Hajavifard Ramin, Maqbool Fawad, Schmiedt-Kalenborn Anke, Buhl Johannes, Bambach Markus, Walther Frank
Department of Materials Test Engineering (WPT), TU Dortmund University, Baroper Str. 303, D-44227 Dortmund, Germany.
Chair of Mechanical Design and Manufacturing, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Wachsmann-Allee 17, D-03046 Cottbus, Germany.
Materials (Basel). 2019 May 20;12(10):1646. doi: 10.3390/ma12101646.
Disc springs are conical annular discs, which are characterized by a high spring force with a small spring travel and good space utilization. In operation, they must meet high demands on the stability of the spring characteristic and the fatigue strength. Under loading, tensile stresses occur which limit the possible applications of disc springs. Compressive stresses can be generated in the stressed areas by means of shot-peening in order to extend the operating limits for a given yield and fatigue strength. Since the spring geometry and characteristics change during shot-peening, the design of the shot-peening treatment is iterative and cumbersome. The present research proposes an incremental forming process for forming and integrated targeted adjustment of residual stresses in disc springs from metastable austenitic stainless steel (MASS), to achieve improved spring properties and high cyclic strength. The main mechanism of residual stress generation is the transformation of metastable austenite into martensite under the action of the forming tool. Different experimental characterization techniques like the hole drilling method, X-ray diffraction, disc compression tests, optical microscopy and cyclic tests are used to correlate the residual stresses and disc spring properties. A numerical model is developed for simulating the martensite transformation in disc springs manufacturing. The results prove that incremental forming enables process-integrated engineering of the desired compressive residual stresses, entailing a higher spring force of metastable austenitic disc springs in comparison to conventional disc springs. Due to martensite formation, the generated residual stresses are stable under cyclic loading, which is not the case for conventionally manufactured springs.
碟形弹簧是锥形环形盘，其特点是在行程小的情况下具有高弹簧力且空间利用率高。在运行中，它们必须满足对弹簧特性稳定性和疲劳强度的高要求。在加载过程中，会产生拉伸应力，这限制了碟形弹簧的可能应用。通过喷丸处理可以在受力区域产生压缩应力，以便在给定的屈服强度和疲劳强度下扩展运行极限。由于在喷丸处理过程中弹簧的几何形状和特性会发生变化，喷丸处理的设计是迭代且繁琐的。本研究提出了一种增量成形工艺，用于对亚稳奥氏体不锈钢（MASS）制成的碟形弹簧进行成形和残余应力的集成定向调整，以实现改善的弹簧性能和高循环强度。残余应力产生的主要机制是在成形工具的作用下亚稳奥氏体向马氏体的转变。使用不同的实验表征技术，如盲孔法、X射线衍射、圆盘压缩试验、光学显微镜和循环试验，来关联残余应力和碟形弹簧性能。开发了一个数值模型来模拟碟形弹簧制造中的马氏体转变。结果证明，增量成形能够对所需的压缩残余应力进行工艺集成工程设计，与传统碟形弹簧相比，亚稳奥氏体碟形弹簧具有更高的弹簧力。由于马氏体的形成，产生的残余应力在循环加载下是稳定 的，而传统制造的弹簧则不然。
