von Mises effective stress, effective-strain curves of two layers and of the full cross section of the drawn material, were experimentally determined. The flow behavior of these regions was compared to that resulting from pure monotonic-tensile processing. The AISI 420 and 304 stainless steels revealed a strain path and a material effect on their work-hardening characteristics. Higher or lower hardening rates were observed in axisymmetric drawing, as compared to pure tension. These phenomena were interpreted by considering the dislocation arrangements caused by initial drawing straining and their subsequent restructuring, associated with the strain-path change represented by tension after drawing. The analytical and numerical analyses of the tensile behavior of metals following axisymmetric drawing must consider the strain-path effects on the constitutive equations laws and on the hardening behavior of the material. The redundant deformation factor in axisymmetric drawing (φ) plays a central role in the analysis of the process and on the prediction of the mechanical properties of the final products. This parameter was evaluated considering (a) the strain distribution in the bar cross section caused by drawing or (b) the mechanical properties of the drawn bars. The comparison of the results from these two approaches allowed an unexplained interpretation of a material effect on this parameter.     

专减壁厚拔管拔制力的研究

根据专减壁厚拔管拔制过程的变形特点 ,从分析金属受力情况出发 ,提出了拔制力计算公式及力学参数的研究方法 ;并在实测数据的基础上 ,通过数学处理建立了模型 ,以指导生产实践     

楔横轧反楔堆轧改善空心零件过渡轴肩的壁厚减薄

楔横轧随形轧制空心零件在过渡轴肩位置会产生壁厚减薄,降低零件的力学强度,改善轴肩的壁厚状况是必须解决的问题.本文基于有限元模拟方法,揭示空心零件成形时壁厚减薄的产生原因,提出采用楔横轧反楔堆轧改善轴肩壁厚的成形方法,分析反楔堆轧增加轴肩壁厚的主要影响因素,从而获得轴肩壁厚增厚的成形方法和最佳条件,实现了楔横轧随形轧制空心零件轴肩位置的显著增厚.通过轧制试验,验证了有限元模拟分析模型的可靠性.      

Yield Locus of a Cold Rolled and Solution Treated Nimonic-263 Alloy Sheet,Determined Using Asymmetrical Knoop Micro Hardness Indenter

The Von Mises or perhaps the Tresca criterion is adequate for predicting the onset of yielding under combined stress loading for isotropic materials. However, this prediction is not so straight forward for anisotropic materials in which the magnitude of tensile and compressive yield stresses are different along the different orientations. Such directionality in yield behavior of anisotropic materials may strongly depend on the nature and degree of crystallographic texture. Texture driven yield surfaces are the representatives of the states of plane stress (tension–tension, tension–compression and compression–compression) in thin wall tube by externally applied forces and internal pressure. The applications of yield surfaces are far too wide and particularly have direct relevance to the metal forming, such as cold rolling. A simple procedure based on Knoop microhardness measurements has been proposed in the literature for determining the plane stress yield surface of the sheet materials. In the present study, an attempt has been made to describe this technique and the procedure to determine the yield locus using Knoop microhardness indenter and compare the yield surface anisotropy determined with the experimentally observed tensile properties in the in-plane directions and thus establish the usefulness of this technique in case of a cold rolled and solution treated Nimonic-263 alloy sheet of 1.0 mm thickness in solution treated condition.     

Numerical simulation of tube profile growth during spray forming process

Spray forming is a new type of metal material forming process,which can produce metal blanks such as billet,tube,plate etc.A mathematical model has been developed to forecast the shape evolution of tube billets during the spray forming process.The atomizer mass flux as,radial distribution coefficient bs,draw velocity and diameter of mandrel were considered in this model and the influence of different parameters such as metal flowrate,draw velocity of mandrel,diameter of mandrel on the tube’s shape change were simulated and analyzed in this paper.The simulation results obtained from this model can be provided to engineers as reference.     

Application of computer modelling in part,die, and process design for manufacturing of automotive stampings

Recent studies in sheet metal forming, conducted at universities world wide, emphasize the development of computer aided techniques for process simulation. To be practical and acceptable in a production environment, these codes must be easy to use and allow relatively quick solutions. Often, it is not necessary to make exact predictions but rather to establish the influence of process variables upon part quality, tool loads, material flow, and material thickness variation. In cooperation with its industrial partners, the ERC for Net Shape Manufacturing at the Ohio State University has applied a number of computer codes for analysis and design of sheet metal forming operations. This paper gives a few selected examples taken from automotive applications and illustrates practical uses of computer simulations to improve produtivity and reduce tool development and manufacturing costs.     

Ni-Cr-Co-W-Mo-Al-Ti合金制备多孔材料的组织与性能研究

用粉末烧结法制备了孔结构为球形中空孔和线型中空孔的镍基多孔高温合金材料.对试样进行显微组织观察和力学性能测试.结果表明:制备的多孔高温合金材料的孔隙分布均匀,孔径大小一致.通过高温烧结,多孔合金骨架处的金属颗粒之间形成了烧结颈,发生了烧结结合.生成孔的孔隙度随造孔剂(尿素)的添加量增加而增加,当造孔剂的质量分数为40%时,可得到孔隙度为81.62%的球形多孔材料.多孔材料具有优良的能量吸收性能,其压缩性能随孔隙度和孔径的增加而下降.     

CT20钛合金薄壁管材数控冷弯成形行为研究

薄壁管材的小弯曲半径数控弯曲成形十分困难,外侧壁厚减薄是弯管成形中的加工缺陷之一,对于钛合金薄壁管尤为严重。采用模拟与实验相结合的方法,对规格为58 mm×1.5 mm的CT20钛合金管材数控弯曲成形过程中弯曲段的壁厚减薄进行了研究,得到相对弯曲半径对壁厚减薄的影响规律。结果表明,CT20钛合金管材冷弯成形时的极限相对弯曲半径(R/D)为2。     

Experimental Analysis on the Frictional Behaviour of Drawbeads in Sheet Metal Forming

In sheet metal forming, drawbeads are commonly used to control uneven material flow, which may cause defects such as wrinkles, fractures, surface distortion and springback. Although friction may not directly change the limiting strain of steel sheets, the tribological conditions in the contact zone between the sheet surface and the tool surface play an important role in determining the limits of the forming process. Friction in the drawbead contact zones affects the flow of the material in the tool and is used deliberately to control the stamping process. Therefore in this study, the frictional behaviour of drawbeads is experimentally investigated by the drawbead friction test. To characterize the effect of processing variables on the friction coefficients, tests are performed for various sheets, lubricants and bead materials suffering different surface treatments. The results obtained from the drawbead friction test show that the friction and drawing characteristics of deforming sheets were strongly influenced by the strength of sheet, viscosity of lubricant and hardness of bead surface.     

Poromechanics of Anisotropic Hollow Cylinders

It has been known that inherent material anisotropy influences the mechanics of geoengineering applications. Aiming at the experimental studies associated with geoengineering applications in anisotropic materials, this paper proposes a poromechanics analysis of a fully saturated transversely isotropic hollow cylinder. Closed-form analytical solutions for the pore pressure and stress fields were derived. These solutions are obtained under various loading conditions that are encountered in laboratory testing procedures. Numerical analyses were carried out to demonstrate the material anisotropy effect on stress, displacement, and pore pressure distributions in the cylinder. It is also shown that uncertainties in the estimation or measurements of the poromechanical parameters have proven effects on the time-dependent responses of the hollow cylinder geometry during laboratory testing.