Design of a Machine-integrated Optical Measuring System for Electrode Positioning for Electro-Thermal Precision Ablation

Abstract

Besides traditional machining processes, unconventional machining by EDM (Electrical Discharge Machining) is used, especially when precise cavities with complicated shapes are required or hard to machine alloys need to be machined. For the production of a geometrically complicated workpiece, numerous differently shaped electrodes are required due to the variety of the single cavities and the tool wear. Due to the process-related tool wear, the electrodes can only be reused a few times. Thus, process chains consisting of milling electrode production, automated electrode changing and CNC-controlled erosion process are frequently used. After fabrication of the milling electrode, the electrode geometry is measured for quality control usually using a tactile measuring device. In order to assist in the orientation of the electrode in the EDM system, the consideration of measurement results with respect to a reference point would be helpful. However, the transfer of the measured coordinate parameters from the measurement system to the EDM system is not possible in most cases since there is no connection between the measurement system and the EDM system. In addition, the tactile electrode measurement is time consuming. With the help of a machine-integrated optical measuring system, it will be possible to save time for measuring the electrodes by automated optical measurements and thus replacing the tactile measuring method. The present study describes the technological development of a machine-integrated optical measuring system, which enables a qualitative optimization of the process chain from the production of the EDM electrode and the subsequent erosion process. The design of an optical measuring system consisting of CCD (Charge Coupled Device) sensors and a custom software for the evaluation of the results of the optical measurements are presented. The presented solution will prospectively be implemented into an industrial EDM-machine with the aim to achieve a more efficient process chain and to avoid incorrect machining.