Sequential Laser and EDM Micro-drilling for Next Generation Fuel Injection Nozzle Manufacture

High quality holes of diameters less than 145 μm are required for the manufacture of next generation diesel fuel injection nozzles for improved combustion efficiency and reduction of emission to the environment. The current practice of using electro-discharge machining (EDM) drilling of fuel injection nozzles is limited in terms of the hole size it can produce effectively and the length of time needed to drill. In addition, the tooling cost is high. This paper reports on an investigation into a sequential laser and EDM micro-drilling technique for the manufacture of next generation fuel injection nozzles. A laser-drilled pilot hole is rimmed out by EDM drilling. It was found that this hybrid process has eliminated the problems of recast and heat affected zones typically associated with the laser drilling process. The new process has enabled a 70% reduction in total drilling time compared to standard EDM drilling as less material is removed by the EDM. The quality of the holes is as good as direct EDM drilling, thus eliminating the need for re-certification of the drilling process. Various combinations of laser/EDM drilling conditions have been examined. Optimum diameters for the pilot hole and the EDM electrode have been identified for a particular diameter of fuel injection nozzle, giving the minimum total drilling time and the best quality holes. A special system was designed to enable the alignment of nozzles to be controlled to within ± 20 μm. The technique has enabled valuable cost savings and increase in production capacity for next generation fuel injection nozzle manufacture.