Mechanical Engineering PhD Thesis Defense by Mohammad Akmal








Title:             Development of High Performance Cutting Tools for Machining of Gamma-Titanium Aluminide Intermetallic Alloys, Ti6Al4V and Inconel 718 in Aerospace Applications


Speaker:       Mohammad Akmal


Time:            October 17, 2017 Tuesday 2:30 p.m.


Place:            ENG B203-Manufacturing and Automation Research Center

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul


Thesis Committee Members:

Professor Dr. İsmail Lazoğlu (Advisor, Koç University)

Professor Dr. Alphan Sennaroğlu (Koç University)

Assistant Professor Dr. Arif Karabeyoğlu (Koç University)

Associate Professor Dr. Mustafa Bakkal (Istanbul Technical University)

Assistant Professor Dr. Umut Karagüzel (Işık University)



Aerospace industry use advance engineering materials such Titanium and Nickel super alloys due to their superior mechanical and thermal properties. Ti6Al4V, Inconel 718 and Gamma-Titanium Aluminide are critical materials, especially for the aircraft engines and rockets.  In this research, milling tools are designed and investigated for the machining of the famous aerospace alloys, namely, the intermetallic compound gamma titanium aluminide, the nickel alloy Inconel 718, the titanium alloy Ti6Al4V and the aircraft structural material Aluminum alloy Al7050. Besides the milling process, the drilling of Ti6Al4V and Al7050 workpiece was also investigated. Solid carbide end-mills are designed for milling the intermetallic alloy gamma titanium aluminide and Ti6Al4V. Besides the geometry of the end-mill, the effect of the surface finishing techniques and the coating material is investigated on the performance of the solid carbide end-mill. The designed tools are produced using three surface finish techniques; the magnetic powder finish, drag finish and wet sandblast finish. Whereas, the two types of surface coating materials investigated for the study are the aluminum chromium nitride AlCrN and the aluminum titanium nitride AlTiN. The performance of the designed end-mills is evaluated using the cutting forces magnitudes, specific cutting forces, tool wear and friction coefficient. A new method is proposed to establish the friction coefficients for the coating material and workpiece pairs directly from the mechanics of the milling process and machining force data. The method was applied to find the friction coefficient for the AlCrN and AlTiN coatings on Ti6Al4V and Al7050.  Furthermore, the thermal analysis of the drilling process is provided through a semi-analytical approach for predicting the temperature distribution on the drill tool when drilling Ti6Al4V. The simulation results were confirmed through a novel rotary tool temperature measuring device. The simulation of machining of the Inconel 718 alloy is achieved by providing the constitutive model to establish the necessary mechanical properties for simulating the cutting process in the milling process. The constitutive model was then used to estimating the cutting coefficients and for predicting the cutting forces for the milling process. Subsequently, the validated simulation model is used for the parametric analysis to establish the ideal end-mill design for high-performance milling of the Inconel 718 alloy. A new monolithic ceramic end-mill is designed, manufactured and validated for the high-performance milling of the Inconel 718 alloy. The experimental results confirmed the improvement in productivity in the milling of Inconel 718.