共查询到20条相似文献,搜索用时 31 毫秒
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During heat treatment process, the distortion behavior inevitably appears in hydraulic turbine blade castings. In this research, a technology was developed for real-time measurement of the distortion in hydraulic turbine blade castings at the still air cooling and forced air cooling stages during heat treatment process. The method was used to measure the distortion behavior at the cooling stages in both normalizing and tempering processes. At the normalization, the distortion at the blade corner near outlet side undergoes four stages with alternating bending along positive and negative directions. At the tempering stage, the distortion could be divided into two steps. The temperature difference between the two surfaces of blade casting was employed to analyze the distortion mechanism. The measured results could be applied to guide the production, and the machining allowance could be reduced by controlling the distortion behavior. 相似文献
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P. Hofer E. Kaschnitz P. Schumacher 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(9):1638-1646
Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys. 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):324-329
AbstractThree algorithms are presented to address three problems in stress analysis of castings: difficulties for enmeshment of complicated casting into finite element meshes, coupling of thermal and stress analysis, and determination of inverse deformation, respectively. An algorithm of conversion of finite difference meshes into finite element meshes is achieved by reformatting the data of meshes. An algorithm of the heat transfer coefficient at the casting/mould interface is presented and the coupling of thermal and stress analysis is realised with the feedback of stress and deformation to heat transfer. Machining allowance is applied as a criterion for deformation evaluation of castings. And insufficient machining allowance is transformed to inverse deformation which is fed back to the original casting design for recalculation of stress and deformation. Therefore, the design of casting with appropriate inverse deformation is obtained. Case studies about a cylinder block and a hydro turbine blade casting are illustrated. 相似文献
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A. M. A. Pazooki M. J. M. Hermans I. M. Richardson 《Science & Technology of Welding & Joining》2017,22(1):7-21
The locally introduced heating and cooling cycle of welding generates residual stresses and distortion. Costly post-weld heat treatments are required in order to reduce welding residual stresses and distortion. Thermal tensioning is one of the more promising in-process techniques to control welding distortion and can be classified into transient thermal tensioning (TTT) and side heating (SH). In thermal tensioning additional heat sources are applied during welding. If the additional heaters are close to the weld centre line and influence the thermal field of the weld, the process is called TTT. If there is no interference to the thermal field of the weld, the process is called SH. In this work, the SH during welding of 2?mm thick DP600 steels has been extensively investigated using numerical and experimental approaches. The thermal and mechanical fields during conventional welding and SH were examined by means of finite element models, and validated by comparison with experimental observation of temperature, distortion and residual stresses. The microstructure was investigated experimentally. 相似文献
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自行研制了能够模拟厚大铸件冷却环境的小型凝固装置,通过控制不同的环境温度和冷却速度,来获取厚大断面球墨铸铁件凝固过程温度场的分布和变化规律。与空冷凝固时间相比,延长了300%的冷却凝固时间,验证了这一装置在实验中的有效性。 相似文献
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This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulic turbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the rapid growth of the national economy in recent years and the expected high growth in the coming 10 to 20 years. Some heavy and large castings such as mill housing and hydraulic turbine runner crown, blade and band for Three Gorges Project have been successfully made. However, the domestic production capability is still far from meeting the gigantic requirements. The domestic capability still lags behind the world class level, and a lot of heavy castings still depend on import. The paper also gives a particular introduction of the key technologies in the manufacturing of heavy steel castings like metal melting, foundry technology, heat treatment technology and numerical simulation technique, etc. In addition, several case studies on the application of numerical simulation in the production of heavy steel castings are presented. 相似文献
