National Research Institute of Mechanical Engineering plans to organize the Institute-level doctoral thesis evaluation council for doctoral candidate Le Thi Phuong Thao in mid-November 2025. The Institute hereby publishes the information on the doctoral thesis of the candidate as follows:

Full name of doctoral candidate:  Le Thi Phuong Thao

Supervisors: Dr. Vu Trung Tuyen and Dr. Nguyen Thi Quoc Dung

Field: Mechanical Engineering - Code: 9520103

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

Thesis title: Study on the influence of some technological parameters and graphite electrode types on productivity and quality in electrical discharge machining of the outer cylindrical surface of 90CrSi steel parts.

Summary of new findings of the thesis

1. Scientific significance:

- Through experiments on the electrical discharge machining (EDM) process on 90CrSi tool steel material, the study established a quantitative relationship between input technological parameters (including: discharge current IP, voltage SV, pulse-on time Ton, pulse-off time Toff) and three types of graphite electrodes (HK0, HK15, HK20) with output indicators including: material removal rate (MRR), electrode wear rate (EWR), and surface roughness (Ra). These results enable the determination of the most suitable combination of technological parameters and electrode type to optimize each individual criterion. 

- The study also clarified the simultaneous influence of the aforementioned input factors on all three output indicators. Through correlation analysis and multi-objective optimization, the thesis identified a reasonable set of technological parameters and graphite electrode type, ensuring simultaneously high material removal rate, low electrode wear rate, and best surface quality. This serves as an important practical basis for improving the overall efficiency of the EDM process for shaping cylindrical surfaces on difficult-to-machine alloy steel.

- The findings from the research contribute to supplementing and perfecting the theoretical scientific foundation for the field of electrical discharge machining, while also contributing to the development of modern mechanical machining, especially in the context of increasing requirements for precision, productivity, and quality in the production of complex technical components.

2. Practical significance

- Based on the results identifying the optimal combination of technological parameters and graphite electrode type, the study conducted EDM experimental machining to successfully manufacture a set of shaped stamping dies, applied in the production of compressed tablets for the pharmaceutical industry. The experimental product meets technical requirements regarding shaped form, surface quality, and working durability, thereby confirming the feasibility and practical applicability of the research results.

- Additionally, the results of the thesis can be used as valuable reference materials for teaching, research, and technology transfer in the field of modern mechanical machining, particularly for content related to non-traditional machining methods and production process optimization.

3. New contributions of the thesis

 The thesis conducted a systematic experimental study on the electrical discharge machining (EDM) process of the outer cylindrical surface of hardened 90CrSi tool steel parts, using three different types of graphite electrodes. Through this, the thesis established a quantitative relationship between input technological parameters and electrode material characteristics with output criteria, helping to determine the most suitable set of technological parameters and graphite electrode type for each machining objective.

In particular, the thesis proposed an optimal technological regime for the EDM process of shaped cylindrical surfaces on 90CrSi steel using graphite electrodes. This regime ensures improved material removal rate (MRR), reduced electrode wear rate (EWR), and enhanced surface quality (Ra), thereby providing an effective technological solution with high practical applicability in the production of complex shaped components in the precision stamping die field.

Detailed content of the thesis of candidate Le Thi Phuong Thao can be viewed here