核电用大型饼类锻件锻造过程的数值模拟研究

发布时间：2018-02-27 10:57

本文关键词： 大型饼类锻件预镦粗终锻成形数值模拟　出处：《东南大学》2016年硕士论文　论文类型：学位论文

【摘要】：管板、封头和端盖等核电用大型饼类锻件是核反应堆和蒸汽发生器的重要部件,工作环境恶劣,其锻造质量直接关系到核电站的运行安全。本文根据大型饼类锻件的锻造技术要点制定预镦粗和终锻成形的工艺方案,并基于DEFORM-3D仿真分析软件建立有限元模型对其锻造过程进行数值模拟。分别从锻件内部应力场、应变场的分布和变化规律等方面研究了不同工艺参数下的宽平砧预镦粗工艺、锥台砧预镦粗工艺和终锻成形工艺对锻件质量的影响规律,以获得合理的工艺方案和工艺参数,指导实际锻造过程。研究了宽平砧预镦粗时,不同初始高径比坯料的应力场和应变场的分布规律；结果表明,端面附近存在较大的难变形区,且比例随着压下率线性增大；心部区域的应变增大较快,导致心部在高度方向上应变均匀性的急剧下降,从而产生层状剪切裂纹；从坯料心部获得三向压应力状态、控制侧表面的切向拉应力和避免心部出现层状裂纹的应变条件出发,不同初始高径比坯料的压下率应严格控制在一定范围内。针对宽平砧镦粗时应变不均的问题,将预镦粗工序分为锥台砧镦粗和平砧端面整平两个阶段,分别研究了锥台砧锥角和压下率对镦粗过程的影响,平砧旋转锻造方式和下砧砧形对端面整平过程的影响；结果表明,锥台砧能够有效促使端面难变形区变形,并增大心部大变形区范围,提高锻件的应变均匀程度,同时降低侧表面的切向拉应力和锻造设备载荷;综合分析应变均匀程度、剪切裂纹的产生、坯料表面的切向拉应力以及心部的应力状态,对于初始高径比为2.0的坯料,最大压下率取60%,锥台砧锥角取14°～15°较为有利；在端面整平过程中,采用外缘旋转锻造法,锻打上端面时上砧使用窄平砧,下砧使用锥台砧,可使心部获得较好的三向压应力状态,且应变较为均匀。对终锻成形工序进行了模拟分析,分别研究了4种排砧工艺方案和2种旋转锻造工艺方案对锻件内部应力应变状态的影响：结果表明,对称排砧工艺能够在压中部区域时获得相对较大的静水压应力,有利于锻合心部缺陷,同时相邻道次错砧能够消除内部应变的不均匀性,较大提高锻件的变形均匀程度,有效降低产生剪切裂纹的可能性：对相邻道次错砧的排砧工艺的工艺参数进行了研究,当压下率取15%并保证进砧量大于临界进砧量可使锻件获得良好的应力应变状态。
[Abstract]:Large cake forgings for nuclear power, such as tube plates, seals and end caps, are important components of nuclear reactors and steam generators, and work in harsh conditions. The forging quality is directly related to the operation safety of the nuclear power station. According to the main points of forging technology of the large cake forgings, the technological scheme of preheading and final forging is established in this paper. The forging process was simulated by finite element model based on DEFORM-3D software. The pre-upsetting process of wide flat anvil under different technological parameters was studied from the aspects of stress field and strain field distribution and variation law of forgings. The influence of preheading and final forging on the quality of forgings is studied in order to obtain reasonable technological scheme and parameters and guide the actual forging process. The distribution law of stress field and strain field of billet with different initial aspect ratio shows that there is a large area of difficult deformation near the end face, and the proportion increases linearly with the reduction rate, and the strain increases rapidly in the center region. As a result, the strain uniformity of the center decreases sharply in the height direction, thus the layered shear crack is produced, and the triaxial compressive stress state is obtained from the center of the blank, which controls the tangential tensile stress on the side surface and avoids the strain condition of the layered crack in the center. The reduction rate of blanks with different initial aspect ratios should be strictly controlled within a certain range. Aiming at the problem of uneven strain during upsetting of wide flat anvil, the preheading process is divided into two stages: conical anvil upsetting and anvil face leveling. The effects of cone angle and reduction rate on upsetting process, rotation forging mode of flat anvil and the influence of lower anvil shape on the end face leveling process are studied respectively, the results show that the cone anvil can effectively promote the deformation of the hard deformation zone of the end face. At the same time, the tangential tensile stress on the side surface and the load of forging equipment are reduced, and the strain uniformity degree is analyzed synthetically, and the shear crack is produced, and the strain uniformity is increased, the strain uniformity of the forging is increased, and the tangential tensile stress and the forging equipment load are reduced. The tangential tensile stress on the surface of the blank and the stress state of the center are more favorable for the blank with the initial ratio of height to diameter 2.0, the maximum reduction rate is 60 and the cone angle of the cone anvil is 14 掳/ 15 掳. In the process of face leveling, the external edge rotating forging method is used. When the upper end face is forged, the upper anvil uses the narrow flat anvil and the lower anvil uses the cone bench anvil, which can make the center obtain a better triaxial compressive stress state, and the strain is more uniform. The final forging process is simulated and analyzed. The effects of four kinds of anvil arrangement and two rotating forging schemes on the stress and strain state of forgings are studied. The results show that the symmetrical anvil arrangement process can obtain relatively large hydrostatic stress in the middle part of the forging. At the same time, the adjacent secondary anvil can eliminate the inhomogeneity of internal strain and improve the deformation uniformity of forgings. The possibility of producing shear crack is effectively reduced: the technological parameters of the anvil discharging process of adjacent secondary anvil are studied. When the reduction rate is 15% and the quantity of anvil feed is larger than the critical anvil quantity, the forgings can obtain a good stress-strain state.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM623;TG316

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