Doctoral thesis information of PhD candidate Hoang Xuan Tu (revised version after the Institute-level Thesis Evaluation Committee):

Full name of PhD candidate: Hoang Xuan Tu

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 the electrical discharge machining process of hardened SKD11 steel in square cylindrical form using dielectric fluid mixed with SiC powder of different particle sizes”

Summary of the new findings of the thesis

1. Scientific significance:

- Based on theoretical research and analysis of experimental results using a reliable design of experiments method, the thesis has determined the influence of input parameters on output indicators and proposed reasonable PMEDM parameters that achieve the best single output objectives when using SiC powder in machining square cylindrical SKD11 steel parts;

- Multi-criteria decision-making methods and multi-objective optimization with high reliability were applied to determine the best PMEDM parameters. The specific reasonable PMEDM parameters aimed at achieving the optimal ratio of material removal rate to electrode wear, while ensuring the best surface roughness, include: 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, gap voltage (SV) = 5 V;

- The study has analyzed and proposed a wear model of the electrode when machining external shaped cylindrical parts, serving as a basis to ensure accuracy in electrical discharge machining of such parts. It also investigated the influence of PMEDM parameters using SiC powder on the wear and wear form of the electrode when machining hardened SKD11 steel.

2. Practical significance

- The results of the thesis can be used for reference and application in production facilities when machining shaped cylindrical parts such as shaped tablet punches, shaped stamping punches with complex profiles that are difficult to machine by traditional methods, aiming to improve economic and technical efficiency;

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

3. New contributions of the thesis

- Confirmed the feasibility and effectiveness of the PMEDM method when machining square shaped cylindrical parts made of hardened SKD11 steel using dielectric fluid mixed with SiC powder and copper electrode through theoretical research and analysis of experimental results. This is also a type of workpiece that has not been mentioned in previous studies;

- The influence of six specific PMEDM technological 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) was analyzed, and reasonable pulse parameters were proposed to achieve the best single objectives. Particularly, the influence of SiC particle size and powder concentration in the dielectric fluid on each single output objective and the multi-objective function was 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 mentioned in previous studies;

-  By using the Taguchi experimental design method combined with multi-criteria decision-making methods and grey relational analysis, multi-objective optimization research was also conducted to propose reasonable PMEDM parameters that simultaneously satisfy the criteria of electrode wear rate, surface roughness, and material removal rate in the best manner;

- The study has determined and proposed a wear model of the electrode when machining external shaped cylindrical parts during machining of hardened SKD11 steel (previous studies only addressed wear form when machining cavity-type parts). The impact of SiC powder in the PMEDM method on electrode wear form was assessed and compared with traditional EDM method. The wear form analysis results serve as a basis for applying this method in practice to ensure shape and dimensional accuracy of machining and reduce electrode costs.

View detailed thesis information at here