Explorative study of tandem skew rolling process for producing seamless steel tubes

The tandem skew rolling (TSR) process is a new metal forming technique for producing seamless steel tubes of various dimensions. In this paper, the overall details of the TSR process are described and the important process parameters that control the TSR process are systematically discussed. A new experimental method, developed under laboratory conditions, showed that the TSR process can produce seamless steel tubes with high manufacturing quality. Numerical simulations of the TSR process were carried out using commercially available FEM software (Deform) to show the stress, strain, and temperature distributions in the rolled tubes. In addition, the variation of forces and rolling torques during the process are analyzed. Based on the experimental and numerical investigations, the TSR technique has been found to be a viable process for enhancing the quality and productivity of formed tubular products.     

Deposition and characteristics of chromium nitride thin film coatings on precision balls for tribological applications

Thin film hard coatings on rolling element surfaces can enhance the overall wear resistance of rolling element bearings, as demonstrated previously for coated tapered, cylindrical, and spherical roller bearings. Hard coatings in ball bearings are less common because of the difficulty in achieving uniform film thickness on a ball surface. This limitation is overcome by a new process for depositing chromium nitride coatings with uniform thickness on precision balls using ion beam assisted deposition (IBAD) e-beam evaporation. Scanning electron microscopy indicated that the deposited films were smooth and conformal on the ball surfaces with no areas of localized delamination. Auger electron spectroscopy confirmed that Cr₂N and CrN bulk film stoichiometry was achievable by modulating the argon to nitrogen process gas ratio during deposition. Transmission electron microscopy revealed dense, polycrystalline film structure. Film hardness and elastic modulus as measured using nanoindentation on the coated balls met expectations for chromium nitride, and tribological testing of the coated balls in angular contact ball bearings under moderate contact stress levels demonstrated adequate film adhesion for practical use of these coatings in bearing applications.     

Determination of residual stress in spherical balls by resonant ultrasound spectroscopy

In this study, resonant ultrasound spectroscopy (RUS) for determining residual stress in small size spherical balls was examined. Natural frequencies of spherical balls with residual stress were analysed by finite element method. Resonant frequencies of spherical balls were experimentally measured by a RUS system. Both natural frequencies in the analysis and the resonant frequencies measured in the experiment decreased as the compressive circumferential stress at the ball surface increased. It was concluded, on the basis of both analytical and experimental results, that the measurement of the resonant frequency by the RUS system along with the analysis of natural frequency are effective for determining the values and distributions of unknown residual stress in spheres.     

Surface flexible rolling for three-dimensional sheet metal parts

To realize highly effective and continuous fabrication of three-dimensional (3D) sheet metal parts, a new forming method, surface flexible rolling forming, has been investigated. This method takes only two integral flexible rolls as the forming tool. In the forming process, a non-uniform elongation in the rolling direction and a bending deformation in the thickness direction occur simultaneously, and finally three-dimensional surface parts are formed. In this work, the basic principle and forming mechanism of surface flexible rolling are studied. A method to calculate the transversal curvature radius of the arc-shaped roll is brought forward, while the feasibility is verified by the explicit dynamic finite element analysis. An experimental device has been developed and the forming experiments have been performed. Typical 3D surface parts including the convex and saddle surface parts have been obtained. Finite element model of surface flexible rolling is established and the effect of forming parameters such as reduction, velocity, bending radius and friction on the surface shape is analyzed. The forming effects including shape errors and thickness changes are studied by the deviation analysis. The results indicate that the formed surface is quite close to the criteria one; the thickness of the parts changes gradually and keeps within a narrow range. The experimental formed parts are measured and the forming accuracy is investigated. The results show that the accuracy is high, and are consistent with the simulation.     

关注薄板坯连铸连轧技术的热点问题

对薄板坯连铸连轧技术中当前的几个热点技术 ,即薄及超薄规格产品的轧制、表面质量、薄及超薄规格产品的力学性能、钢种和技术发展的现状进行了分析介绍 ,并指出 ,“以热代冷”直接取代普通冷轧冷成型薄板和汽车外部冲压件用冷轧薄板的基板生产是该技术发展的主要方向     

New technique of in situ rolling friction stir welding

Abstract

A new technique of in situ rolling friction stir welding (IRFSW) has been developed to reduce the residual stress and distortion. It can eliminate the weld flashes and improve corrosion resistance of the FSW seam. A new kind of FSW tool consisting of rolling balls was designed to achieve IRFSW. The residual stresses across the weld were measured by ultrasonic stress measurement experimental installation. The 3·5%NaCl solution was used to corrode the surface of welded joint, and corrosion current and potential were determined by an electrochemical analyser. The results shown that the residual tensile stress was reduced, the weld flashes were eliminated, and the corrosion resistance was improved. By applying IRFSW, the reduction of distortion was ～34·4% compared with that of conventional FSW joint for aluminium plant with 3 mm in thickness and 300 mm in length.     

