On a plastic instability criterion for ultra-large radial-axial ring rolling process with four guide rolls

A dynamic mechanical model is proposed to describe the complexing actions of all the rolls on the ring during the ultra-large radial-axial ring rolling(RARR)process with four guide rolls.Based on the model,the calculation models for bending moment and normal stress at any section of the ring are deduced by force method.If the maximum section bending normal stress exceeds the yield stress of the ring materials,the ring will be distorted thus leading to the instability of the RARR process.According to this,a plastic instability criterion for the ultra-large RARR process with four guide rolls is developed,based on which a mathematical model to calculate the critical guide force for avoiding plastic instability of ring is obtained.The influence rule of the position of guide roll on the dangerous ring section of plastic instability is revealed,from which it is found the dangerous ring section mainly appears at the radial and axial deformation regions and the contact positions of the guide rolls and ring.The optimized layout of guide roll around the ring in favor of stability is determined to be about a1=61°and a2=119°.The plastic instability criterion is proven to be reliable from the aspects of the critical guide force,the section bending moment and normal stress and the dangerous ring section of plastic instability.Intelligent simulation case studies for the RARR process of ultra-large aluminum alloy ring indicate that the stable forming of the process can be effectively realized by regulating the guide force based on the plastic instability criterion.This work could provide a valuable guidance for the control of guide rolls and the optimization of the ultra-large RARR process with four guide rolls.

Modeling and Simulation of Radial-Axial Large Ring Rolling

Finite element model is constructed according to the principle and characteristics of radial-axial large ring rolling technology. Dynamic explicit finite element method is used to simulate the rolling process. An effective modeling method of guide roller is proposed. Simulation indicates that high quality ring product could be obtained when rational rotational speed of rollers and feed rate in the radial and axial rolling are assigned.

Deformation mechanism of cold ring rolling in view of texture evolution predicted by a newly proposed polycrystal plasticity model

An explicit polycrystal plasticity model was proposed to investigate the deformation mechanism of cold ring rolling in view of texture evolution. The model was created by deducing a set of linear incremental controlling equations within the framework of crystal plasticity theory. It was directly solved by a linear algorithm within a two-level procedure so that its efficiency and stability were guaranteed. A subroutine VUMAT for ABAQUS/Explicit was developed to combine this model with the 3D FE model of cold ring rolling. Results indicate that the model is reliable in predictions of stress-strain response and texture evolution in the dynamic complicated forming process; the shear strain in RD of the ring is the critical deformation mode according to the sharp Goss component （{110}？100？） of deformed ring; texture and crystallographic structure of the ring blank do not affect texture type of the deformed ring;texture evolves rapidly at the later stage of rolling, which results in a dramatically increasing deformation of the ring.

Comparison of evolution laws of stress and strain fields in hot rolling of titanium alloy large rings with different sizes

For hot rolling of titanium alloy large rings,evolution laws of stress and strain fields in rings with various sizes were explored and compared based on a reliable coupled thermo-mechanical three-dimensional （3D） finite element （FE） model.The results show that for forming processes of different rings,as γ^-（the equivalent distribution ratio of feed amount per revolution of a process） decreases,the final peak Mises stress may transfer from the biting point at the driver roll side to that at the idle roll side,and the final peak equivalent plastic strain may transfer from the outside surface to the inside surface;as L^- （the equivalent deformation zone length of a process） increases,the final peak Mises stress may appear in the middle layer.The final positions of peak Mises stress and equivalent plastic strain are the combined effects of the above two aspects.In the deformation zone of a deformed ring,the surface layers are in the 3D compressive stress state,while the middle layer is in the 1D compressive and 2D tensile stress state or 2D compressive and 1D tensile stress state;the whole ring is in the 1D compressive and 2D tensile strain state.

STRESS ANALYSIS OF ROLL RING FOR HIGH SPEED WIRE ROLLING MILLS

This paper introduces a new method for fixing type of the tungsten carbide roll ring for high speed wire rolling mills, and analyses the stresses of the roll ring. The lifetime of roll pass is twice longer that of the old one.

