Information on the doctoral thesis of PhD candidate Le Thi Phuong Thao (revised version after the Institute-level Thesis Evaluation Council)

Full name of PhD candidate: Le Thi Phuong Thao

Supervisory team: Dr. Vu Trung Tuyen and Dr. Nguyen Thi Quoc Dung

Major: Mechanical Engineering - Code: 9520103

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

Thesis title: "Research on the influence of some technological parameters and types of graphite electrodes on productivity and quality when electrical discharge machining 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 of 90CrSi tool steel, the study established quantitative relationships between input technological parameters (including: discharge current IP, servo 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 obtained results contribute to supplementing and perfecting the scientific theoretical foundation for the field of electrical discharge machining, while also contributing to the development of the modern mechanical processing specialty, especially in the context of increasing requirements for accuracy, productivity, and quality in the production of complex technical parts.

2. Practical significance

- Based on the results identifying the optimal combination of technological parameters and graphite electrode type, the study conducted experimental EDM processing to successfully manufacture a set of shaped stamping punches, applied in the production of compressed tablet molds for the pharmaceutical industry. The experimental product meets technical requirements regarding shape, surface quality, and working durability, thereby affirming the feasibility and practical application 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 processing, particularly for content related to non-traditional machining methods and production process optimization.

3. New contributions of the thesis

The thesis systematically conducted experimental research 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 quantitative relationships 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 an increase in material removal rate (MRR), a reduction in electrode wear rate (EWR), and an improvement in surface quality (Ra), thereby contributing to providing an effective and highly applicable technological solution in the production of complex shaped parts in the field of precision stamping dies.

View the detailed content of PhD candidate Le Thi Phuong Thao's thesis here