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This papers details the development of a novel technique to produce reverse tapered micro-holes (EDM electrode exit diameter is larger than EDM electrode entry diameter) using EDM (electro-discharge machining), to a production standard that could be applied to real products in industry. Existing EDM systems are generally used to produce straight, parallel-walled holes. However there are certain application areas where tapered holes, especially reverse taper, can give an advantage. One such application area is where fluid is flowing through an orifice (entering at the large diameter and exiting at the small diameter). A reverse tapered hole increases the coefficient of discharge of the hole. Existing EDM systems generally produce poor quality reverse tapered holes and in most cases it is not possible. This paper reports the development of a new technique which enables reverse tapered holes to be produced. Tapered holes with 100 m diameter at electrode entry and 160 m diameter at electrode exit can be produced with this technique. The quality of the holes produced is examined using a novel 3D impression technique, as well as SEM, surface roughness, and 3D optical measurements.

Hydroerosive grinding of small orifice components often creates a feature known, for the purposes of this paper, as a keyhole. The keyhole is created by undesirable erosion close to the entry of a hole, which results in an asymmetrical geometrical form and poor quality. This paper details how the keyhole problem can be eliminated and applied to diesel fuel injection nozzle manufacture.The hydroerosive grinding process consists of a low viscosity fluid, similar to the viscosity of diesel fuel, containing abrasive particles such as silicon carbide and boron carbide. A fuel injection nozzle tends to have five to seven injection holes ranging in diameter from 100 mm to 200 mm. This fluid is passed through the injection holes in a fuel injection nozzle to calibrate the nozzle flowrate, improve surface finish, pre-age the nozzle radius and microdeburr the hole edge at the fuel inlet, and to improve the flow efficiency of the hole. The paper addresses problems associated with hydroerosive grinding, such as the keyhole feature and asymmetrical holes, and describes a solution to eliminate the keyhole effect and to increase the flowrate of the nozzle without resulting in poor hole geometry. The paper contains a study on the process development, understanding of the two-phase flow characteristics, and practical implementation of the technique.

Laser drilling has become a valuable tool for the manufacture of high precision micro holes in a variety of materials. Laser drilled precision holes have applications in the automotive, aerospace, medical and sensor industry for flow control applications. The technology is competing with conventional machining micro electro-discharge machining in the field of fuel injection nozzle for combustion engines. Depending on the application, laser and optics have to be chosen which suits the requirements. In this paper, the results achieved with different lasers and drilling techniques will be compared to the hole specifications in flow control applications. The issue of geometry control of high aspect ratio laser drilled holes in metals will be investigated. The comparison of flow measurement results to microscopic hole dimension measurement show that flow characteristics strongly depend on cavitation number during flow.