Dynamic explicit FE modeling of hot ring rolling process

A new FE modeling method of hot ring rolling was presented by solving key technologies such as contact and heat boundary conditions,motion control over guide rolls,and mass scaling.The method has the following features:1)the elastic-plastic dynamic explicit approach instead of the static implicit approach is adopted to solve the process so as to greatly improve computational efficiency without sacrificing computational accuracy;2)the coupled thermal-mechanical effect is considered as opposed to the conventional isothermal assumption,which is more practical;3)in contrast to the simplified 2D or local 3D ring model,the full 3D ring is modeled to simulate the process.Based on the FE modeling method,two cases of hot plain ring rolling are simulated in the FEA software ABAQUS/Explicit.The simulation results are compared with the experimental measurements and the good agreement between them is observed regarding the material flow and the temperature distribution of the ring.

Role of Friction in Cold Ring Rolling

Cold ring rolling is an advanced but complex metal forming process under coupled effects with multi-factors, such as geometry sizes of rolls and ring blank, material, forming process parameters and friction, etc. Among these factors, friction between rolls and ring blank plays an important role in keeping the stable forming of cold ring rolling. An analytical method was firstly presented for proximately determining the critical friction coefficient of stable forming and then a method was proposed to determine the critical friction coefficient by combining analytical method with numerical simulation. And the influence of friction coefficient on the quality of end-plane and side spread of ring,rolling force, rolling moment and metal flow characteristic in the cold ring rolling process have been explored using the three dimensional （3D） numerical simulation based on the elastic-plastic dynamic finite element method （FEM） under the ABAQUS software environment, and the results show that increasing the friction on the contact surfaces between rolls and ring blank is useful not only for improving the stability of cold ring rolling but also for improving the geometry and dimension precision of deformed ring.

Microstructural evolution and enhanced mechanical properties of Mg?Gd?Y?Zn?Zr alloy via centrifugal casting, ring-rolling and aging

A ring-shaped Mg?8.5 Gd?4 Y?1 Zn?0.4 Zr(wt%) alloy was manufactured via centrifugal casting and ring-rolling process. The effects of accumulative ring-rolling reduction amount on the microstructure, texture, and tensile properties of the alloy were investigated. The results indicate that the microstructure of centrifugal cast alloy consists of equiaxed grains and network-like eutectic structure present at grain boundaries. The ring-rolled alloy exhibits a characteristic bimodal microstructure composed of fine dynamic recrystallized(DRXed) grains with weak basal texture and coarse un-DRXed grains with strong basal texture, along with the presence of LPSO phase. With increasing amount of accumulative ring-rolling reduction, the coarse un-DRXed grains are refined via the formation of increasing amount of fine DRXed grains. Meanwhile, the dynamic precipitation of Mg5 RE phase occurs, generating a dispersion strengthening effect. A superior combination of strength and ductility is achieved in the ring-rolled alloy after an accumulative rolling reduction of 80%. The tensile strength of this ring-rolled alloy after peak aging is further enhanced, reaching 511 MPa, while keeping a reasonable ductility. The salient strengthening mechanisms identified include the grain boundary strengthening of fine DRXed grains, dispersion strengthening of dynamic precipitated Mg;RE phase, short fiber strengthening of LPSO lamellae/rods, and precipitation strengthening of nano-sized prismatic β precipitates and basal γ precipitates.

Effect of annealing cooling rate on microstructure and mechanical property of 100Cr6 steel ring manufactured by cold ring rolling process

Pre-heat treatment is a vital step before cold ring rolling and it has significant effect on the microstructure and mechanical properties of rolled rings.The 100Cr6 steel rings were subjected to pre-heat treatment and subsequent cold rolling process.Scanning electron microscopy and tensile tests were applied to investigate microstructure characteristic and mechanical property variations of 100Cr6 steel rings undergoing different pre-heat treatings.The results indicate that the average diameter of carbide particles,the tensile strength and hardness increase,while the elongation decreases with the decrease of cooling rate.The cooling rate has minor effect on the yield strength of sample.After cold ring rolling,the ferrite matrix shows a clear direction along the rolling direction.The distribution of cementite is more homogeneous and the cementite particles are finer.Meanwhile,the hardness of the rolled ring is higher than that before rolling.

