铲刃板压力淬火过程的数值模拟与变形分析

利用弹塑性有限元法数值模拟的基本原理,研究了铲刃板在冷却过程中的数值模拟与变形。以对流换热边界条件为基础,对不同冷却模式下铲刃板进行三维建模,对冷却过程中的温度和变形量进行数值模拟,对得到的温度时间曲线和各方向上的变形量进行对比分析。结果表明在相同冷却条件下,脉冲式压力淬火可以有效控制工件各个方向上的变形,在厚度方向上的变形控制最为显著。此分析结果为该类工件的压力淬火工艺制定及淬火冷却设备的设计提供了理论基础。     

Distortion Behaviour and Mechanical Properties of AlCu4Mg1 Sheet Components after High‐Pressure Gas Quenching in Comparison to Liquid Quenching

The quenching process after solution annealing of age hardenable aluminium alloys is necessary for an improvement of the mechanical properties, but also tends to result in distortion, especially in thin or complex shaped parts, and requires a costly reworking. High‐pressure gas quenching can reduce distortion compared to liquid quenching, because of the better temperature uniformity during quenching. A determination of the distortion behaviour of different serial parts of the aluminium wrought alloy 2024cl (AlCu4Mg1,clad) points out, that high‐pressure gas quenching offers predominantly excellent values regarding the dimensional accuracy after quenching compared to liquid quenchants. In comparison to the conventional heat treatment, similar values in strength, hardness and electrical conductivity have been determined after gas quenching and aging of different aluminium alloys (2024, 6013, and 7075), Furthermore, the residual stresses have been investigated and could be clearly reduced after gas quenching.     

Quenching Distortion of Aluminium Castings – Improvement by Gas Cooling

For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used, which can lead due to the Leidenfrost phenomenon to a non‐uniform cooling of the parts and thus to distortion. Particularly at thin‐walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological, ecological, and economical advantages. The quenching intensity can be adjusted by the variable parameters gas pressure and gas velocity as well as the kind of gas and thus can be adapted to the requirements of the part. The distortion behaviour of serial production aluminium parts was researched after high‐pressure gas quenching with nitrogen 10 bar and after water quenching. Aluminium castings and forgings are considered as interesting applications of gas quenching, because of their near‐net shape before age hardening. Cost savings would be possible, because of reduced distortion and therefore less reworking.     

From Single Production Step to Entire Process Chain – the Global Approach of Distortion Engineering

Minimizing or even avoiding of heat treatment distortion is one of the key factors in the machine industry. Although known as a multi‐parameter problem, in the past investigations had focused on single effects or isolated steps in a process chain only. For example segregation patterns in raw materials, forming technologies, machining parameters and quenching was subject of intensive research. A new global approach, treating distortion as a system attribute, analyses the entire process chain from steelmaking to heat treatment. Optimizing distortion by this new methodology is called “Distortion Engineering”, which is the name of the corresponding Collaborative Research Center, established by the Deutsche Forschungsgemeinschaft (DFG) at the University Bremen in 2001. The investigation of “distortion potential” and application of “compensation potential” of different manufacturing steps will lead to an intelligent control of distortion and future improvements in profitability of production.     

Entwicklung des dynamischen Abschreckens in Hochdruck‐Gasabschreckanlagen

Development of dynamic quenching in high pressure gas quenching cells A new quenching sensor was developed for measuring the quenching conditions in high‐pressure gas quenching cells. This QC³‐Sensor (Quench Control in Cold Chambers) measures the cooling curve in a pre‐heated sensor‐head. The sensor can be used for process‐monitoring, process‐control and process‐steering. This quenching sensor was successfully tested for the precise initiation of “dynamic quenching”. The newly developed dynamic quenching consists of a gas‐quench with varying quenching intensity. It was shown on simple rings and on gear wheels made of the steel grade 16MnCr5 that the dynamic quenching has the potential to reduce heat treatment distortions. Especially the spread of the geometry‐changes can be reduced significantly, if the quenching intensity is lowered during quenching.     

Homogenization of hardness distribution and distortion in high pressure gas quenching

Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching.     

