Increasing the range of producible geometries in open-die forging through superimposed stress states

开式模锻是一种渐进体积成形工艺，主要用于生产简单截面的长而直的零件。用开式模锻生产复杂几何形状通常需要额外的制造步骤，或者只能通过大量的机械加工才能实现。然而，对开式模锻生产的复杂零件有一定的需求，例如用于航空航天或安全相关零件。在其他金属成形工艺中，如生产弯曲挤压或管的工艺集成弯曲，增加可生产的几何范围的一种方法是施加叠加应力，以使工件朝向预期的几何形状成形。本研究项目旨在将这一概念转化为开式模锻，以显著增加可生产几何尺寸的范围。在第一个资助期，主要重点是总体上证明这一概念的可行性，并分析其技术潜力。在分析了一次成形工序的基本一致性后，提出了一次锻造加工曲面零件的运动学概念，并成功地转移到IBF的开式锻造车间。这样，就有可能用钢和铝来生产不同几何性能的零件，这些零件的半径和角度都不同，这是传统开式锻造无法生产的。第二个资助期的目的是进一步使关于可实现几何形状的概念更加灵活，并对工艺边界进行详细分析。为此，第一步将详细分析垂直方向的弯曲，因为这防止了观察到的工件在锻模之间的滑动，并且可以在工业开式锻造机械手上更好地实现。应通过研究3D空间中任意取向的弯曲方向来分析可产生几何的进一步增加。最后，将详细分析工艺边界并对概念进行评估，如何根据这些工艺边界优化工艺以实现概念的工业应用。

Open-die forging is an incremental bulk forming process which is mainly used for the production of long and straight workpieces with a simple cross-section. The production of complex geometries by open-die forging usually requires additional manufacturing steps or can only be realized by a high amount of machining. Nevertheless, there is a certain demand for complex workpieces produced by open-die forging e.g. for aerospace applications or safety relevant parts.In other metal forming processes as for the production of curved extrusion or the process-integrated bending of tubes one approach to increase the range of producible geometries is the application of superimposed stresses in order to form the workpiece towards the intended geometry. This research project aims at the transfer of this concept to open-die forging to increase the range of producible geometries significantly.In the first funding period, the main focus was to generally prove the feasibility of the concept and analyze the technological potential. After analyzing the fundamental coherences for a single forming step, a kinematic concept for the production of curved workpieces in one forging pass was developed and successfully transferred to the open-die forging plant at the IBF. By this, it was possible to produce workpieces both from steel and aluminium with varying geometrical properties regarding the radius and workpiece angle which cannot be produced by conventional open-die forging. Additionally, the process-integrated torsion could be realized successfully.The second funding period aims at a further flexibilization of the concept regarding the achievable geometries and a detailed analysis of the process borders. For this purpose, in a first step the bending in vertical direction will be analyzed in detail, since this prevents the observed sliding of the workpiece between the forging dies and can be realized better on industrial open-die forging manipulators. A further increase of producible geometries shall be analyzed by investigating arbitrarily oriented bending direction in the 3D-space. Finally, the process borders will be analyzed in detail and concept will be evaluated, how the process can be optimized regarding these process borders for an industrial application of the concept.