Strengthening of Ultrafine Lamellar-Structured Martensite Steel via Tempering-Induced Nanoprecipitation

An ultrafine lamellar-structured martensite steel fabricated by heavy warm rolling(HWR) has shown an excellent combination of strength and ductility.By appending tempering at 400 ℃ to HWR,we show that the comprehensive mechanical property of a lamellar-structured low-carbon martensite steel can be further improved to reach a yield strength of～1.8 GPa,an ultimate tensile strength of～2.0 GPa and a total elongation of～9.3%.This is achieved by tempering the HWR steel from 300 to 750 ℃,and the optimu...     

汽车半轴摆辗新工艺及模具寿命研究

介绍了汽车半轴工艺原理、特点,并与传统胎模锻工艺在生产流程、生产成本、劳动强度、工件质量、生产效率以及工作环境方面进行了比较.分析了BJ130汽车半轴原工艺的不足,介绍了BJ130汽车半轴摆辗新工艺、设备选择及模具设计要点,该方案获得了较好的经济效益.     

热轧钢筋新标准下棒材轧机改造工艺技术分析

热轧带肋钢筋是我国产量最大的钢材产品,而提高钢筋产品质量并降低生产成本一直是技术创新的动力。为了使高强度钢筋轧制工艺和装备适应我国热轧带肋钢筋新标准的要求,对其控轧控冷工艺进行了探讨,对现有棒材轧机进行改造的工艺进行了详细分析,比较了切分轧制和高速轧制两种工艺的优缺点,提出了工艺布置新思路,为新钢筋生产线工艺设计,老线改造设计,或者钢铁企业工程技术人员开发品种提供了独特的途径。     

基于ADAMS的滚珠丝杠副动力学建模与仿真

运用三维建模软件Pro/E建立了滚珠丝杠副系统的零件装配模型,并通过ADAMS对建立的滚珠丝杠副仿真系统进行动力学仿真分析,绘制出滚珠间的碰撞力曲线图和滚珠线速度与自旋速度的变化数据表。结果表明:滚珠之间的碰撞在滚道内要比在反向过程内剧烈,且滚珠的自旋速度变化比滚珠线速度变化强度大。同时,验证了滚珠在滚道内的自旋速度和线速度变化确实比在反向过程中剧烈。仿真结果证实了所建仿真模型的有效性,为改善滚珠丝杠副性能,提高流畅性提供了技术支持。     

Investigation of the coating thickness of plasma-transferred arc deposition welded and cross wedge rolled hybrid parts

Most of today’s technical parts and components are made of monolithic materials. These mono-material components produced in established production processes reach their limits due to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be achieved by combining different materials in one part. Bulk forming of previously joined semi-finished products to net shape hybrid components that consist of two different materials is a promising method to produce parts with locally optimized characteristics. This new production process chain offers a number of advantages compared to conventional manufacturing technologies. Examples are the production of specific load-adapted forged parts with a high level of material utilization, an improvement of the joining zone caused by the following forming process and an easy to implement joining process due to the simple geometries of the semi-finished products. This paper describes the production process of hybrid steel parts, produced by combining a plasma-transferred arc deposition welding process with a subsequent cross wedge rolling process. This innovative process chain enables the production of hybrid parts. To evaluate the developed process chain, coating thickness of the billet is analysed before and after cross wedge rolling. It could be shown, that the forming process leads to an improvement of the coating, meaning a more homogeneous distribution along the main axis.     

偏心圆截面轴类零件的楔横轧成形数值模拟

提出了一种偏心轴类零件楔横轧成形新工艺,给出了楔横轧成形偏心轴类零件轧辊的辊型曲面.利用三维弹塑性有限元软件LS-DYNA对一种典型偏心轴类零件楔横轧成形进行了数值模拟,分析了其成形过程、应力应变场分布及工艺特点.模拟结果表明,从起楔开始就将坯料轧制成偏心圆截面的偏心轴类零件的楔横轧工艺是完全可行的,而且具有轧制力小、变形容易控制等优点.     