Technologic parameter optimization of gas quenching process using response surface method

A step function model with time is presented in the paper, and an axisymmetric component is regarded as the study objective in this model. The heat transfer coefficient during the gas quenching process is described as a function of time in this model, and five design variables are selected to do the design of Box–Behnken experiment with five factors and three levels. The levels of design variables that attain from the result of Box–Behnken experiment design are regard as the technical parameters of gas quenching to simulate the gas quenching process using the FEM software developed in the paper. Some mathematical models of response surface are gained by the mixed regression method and response surface method. These mathematical models show the dependencies of distortion, surface average equivalent residual stress, standard deviation of equivalent residual stress, average surface hardness and standard deviation of surface hardness with respect to the design variables. The optimization model is presented with the distortion as the optimization objective, and the model is optimized with an upper limit, a lower limit and the constraint function by the non-linear method and the Lagrange multiplier method.     

Calculation of transformation sequences in quenched steel components to help predict internal stress distribution

Abstract

In this paper are described briefly the foundations of an on–line information system developed mainly for optimizing heat treatment technologies and steel selection by predicting the progress of transformation during quenching at various points in engineering components of different chemical compositions. The flexible generation of the recently introduced workpiece transformation diagrams and the distribution of the free specific dimensional changes through the cross–section of the components are presented. Finally, the practical adaptability of the computerized system for judging incidental distortions and quenching cracks, and for providing input data for calculations of internal stresses by the finite–element method is discussed.

MST/87     

Computer predictions of progressive induction hardening of cylindrical components

Abstract

In this paper progressive induction hardening is treated mainly on a theoretical basis. In contrast to stationary induction hardening, the progressive treatment makes it necessary to include a heat flow in the axial direction of the work piece; a single coil also leads to a magnetic field which changes in the axial direction. A model for heat generation (caused by the magnetic field) is derived based on the magnetic vector potential. The heat conduction equation, in two dimensions, is solved assuming steady–state conditions. The coordinate system is transformed to take the movement of the workpiece into consideration. After adopting steady–state conditions there will be no explicit time dependency in the heat conduction equation. Phase transformations are therefore calculated by following a node when it travels under the inductor and quenching ring. The actual speed gives temperature as a function of time. Stresses are evaluated in a similar way; it is assumed that a state of generalized plane strain exists, a one–dimensional model can then be used and a strip travelling under the inductor and quenching ring is studied. Some. theoretical results and comparisons with measurements are presented.

MST/20     

大型齿圈淬火温度场计算机模拟及畸变控制

通过ANSYS模拟软件对大型渗碳齿圈淬火冷却过程进行计算机模拟,得到了齿圈淬火时温度场的动态分布,进而求出齿圈和工装在塑性温度区的最大温差。利用该温差,运用金属材料的高温塑性及相变塑性理论,设计特殊的工装,使齿圈在二次淬火的同时能够自行修正渗碳时造成的椭圆,达到整圆和防止椭圆的目的,可以省去热处理后压力校圆工序。与常规的淬火后再进行压力校圆的方法相比,该方法畸变量小、生产质量稳定、工艺效率高、成本低,而且避免了热处理后校圆开裂现象。     

Using mathematical optimization in the CFD analysis of a continuous quenching process

This paper describes the use of Computational Fluid Dynamics (CFD) and mathematical optimization to determine the optimum operating conditions and geometry of a continuous quenching process. The pump power as well as the quench rate of the steel plate in this process is influenced by many parameters. These include the nozzle and header geometry, plate speed, water flow rate, etc. Since an experimental approach is time consuming and costly, use is made of numerical techniques. Furthermore, it is sometimes impossible to measure certain values in this manufacturing process (e.g. the quench rate at a certain depth in the plate). These quantities can be obtained by CFD techniques. Using CFD without optimization on a trial‐and‐error basis, however, does not guarantee optimal solutions. A better approach, that has until recently been too expensive, is to combine CFD with mathematical optimization techniques, thereby incorporating the influence of the variables automatically. The current study investigates a simplified two‐dimensional continuous quenching process. The first part of the study investigates the operating conditions required to quench a plate at a specific quench rate. The second part of the study minimizes the pump power to quench a plate at a specific quench rate. The CFD simulation uses the STAR‐CD code to solve the Reynolds‐Averaged Navier–Stokes equations with the k–ϵ turbulence model. The optimization is carried out by means of Snyman's DYNAMIC‐Q method, which is specifically designed to handle constrained problems where the objective or constraint functions are expensive to evaluate. The paper illustrates how this optimization technique can be used to obtain the operating conditions needed for a manufacturing process with complex flow and heat transfer phenomena. The paper also illustrates how these techniques can be used in the design phase of such a manufacturing process to determine the optimum geometry and process parameters. Copyright © 2000 John Wiley & Sons, Ltd.     

