Criteria for the closure and pressure welding of pores in open die forging

开式模锻气孔封闭和压焊标准

• 批准号: 283878720
• 负责人: Professor Dr.-Ing. Gerhard Hirt
• 金额: --
• 依托单位: Institut für Bildsame Formgebung (IBF)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/283878720?language=en
• 关键词: Criteria; closure; pressure; welding; pores

Ingots produced from ingot casting for open-die forging have pores and shrinkage cavities due to volume shrinkage during solidification, which can cause cracks to form in the later component under load and thus lead to critical failure. The aim of open-die forging is therefore to close these pores so that the pore surfaces come into contact and then weld them together to form a material bond. There are already a large number of criteria for describing pore closure, but for most criteria significant deviations in the prediction remain compared to numerical and experimental investigations. Welding and especially the possible re-opening of pores due to the prevailing forming conditions is not considered in any known criterion.Therefore, it was the aim of the first funding period to select a criterion which can describe the pore closure as a function of different pore geometries and orientations with respect to the load direction. The "Cicaporo" criterion fulfils these conditions for a constant load direction, so this was first selected and parameterised. Furthermore, it has been extended in such a way that it can describe pore closure even under changing load directions, as is usually the case in open die forging due to the rotation of the component. The criterion was implemented in the finite element (FE) simulation and validated experimentally by simulations with representative volume elements and forging tests. Furthermore, model experiments for the description of the bond formation were carried out, in which for different temperatures, deformations and surface conditions the derivation of a criterion for the description of the welding of pores after closing was made possible.Based on these findings, the aim of the second funding period is to minimise further inaccuracies in the prediction of the criterion developed in the first funding period. Therefore, the criterion has to be extended to take into account the influence of occurring shear during pore closure, since shear is generated in the material, among other things, at the die edges of each stroke. Furthermore, a criterion based on the model experiments of the first funding period has to be derived, which can assess the welding of the pores after closure. This can be a lower-bound statement, such as "safely or not safely welded" or a more complex description of the connection, e.g. by specifying a bond strength between the contacting pore surfaces. The criteria for pore closure and welding should then be implemented in combination in the FE simulation and validated experimentally. Once this has been done, the application possibilities are to be extended to other material classes typical for open-die forging.

用于开模锻造的铸锭由于凝固过程中的体积收缩而产生气孔和缩孔，这会导致后续部件在载荷作用下形成裂纹，从而导致严重失效。因此，开模锻造的目的是封闭这些孔，使孔表面接触，然后将它们焊接在一起以形成材料结合。已经有大量的标准来描述孔隙闭合，但对于大多数标准来说，与数值和实验研究相比，预测仍然存在显着偏差。任何已知的标准都没有考虑焊接，尤其是由于主要形成条件而可能重新打开的孔隙。因此，第一个资助期的目的是选择一个标准，该标准可以将孔隙闭合描述为不同孔隙几何形状和相对于载荷方向的方向的函数。 “Cicaporo”准则满足恒定载荷方向的这些条件，因此首先选择该准则并对其进行参数化。此外，它还以这样的方式进行了扩展，即使在变化的载荷方向下，它也可以描述孔隙闭合，就像在开模锻造中由于部件旋转而通常出现的情况一样。该准则在有限元 (FE) 模拟中实施，并通过代表性体积单元模拟和锻造试验进行实验验证。此外，还进行了描述粘合形成的模型实验，其中对于不同的温度、变形和表面条件，可以推导描述闭合后孔隙焊接的标准。基于这些发现，第二个资助期的目标是最大限度地减少第一个资助期开发的标准预测中的进一步不准确性。因此，必须扩展该标准以考虑孔闭合期间发生剪切的影响，因为除其他外，材料中会在每个冲程的模具边缘处产生剪切。此外，还必须基于第一个资助期的模型实验得出一个标准，该标准可以评估闭合后孔的焊接情况。这可以是下限声明，例如“安全或不安全焊接”或更复杂的连接描述，例如通过指定接触孔表面之间的粘合强度。然后，应在有限元模拟中结合实施孔隙闭合和焊接的标准，并通过实验进行验证。一旦完成，应用可能性将扩展到开模锻造的其他典型材料类别。