Empirical Analysis of Mechanical and Thermal Effects on Elastic Workpiece Deformations during Broaching of Safety-Critical Components

Abstract

Constructive measures in the design of aircraft engines aiming for CO2 and NOx emission reduction result in a miniaturization of the components, e.g. the rotating turbine disks. The resulting filigree structures determine a reduction of the resistance against elastic workpiece deformations during the machining process. Geometrical shape and form deviations resulting from varying chip thicknesses can exceed the tight tolerances of safety-critical components. In turbine disks, e.g. fir-tree slots as the fixing for the turbine blades are classified as those. Broaching is the state-of-the-art process manufacturing these slots. The broaching process is characterized by high cutting forces, a multi-edge tool engagement and complex tool-workpiece engagement conditions.

In this paper, an empirical test setup with multiple sensor integration on a broaching machine tool is presented and used to determine the occurring elastic deformations during the machining process. Eddy-current sensors in different positions along the workpiece were used to measure and quantify the elastic workpiece behavior and to get a three-dimensional understanding of bending and tilting effects in broaching. This paper presents a parameter study on the influence of different workpiece geometries and process parameters. Furthermore, the interaction of successively entering cutting edges on the elastic deformation and the resulting geometrical deviations of the workpiece was studied. Additionally, the investigation have shown significant thermal expansion effects with increasing broaching tool length. Therefore, this paper contains an analysis of both mechanical and thermal influences on the elastic workpiece behavior and the resulting geometrical deviations in broaching.

Keywords: Broaching, Geometrical accuracy, Elastic deformations