真空高压气淬炉中淬火气体压力、流速和类型对工件冷却性能影响的数值模拟

本文运用FLUENT软件,通过大量的计算机模拟,研究了真空高压气淬炉中淬火气体压力、进口速度、气体类型对工件冷却性能的影响.通过对比氮气在0.45 MPa、0.6 MPa、1.0 MPa和1.5 MPa淬火压力下工件的冷却速度,量化了淬火压力对工件冷却速度的影响程度.氮气在0.6 MPa下,将气体速度由40 m/s增至60m/s,工件冷却速度提高27％,但风机功率增加3.4倍.由于气体体积流量一定的情况下,淬火气体比热和密度的协同影响了换热系数的大小,通过计算机模拟了四种淬火气体氢气、氦气、氮气和氩气对工件冷却速度的影响,得出在相同气体压力和流量下,四种气体的冷却能力是:氮气＞氢气＞氦气＞氩气;在消耗相同的风机功率下,密度小比热大的气体冷却能力高,四种气体的冷却能力依次是氢气＞氦气＞氮气＞氩气.     

改善09MnNi容器钢低温冲击韧性的机理

用热膨胀法测量了典型容器用09MnNiDR钢的Ac1和Ac3温度,并用在此基础上设计的淬火工艺对其进行热处理。使用扫描电镜、EBSD和夏比冲击试验机等手段研究了09MnNiDR钢在其厚度方向1/2处的组织、织构和低温冲击性能。结果表明：实验钢的Ac1=692.9℃,Ac3=883.1℃。与“准亚温淬火+回火”或“准亚温淬火+亚温淬火+回火”热处理工艺相比,采用“预淬火+准亚温淬火+回火”热处理,能使09MnNiDR钢板1/2厚度处的低温冲击性能有较大的提高。其原因,一是晶粒的细化,二是织构的漫散分布。     

铝合金板材热成形-淬火一体化工艺研究进展

为解决铝合金室温塑性差和成形后热处理变形的问题,发展起来了一种铝合金板材热成形-淬火一体化新工艺。该工艺是将热处理和热成形在同一工步完成,即固溶后板材快速转移到模具中成形,然后完成模内淬火,最后通过时效来提高其强度。高温成形可提高板材成形性能,模内淬火能够保证其强度和尺寸精度。重点介绍了铝合金板材热成形-淬火一体化工艺关键技术及最新研究进展,总结了铝合金板材热成形-淬火一体化工艺实验研究和数值模拟的研究现状。     

热处理工艺路径对9Ni低温钢组织和性能的影响

对9Ni低温钢进行淬火＋回火（QT）、淬火＋淬火＋回火（QQT）不同工艺路径的热处理试验,分析了不同热处理工艺路径下9Ni低温钢组织和性能的影响。结果表明：不同的热处理工艺路径直接影响9Ni低温铜最终的性能。相较于淬火＋回火（QT）工艺路径,采用含有两相区淬火的QQT工艺能明显提高9Ni低温铜的低温韧性,但降低强度。在淬火＋回火（QT）工艺路径下,随着回火温度的升高,9Ni钢回火析出组织更加充分均匀,其低温韧性呈上升趋势。在淬火＋淬火＋回火（QQT）工艺路径下,9Ni钢的低温韧性随两相区淬火温度的升高呈下降趋势。     

Research on key technologies of FEM simulation of temperature field in the process of quenching

In this paper, some key technologies of computing the quenching temperature field are given. According to the characteristics of quenching process, a new method of computing phase-transformation latent heat is presented to ensure the computation accuracy of temperature. The phase-transform latent heat is regarded as the internal heat source because it can result in the rise of temperature in the process of cooling. A new method of self-control and adaptive time-step is presented in this paper. This method can be used to compute the time-step according to maximum and minimum difference values of the temperature field between the previous simulating step and the current simulating step. A finite element method (FEM) software for evaluating the temperature and the phase-transformation is developed by using the methods presented in this paper, the lump parameters method and fine mesh method. The experimental results or analytical values of two cases are used to check the accuracy of FEM simulation. The comparisons show that the simulation results of FEM software are consistent with experimental results or analytical values.     

