Development and optimization of the die-sinking EDM-technology for machining the nickel-based alloy MAR-M247 for turbine components

摘要

In this paper, the results regarding the optimization of the die-sinking EDM-technology for the fabrication of turbine components are presented. The main objective of this work was the reduction of machining time while producing cavities with a depth of 11 mm in the alloy MAR-M247, with respect to the requirements for surface roughness and sub-surface damage. The study was conducted using graphite electrodes of three different dimensions, totalizing 12 electrodes and a total electrode area of 89.50 mm~2. The machine tool GENIUS 1000 THE CUBE was used in the experiments and IonoPlus IME-MH was used as dielectric fluid. The Design of Experiments Methods (DoE) was applied in the planning and execution of all experiments. Firstly, experiments were conducted to estimate the maximal discharge current that can be applied for fulfilling the quality criteria regarding both surface roughness and thickness of affected sub-surface, since discharge current is known as the main influencing process parameter affecting both factors. In the second stage, the process was optimized by varying following electrical parameters of the machine tool: discharge current (i_e), discharge duration (t_i), pause duration (t_0), ignition voltage (V) and duty factor (τ). Finally, both process parameters as well as machine tool's control parameters were adjusted to achieve optimized results regarding the total machining time and electrode wear with respect to the surface requirements of produced parts. A total machining time reduction of more than 50% in comparison to the technology currently employed by the industry was achieved. Requirements on both arithmetical surface roughness as well as affected sub-surface thickness could be fulfilled. This robust technology was developed for producing the cavities in MAR-M247 and all applied methods, studied parameters as well as the results regarding machining time, electrode wear and the quality of the achieved work piece are presented.