Finite element analysis of the bulge defect forming and eliminating on tube continuous rolled by full floating mandrel mill

Based on the ABAQUS explicit dynamic simulation platform,the finite element model of single stand mill with restrained mandrel was adopted to research the influence of mandrel - roller velocity ratio (MRVR),mandrel friction and tension between stands on rolling force.The analysis results show that when the MRVR is lower than 1,the rolling force increases obviously with the increase of MRVR and reaches the peak value when the MRVR is about 1.The rolling force increase induced by the MRVR increase is the main reason of the formation of the bulge defect on the tube head and tail at the entering and exiting stage during tube continuous rolling process by full floating mandrel mill,which can be intensified by the increase of mandrel friction coefficient.The rolling force decreases with the increase of tension.As the tension is larger, the rolling force decrease amplitude is larger.The influence of backward tension on rolling force is greater than that of forward tension distinctly.Tension control can be used to decrease the rolling force increase induced by the MRVR increase,which is imposing tension at the same time when the MRVR increases,in order to improve even eliminate the bulge defect,and enhance the tube dimension precision.

MODELING OF CONTROLLED THERMO-MECHANICAL PROCESSING OF TUBES FOR ENHANCED MANUFACTURING AND PERFORMANCE

An integrated mathematical model to simulate seamless tube rolling processes has been developed at The Timken Company. The model is capable of simulating the thermal, deformation and microstructure evolution in the piercing, elongating and reducing/sizing and the austenite decomposition in the mill annealing and cooling operations. Finite difference schemes are employed to model cooling, reducing/sizing and stretch reducing, and finite-element schemes are employed to simulate piercing and elongating. The model predicts the thermal history, deformation, rolling load, torque, recrystallization and grain growth in hot tube rolling, austenite decomposition in cooling or annealing, and the final structure-properties. In this paper mathematical models which are employed to describe the thermal, deformation and microstructure evolution along with the modeling results are presented. The developed 'tube rolling mill in the computer' provides a powerful tool for engineers for product and process development, process control, process optimization and quality control.

Effect of mandrel on cross section quality of thin-walled tube numerical controlled bending

The effect of mandrel with the structure of ball and socket on the cross section quality of thin-walled tube numerical controlled(NC) bending was studied by numerical simulation method, combined with theoretical (analysis) and experiment. Influencing factors of the mandrel include the count of mandrel heads, the diameter of mandrel and its position. According to the principle of NC tube bending, quality defects possibly produced in thin-walled tube NC bending process were analyzed and two parameters were proposed in order to describe the cross section quality of thin-walled tube NC bending. According to the geometrical dimension of tube and dies, the range of mandrel protrusion was derived. The finite element model of thin-walled tube NC bending was established based on the DYNAFORM platform, and key technological problems were solved. The model was verified by experiment. The effect of the number of mandrel heads, the diameter of mandrel and the protrusion length of mandrel on the cross section quality of thin-walled tube NC bending was revealed and how to choose mandrel parameters was presented.

Fracture Behavior of TiNi Based Shape Memory Alloy Cold-rolled Tube

The microstructures and interracial characteristics of matrices at the inwalls and the out-walls of the cold-rolled tube with different amounts of deformation were investigated by the scanning electronic microscope （SEM）, the optical microscope （OM）, and the transmission electronic microscope （TEM） techniques. It was observed that as the amount of deformation increases, the flaws nucleate at the out-walls of the cold rolled tube, the stress-induced martensites change from （111 ） type Ⅰ twins to （011） type Ⅱ twins and then to （100） compound twins, nanocrystals and bulk amorphisation happen, the high density dislocation causes stress concentration at the out-walls of the Ti50Ni50 cold-rolled tube, and then precipitates its fracture, and the Ti2Ni particles strengthen the grain boundaries and curb the dislocation movements during plastic deformation. The inhomogeneity level of the grains in the Ti50Ni50 alloy plays an important role on the fracture of the Ti50Ni50 cold rolled tube.

Three-Dimensional Thermo-mechanical Coupled FEM Simulation for Hot Continuous Rolling of Large-Diameter Mandrel Bar

Based on the important boundary conditions of rolling simulation including friction, heat conduction and interactionsof the workpiece and rolls, the hot continuous rolling processes of large-diameter mandrel round bar (200 mm indiameter) in 6VH-stand hot tandem mill are successfully simulated by three-dimensional coupled thermomechanicalelastoplastic finite element method (FEM). The distributions of stress, strain, temperature and the rolling force andtorque for the two-pass and four-pass continuous rolling are calculated respectively. Thus, the two and four-passroll schedules are verified, respectively. The simulation results show that it is safe to produce 200 mm round barby the two-pass (oval pass and round pass) continuous rolling on the existing equipment compared to the four-passcontinuous rolling. There are concave surfaces and increased widths occurring at the end of rolled billet due touneven deformations between the outside and inside of the workpiece as well as the free spreading close to the rollgap of the final pass.