提高铝合金压铸模使用寿命的途径

针对3Cr2W8V钢制铝合金压铸模,采用真空亚温淬火加浅层氮碳共渗改进的热处理工艺,并找出了适宜的工艺参数.结果表明,该工艺能明显提高模具的抗热疲劳性能和使用寿命.     

Simulation der Wärmebehandlung von Stählen am Institut für Werkstoffkunde I

Simulation of the heat treatment of steels at the Institut für Werkstoffkunde I The simulation of manufacturing processes is an important tool in simultaneous engineering. The aim is to cut the time necessary for development and to optimize processes by simulation of the complete manufacturing chain. The field of heat treatment offers a large variety of applications for the use of simulation tools. The geometry of the part, the composition of the material, the heat treatment process as well as the initial state of the parts interact with each other in complex ways and have an influence on the distortion of the part. The calculation of the microstructure and of the hardness distribution helps to determine suitable charging and quenching conditions as well as plant engineering. Calculated residual stresses and distortions can be taken into account in the development and construction of new parts. The Institut für Werkstoffkunde I of the Universität Karlsruhe (TH) is engaged in research programms in this field dealing with numerical as well as experimental problems for almost 30 years.     

Thermal and mechanical evolution of welding‐induced buckling distortion

Abstract

The evolution of the buckling phenomenon starts during the weld cooling cycle, caused by an onset inelastic strain incompatibility condition. This initial bifurcation phenomenon may continue to grow until the completion of the cooling cycle, which results in the final buckling distortion of the plate. With lower heat input and/or smaller plate dimensions this initial instability may stop during the cooling cycle due to diminishing strain incompatibility and recovering of the plate rigidity. The buckling evolution process is complex due to the highly nonlinear nature of the welding problem. This paper studies this buckling evolution process using an integrated experimental and numerical approach. Bead‐on‐plate welds of AH36 steel were experimentally studied. The welding process was numerically simulated and analyzed using a three‐dimensional, thermo‐elastic‐plastic, large deformation model. The transient stress bifurcation phenomenon and the displacement evolution process were analyzed to understand the critical weld conditions causing the final buckling distortion of the weldment. The critical weld conditions were evaluated on the longitudinal inherent shrinkage (plastic) strain distribution in the weldment.     

Numerical simulation of fluid flow and temperature field in keyhole double‐sided arc welding process on stainless steel

Double‐sided arc welding process powered by a single supply is a type of novel high‐production process. In comparison with the conventional single‐sided arc welding, this process has remarkable advantages in enhancing penetration, minimizing distortion and improving welding production. In this paper, a three‐dimensional steady numerical model is developed for the heat transfer and fluid flow in plasma arc (PA)–gas tungsten arc (GTA) double‐sided keyhole welding process. The model considers the surface tension gradient, electromagnetic force and buoyancy force. A CCD camera is used to observe the size and shape of the keyhole and weld pool. The acquired images are analysed through image processing to obtain the surface diameters of the keyhole on the two sides. A double‐V‐shaped keyhole geometry is then proposed and its characteristic parameters are derived from the images and cross‐section of weld bead. In the numerical model, the keyhole cavum within the weld pool is treated as a whole quality, whose temperature is fixed at the boiling point of the workpiece material. The heat exchange between the keyhole and weld pool is treated as an interior boundary of the workpiece. Based on the numerical model, the distributions of the fluid flow and temperature field are calculated. A comparison of cross‐section of the weld bead with the experimental result shows that the numerical model's accuracy is reasonable. Copyright © 2005 John Wiley & Sons, Ltd.