National Research Institute of Mechanical Engineering plans to organize the Institute-level Doctoral Thesis Evaluation Council for doctoral candidate Hoang Xuan Tu in late September 2024. The Institute hereby publishes the information of the doctoral candidate's thesis as follows:

Full name of doctoral candidate: Hoang Xuan Tu

Scientific supervisors: Prof. Dr. Vu Ngoc Pi and Assoc. Prof. Dr. Le Thu Quy

Field: Mechanical Engineering - Code: 9520103

Training institution: National Research Institute of Mechanical Engineering - Ministry of Industry and Trade

Thesis title: "Study on electrical discharge machining process of hardened SKD11 steel square-shaped cylindrical workpieces using dielectric fluid mixed with SiC powder of different particle sizes".

Summary of new conclusions of the thesis

1. Scientific significance:

- Based on theoretical study and analysis of experimental research results using reliable planning methods, the thesis has determined the influence of input parameters on output indicators and proposed optimal PMEDM regimes for achieving the best single output objectives when using SiC powder in machining square-shaped cylindrical workpieces made of SKD11 steel;

- Multi-criteria selection methods and multi-objective optimization with high reliability have been applied to determine the best PMEDM regime. The specific optimal PMEDM regime to achieve the best ratio of material removal rate to electrode wear, while ensuring optimal surface roughness includes: powder concentration (C_p) = 2 g/l, particle size (S_p) = 1000 nm, pulse-on time (T_on) = 30 μs, pulse-off time (T_off) = 20 μs, peak current (I_P) = 4 A, servo voltage (SV) = 5 V;

- The study has analyzed and established the electrode wear pattern model for machining external shaped cylindrical workpieces, providing a basis for ensuring accuracy in electrical discharge machining of such components, and has also investigated the influence of PMEDM process parameters using SiC powder on electrode wear and wear pattern when machining hardened SKD11 steel.

2. Practical significance

- The results of the thesis can be used as reference and applied in production facilities when machining shaped cylindrical components such as shaped tablet punches, complex-profile forming punches that are difficult to machine using conventional methods, thereby improving economic and technical efficiency;

- The thesis can be used as reference for scientific research as well as for training in the field of EDM in general and PMEDM in particular. 

3. New contributions of the thesis

- The feasibility and effectiveness of the PMEDM method for machining square-shaped cylindrical workpieces made of hardened SKD11 steel using dielectric fluid mixed with SiC powder and copper electrodes have been confirmed through theoretical study and analysis of experimental research results. This workpiece type has not been addressed in previous studies;

- The influence of 6 specific PMEDM process parameters including: I_P, SV, T_on, T_off, C_p and S_p on specific objectives such as electrode wear rate (EWR), surface roughness (Ra), material removal rate (MRR) has been analyzed, and optimal pulse regimes for achieving the best single objectives have been proposed. Notably, the influence of SiC particle size and powder concentration in the dielectric fluid on each individual output objective and the multi-objective function has been analyzed and evaluated, demonstrating the effectiveness of powder in improving machining quality. The investigated particle size range from 100 nm to 1000 nm has also not been addressed in previous studies;

-  By employing the Taguchi experimental design method combined with multi-criteria decision-making methods and grey relational analysis, multi-objective optimization research has been conducted, and an optimal PMEDM regime has been proposed to simultaneously satisfy the criteria of electrode wear rate, surface roughness, and material removal rate at the best levels;

- The study has identified and established the electrode wear pattern model for machining external shaped cylindrical workpieces made of hardened SKD11 steel (previous studies only addressed wear patterns for cavity-type workpieces). The impact of SiC powder in the PMEDM method on electrode wear pattern has been evaluated and compared with the conventional EDM method. The wear pattern analysis results provide a basis for applying this method in practice to ensure machining shape and dimensional accuracy while reducing electrode costs.

Detailed information of the thesis can be found here