Study on the influence of the actual industrial constrains during WEDM roughing of Fir Trees on Inconel® 718 disks

Abstract

The manufacture of Fir Trees on aeronautical discs is an operation with high requirements in terms of accuracy and surface integrity. In recent years, Wire EDM has become a real alternative thanks to the last developments on generator technology with minimum thermal damage and the better understanding of EDM effects on the part surface. However, to achieve a competitive production, the cutting speed needs to be increased in industrial conditions. This work focuses on the WEDM rough of Fir Trees. In this stage, a high removal rate (MRR) is prioritized over quality concerns because the final surface integrity and accuracy is achieved by the finishing passes. In most of the cases, the geometry of the discs imposes the part to be allocated on a two-axis rotary table, relative far from the nozzles and then machine table. This is a non-optimal position because the WEDM process is developed in bad flushing conditions and the wire guides are also far from the cut zone. The MRR is the main parameter affected but additionally, other secondary effects like the process of wear in the current feeders can influence the overall performance. To study these effects, it was proposed to analyse the discharge process under different industrial conditions for the rough cut of Inconel 718 parts. Discharge current and voltage were acquired and post-processed using advanced algorithmics in order to extract the most significant characteristics of the process. Results show how the energy input decreases when cutting height increases, a rotary axis is included or depending of the current feeder wear. The effects on part accuracy and surface integrity were also analysed.