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镍基高温合金真空电磁约束成形与定向凝固 总被引:13,自引:0,他引:13
介绍了高熔点大密度铁、镍基合金的电磁约束成形定向凝固的两种先进技术。在系统研究电磁场与温度场及其耦合作用的基础上 ,利用特殊设计的双频双感应器成功地实现了多种截面形状的不锈钢及高温合金的无容器电磁约束成形。借助于特制的磁结晶器获得了电磁软接触的高温合金近终形定向凝固叶片样件。 相似文献
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建立了30Cr3SiNiMoVA钢大长径比薄壁壳体零件的金属-热-力耦合有限元数值分析模型,通过反传热计算获得了壳体不同位置表面综合换热系数曲线,研究了真空气淬过程中薄壁壳体零件的温度场和组织场的演变规律,并对其畸变行为进行了详细分析。研究表明:同一换热面上的冷速大小为薄壁部位>顶部>台阶部位,且阳面的温度变化更为剧烈;应力演变曲线均出现两个峰值,第一个峰值是由温度差异导致的热应力引起的,第二个峰值是由马氏体转变产生的组织应力引起的;淬火之后,阳面高度增加了2.08 mm,增加幅度为0.082%,阴面高度增加了2.33 mm,增加幅度为0.092%,薄壁位置处外径增加了0.81 mm,增加幅度为0.270%,台阶位置处外径增加了0.57 mm, 增加幅度为0.186%。实测结果与模拟结果相符,误差小于10%。 相似文献
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ABSTRACTA new method of hybrid technology for controlling welding residual stress and distortion is proposed, which contains the transient thermal tensioning with two symmetrical heat sources ahead and the trailing intensive cooling with a cooling source behind the welding heat source during the welding process. Welding temperature, stress and distortion were compared and discussed under different welding processes by experimental and numerical methods. The results reveal that the hybrid technology adjusted the temperature field during welding and redistributed the longitudinal residual stress of welding joint. Thus, the welding residual distortion was reduced. Compared with conventional metal inert gas welding, the reductions of the welding residual stress and distortion of joint by the hybrid technology reached 65% and 58%, respectively. 相似文献
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为实现铝合金铸件热处理过程的温度场调控、减轻变形,采用数值模拟方法,研究了不同料架结构对铝合金铸件表面温度场及温度均匀性的影响。结果表明,模拟仿真能够实现热处理过程铸件表面温度场的准确模拟,同时,热处理料架对铸件表面温度场具有重要影响。针对铝合金舱体铸件,采用φ30mm小孔+φ600mm大孔的料架底板,铸件表面不同位置温度均匀性最好,温度误差在±5℃范围内。 相似文献
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采用SYSWELD软件对A-100钢复杂连接件进行了有限元建模,对其在无刚性约束条件下淬火过程中温度场和形变进行了模拟仿真,并对模拟结果进行了试验验证。温度场结果表明:冷却0.13 s时温度分布均匀,零件表面温度在820 ℃左右;冷却5~60 s时,零件表面的温度分布极为不均匀,零件头部型腔的棱角处温度较低,而位于底部的支臂与翼面连接处温度较高;而当冷却时间延长至160 s左右时,零件的整体温度已降至60 ℃以下。形变场结果表明:当冷却时间为0.5~10 s时,翼面远离加强筋部位产生较大淬火畸变,顶端棱角处畸变达3 mm;冷却到600 s时,最大畸变量减小至0.65 mm。根据畸变模拟结果设计了专用淬火工装,校形率达到70%左右。 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):308-312
AbstractAs the key parts of turbine engines, single crystal superalloy turbine blades directly determine the engine's performance and service time. In this paper, a mathematical model based on the modified cellular automaton and finite difference method was developed for the three-dimensional simulation of solidification process of single crystal turbine blade castings. Using a ray tracing method, the complex heat radiation among the multiple blade castings and the furnace wall was considered in the model. The microstructure evolution was simulated with the modified cellular automaton method. A discrete layer by layer calculation method was proposed to couple the macro- and microsimulations.Simulation results show that with proper varying withdrawal rates, it is possible to increase the productivity and avoid the grain defects at the same time for single crystal blade castings. Experiments with constant and varying withdrawal rates were carried out to validate the proposed model. 相似文献
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A. Irretier O. Kessler F. Hoffmann P. Mayr 《Journal of Materials Engineering and Performance》2004,13(5):530-536
When precipitation-hardenable aluminum parts are water quenched, distortion occurs due to thermal stresses. Thereby, a costly
reworking is necessary, and for this reason polymer quenchants are often used to reduce distortion, with the disadvantage
that the quenched parts have to be cleaned after quenching. In opposition to liquid quenchants, gas quenching may decrease
distortion due to the better temperature uniformity during quenching. Furthermore, cleaning of the quenched parts can be avoided
because it is a dry process. For this purpose, a heat-treating process was evaluated that included a high-pressure gasquenching
step. Gas quenching was applied to different aluminum alloys (i.e., 2024, 6013, 7075, and A357.0), and tensile tests have
been carried out to determine the mechanical properties after solution annealing, gas quenching, and aging. Besides high-pressure
gas quenching, alloy 2024 was quenched at ambient pressure in a gas nozzle field. The high velocity at the gas outlet leads
to an accelerated cooling of the aluminum alloy in this case. Aluminum castings and forgings can be classified as an interesting
field of application of these quenching methods due to their near-net shape before the heat treatment. Cost savings would
be possible due to the reduced distortion, and therefore, less reworking after the precipitation hardening. 相似文献