Length-wise tool wear compensation for micro electric discharge drilling of blind holes

Abstract

Blind hole drilling using micro electric discharge machining (EDM) faces the difficulty to achieve intended depth as the tool electrode erodes continuously. A practical solution for this problem is to give a lengthwise compensation during the machining process. There are two kinds of compensation strategies exist. Online strategies compensate for the reduction in length by counting the discharge pulses and mapping it with a material removal model. Offline strategies often use the periodical measurements of tool length or electro thermal models to predict the anticipated tool wear for a particular depth. Periodical measurements are much simpler and effective compared to the discharge counting techniques, but the machining operation has to be stopped for the measurements. In this paper, a new tool wear compensation method is realized which integrates the micro EDM machine tool to an image processing module and computer controlled tool wear prediction algorithm. The proposed system is capable of updating the part program constantly according to the forecasted tool wear. A series of blind holes of 200 µm intended depth is drilled using the proposed methodology and compared it with hole drilling without compensation along with the other compensation methods. The proposed method gives 0.3–1% deviation from the intended depth of the hole. This will help in drilling blind holes with a minimum relative error with respect to the intended depth which will be useful for fabrication of series of holes or pattern.