The National Research Institute of Mechanical Engineering plans to organize the Institute-level Doctoral Thesis Evaluation Council for PhD candidate Tran Thi Phuong Thao in February 2026. The Institute hereby publishes the information on the doctoral thesis of the PhD candidate as follows:

Full name of PhD candidate: Tran Thi Phuong Thao

Supervisory team: 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: Research on determining reasonable technological parameters when electrical discharge machining (EDM) of external cylindrical surfaces of 90CrSi steel with ultrasonic vibration assistance.

Summary of new findings of the thesis

1. Scientific significance:

- The research introduced high-frequency vibration into the EDM process of external cylindrical surfaces of hardened 90CrSi material, clarifying the effect of vibration on the EDM process and determining optimal vibration parameters and input parameters to enhance the efficiency of the EDM process.

- The research will contribute several findings to the field of vibration-assisted EDM research.

- The combined theoretical and experimental research method presented in the study can serve as a reference basis for scientific research in the field of mechanical machining.

2. Practical significance

- Application of vibration to the EDM process of external cylindrical surfaces to improve the efficiency of the EDM process in practice, such as machining forming tablet punches or shaped steel punches, etc.

- The research results can serve as reference material for teaching and research activities in the field of mechanical machining.

3. New contributions of the thesis

- The research results of the thesis have shown that ultrasonic vibration-assisted EDM provides superior material removal rate compared to conventional EDM when the vibration amplitude is appropriate for the EDM process parameters. The outstanding results of the study include:

- Successfully utilized the ultrasonic vibration-assisted EDM process applied to the copper electrode for machining shaped external cylindrical surfaces made of 90CrSi material.

- Evaluated the influence of main input technological parameters including pulse-on time, pulse-off time, discharge current, discharge voltage, and vibration amplitude on output parameters such as material removal rate, surface roughness, and electrode edge wear.

- Determined the optimal single-objective EDM regime to achieve maximum material removal rate, minimum surface roughness, and minimum electrode edge wear using the Response Surface Methodology (RSM) and improved the single-objective optimization model for surface roughness and electrode edge wear using Gaussian Process Regression.

- Combined the NSGA-II method with Knee point, AHP, and TOPSIS to perform a comprehensive multi-objective optimization problem to select optimal EDM process parameters suitable for machining performance constraints.

- Analyzed the surface morphology of the machined part under optimal conditions and compared between vibration-assisted EDM and non-vibration EDM machined parts.

Detailed information on the thesis of PhD candidate Tran Thi Phuong Thao can be found here