INVESTIGATION OF THE EFFECT OF ASSIST GAS PRESSURE AND PULSE FREQUENCY ON SELECTED HOLE CHARACTERISTICS IN Nd:YAG LASER PERCUSSION DRILLING

Document Type : Original Article

Authors

1 Graduate student, Dpt. of Machine Design and Production, MTC, Cairo, Egypt.

2 Ph.D., Dpt. of Machine Design and Production, MTC, Cairo, Egypt.

3 Professor, Dean of Faculty of Technology, Workers University, Cairo, Egypt.

Abstract

Laser drilling has been widely used in many applications especially in aerospace industry for drilling cooling holes in gas turbine engine components. Spatter formation is one of the inherent defects associated with laser drilling. It is formed around the hole rim due to the deposition of the molten or vaporized material that is expulsed from the workpiece during drilling. Hole taper is another problem facing laser drilling. The manufacturers usually use a gas jet (assist gas) in tandem with laser beam when material removal by laser. In this study an investigation of the effect of oxygen pressure -as assist gas- on the spatter deposition area, inlet diameter, and taper of holes drilled on superalloy is carried out. The effect of laser pulse frequency on the same hole characteristics is also presented. A trial to find the effect of assist gas pressure and pulse frequency on the total volume removed from the laser-drilled holes is also done. The drilling operation was carried out by a fiber-optic delivered 400 W pulsed Nd:YAG laser system. Scanning electron microscope (SEM) was used to capture images of the laser-drilled holes at the workpiece surface. An image processing software was employed to measure both spatter deposition area and inlet hole diameter. Exit hole diameter was measured by digital optical microscope. It was found that the increase of assist gas pressure could increase the spatter deposition area, inlet hole diameter, and hole taper. The increase of pulse frequency may lead to the same results. Continuous increase of gas pressure and pulse frequency could decrease spatter deposition area.

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