Modeling,Simulation and Experiment of Electro-hydraulic Screw Down Servo System of Seamless Tube Rolling Mill

Electro-hydraulic screw down servo system（HSDS） is widely used in seamless tube rolling mill in western companies.But in Chinese companies,mechanical screw down system（MSDS） is popularly equipped and has a serious disadvantage that the roller would often be locked when it is overloaded.For the purpose of designing the first set of domestic twin-roller,four-cylinder and six-framework electro-hydraulic HSDS of seamless tube rolling mill,an experiment system that can simulate the process of seamless tube rolling is constructed.A digital simulation model of the experiment system is built with AMESim software and validated by comparing the simulation results with experiment results.The sudden load response of the screw piston position is studied with the built model and the experiment system.To improve the HSDS＇s positioning accuracy with large load,a hybrid control scheme of combining load disturbance feedforward compensation（LDFC） method based on servo valve＇s pressure-stroke feature and anti-saturation integral control（ASIC） is proposed.Both results of simulation and experiment indicate that the transient response time of the single-roller HSDS with the proposed scheme decreases from 0.65 s to less than 0.2 s without static error.To improve the system dynamic stiffness and production qualified rate,a flow rate feedforward compensation（FFC） control strategy based on oil compressibility to dynamic position error is proposed.This FFC strategy is validated with experiments in which the transient error caused by sudden load is reduced to less than 25% of that without FFC.By extending the simulation model to HSDS of a twin-roller,four-cylinder rolling mill,analyzing the mill deformation,and applying the LDFC,ASIC and FFC to the HSDS,the dynamic performance and positioning accuracy of compensated multi-roller HSDS at biting moment are predicted.The research results provide a theoretical and experimental basis for the design of HSDS of seamless steel tube rolling mill.

Evolution of microstructure of aluminum alloy hollow shaft in cross wedge rolling without mandrel

During the process of cross wedge rolling of aluminum alloy hollow shaft, the evolution of its microstructure has an important influence on the mechanical properties of the rolled piece. In order to obtain the microstructure evolution law of aluminum alloy hollow shaft in cross wedge rolling without mandrel, a finite element model is constructed through the finite element software Deform-3D. The influences of rolling temperature, sectional shrinkage,spreading angle and forming angle on the average grain size of rolled piece are studied by numerical simulation of microstructure evolution. The cellular automata method reveals the inherent relationship between the process parameters and the evolution of the microstructure, and provides a reference for optimizing the rolling process parameters of aluminum alloy hollow shafts and improving the forming quality. The results show that the average grain size of the rolled piece increases with the increase of the rolling temperature, decreases with the increase of the sectional shrinkage,and decreases first and then increases with the increase of the spreading angle, and changes little with the increase of the forming angle.

Influence of process parameters on the microstructural evolution of a rear axle tube during cross wedge rolling

In the shaping process of cross wedge rolling（CWR）, metal undergoes a complex microstructural evolution, which affects the quality and mechanical properties of the product. Through secondary development of the DEFORM-3D software, we developed a rigid plastic finite element model for a CWR-processed rear axle tube, coupled with thermomechanical and microstructural aspects of workpieces. Using the developed model, we investigated the microstructural evolution of the CWR process. Also, the influence of numerous parameters, including the initial temperature of workpieces, the roll speed, the forming angle, and the spreading angle, on the grain size and the grain-size uniformity of the rolled workpieces was analyzed. The numerical simulation was verified through rolling and metallographic experiments. Good agreement was obtained between the calculated and experimental results, which demonstrated the reliability of the model constructed in this work.

Development of Technology and Equipment for Non-destructive Testing of Defects in Sewing Mandrels of a Three-roll Screw Mill 30-80

The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established that multiple cycles of heating up to 600℃ and cooling with water up to 80℃ for about 7 seconds/1 cycle lead to the formation of ridges,shells and cracks on the surface and in the volume of the tool.The loss of structural strength of the material leads to the breakdown of the mandrel during the stitching process.The technique and equipment of magnetic powder control have been developed to establish the dynamics of the growth of internal and external defects of mandrels.An equation is obtained that allows determining the increase in the number of defects in the sewing tool of a screw rolling mill.The technology of non-destructive testing made it possible to develop a rational plan for replacing the sewing mandrels,which allows for predicting the appearance of defects leading to a complex breakdown of the deforming tool at the NPO Pribor machine-building enterprise.