A new approach to study material bonding in extrusion porthole dies

Porthole die extrusion processes are widely spread even for most recent industrial applications. In turn knowledge base is often linked to make best expertise rather than to scientific fundaments. In the last years several FE models were developed but actual material bonding was not taken into account. In the paper a new approach is presented determining the critical value of the bonding criterion from flat rolling experiments and modelling the actual welding occurring in extrusion of complex profiles.The criterion was tested considering an industrial porthole die extrusion process and experimental parts were analysed to validate the proposed approach.     

Development of a warm cross wedge rolling process using FEA and downsized experimental trials

Cross wedge rolling is a forming technology that offers a lot of advantages: No flash occurs, cycle times are low, lubricants are not necessary and the machines are easy to automate. Currently, cross wedge rolling is applied at hot temperatures only. An adaption of this technology to warm temperatures (about 500?C950?°C) can increase the geometrical spectrum of warm forgings. The advantages of warm forged parts in comparison to hot forged parts are closer tolerances, reduced surface roughness, no scale and reduced decarburization. To apply cross wedge rolling at warm temperatures, the possibilities of defects e. g. internal voids and improper formed work pieces must be analysed. This paper describes the development of a warm cross wedge rolling process with one area reduction. The paper also includes results of finite element analysis (FEA), experimental trials with a downsized work piece and the adaption to the industrial work piece in original size. In the FEA simulations tools with serrations on the side have been used. The downsizing method is explained and the difference between FEA, downsized and originally sized work piece with the focus on forming forces, temperature distribution and defects are presented.     

BJ130汽车半轴摆动辗压新工艺

介绍了汽车半轴摆辗工艺原理、特点,并与传统胎模锻工艺在生产流程、生产成本、劳动强度、工件质量、生产效率以及工作环境方面进行了比较.     

BJ130汽车半轴摆动辗压新工艺

介绍了汽车半轴摆辗工艺原理、特点,并与传统胎模锻工艺在生产流程、生产成本、劳动强度、工件质量、生产效率以及工作环境方面进行了比较。     

轴承钢丸直径配比对强化研磨内圈沟道面硬度及形貌的影响

为研究强化研磨加工过程中轴承钢丸在不同直径的组合配比条件下对轴承内圈沟道面硬度的影响,通过理论与试验结合研究分析了钢丸法向碰撞内圈表面的过程,同时采用了扫描电子显微镜(SEM)观察内圈沟道面形貌的变化,并通过激光共聚焦显微镜与洛氏硬度计检测了其加工前后的表面粗糙度与硬度。研究结果表明:在试验所设定的工艺参数条件下,使用直径为2、3 mm的钢丸组合配可大大提高沟道面硬度,强化效果最佳,更能保证强化研磨加工质量。     

Study on the inner surface finishing of aluminum alloy 2014 by ball burnishing process

Tubular parts are important in many industrial applications (e.g. joints, fitting, etc.). The internal surface quality plays an important role in the part performance. Internal surfaces of non-ferrous materials are difficult-to-finish due to many problems encountered in grinding which is optimum for ferrous metals. Internal burnishing process is believed to be more suitable since it eliminates sticking, wheel dulling and overheating. In the present study, aluminum alloy 2014 is selected as workpiece material, an 8 mm carbon chromium balls were used for the internal burnishing process.

Statistically based on experimental design (response surface methodology) using central composite second-order rotatable design was used to improve the experimentation design without loss of accuracy for results. Mathematical models are presented for predicting five different surface profile parameters caused by internal ball burnishing process parameters namely; burnishing speed, feed, depth of penetration, and number of passes.

The results show that from an initial roughness of about Ra 4 μm, the specimen could be finished to a roughness average of 0.14 μm. The burnishing speed, feed and number of passes have the most significant effect on all surface profile parameters studied in this work.     

AZ31镁合金板材纵波轧制形变规律及边部损伤分析

纵波轧制+平辊轧制(LFR)是一种减轻镁合金轧制边裂的新型轧制工艺,通过一道次纵波轧制+二道次平轧,可有效减少镁合金板材边裂。为了进一步明晰LFR变形规律,本文通过对比AZ31镁合金板材纵波轧制+平轧(LFR)及平轧+平轧(FFR)热-力耦合有限元虚拟轧制对比和物理实验,分析了纵波轧制变形区金属变形规律及其对板材边部损伤的影响。结果表明：纵波轧制形成了异形搓轧区,板材各部位受到较大的三向剪切作用;急速金属流动产生的塑性变形热避免了板材边部温降,有利于提升塑性;剪切及温度影响促使LFR板材形成混晶组织,降低了波谷部位损伤,进而有效抑制了镁合金板材边裂的产生及发展。