Doctoral thesis information of PhD candidate Tran Thi Phuong Thao (revised version after Institute-level thesis evaluation committee)

Full name of PhD candidate: Tran Thi Phuong Thao

Supervisory team: Prof. Dr. Vu Ngoc Pi and Assoc. Prof. Dr. Le Thu Quy

Major: Mechanical Engineering - Code: 9520103

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

Thesis title: "Research to determine reasonable technological parameters when EDM external cylindrical surface of 90CrSi steel with assistance of ultrasonic vibration"

 Summary of new findings of the thesis

1. Scientific significance:

- The thesis 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 improve EDM efficiency.

- The thesis contributes some results to the research direction of vibration-assisted EDM.

- The combined theoretical and experimental research methodology presented in the thesis 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 EDM efficiency in practice, such as machining forming punch dies or steel forming punches, etc.

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

3. New contributions of the thesis

- The research results of the thesis indicate that ultrasonic vibration-assisted EDM provides superior machining productivity compared to conventional EDM when the vibration amplitude is suitable for the EDM parameters. The outstanding results of the study include:

- Successfully applied ultrasonic vibration-assisted EDM with vibration applied to the copper electrode to machine profiled external cylindrical surfaces made of 90CrSi material.

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

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

- Combined NSGA-II 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 machined parts under optimal conditions and compared between vibration-assisted EDM and non-vibration EDM parts.

Detailed content of the doctoral thesis of PhD candidate Tran Thi Phuong Thao can be viewed here