Vladimir Bäcker

Influence of process and geometry parameters on the surface layer state after roller burnishing of IN718

Highly stressed components of modern aircraft engines, like fan and compressor blades, have to satisfy stringent requirements regarding durability and reliability. The induction of compressive residual stresses and strain hardening in the surface layer of these components has proven as a very promising method to significantly increase their fatigue resistance. The required surface layer properties can be achieved by the roller burnishing process, which is characterised by high and deeply reaching compressive residual stresses, high strain hardening and excellent surface quality. In order to achieve a defined state of the surface layer, the determination of optimal process parameters for a given task still requires an elaborate experimental set-up and subsequent time-consuming and cost-extensive measurements. The development of well funded process knowledge about the correlation of the process parameters, the processed geometry and the surface layer state is the subject of this article.

Analysis of the deep rolling process on turbine blades using the FEM/BEM-coupling

Highly stressed components of aircraft engines, like turbine blades, have to satisfy stringent requirements regarding durability and reliability. The induction of compressive stresses and strain hardening in their surface layer has proven as a promising method to significantly increase their fatigue resistance. The required surface layer properties can be achieved by deep rolling. The determination of optimal process parameters still requires elaborate experimental set-up and subsequent time- and cost-extensive measurements. In previous works the application of the Finite Element Method (FEM) was proposed as an effective and cost reducing alternative to predict the surface layer state for given process parameters. However, FEM requires very fine mesh in the surface layer to resolve the high stress gradients with sufficient accuracy. The hereby caused high time and memory requirements render an efficient simulation of complete turbine components as impossible. In this article a solution is offered by coupling the FEM with the Boundary Elements Method (BEM). It enables the computing of large scale models at low computational cost and high result accuracy. Different approaches of the FEM/BEM-coupling for the simulation of deep rolling are examined with regard to their stability and required computing time.

Finite element simulation of an analogy process for the fine blanking of helical gears

Fine blanking can today be used for the production of spur gears but not for helical gears. Based on a newly developed process principle for the fine blanking of helical gears, an analogy process was set up and investigated in finite element simulations using the software Deform-3D. For the numerical model, the tool components were assumed rigid, while workpiece behavior was modeled as plastic with isotropic strain hardening. Damage initiation was included by using a normalized formulation of the Cockroft and Latham damage criterion. Results show, that sheet thickness and helix angle are key influence factors for the final workpiece properties as well as for the stress distribution in the workpiece during the process. Their influence varies with respect to the tooth section, i.e. tooth flanks and tooth tip.