Session: 03-10-02: Laser-Based Advanced Manufacturing and Materials Processing

Paper Number: 145332

145332 - Experimental Investigation on the Annular Drilling of Acute Angle Micro-Holes in Nickel Based Superalloy With Femtosecond Laser 

In advanced cooling techniques for aerospace engines, a large number of micro holes are required on high-strength alloy components such as turbine blades, vanes, and compressor walls.   Micron-size holes (<1mm) are highly demanded for improving the performance of gas turbine engines [1]. Due to the development of the aerospace industry, the thrust-to-weight ratio of new aero engines keeps increasing, and the most effective method to realize a high thrust-to-weight ratio is to increase the turbine inlet temperature. However, an increase in turbine inlet temperature will reduce the heat tolerance and reliability of the engine [2]. The front inlet temperature of turbines is higher than the melting temperature of blade material and affects the service life of rotating components in aerospace engines. Film cooling technology has become an important way to solve this problem [3]. The film cooling concerns the bleeding of the internal blade, cooling air through the external walls of the blade to form a thin protective layer of cooling between the hot gases and the blade's external surface [4]. 

The primary machining methods for cooling holes are ECM (electrochemical machining), EDM (electric discharge machining), and traditional nanosecond laser processing. The disadvantage of EDM is that because of the tool's wear, it is complicated to make and repair, and the production efficiency of both EDM and ECM is low. They can only process the electrically conductive materials. Nanosecond laser drilling has higher efficiency than EDM; it can process the micro holes with intricate shapes, and the drilling cost is lower but leads to the recast layer and micro cracks. Therefore, the above drilling methods must be followed by the finishing treatment [2]. Increasing attention has been given to femtosecond laser drilling/machining, which has the advantages of high efficiency and extremely tiny structures in almost any material without thermal damage and micro cracks [3]. 

Micro holes play a pivotal role in enhancing the efficiency of aero engines. These micro holes necessitate precise drilling at acute angles relative to the surface to optimize cooling effects and enhance film cooling effectiveness. Inclined holes offer an advantage over those perpendicular to the surface by promoting more uniform airflow, thereby facilitating better dispersion of coolant.  This study introduces femtosecond laser annular drilling as a novel method for fabricating acute-angle micro holes. Cylindrical micro holes with a diameter of 400 µm are drilled at angles of 30°, 45°, 60°, and 75° from the surface of 0.68 mm thick IN718 plates. The impact of inclination angle and laser scanning speed on surface roughness, taper angle, and aperture circularity is thoroughly evaluated and discussed. The cross-section morphology analysis is conducted using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS). Additionally, electron backscatter diffraction (EBSD) analysis is performed to examine the microstructure of micro hole sidewalls resulting from this innovative drilling technique.

Preliminary experiments have been carriedout  using proposed drilling method with femtosecond laser. The diameters of entry and exit holes were assessed using a 3D microscope. The surface roughness of the sidewalls found to be 0.994 µm and 1.25 µm for Ra and Rq parameters. Subsequent experiments will aim to generate acute angle holes of superior quality, with the experimental results opening up new avenues for refining the femtosecond laser drilling process.

Presenting Author: Sunil Kumar Indian Institute of Technology Madras

Presenting Author Biography: Sunil is currently pursuing PhD in the Manufacturing Engineering Section within the Department of Mechanical Engineering at the Indian Institute of Technology, Madras, located in Chennai, India. Sunil’s research focuses on utilizing ultrashort pulsed laser technology, specifically femtosecond lasers, for micromachining purposes. The objective is to fabricate intricate microfeatures on high-strength superalloys intended for aerospace applications.

Sunil have done graduation in Mechanical Engineering Department, from Raj Kumar Goel Engineering College, Ghaziabad, India, in 2011 – 2015. Sunil has done masters, in Mechanical Engineering Department, from Indian Institute of Technology, Guwahati, India in 2018-2020.

Authors:

Sunil Kumar Indian Institute of Technology Madras
G. L. Samuel Indian Institute of Technology