Soft measurement model of ring's dimensions for vertical hot ring rolling process using neural networks optimized by genetic algorithm

Vertical hot ring rolling(VHRR) process has the characteristics of nonlinearity,time-variation and being susceptible to disturbance.Furthermore,the ring's growth is quite fast within a short time,and the rolled ring's position is asymmetrical.All of these cause that the ring's dimensions cannot be measured directly.Through analyzing the relationships among the dimensions of ring blanks,the positions of rolls and the ring's inner and outer diameter,the soft measurement model of ring's dimensions is established based on the radial basis function neural network(RBFNN).A mass of data samples are obtained from VHRR finite element(FE) simulations to train and test the soft measurement NN model,and the model's structure parameters are deduced and optimized by genetic algorithm(GA).Finally,the soft measurement system of ring's dimensions is established and validated by the VHRR experiments.The ring's dimensions were measured artificially and calculated by the soft measurement NN model.The results show that the calculation values of GA-RBFNN model are close to the artificial measurement data.In addition,the calculation accuracy of GA-RBFNN model is higher than that of RBFNN model.The research results suggest that the soft measurement NN model has high precision and flexibility.The research can provide practical methods and theoretical guidance for the accurate measurement of VHRR process.

Effect of driver roll rotational speed on hot ring rolling of AZ31 magnesium alloy

Based on the ABAQUS/Explicit code,A 3D elastic-plastic and coupled thermo-mechanical FE model of radial ring rolling of AZ31 Magnesium alloy has been proposed to analyze the influence of rotational speed of driver roll to study the inhomogeneity distribution of strain and temperature,fishtail coefficient,rolling force parameters.The results show that:(1)when the rotational speed of driver roll n increases,the strain distribution of the rolled ring becomes less homogeneous,and the temperature distribution more homogeneous yet,and leading to an optimal n value;(2)the fishtail coefficient firstly decreases,then increases with the increase of n;(3)the rolling force,contact area and rolling moment gradually descend with the increase of n.

Thermo-mechanical coupled analysis of hot ring rolling process

A 3D rigid-plastic and coupled thermo-mechanical FE model for hot ring rolling(HRR) was developed based on DEFORM 3D software,then coupled heat transferring,material flow and temperature distribution of the ring in HRR were simulated and the effects of process parameters on them were analyzed.The results show that the deformation nonuniformity of ring blank increases with the increase of the rotational speed of driver roll and friction factor or the decrease of the feed rate of idle roll and initial temperature of ring blank.The temperature nonuniformity of ring blank decreases with the increase of the feed rate of idle roll or the decrease of initial temperature of ring blank and friction factor.There is an optimum rotational speed of driver roll under which the temperature distribution of ring blank is the most uniform.The results obtained can provide a guide for forming parameters optimization and quality control.

Effect of sizes of forming rolls on cold ring rolling by 3D-FE numerical simulation

During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree of inhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.

Hourglass Control in Dynamic Explicit Simulation of Cold Ring Rolling Process

Hourglass is remarkably aroused in ring rolling simulation with reduced integration element because of violent ring vibration and small contact area of ring with forming rollers. Hourglass energy can be reduced by improving mesh density. Combined approach of artificial damping and artificial stiffness can control the hourglass. A ring with rectangular section is simulated with the weight factor of artificial stiffness resistance set to 0.2. The artificial damping hourglass control coefficient is set to 0.1, and the artificial stiffness hourglass control coefficient is set to 0.001. The ratio of hourglass energy to internal energy is reduced to 2.5 percent. Compared with axial spread width test, the effectiveness of hourglass control in ring rolling simulation is verified.

Microstructure and anisotropy of mechanical properties in ring rolled AZ80-Ag alloy

The microstructure,anisotropy in tensile strength and tensile creep resistance of the ring rolled AZ80-Ag alloy were studied.The ring exhibited higher strength along rolling direction(RD)than transverse direction(TD).The microstructure characterization and texture analysis demonstrated that the tilted basal texture was responsible for the higher tensile performance along RD.Investigations on the creep anisotropy revealed that the samples along RD had lower creep resistance,higher creep strain and higher steady creep rate at 70−80 MPa,compared with that along TD.The nominal creep stress exponent(n)values,1.13 for RD and 3.86 for TD,indicated that diffusional creep and dislocation climb were the two corresponding creep mechanisms.During creep of the alloy,Mg_(17)Al_(12) phase discontinuous precipitations were witnessed and their volume fraction enhanced with increasing stress.