基于可变终端Tube-Based MPC的机场除雪车横向稳定性控制方法

为了提高机场路面自动驾驶除雪车作业过程中的侧倾稳定性,提出了一种基于可变终端tubebased MPC的机场除雪车横向稳定性控制方法。建立了除雪车作业的三自由度侧倾动力学解耦模型,采用tube-based MPC控制算法,基于除雪车横向稳定性、误差跟踪特性等约束条件设计了LQR函数,使MPC具有更好的鲁棒性,并在此基础上针对除雪车高速情况下可能出现的跟踪偏差发散设计了可变终端集。设计了多重模糊控制策略,确保除雪车在安全可行域内的灵活性和极端情况的安全性。仿真结果表明,采用tube-based MPC对比传统MPC在高速下除雪车综合跟踪性能提升80.22%,车身稳定性提升66.62%;加入多层模糊控制和可变终端约束的tube-based MPC对比可变终端约束的tube-based MPC在高速情况下除雪车综合跟踪性能提升71.77%,车身稳定性提升26.27%。

Assel斜轧生产线钢管主要缺陷及分析

根据某钢管厂Assel斜轧机组实际的生产情况及斜轧的特点,对投产以来生产中出现的部分钢管缺陷问题进行了分析。运用理论和经验相结合的方法,辅以有限元分析,确定缺陷产生的原因,达到预防缺陷产生,提高产品质量的目的。

Assel轧管机的技术特点

介绍了Assel轧管机技术的发展和改进,重点论述了Assel轧管机咬入速度的时间段控制,并阐述了Assel轧管机使用限动芯棒和单独传动的优势,表明限动芯棒Assel轧管机组可以满足大直径钢管的生产。

FE SIMULATION OF CENTER CRACK OCCURRENCE IN TUBE ROUNDS DURING TWO-ROLL ROTARY ROLLING PROCESS

With the aid of FE （finite element） code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile fracture criteria. A simple modeling is put forward based on the spiral motion of the workpiece as an essential characteristic in movement. The influence of the feed angle and the entry cone angle of the main roll on the process was taken into account in the modeling. The soundness for simplifying the 3-D rotary rolling into a 2-D problem was discussed. By adopting the parameters of Diescher piercer in 140mm mandrel mill of Bao Steel, the distribution and development of strain/stress were analyzed, and the eigen value of ductile fracture as well. The critical percentage of diameter reduction was obtained from the simulation. The result showed a good agreement with the experimental value, and therefore was of widely guiding significance to the practical process for rationally formulating the deformation parameters of steel tube piercing.

Assel轧管机轧制力计算研究

分析金属在Assel轧管机轧制时的变形特征,将轧制过程分为减径部分和减壁部分,建立其轧制力与轧制力矩的数学模型;依据该数学模型计算出不同钢种的轧制力和轧制力矩,并将计算值与现场实测值进行对比,以验证数学模型的准确性。最后根据前述数学模型,用Matlab软件编制专用的Assel轧管机力能计算软件。

Fin formation model during pre-roll ploughing of copper 3D outside fin tube

The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.

Φ100mm Assel轧管机组各变形工序钢管壁厚精度演变的研究

以无锡西姆莱斯钢管有限公司的Φ100mmAssel轧管机组为研究对象，对厚、中、薄壁不同规格钢管各工序的壁厚、壁厚相对偏差和壁厚绝对偏差的分布形态及演变过程进行了分析。研究表明：各工序钢管的空厚、壁尽相对价差和壁厚绝对值差的分布均具有偏心螺旋形特征；在穿孔、Assel轧管、张力减径各工序中，Assel轧管是影响成品管壁厚精度的关键工序；不同D／S的荒管，其壁厚偏差绝对值在数量级上基本相同；降低壁厚偏差的绝对值是提高钢管壁厚精度的主要途径。

Φ325mm Assel轧管机组工艺技术的集成创新与应用

分析了传统Assel轧管机组在生产时存在的问题,介绍了Φ325 mm Assel轧管机组工艺技术的创新情况,主要体现在轧管工艺路线、芯棒预穿和小循环、轧制方式等方面,并与传统工艺生产产品的质量进行对比。应用结果表明:该创新工艺解决了传统生产工艺中的弊端,可节约生产成本约30%,且产品质量优良。

浅谈Assel轧管机与Accu Roll轧管机的性能对比

简要介绍了Asse轧管机和Accu Roll轧管机各自的特点和适用范围,重点对二者的性能优劣进行了对比分析。Accu Roll轧管机轧制薄壁管的速度快,轧制过程相对稳定;两种轧管机组所轧制的荒管精度都很高,但Accu Roll轧管机的导盘有时会影响荒管质量,且导盘和轧辊消耗大,更换耗时;Assel轧管机的设备重量轻,投资成本低,收回成本时间短。因此,Asse轧管机的综合性能指标优于Accu Roll轧管机。

Φ273mm Assel轧管机组生产薄壁无缝钢管的工艺开发

Assel轧管机生产薄壁无缝钢管(径壁比≥25)时,存在着荒管头部易产生喇叭口,轧制过程中荒管甩动大,内表面易产生内螺纹缺陷等问题,严重制约着机组产能的释放。湖北新冶钢有限公司通过采用增设轧管机后台导卫装置及前台检测装置,改进轧管机辊型,优化轧制工艺参数等措施,大大减少了轧制过程中轧扭、卡钢事故的发生,轧制的薄壁无缝钢管内螺纹缺陷也明显减轻,壁厚精度达到±8%,成材率在90%以上。

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.