Study of High-Speed Microhole Drilling by Combined Process using Laser and EDM-Apply for fuel injection nozzle-

In the automobile industry, increasing the demands for better environment protection and resource conservation entails for lowering both fuel cost and exhaust emission. This is because combustor efficiency is markedly influenced by grain size, spray pattern, and the injection volume of fuel atomization. Therefore, to increase combustor efficiency it is effective to improve the size, pattern, and accuracy of nozzle holes. In mass production, conventional processing methods for nozzle holes include stamping and drilling. Noncontact processes such as electric discharge machining (EDM) has the advantages of smaller size, better pattern flexibility and better accuracy, however, they are not suitable for mass production. In this study, we introduced a new EDM method with both good accuracy and good productivity that are suitable for the finish machining of microholes having a diameter less than 0.2 mm. We found that for finish boring by EDM, the smaller the depth of cut, the lower the processing efficiency. Thus, to solve this problem, we suggested a new method that entails overlaying high frequency vibration to the electrode, and verified the effectiveness of the method by experiments. We verified the effective use of a high-frequency electrode feeding device together with the direct drive method for improving the processing efficiency. The finish EDM developed method is now in practical use in the mass production of fuel injection nozzle holes, which start as preholes made using a YAG laser.