A Block Divided EDM Process for Diffuser Shaped Film Cooling Holes

Abstract

Diffuser shaped film cooling holes are more and more used on the hot side blade of advanced aeroengines or gas turbines. The machining of diffuser holes is a key problem for its complicated shapes and Ni base superalloy. Currently die-sinking electrical discharge machining (EDM) is still considered to be an available process for the machining of diffuser holes. However, the tool electrode shape changes after each process due to electrode wear in EDM, therefore traditional die-sinking EDM process can not meet the requirements of shape precision and machining efficiency for film cooling holes. In this study, a novel EDM process named block divided EDM is proposed. In this process, the space of the complex shape of the hole is divided into several blocks. A slender rod electrode with simple cross-section is employed to form the blocks, each of which can be processed by feeding once. When the tip shape of the electrode changes due to electrode wear, it can be repaired efficiently because of the simple electrode shape. In order to analyze the machining error caused by electrode wear under different machining parameters, a geometry simulation model of the block division EDM process is established. In this simulation model, the shapes of electrode and workpiece are represented by three-dimensional matrix. The electrode motion, the spark gap, and the electrode wear ratio are taken into account. Finally, confirmatory experiments are carried out. It is shown that laidback fan-shaped holes, one type of diffuser shaped film cooling holes can be efficiently formed by the proposed process.