超大直径铝合金环形锻件轧胀成形工艺与装备关键技术研究

介绍了重载火箭用铝合金大型环形锻件的制作工艺,重点分析了径轴向数控轧制环形锻件的制作工艺。介绍了大型环形锻件轧制和胀形结合成形的制作工艺,采用有限元模拟了Φ10和Φ1.2 m环形锻件的轧制和胀形结合成形工艺过程,并对Φ1.2 m环形锻件的轧制和胀形成形过程进行了试验验证。结果表明:轧制和胀形结合的成形工艺技术能有效地改善产品组织,使组织更致密,提高了产品的晶粒度;轧制和胀形工艺技术能有效地提高产品的屈服强度,从而提高产品的使役性能。胀形工艺对产品有明显的整形作用。在此基础上提出Φ10 m环形锻件径轴向数控轧制和液压胀形结合的成形工艺。

滚子与内圈打滑行为诱导的振动特性

针对滚子打滑试验研究困难的问题,通过分析滚子-内圈运动副的相对运动关系得出运动副振动特征频率的计算公式,在此基础上开展打滑试验,提取滚子纯滚动、打滑状态下的振动信号并采用短时傅里叶变换进行时频域分析,结果表明:滚子打滑会诱发一定的振动响应,其频率与滚子、内圈的转动频率相关,理论计算结果与试验结果较为吻合,可用于测算滚子打滑程度;滚子由纯滚动状态转变为打滑状态或由打滑状态转变为纯滚动状态时,纵向、切向振动的幅值均会发生突变,切向振动信号占主要成分且幅值更大。

大型轴承套圈超声相控阵曲面自适应聚焦与多通道自动化检测方法

大型轴承套圈作为风电、轨道交通、工程机械领域装备的关键部件,其制造过程中产生的裂纹、夹渣、孔洞等缺陷会严重影响装备整机的服役性能与质量安全。针对大型轴承套圈尺寸大和结构复杂等特点,研究了液固耦合曲面结构中阵列声场分布规律和超声相控阵曲面自适应聚焦法则,给出了大型轴承套圈超声相控阵分区检测方法,开发了大型轴承套圈超声相控阵自动化检测系统,对直径2958 mm的某型风电轴承套圈进行自动化检测应用验证,可有效检出套圈曲面试块的横通孔缺陷和套圈的平底孔缺陷。

航发轴承套圈电磁辅助轧制成形残余应力和组织演变

8Cr4Mo4V轴承钢被广泛应用于航空发动机主轴轴承,其热轧成形过程中易出现晶粒粗大等缺陷,导致强韧性不足。冷轧成形可实现晶粒细化,提高轴承钢的综合力学性能,具有巨大应用潜力,但8Cr4Mo4V轴承钢的碳含量和合金含量较高,冷轧过程中易产生微纳损伤和应力集中等缺陷。提出了电磁能场辅助轴承钢冷轧成形的创新技术思路,研究电磁辅助轧制对8Cr4Mo4V轴承钢残余应力和组织演变的影响。结果表明,电磁辅助轧制可调控轴承钢位错密度,减少碳化物与相界处的位错缠结,使残余应力均匀化并提高拉伸性能,实现8Cr4Mo4V轴承钢细晶低损伤成形。

用于铝压延厂房油雾控制的环吸式排风罩设计方法

环吸式排风罩是针对铝压延加工工艺油雾散发特征而提出的一种高效捕集设备,可以大幅降低系统风量,从而减少能耗和降低碳排放量,但目前仍缺乏此类排风罩的通用设计方法。本文选取10个铝压延车间铝冷轧机及排风罩为研究对象,探究了不同轧机尺寸组合下排风罩罩口处污染物扩散断面尺寸和排风罩捕集性能,通过回归分析得到了排风罩罩口设计尺寸和设计风量的计算方法,可供工程设计人员参考。